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Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

Experimental study of the effect of pH on the kineticsof montmorillonite dissolution at 25 �C

M. Luisa Rozalen a,b, F. Javier Huertas a,*, Patrick V. Brady b, Jordi Cama c,Susana Garcıa-Palma a, Jose Linares a

a Estacion Experimental del Zaidın – CSIC, Department of Environmental Geochemistry, Profesor Albareda 1, 18008 Granada, Spainb Sandia National Laboratories, Albuquerque NM 87185-0754, USA

c Institute of Earth Sciences Jaume Almera – CSIC. C/ Lluıs Sole i Sabarıs s/n. 08028 Barcelona, Spain

Received 18 July 2007; accepted in revised form 28 May 2008; available online 24 June 2008

Abstract

The effect of pH on the kinetics of smectite (K-montmorillonite) dissolution was investigated at 25 �C in batch and stirredflow-through reactors over the pH range of 1–13.5, in KNO3 solutions. Dissolution rates were obtained based on the releaseof Si and Al at steady-state under far from equilibrium conditions. Dissolution was non-stoichiometric between pH 5 and 10,due to adsorption/precipitation of Al. Dissolution rates computed from batch and flow-through experiments were consistent,irrespective of the Si and Al concentrations. Sample pre-treatment and the interlayer cation do not affect the steady-state dis-solution rate or stoichiometry of cation release. The rate dependence on pH can be described by:

Rðmolm�2s�1Þ ¼ 10�12:30a0:40Hþ þ 10�14:37 þ 10�13:05a0:27

OH�

The experimental results are consistent with a dissolution mechanism involving inward movement of a dissolution front fromcrystal edges. Consequently, normalization of the dissolution rates should take into account the reactive surface located on thesmectite edges.� 2008 Elsevier Ltd. All rights reserved.

1. INTRODUCTION

The formation of smectite clays is a critical step in theweathering of crustal silicates. Once-formed, smectite claysplay a key role in limiting the movement of nutrients and pos-sibly industrial toxins through soils and sediments. At thesame time, bentonite and smectite-rich clays are routinely usedas landfill liners and (potentially) as high-level radwaste back-fills; where aggressive acid or alkali-rich solutions mightpotentially affect clay reactivity and overall stability. To antic-ipate the long-term stability in both natural and industrial set-tings requires that the mechanistic controls over smectitedissolution into aqueous solutions be carefully assessed.

0016-7037/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.gca.2008.05.065

* Corresponding author. Fax: +34 958 129 600.E-mail address: javier.huertas@eez.csic.es (F.J. Huertas).

The dissolution of dioctahedral smectites has beeninvestigated for more than five decades and it is still thefocus of many recent studies (e.g. Heydemann, 1966;Novak and Cicel, 1978; Kline and Fogler, 1981a,b; Furreret al., 1993; Zysset and Schindler, 1996; Bauer and Berger,1998; Cama et al., 2000; Huertas et al., 2001; Tournassatet al., 2003; Nakayama et al., 2004; Amram and Ganor,2005; Choi et al., 2005a,b; Metz et al., 2005a,b; Sato etal., 2005; Sanchez et al., 2006; Golubev et al., 2006) thathave considered dissolution-affecting processes including:formation of surface complexes, evolution of reactive sur-face area, effects of solution saturation, and rate controlby steady state vs. initial dissolution reaction(s). The re-sults are in some cases discrepant as they were obtainedunder different experimental conditions (batch or flow-through reactors, far or close to equilibrium conditions),using different smectites (in addition to raw or pretreated,

Smectite dissolution at 25 �C 4225

with or without accessory minerals), and applying differentmodels to represent the dissolution mechanism. Additionalsupporting information comes from dissolution experi-ments on other phyllosilicates such as kaolinite (Carroll-Webb and Walther, 1988; Wieland and Stumm, 1992;Ganor et al., 1995; Devidal et al., 1997; Bauer and Berger,1998; Huertas et al., 1998, 1999; Cama et al., 2002), illite(Kohler et al., 2003; Choi et al., 2005a,b), chlorite (Brandtet al., 2003; Lowson et al., 2005) or micas (Lin andClemency, 1981; Knauss and Wolery, 1989; Kalinowskiand Schweda, 1996; Malmstrom and Banwart, 1997).There exists a general agreement that dissolution pro-gresses by breaking of bridge oxygen bonds, Si–O–Al, atthe crystal edges, although in some cases basal planesmay contribute to the dissolution reaction (Wieland andStumm, 1992; Huertas et al., 1999).

In the present study, the effect of solution pH on thesmectite (montmorillonite) dissolution is analyzed over awide range of pH conditions, from very acidic to very alka-line, under far from equilibrium conditions. In further stud-ies the effects of temperature and proton and ligandadsorption on the dissolution mechanism will be addressed.

2. MATERIALS AND METHODS

2.1. Characterization of the montmorillonite

All the experiments were carried out with bentonite fromCabo de Gata (Almerıa, SE Spain), from the La Serrata—Cortijo de Archidona deposit. This bentonite, formed byhydrothermal alteration of volcanic tuff (Leone et al., 1983;Caballero et al., 1983, 2005), has been extensively character-ized during the FEBEX project (Huertas et al., 2000), since itis used as the reference bentonite for the Spanish concept ofnuclear waste repository (Huertas et al., 2000). The naturalbentonite is approximately 92% montmorillonite; the restconsists of accessory/companying minerals (quartz, feld-spars, micas, calcite, amphibole) and volcanic glass.

The natural bentonite was pretreated to enrich the solidin smectite. The <4 lm fraction was collected by repeatedsedimentation-suspension in water. Later, the smectitewas saturated in K+ by dispersion three times in 0.5 MKCl. The solid was then washed with KCl solutions ofdecreasing concentration (0.05 and 0.005 M, three timesfor each). Finally the solid was rinsed with Milli-Q waterand centrifuged until it tested negative for Cl�. The K-smectite sample was dried in an oven at 40 �C, ground withan agate mortar and pestle and stored in a polyethylenebottle as the starting material. Chemical analysis of majorelements was performed by X ray fluorescence. The cationexchange capacity (CEC) and the exchangeable cationswere independently analyzed (Soil Conservation Service,1972). The CEC yielded a value of 99.8 cmol(+) kg�1 andK+ was the only exchangeable cation. The calculated struc-tural formula of the K-smectite (based on half unit cell) cor-responds to a montmorillonite (Newman and Brown, 1987):

K0:44ðAl1:27Fe3þ0:22Mg0:56ÞðSi3:95Al0:05ÞO10ðOHÞ2

The corresponding atomic ratios Al/Si, Mg/Si and Fe/Siare, respectively, 0.333, 0.142 and 0.057. Uncertainty asso-

ciated with atomic ratios in the solid sample is ±0.001. Only0.19 K+ ions per half formula unit are exchangeable whichindicates the presence of a small proportion of non-swellinglayers. X-ray diffraction (XRD) patterns recorded on pow-der specimens and on oriented and glycolated mounts showthat the sample is composed of a dioctahedral smectite withapproximately 10–15% non-swelling layers, in agreementwith the presence of non-exchangeable potassium deter-mined by chemical analysis. No accessory phases were de-tected. The specific surface area of the K-smectite wasmeasured by the Brunauer–Emmett–Teller (BET) method,using 5-point N2 adsorption isotherms, after degassing thesample for two days at 110 �C. The specific surface areawas 111 m2 g�1 (with an estimated uncertainty of 10%).Scanning (SEM) and transmission (TEM) electron micros-copy images show rough grains composed of smectite flakesof montmorillonitic composition (Fig. 1), whose particledimension is lower that 0.3 lm. The use of SEM equippedwith a field emission (FE) gun revealed that the smectiteparticle aggregates consist of stacks of smectites flakes�30 A thick, which corresponds to 2–3 smectite plateletsaccording to XRD. No accessory/companying mineralswere observed by SEM or TEM.

2.2. Experimental design

Two types of experimental designs were used to deter-mine smectite dissolution rates: batch reactors and stirredflow-through cells. In the latter, the dissolution rate is mea-sured under fixed saturation state conditions by modifyingthe flow rate, initial powder mass and composition of theinput solution. The batch dissolution experiments can pro-vide dissolution rates under far from equilibrium condi-tions, and equilibrium data as the saturation stateapproaches equilibrium.

2.2.1. Flow-through experiments

A set of dissolution experiments was performed in stir-red flow-through cells (Fig. 2) fully immersed in a ther-mostatic water-bath held at a constant temperature of25 ± 1 �C. The flow rate was controlled with a peristalticpump that injects the input solution into the bottomchamber of the cell, where the solution is homogenizedby a magnetic bar before reaching the upper chamber.The solid sample is confined within the upper chamberby membrane filters (a 5 lm nylon mesh plus a 1.2 lmDurapore membrane at the bottom, and a 0.45 lmDurapore membrane at the top). The total volume ofthe cell is 46 mL.

The smectite dissolution rate was determined betweenpH 1 and 13.5, using different reagents to control the pHof the input solutions (Table 1). In the experimentsKNO3 was used as background electrolyte in concentrationof 0.01–0.05 mol L�1. All chemicals were suprapur or re-agent grade. No smectite structural cations (Si, Al, Mg,Fe) were added to the input solutions. Acetic acid/acetatewas used as buffering agent at pH 4–6. Golubev et al.(2006) observed a slight effect of acetate on smectite disso-lution. However, Ward and Brady (1998) or Huertas et al.(1999) did not detect any relevant effect of acetate ions. We

Fig. 1. Micromorphology of the montmorillonite used as startingmaterial: (a) SEM image of the grains, (b) detail of the surface onthe smectite aggregates obtained by FE-SEM that allow theestimation of the thickness of the smectite plateles (�30 A) and (c)single smectite particles observed by TEM.

Fig. 2. Design of a cell used in flow-through dissolutionexperiments.

4226 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

assume that any effect of acetate on smectite dissolution islimited.

In each run, the flow rate and the input pH were heldconstant for a long enough time so that close to steady-stateconditions were achieved. There exist difficulties in practicaldefinition of steady-state conditions, which according toKohler et al. (2005) may not be attained for dissolvingclays. Furthermore, analytical errors at very low concentra-

tions contribute to scatter the output value. In this studythe steady state was assumed to previal when the Si outputconcentration remained approximately constant and dif-fered by less than 6% between consecutive samples. Whenpossible, the same criterion was applied to Al output con-centrations. The duration of every dissolution test de-pended on the experimental conditions, but was nevershorter than 800 h. Dissolution is expected to proceed un-der far from equilibrium conditions. All the experimentsconsisted of a single stage; the cell was dismantled aftersteady-state was achieved.

Output solutions were collected every day and analyzedfor pH and total dissolved Si, Al, Fe and Mg. After reac-tion, the pH of the output solution was immediately mea-sured using Crison combination electrodes, standardizedagainst pH 4, 7 and 9.2 buffer solutions. The reported accu-racy was of ±0.02 pH units. If necessary, the output solu-tions were further acidified to pH 3 with ultrapure HNO3

to prevent precipitation of Al- or Fe-bearing phases duringstorage. Silicon level was determined by colorimetry, usingthe molybdate blue method (Grasshoff et al., 1983) with aVisible/UV spectrophotometer. Dissolved aluminum wasmeasured by fluorimetry using lumogallion as complexingagent (Hydes and Liss, 1976). Dissolved Mg and Fe weredetermined by inductively couple plasma spectrometry(ICP-MS). The detection limits are 5 ppb for Si, 0.3 ppbfor Al and Mg, and 3 ppb for Fe. The uncertainty in mea-sured Si and Al was less than 3%, and in Fe and Mg lessthan 5%.

Reacted solids were analyzed by XRD and BET nitro-gen adsorption. In the XRD patterns no precipitation ofsecondary phases could be detected, but a slight increasein the proportion of non-swelling layers in the smectitewas observed. The mass of smectite remaining after singledissolution experiments was not enough to be accuratelymeasured by BET surface. Instead changes in surface areawere estimated using some smectite samples preconditionedduring two months at several pH conditions and the solid

Table 1Composition of initial solutions used as buffers in dissolutionexperiments, measured at 25 �C

InitialpH

Composition

Flow-through cells

1.3 KNO3 0.01 M, HNO3 0.1 M2.2 KNO3 0.01 M, HNO3 0.01 M3.3 KNO3 0.01 M, HNO3 0.001 M4.0 KNO3

*0.01 M, CH3COOH 0.001 M5.0 KNO3 0.05 M, CH3COOH 0.00043 M, KCH3COO

0.0018 M9.2 KNO3 0.05 M, KHCO3 0.0015 M, K2CO3 0.00042 M

10.1 KNO3 0.01 M, KHCO3 0.0005 M, K2CO3 0.0015 M11.7 KOH 0.005 M12.5 KOH 0.05 M13.5 KOH 0.5 M

Batch reactors: Series A (smectite 0.1 g L�1, KNO3 0.05 mol L�1)

and series B (smectite 2 g L�1, KNO3 0.1 mol L�1)

1.0 HCl 0.1 M2.1 HCl 0.01 M3.1 HCL 0.001 M4.0 CH3COOH 0.01 M, KCH3COO 0.0015 M5.0 CH3COOH 0.0013 M, KCH3COO 0.0005 M6.0 CH3COOH 0.01 M, KCH3COO 0.0005 M8.4 KHCO3 0.0021 M9.1 KHCO3 0.0021 M

10.3 KHCO3 0.004 M, K2CO3 0.0061 M11.5 KOH 0.005 M12.5 KOH 0.05 M13.5 KOH 0.5 M

* NaNO3. in series Sm-25-4Na.

Smectite dissolution at 25 �C 4227

after the batch dissolution experiments. This estimation as-sumes that the changes in surface area occur during the firststages of the dissolution reaction and thereafter remainsstable (Cama et al., 2000). The BET surface areas were sim-ilar in value to that of the starting potassium montmorillon-ite within the uncertainty of the measurement.Consequently initial surface area was used to normalizeall the dissolution rates. The total mass dissolved duringthe experiment was less than 5% of the initial smectite mass,except in hyperalkaline solutions (pH > 11) where up to10% of the initial smectite dissolved (this loss was correctedfor in the evaluation of the dissolution rate).

2.2.2. Batch experiments

Short-term dissolution experiments were carried out inbatch reactors. Two sets of experiments were performedusing a solid/solution ratio of 0.1 (series A) and 2 g L�1

(series B), in order to calculate dissolution rates at differentsaturation conditions. The K-smectite was placed directlyin acid-cleaned PFA bottles containing 250 mL of a buffersolution (Table 1). The temperature was controlled by par-tially immersing the reaction vessels in a water bath at roomtemperature (25 ± 2 �C). The reactors were stirred everyday for 10 min. An aliquot of the suspension was periodi-cally withdrawn and analyzed to monitor the dissolutionreaction. The reaction bottles were stirred vigorously beforeand during sampling to minimize changes in the solid/solu-

tion ratio. The sample was centrifuged at 5000 rpm for10 min and the supernatant was filtered through a0.45 lm Durapore membrane into an acid cleaned polyeth-ylene bottle. Solution pH was measured at 25 �C immedi-ately after filtration and the solution was acidified withultrapure HNO3 to pH 3 if necessary. Concentrations ofSi, Al, Fe and Mg were measured as described before.The remaining solid was rinsed with Milli-Q water, driedand stored for further mineralogical analyses.

The BET surface area of solid samples in a batch seriesexperiment showed no substantial change due to dissolu-tion reaction, within the uncertainty of the measurements.The initial surface area of the starting montmorillonitewas therefore used to normalize dissolution rates (Allexperimental data produced in this study can be obtainedby contacting the communicating author).

2.3. Kinetics calculations

The dissolution rate, Rate (mol m�2 s �1), in a well-mixed flow-through reactor can be calculated based onmass balance of a given mineral component j. Under stea-dy-state conditions, it is given by the following equation(e.g. Cama et al., 2000):

Ratej ¼ �1

mj

qSMðCj;out � Cj;inÞ ð1Þ

where mj is the stoichiometric coefficient of component j inthe dissolution reaction, q stands for the fluid volume flowthrough the system, S designates the specific surface area,M represents the mass of smectite and Cj,out and Cj,in corre-spond to the concentrations of component j in the outputand input solutions, respectively. In this formalism the rateis defined to be negative for dissolution and positive for pre-cipitation. The error in the calculated rate is estimated usingthe Gaussian error propagation method, as described inCama et al. (2000).

In batch experiments, the dissolution rate is computedfrom the variation of mineral component j concentrationin the reactive solutions as time progresses:

Ratej ¼ �1

mj

VSM

dCj

dtð2Þ

where V is the volume of solution and t represents the time.The uncertainty associated to the rate constants is betterthan 15% and is dominated by the uncertainty in BET sur-face area.

The saturation state of the solution with respect to solidphases is calculated in terms of free energy of reaction, DGr:

DGr ¼ RT lnIAPKeq

� �ð3Þ

where R is the gas constant, T designates the absolute tem-perature, IAP and Keq, respectively, stand for the ion activ-ity product and the equilibrium constant for the dissolutionreaction. Aqueous activities and chemical affinities in thepresent study were generated using the EQ3NR geochemi-cal code (Wolery, 1992) and the equilibrium constants in-cluded in the software database for aqueous complexesand minerals other than the studied montmorillonite. The

4228 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

equilibrium constant for the dissolution reaction of the K-montmorillonite used in this study was computed from theequations and parameters reported by Vieillard (2000),according to the following hydrolysis reaction:

K0:44ðAl1:27Fe3þ0:22Mg0:56ÞðSi3:95Al0:05ÞO10ðOHÞ2 þ 6:18Hþ

! 0:44Kþ þ 1:32Al3þ þ 0:22Fe3þ þ 0:56Mg2þ

þ 3:95SiO2 þ 4:09H2O ð4Þ

The logarithm of the equilibrium constant of this reactionat 25 �C and 1 atm. is estimated in log Keq(K–Sm) = 5.76.Errors in free energy values estimated by this approach tendto be less than 0.5%.

The pH dependence of the proton (or hydroxyl) pro-moted dissolution of oxide minerals has empirically beendescribed by a rate law that relates the dissolution rate withthe proton activity powered to an n order:

Rate ¼ k � anHþ ð5Þ

This equation is a particular case of the following generalrate law (Lasaga, 1995, 1997):

Rate ¼ k0 � A � expð�Ea=RT Þ � anHþHþ�Y

i

anii � gðIÞ � f ðDGrÞ

ð6Þ

where k0 is a proportionality constant, A is the reactive sur-face area of the mineral, Ea is the apparent activation en-ergy of the overall reaction, R is the gas constant, T is theabsolute temperature, aH+ and ai are the activities in solu-tion of protons and species i, nH+ and ni are the orders ofthe reaction with respects these species, g(I) is a functionof the ionic strength I and f(DGr) is a function of the satu-ration state. According to Eq. (6), the effect of saturation ondissolution rate is negligible under far from equilibriumconditions.

3. RESULTS

3.1. Flow-through experiments

The temporal evolution of output solution compositionsof several representative experiments is shown in Fig. 3.Concentrations of Al and Si, and pH were monitoredthroughout the duration of all experiments, whereas Feand Mg were measured only in selected output solutions -when steady-state conditions were observed for Si. In thenear neutral dissolution experiments the Fe concentrationin solution was below the detection limit. For these condi-tions it was assumed that the total Fe concentration wascontrolled by equilibrium with amorphous Fe(OH)3 (Camaet al., 2000). The experimental conditions of all experi-ments, and the average pH and concentrations of Si andAl at steady-state, are presented in Table 2. Cation releaserates tend to decrease significantly with elapsed time. HighSi and Al concentrations are observed at the beginning ofthe experiments; over time their concentrations decreaseuntil steady state is approached (Fig. 3). In some series ini-tial Al concentrations are low, even lower than the Al con-centration observed at steady state. Metz et al. (2005a)ascribed such behavior to the dissolution of labile silica-rich

accessory phases in the smectite sample. Dissolution rateswere calculated based on Si and Al steady-state concentra-tions according to Eq. (1) (Table 2). The uncertainty in dis-solution rates is less than 15%.

3.2. Batch experiments

The evolution of pH and Si, Al, Fe and Mg concentra-tions in the batch experiments (Appendices A and B) areshowed in Fig. 4 for several representative runs. Both setsof batch experiments (series A and B) showed similarbehavior, although series B evolves faster than series A,due to the different solid/solution ratio. The pH of the solu-tions remains constant during the time of the experiment.In some cases at near neutral or slightly alkaline conditions,the pH drifted from the initial value but stabilized later. Atthe beginning of the experiments, Si is rapidly released andwith elapsed time the Si release rate decreases and reaches atime interval where the increase in Si concentration isapproximately proportional to the elapsed time. For longertime, the Si release rate tends again to decrease as the solu-tion becomes more saturated. The evolution of Al, Fe andMg is similar to that of Si for stoichiometric dissolution.

Similar trends have been observed for many minerals,including kaolinite (Carroll-Webb and Walther, 1988;Wieland and Stumm, 1992; Huertas et al., 1999), illite(Kohler et al., 2003), smectite (Furrer et al., 1993; Zyssetand Schindler, 1996; Huertas et al., 2001). Three differentstages can be identified: (i) an initial stage of fast dissolu-tion, dominated by dissolution of fast dissolving phasesor particles; (ii) a second stage of time-independent dissolu-tion under conditions below saturation, and (iii) a thirdstage that occurs after the solution has attained saturationwith respect to solids, as evidenced by a decrease in the rate.Determination of the smectite dissolution rate is possibleonly in the second region, where the variation of dissolvedconcentrations is primarily due to smectite dissolution. Asin previous studies (e.g., Huertas et al., 1999; Kohler etal., 2003) Si release rates are used in the present study tocalculate dissolution rates because Si is less likely to beincorporated into secondary phases at near to neutral con-ditions. If dissolution progresses stoichiometrically, theconcentrations of other cations (Al, Fe, Mg) can be alsoused to calculate the montmorillonite dissolution rate.

4. DISCUSSION

4.1. Initial dissolution and sample preconditioning

Early, fast dissolution has been observed for numeroussilicates and has been attributed to processes such as disso-lution of fine grained materials, highly strained areas onlarge grains or defects (Holdren and Berner, 1979; Schottet al., 1981; Chou and Wollast, 1984, 1985; Knauss andWolery, 1988, 1989; Stillings and Brantley, 1995). In orderto reduce the effect of the initial dissolution process andreach steady-state conditions faster, numerous authors ap-plied some pretreatment to their samples. Some authorssoaked the sample with acidic or alkaline solutions (e.g.,Wieland and Stumm, 1992; Bauer and Berger, 1998),

2

3

4

40

60

Hatio

n (u

M)

Si Al pH

aSm_25_2E

0.6

0.8

1

atom

s)

aSm_25_2E

0

1

2

0

20

0 500 1000 1500 2000 2500

p

Con

cent

ra

Time (h)0

0.2

0.4

0 500 1000 1500 2000 2500

Al/S

i (a

Time (h)

2

4

6

10

20

30

pH

Con

cent

ratio

n (u

M)

Si Al pH

bSm_25_4E

0.2

0.4

0.6

0.8

1

Al/S

i (at

oms)

bSm_25_4E

000 500 1000 1500 2000

C

Time (h)0

0 500 1000 1500 2000Time (h)

10

11

20

30

n (u

M)

Si Al pH

cSm_25_10

0.8

1

ms)

cSm_25_10

7

8

9

0

10

20

0 500 1000 1500 2000 2500

pH

Con

cent

ratio

n

Time (h)

0

0.2

0.4

0.6

0 500 1000 1500 2000 2500

Al/S

i (at

om

Time (h)Time (h) Time (h)

14

15

40

60

80

100

pH

entr

atio

n (u

M)

Si Al pH

dSm_25_13.5c

0.4

0.6

0.8

1

SI (a

tom

s)

dSm_25_13.5c

12

13

0

20

0 500 1000 1500 2000 2500

Con

ce

Time (h)

0

0.2

0 500 1000 1500 2000 2500

Al/S

Time (h)

Fig. 3. Evolution of the pH, concentrations of Si and Al, and Al/Si atomic ratio in the output solutions of a selected group of dissolutionexperiments conducted in flow-through cells. Output solutions used to calculate average steady state are denoted by open symbols.

Smectite dissolution at 25 �C 4229

whereas in other cases the sample was left for some time ina solution similar to the one that was subsequently used forthe dissolution experiment (e.g., Nagy et al., 1991; Ganor

et al., 1995; Cama et al., 2000, 2002). A particular pretreat-ment applied to phyllosilicates, which does not otherwisemodify the dissolution properties appreciably, is to saturate

Tab

le2

Exp

erim

enta

lco

nd

itio

ns

and

resu

lts

of

flo

w-t

hro

ugh

dis

solu

tio

nex

per

imen

ts

Ru

nD

ura

tio

n(h

)F

low

rate

(mL

/min

)In

itia

lm

ass

(g)

Fin

alm

ass

(g)

pH

inp

Ho

ut

CS

i,o

ut

(lm

ol

L�

1)

CA

l,o

ut

(lm

ol

L�

1)

CM

g,o

ut

(lm

ol

L�

1)

CF

e,o

ut

(lm

ol

L�

1)

Al/

Si

log

RS

i(m

ol

m�

2s�

1)

log

RA

l(m

ol

m�

2s�

1)

DR

Si

%D

R

Al

%

Sm

_25_

1E26

880.

0216

0.09

140.

0577

1.31

1.02

33.6

11.5

5.5

3.0

0.34

�12

.63

�12

.63

10.8

10.9

Sm

_25_

1Eb

1177

0.02

140.

0914

0.08

530.

971.

0631

.610

.85.

5—

0.34

�12

.83

�12

.81

10.5

10.8

Sm

_25_

2E21

340.

0207

0.09

060.

0857

2.23

2.23

13.9

6.0

5.2

1.1

0.44

�13

.20

�13

.08

10.6

10.6

Sm

_25_

3E17

650.

0205

0.09

060.

0879

3.32

3.26

7.7

3.7

1.2

0.1

0.47

�13

.46

�13

.31

10.3

10.6

Sm

_25_

4b_I

1008

0.02

110.

0900

0.08

683.

973.

904.

01.

170.

71.

20.

28�

13.7

3�

13.8

010

.510

.5S

m_2

5_4b

_II

2710

0.02

110.

0900

0.08

613.

974.

122.

40.

710.

81.

20.

30�

13.9

7�

14.0

210

.910

.9S

m_2

5_4E

1941

0.02

370.

0909

0.08

923.

984.

082.

90.

871.

90.

40.

30�

13.8

4�

13.8

810

.510

.5S

m_2

5_4N

a22

230.

0216

0.09

080.

0891

4.00

4.34

2.4

1.01

——

0.43

�13

.96

�13

.85

10.5

10.4

Sm

_25_

5c17

730.

0201

0.09

080.

0897

5.15

5.69

1.8

0.34

0.6

1.3

0.19

�14

.12

�14

.38

10.5

11.0

Sm

_25_

5b20

390.

0197

0.09

030.

0891

5.00

6.35

1.3

0.32

0.5

0.1

0.24

�14

.25

�14

.40

10.5

10.5

Sm

_25_

9b_I

I19

630.

0201

0.09

020.

0882

9.24

8.73

2.7

0.63

0.5

0.1

0.23

�13

.93

�14

.09

10.5

10.5

Sm

_25_

1020

390.

0206

0.09

010.

0885

10.1

59.

462.

91.

080.

70.

50.

38�

13.8

9�

13.8

610

.411

.0S

m_2

5_10

b16

370.

0213

0.09

050.

0891

10.0

39.

372.

20.

61—

—0.

28�

14.0

0�

14.1

010

.511

.0S

m_2

5_11

.5b

1673

0.02

000.

2708

0.26

0311

.77

11.2

513

.34.

20.

31�

13.7

2�

13.7

410

.710

.7S

m_2

5_12

.519

160.

0205

0.09

050.

0863

12.4

712

.51

9.7

3.6

2.8

0.8

0.37

�13

.38

�13

.36

11.1

11.7

Sm

_25_

13.5

1410

0.02

050.

0900

0.08

3713

.50

13.3

018

.43.

2—

—0.

19�

13.0

9�

13.3

710

.911

.0S

m_2

5_13

.5b

1480

0.02

060.

0904

0.08

4713

.53

13.4

718

.62.

80.

50.

70.

15�

13.0

9�

13.4

211

.011

.0S

m_2

5_13

.5c

2041

0.02

260.

0901

0.08

3113

.65

13.7

415

.24.

8—

—0.

32�

13.1

1�

13.1

210

.510

.5

4230 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

the clay with a single cation (e.g., Zysset and Schindler,1996; Kohler et al., 2003). Recently, Kohler et al. (2005)interpreted early rapid dissolution to be caused by changesin reactive surface area. Because the edges dissolve fasterthan the basal planes clay mineral dissolution is preventedfrom reaching steady-state.

In order to compare the effect of pretreatment and thepresence of interlayer cations, three samples were dissolvedfor more that 2000 h in flow-through cells at pH 4: theK-smectite used as general starting material (Sm-25-4b-II); a sample of K-smectite preconditioned in 0.01 MKNO3 solution at pH 3 (HNO3) was equilibrated fortwo months (Sm-25-4E), and finally a smectite sampleexchanged with Na (Sm-25-4Na) was used. Fig. 5 showsthe evolution of the Si and Al concentrations and Al/Si ra-tio in the output solutions. The three trends are generallysimilar, but there are some differences. The initial dissolu-tion stage takes approximately 700 h. During this period,the Si released in the series Sm-25-4b-II is approximatelytwice the Si released in the other two series. The precondi-tioning treatment apparently removed some sorbed silicafrom the smectite surface, but it did not change the stoichi-ometry of the dissolution reaction, which is very similar inall three cases. The dissolution rates at pH 4 are similar forthe three series, within the uncertainty of the measurement(Table 2). The preconditioning reduced the time necessaryto attain steady-state conditions to approximately 1000 hfor K-smectite, in aggreement with Metz et al. (2005a).The Si-release behavior of the Na-exchanged sample largelyresembles that of the preconditioned sample. The reason forthe difference in the initial Si release between the K and Nasmectites is not clear. The Na saturation procedure,although virtually identical to the K saturation one,removed some sorbed silica from the external surfacesand shortened the time necessary to achieve steady-stateconditions to �500 h (see Table 3).

4.2. Stoichiometry

Dissolution stoichiometry depends on time and pH. Thestoichiometry of the initial transient period varies with thepH of the experiment. Fig. 6 shows the Al/Si atomic ratioduring initial dissolution stage (stoichiometry is comprisewithin ±10% atomic ratios). Al is preferentially releasedover Si in acidic solutions, as observed for smectite (Zyssetand Schindler, 1996; Cama et al., 2000), illite (Kohler et al.,2003), kaolinite (Carroll-Webb and Walther, 1988; Huertaset al., 1999) or feldspars (Blum and Stillings, 1995). This isalso consistent with the model of Lasaga and Lutge (2004),which predicts transient incongruent dissolution because ofsurface modification. In circumneutral pH solutions initialdissolution is incongruent due to readsorption of Al. Disso-lution is stoichiometric in alkaline solutions at pH >11.Similar behavior is observed for the Mg/Si ratio, althoughshifted to alkaline conditions due to Mg sorption from highpH solutions. As dissolution progress towards steady state,Al/Si ratio tends towards stoichiometry except in the rangeof pH 5–10, due to Al sorption (Fig. 7).

Dissolution rates derived from Si and Al concentrationsare consistent with each other, indicating stoichiometric

3

4

1200

1500

1800

(uM

)

Si Al

Mg Fe

pH

B-R01

4

5

400

500

(uM

)

Si Al

Mg Fe

pH

B-R03

1

2

300

600

900 pH

Con

cent

ratio

n(

3

100

200

300

pH

Con

cent

ratio

n(

000 400 800 1200

Time (d)

200 400 800 1200

Time (d)

14

500

600Si Al

Mg Fe

B-R129200

Si Al

Mg Fe

B-R05

12

13

200

300

400

500

pH

Con

cent

ratio

n (u

M)

g

pH

6

7

8

50

100

150

pH

Con

cent

ratio

n (u

M)

Mg Fe

pH

110

100

0 400 800 1200

C

Time (d)

4

5

0

50

0 400 800 1200

C

Time (d)

Fig. 4. Evolution of the pH, and concentrations of Si, Al, Mg and Fe in the dissolution experiments conducted in batch reactors.

Smectite dissolution at 25 �C 4231

dissolution at steady-state conditions in most of the pHrange investigated (Fig. 7). Except under circumneutralpH conditions, where dissolution is incongruent, there isno preferential release of Al or back precipitation on thedissolving surface. On the contrary, Mg is rapidly releasedfrom the silicate network, as denoted RSi < RMg when pH isbelow 10, likely due to ion exchange reactions. Higher pHlikely causes precipitation and/or adsorption of Mg.

4.3. Saturation state of the solutions

The saturation state of the output solutions at steadystate were calculated for the studied K-montmorillonite,for silica, and for several Al, Mg and Fe-bearing phases(Table 4). The most representative results are plottedagainst output pH in Fig. 8. All the experimental runs areundersaturated with respect to K-montmorillonite.

Several sets of experiments (Cama et al., 2000; Metz,2001) have been performed to determine what values ofDGR separate ‘‘far from equilibrium” smectite dissolutionfrom ‘‘close to equilibrium” smectite dissolution. From

Metz’s (2001) results, Amram and Ganor (2005) suggestedthat ‘‘far from equilibrium” smectites dissolution occursunder conditions of DGR 6 �21 kcal mol�1. By this mea-sure, our experiments at pH <4.2 and pH >12 proceededunder far from equilibrium conditions. Consistent with this,precipitation of secondary phases is likely negligible overthis interval, as demonstrated by the equivalence of dissolu-tions rates derived from flow-through cells and batch reac-tors in acidic or alkaline conditions.

The solutions within the interval 4.2 < pH < 12 areundersaturated with respect to the K-montmorillonite, un-der conditions where DGR is between �15.2 and�9.3 kcal mol�1. The closeness to equilibrium is experimen-tally unavoidable. If the flow rate is increased by a factor of10, the concentrations of released cations would also de-crease approximately by 10 and DGR would be below�21 kcal mol�1. However, these concentrations would bevery close to the detection limits for the Si and Al (Mgand Fe would be well below the detection limit), which inaddition would increase the uncertainty associated withthe calculated rate. Furthermore, it is very difficult to

2

3

200

250

300

(uM

)

Si AlMg FepH

A-R01

5

6

30

40

(uM

)

Si AlMg FepH

A-R04

1

50

100

150 pH

Con

cent

ratio

n(

4

10

20 pH

Con

cent

ratio

n(

000 1000 2000 3000

Time (d)

300 1000 2000 3000 4000

Time (d)

1020Si Al

Mg FeA-R07

15100Si Al

Mg FeA-R09

7

8

9

8

12

16

pH

Con

cent

ratio

n (u

M)

g

pH

12

13

14

40

60

80

pH

Con

cent

ratio

n (u

M) pH

6

7

0

4

0 1000 2000 3000

C

Time (d)

11

12

0

20

0 500 1000 1500 2000

C

Time (d)

Fig. 4 (continued)

4232 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

achieve stoichiometric dissolution of aluminosilicates innear neutral fluids due to precipitation/sorption of Al(and Fe) secondary phases. Gibbsite deposits can form onbasal planes of 2:1 phyllosilicates by precipitation andgrowth from supersaturated solutions (DGR = 0–2.1 kcal mol�1) (Nagy et al., 1999). Also kaolinite satura-tion occurs in our experiments at pH 6. Silica phases areundersaturated over the whole pH range studied.

Iron concentrations are below the detection limit at pH6–9. Outside this pH interval, the output solutions areundersaturated with respect to amorphous Fe(OH)3. Simi-lar to previous studies (i.e., Cama et al., 2000), we assumedthat Fe is released from the smectite framework and thenprecipitates as amorphous iron hydroxide, similar to Al.Consequently, as noted earlier, we assume Fe levels to bein equilibrium with Fe(OH)3.

Smectite dissolution under hyperalkaline conditionsshows incongruent release of Mg, and EQ3NR results indi-cate supersaturation of solutions with respect to brucite.While we did not directly observe brucite formation, the

conditions suggest a potential partial precipitation of Mgas brucite or other Mg-rich minerals (e.g., saponite)(Sanchez et al., 2006).

Overall our results suggest that incongruent dissolutionof the smectite is due to the precipitation and/or sorptionof Al, Mg and Fe released during the overall dissolutionof the Si–Al framework. This conclusion is consistent withresults reported in literature (Zysset and Schindler, 1996;Kohler et al., 2003; Amram and Ganor, 2005; Metz et al.,2005a; Golubev et al., 2006).

4.4. Dissolution rates

Smectite dissolution rates at steady-state conditionsfrom flow-through cells as well as those calculated frombatch experiments are plotted as a function of solutionpH in Fig. 9. The rates exhibit the typical variation of thedissolution rate with pH observed for Al-silicates and com-plex multi-oxides: rates decrease as increasing pH at acidicconditions, reach a minimum at near neutral pH and

Table 3Experimental conditions and results of dissolution experiments done with batch reactors: series A and B

Run pH in pH out average log R Si (mol m�2s�1) log R Al (mol m�2s�1) DR Si % DR Al %

A-R01 1.11 1.10 �12.70 �12.68 2.2 5.9A-R02 1.98 1.98 �13.18 �13.11 5.2 2.0A-R03 3.00 3.04 �13.46 �13.51 4.7 8.7A-R04 3.85 3.97 �13.95 �13.98 5.5 3.6A-R05 4.98 7.01 �14.13 — 10.7 —A-R06 10.34 10.47 �13.91 �14.04 13.2 100A-R07 8.44 8.10 �14.20 — 10.7 —A-R08 11.59 11.73 �13.67 �13.68 22.0 22.0A-R09 12.93 12.94 �13.22 �13.24 3.2 5.4A-R10 13.44 13.84 �13.13 �13.06 5.5 11.3

B-R01 1.04 1.09 �12.75 �12.73 6.1 14.2B-R02 2.05 2.11 �13.11 �13.04 7.8 20.1B-R03 3.05 3.63 �13.61 �13.61 6.1 12.1B-R05 5.99 7.53 �14.29 — 18.6 —B-R09 9.09 9.19 �14.01 — 13.8 —B-R10 10.33 10.10 �14.00 — 29.8 —B-R12 12.77 12.50 �13.54 �13.39 10.0 19.5B-R13 13.68 13.58 �13.17 �13.23 13.0 12.5

6

7

80

100Si -Sm_25_4b-II

Si -Sm_25_4E

Si -Sm_25_4Na

pH Sm 25 4b II

a

0.8

1Sm_25_4b-II

Sm_25_4E

Sm_25_4Na

b

560

pHi (μM

)

pH -Sm_25_4b-II

pH -Sm_25_4E

pH -Sm_25_4Na 0.6

(ato

ms)

3

4

20

40Si

0.2

0.4

Al/S

i

200 500 1000 1500 2000 2500 3000

Time (h)

00 500 1000 1500 2000 2500 3000

Ti (h)Time (h) Time (h)

Fig. 5. Evolution of pH and Si concentration in the output solutions as a function of the elapsed time for three dissolution series at pHapproximately 4. See text for a detailed explanation. Lines correspond to stoichiometric release.

Smectite dissolution at 25 �C 4233

increase with increasing pH at basic conditions. In the ab-sence of organic ligands, the species that attack the silicatesurface are mainly protons, water molecules and hydroxyls,which may form surface complexes with cations at surfacesites. The dissolution rate will be proportional to the nth or-der of the proton/hydroxyl activity, according to Eq. (5).From linear regression of short intervals of log Rate versuspH, a fractional reaction order of 0.40 is calculated forpH < 4.5 and of �0.27 for pH > 10.

An operational description of the overall smectite disso-lution rate may be obtained as the sum of the contributionsof the several stages extended to the whole pH range stud-ied. The overall rate law was obtained by non-linear leastsquare regression of the whole set of experimental points,producing the following expression:

Rðmol m�2 s�1Þ ¼ 10�12:30a0:40Hþ þ 10�14:37 þ 10�13:05a0:27

OH�

ð7Þ

The first and third terms correspond, respectively, to theproton- and hydroxyl-promoted dissolution rates. The con-stant term is usually ascribed to a dissolution mechanismpromoted by water molecules. According to the value ofthe rate constants in Eq. (7), the reaction pathways that in-volve protons or hydroxyls are likely much more efficientthan water-promoted mechanism.

A few studies in the literature report smectite dissolu-tion rates, generally measured over limited pH ranges.Zysset and Schindler (1996) studied the dissolution kinet-ics of K-saturated SWy-1 montmorillonite in solutionsof KCl (0.03 to 1 mol L�1) at pH 1–5. Dissolution rates

1Cells

0.6

0.8

omic

ratio

)

Batch ABatch B

0.2

0.4

Al/S

i (at

o

00 2 4 6 8 10 12 14

0 2 4 6 8 10 12 14

pH

pH

1Batch ABatch B

0.6

0.8

atom

ic ra

tio)

Batch B

0

0.2

0.4

Mg/

Si (a

Fig. 6. Al/Si and Mg/Si atomic ratios in solution during thetransient initial dissolution stage after 300, 144 and 240 h for flow-through cells, batch series A and batch series B, respectively. Linescorrespond to stoichiometric release.

-13

-12.5

m2 s)

Acidic

Neutral & slightly alkaline

Alkaline

-14

-13.5

log

Rat

e A

l (m

ol/m

-14.5-14.5 -14 -13.5 -13 -12.5

log Rate Si (mol/m2s)

Fig. 7. Comparison of dissolution rates derived from Al and Siconcentrations. The diagonal corresponds to stoichiometric disso-lution. Data from flow-through cells and batch reactors areincluded.

0

10

20

l)

K-Sm SiO2 am GibbsiteKaolinite Brucite Fe(OH)3

-20

-10

0

ΔGr(k

cal/m

o

-40

-30

0 2 4 6 8 10 12 14pH

Fig. 8. Variation with pH of the saturation state of the outputsolution from flow-through cells at steady-state conditions.

4234 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

decrease with increasing pH. From linear regressions oflog RSi vs. pH the fractional reaction orders with respectto proton concentrations were obtained (0.24–0.35). Thesereaction orders are consistent with those found by Furreret al. (1993). Congruent dissolution was observed for KCl0.1 and 1 mol L�1 concentrations, whereas for0.03 mol L�1 a preferential release of Si was observed.The adsorption of Al on ion exchange sites and edgesinhibits the dissolution reaction. The dissolution processis preponderantly located at the crystal edge faces. Bauerand Berger (1998) performed smectite dissolution experi-ments on two samples in KOH solutions at 35 and80 �C in batch reactors. Under such alkaline conditions,smectites undergo intense dissolution. Dissolution rateswere observed to be proportional to the 0.15 order ofthe hydroxyl activity independent of the experimental tem-perature. No chemical affinity effect was observed. Disso-lution conditions in Huertas et al. (2001) experiments onbentonite from La Serrata outcrop (Cabo de Gata, Almer-ıa, Spain) were limited to a narrow pH interval (7.6–8.5)corresponding to granitic solutions at 20–80 �C. Despitethe influence of temperature, no significant effect of pHwas observed over this albeit narrow range. Amram andGanor (2005) studied the dissolution of SAz-1 smectiteunder far from equilibrium conditions and proposed a ratelaw to describe the combined effects of pH (1–4.5) andtemperature (25–70 �C), based on the application of aLangmuir model for proton adsorption on reactive edgesites. Dissolution rates decrease with increasing pH, hav-ing a fractional reaction order with respect to protons of0.57. The proposed dissolution rate law is a function ofproton activity in solution and temperature-dependentadsorption equilibrium. As discussed in Metz et al.(2005b), dissolution rates were normalized to sample massor AFM edge surface area (ESA) instead of BET surfacearea. Sato et al. (2005) investigated the effect of pH onsmectite dissolution in alkaline conditions at 30 �C andobserved that dissolution rates were proportional to 0.15order of the hydroxyl activity in the range of pH from 8

- 13

-12

2 s)

Si 25ºCAl 25ºCSi 25ºC, Batch AAl 25ºC, Batch ASi 25ºC, Batch B

-14

- 13

log

Rat

e (m

ol/m

2

Al 25ºC, Batch B

-150 2 4 6 8 10 12 14

pH

Fig. 9. Experimental dissolution rates derived from Si and Alconcentrations in outlet solution and calculated dissolution ratesobtained using Eq. (7).

Table 4Saturation state of the output solutions at steady-state conditions computed for the flow-through experiments according to Eq. (3)

Series pHout K-Mont SiO2(am) Qz Gib Kln Ms Brc K-sap Fe(OH)3 Goet

Sm-25-1E 1.02 �35.58 �2.40 �0.65 �14.25 �28.83 �49.35 �27.98 �74.35 �13.09 �6.10Sm-25-1b 1.06 �35.43 �2.44 �0.68 �14.11 �28.61 �48.98 �27.04 �74.06 �12.91 �5.92Sm-25-2E 2.23 �27.51 �2.93 �1.17 �9.19 �19.77 �27.51 �23.64 �63.50 �7.66 �0.67Sm-25-3E 3.26 �22.82 �3.71 �1.51 �5.16 �13.27 �22.86 �21.75 �58.90 �5.87 1.12Sm-25-4b-I 3.90 �20.40 �4.42 �1.90 �2.66 �9.70 �16.32 �19.63 �53.94 �2.73 4.26Sm-25-4b-II 4.10 �19.14 �4.11 �2.17 �2.47 �8.67 �15.08 �20.35 �54.97 �3.12 3.87Sm-25-4E 4.08 �18.14 �3.86 �2.10 �2.74 �8.73 �14.94 �19.14 �50.44 �3.48 3.50Sm-25-4Na 4.34 �17.06 �3.97 �2.22 �1.58 �6.65 — �19.27 �51.23 EQ 6.99Sm-25-5b 5.75 �11.04 �4.68 �2.93 2.16 �0.57 0.48 �15.63 �40.28 EQ 6.99Sm-25-5c2 5.76 �15.23 �4.32 �2.56 1.93 �0.32 0.88 �15.60 �38.92 EQ 6.99Sm-25-9b 8.73 �6.96 �4.40 �2.18 0.15 �4.21 0.80 �6.83 �10.43 �0.42 6.99Sm-25-10 9.45 �9.68 �4.48 �2.28 �0.46 �5.42 �2.64 �4.82 �6.60 �1.08 6.56Sm-25-11.5b 11.25 �11.96 �4.75 �3.04 �2.03 �9.10 �11.96 �1.53 2.09 �4.44 5.91Sm-25-12.5 12.51 �23.41 �7.45 �5.24 �3.96 �18.35 �16.97 2.17 4.01 �4.44 2.55Sm-25-13.5 13.3 �27.80 �8.59 �6.83 �4.81 �22.30 �20.60 4.58 7.57 �4.65 6.99Sm-25-13.5b 13.56 �30.94 �9.14 �7.39 �5.51 �24.83 �24.18 5.20 7.32 �5.17 1.83Sm-25-13.5c 13.74 �33.13 �9.82 �8.07 �5.34 �25.85 �25.48 5.73 6.44 �4.99 2.01

*K-Mont, K-Montmorillonite; SiO2(am), amorphous silica; Qz, Quartz; Gib, Gibbsite; Kln, Kaolinite; Ms, Muscovite; Brc, Brucite; K-Sap,K-saponite; Goet, Goethite; EQ, mineral/solution equilibrium.Shadowed values correspond to saturation.

Smectite dissolution at 25 �C 4235

to 13. Golubev et al. (2006) studied the effect of pH andorganic ligands on the kinetics of SWy-2 montmorillonitedissolution at 25 �C. Dissolution rates in ligand-free, car-bonate solutions show the expected profile as function ofpH, with reaction orders of �0.21 and 0.33 in acidicand basic conditions, respectively.

Although it is not the aim in this study to review ofthe overall dissolution mechanism of phyllosilicates, it isuseful to compare our results with those observed for il-lite, micas and chlorite. Kohler et al. (2003) studied theeffect of pH (1.4–12.4) on illite dissolution at 25 �C inbatch reactors. These results can be compared with disso-lution rates of smectites because of the similarity of struc-ture. Rates decrease with increasing pH under acidicconditions, minimize at near to neutral pH, and increasewith increasing pH at basic conditions. Initial preferential

release of Al and Mg was observed at acidic conditions.At pH between 4 and 11 secondary phases may precipi-tate or Al may be adsorbed. Fractional reaction orderswith respect to protons or hydroxyls at 25 �C were 0.6in both cases.

Kalinowski and Schweda (1996) reported dissolutionrates of muscovite, biotite and phlogopite at pH 1–4 androom temperature. The results are consistent with a frontthat moves from the particle edge inward, producing a Si-rich rim by selective leaching of cations. The dissolution ofphlogopite and biotite were affected by decreasing pH tomuch larger extent than dioctahedral muscovite. The protonreaction order for trioctahedral micas is 0.35�0.61 com-pared to 0.14–0.20 for muscovite. Dissolution rates are high-er for trioctahedral than for dioctahedral phyllosilicates.

The chlorite structure differs slightly from smectite dueto the presence of a hydroxide layer in the interlayer space.Dissolution of the brucite layer is 2–2.5 times faster thandissolution of the TOT structure (Brandt et al., 2003).The overall dissolution rate of chlorite depends on the dis-solution of the TOT structure, which is similar in both chlo-rite and smectite. Dissolution rates of chlorite determinedby Brandt et al. (2003) decreased with increasing pH,according to a proton reaction order of 0.29. Lowson etal. (2005) obtained dissolution rates of chlorite (ripidolite)at 25 �C from pH 3.1 to 10.4. Rates exhibited the commonV-shape profile, with reaction orders of 0.49 and 0.43 in theacidic and basic pH range, respectively. In both studies thedissolution rates are approximately 1–2 orders of magni-tude higher than the smectite dissolution rates, althoughthey exhibited similar dependency on the pH.

Smectites, illites and micas are 2:1 phyllosilicates. Theircrystallography is based on the same structure, a stack ofT–O–T layers, with similar a* and b* cell parameters. Differ-ences are caused by isomorphic substitutions in tetrahedraland/or octahedral sheets and cations within the interlayer

-12

-11

-10

ol/m

2 s)

This study-Sm Zysset-SmAmram-Sm Bauer-SmGolubev-Sm Köhler-IlBrandt-Chl Lowson-ChlKalinowsky-Ms Kalinowsky-BtLin-Ms

BET normalization

-15

-14

-13

log

Rat

e (m

0 2 4 6 8 10 12 14pH

-10

-9Solid mass normalization

-13

-12

-11

log

Rat

e (m

ol/g

s)13

a

b

4236 M.L. Rozalen et al. / Geochimica et Cosmochimica Acta 72 (2008) 4224–4253

space (Newman and Brown, 1987). Focusing on the Aldioctahedral terms, there exist only a few differences inchemistry and structure. So similar reactivity might be ex-pected if the general assumption that the reactivity of mul-ti-oxide minerals is the contribution of the componentoxides is accepted. We might also include chlorites in thisdiscussion, as the overall dissolution rate depends on thebreaking of bridging oxygen bonds in the T–O–T layer(Brandt et al., 2003), as is the case for smectites, illitesand micas.

Our smectite dissolution rates, as well as dissolutionrates of smectite, illite, chlorite and micas at 25 �C collectedfrom literature, are shown in Fig. 10a. The dissolution ratesfor smectites and illite are consistent, with reaction ordersof 0.4 in acidic conditions and 0.3 in alkaline. If crystal-chemistry and structure of both mineral groups are similar,reactive surface sites should also be similar.

The dissolution rates of micas and chlorite are one totwo orders of magnitude higher than those for smectitesand illite. A simpler rate normalization procedure is to massof clay as suggested by Amram and Ganor (2005), who re-ported that BET specific surface area is not proportional tothe mass of clay. When dissolution rates are normalized tomass of mineral, the dissolution rates of the minerals groupmore closely (Fig. 10b) suggesting that similar clay struc-tures dissolve by similar mechanisms.

0 2 4 6 8 10 12 14pH

0 2 4 6 8 10 12 14pH

-14

-9ESA normalization

-12

-11

-10

te (m

ol/m

2 s)

-14

-13log

Rat

c

Fig. 10. Dissolution rates of smectites and other phyllosilicates (a)normalized to BET surface area or (b) mass of solid. (c)Dissolution rates of smectites from different authors normalizedto edge surface area. In the absence of a ESA value, 6.5 m2 g�1 wasused as a proxy (see text for details). Data from literaturecorrespond to Zysset and Schindler (1996), Amram and Ganor(2005), Bauer and Berger (1998), Golubev et al. (2006), Kohleret al. (2003), Brandt et al. (2003), Lowson et al. (2005), Kalinowskiand Schweda (1996), Lin and Clemency (1981).

4.5. Surface area and reactivity

Because dissolution is a surface process dissolution ratesare usually normalized to a specific surface area. Geometricsurface areas, determined by microscopic observations, areusually low because they do not take into account surfaceroughness. BET surface area measured by gas adsorptiongives values that account for surface roughness. The com-mon practice is therefore to normalize clay dissolution ratesto BET surface areas: smectites (Zysset and Schindler, 1996;Bauer and Berger, 1998; Cama et al., 2000), illite (Kohler etal., 2003), chlorites (Brandt et al., 2003; Lowson et al.,2005) and micas (Lin and Clemency, 1981; Knauss andWolery, 1989; Kalinowski and Schweda, 1996; Malmstromand Banwart, 1997). However, some investigations have re-vealed that dissolution reactions occur in particular sites(e.g., etch pits, edges), indicating that reactive and overallsurface areas are neither equivalent nor proportional.

Is a BET surface area representative for the reactive sur-face area of phyllosilicates? The answer may depend on theparticular clay minerals. BET surface area can be a reason-able proxy of surface area of non-swelling phyllosilicates(kaolinite, micas, illite and chlorites) in water suspensions.However, gas adsorption measurements of smectites onlymeasure the external surface, because gases are not accessi-ble to the interlayer space. Furthermore, layer stacks of so-lid sample dispersed in aqueous solution (Verbung andBaveye, 1994; Tournassat et al., 2003) may occlude theinterlayer space at least partially. There is an order of mag-nitude of difference between external (30–120 m2 g�1) andtotal (approximately 750 m2 g�1) clay surface area. How-ever, the agreement between the dissolution rates obtainedfor smectites saturated with different cations and illite from

data of this study or previously published results (Zyssetand Schindler, 1996; Bauer and Berger, 1998; Kohler etal., 2003; Amram and Ganor, 2005; Golubev et al., 2006)suggest that the contribution of interlayer surface to overalldissolution is not significant.

Additional information can be derived from the dissolu-tion mechanism. The rate limiting step silicate dissolution is

Smectite dissolution at 25 �C 4237

the breakdown of bridging oxygen bonds (Bickmore et al.,2001) and the detachment of Si atoms (Oelkers, 2001) in-duced by the previous detachment of octahedral cations.That means that smectites and 2:1 phyllosilicates dissolveinwards from the edges, which has been confirmed byAFM (Bickmore et al., 2001; Kuwahara, 2006) and TEM(Murakami et al., 2003) observations. In other words,AFM observations indirectly support the view that thereactive surface area in phyllosilicates is located on crystaledges.

The BET surface area of smectites is wide—between 30and 120 m2 g�1—primarily due to the swelling properties ofsmectites. Metz et al. (2005b) concluded that smectite BETsurface areas do not represent the area of the mineral/waterinterface because external BET surface areas are not pro-portional to edge AFM surface area. Instead, they sug-gested using AFM measurements of the specific edgesurface area (ESA) as a proxy for the reactive surface areaof smectite (5.5 m2 g�1, SAz-1). Yokoyama et al. (2005)determined the ESA of Kunipa smectite by AFM on singleplates, obtaining 5.4 m2 g�1. Tournassat et al. (2003) mea-sured lateral surface area of smectites by gas adsorptionand AFM (8.5 m2 g�1, MX-80 Wyoming bentonite) andstated that edge surface area does not depend on the num-ber of smectite platelet stacked in a particle, in dry state orin aqueous suspension, as the stacking does not modify theedge surface. They also proposed the use of lateral (edge)surface area to calculate specific sorption site density in claymaterials.

It is difficult to directly estimate the ESA in our sample.First of all, the smectite is composed of particle aggregatesseveral micrometers (Fig. 1a) that consist of clusters ofstacks of clay flakes having an average thickness of 30 A(Fig. 1b) that is roughly 200 nm in diameter (Fig. 1c).The total surface area will therefore include both microand mesoporosity. A t-plot analysis of the BET N2-adsorp-tion isotherm points to a micropore surface area of23.4 m2 g�1 (this mostly excludes the surface area associ-ated to mesopores). However, we cannot separate this valueinto basal and edge surface area contributions because thesurface areas of dry samples consist of large aggregates thatmay not be representative of reactive area of clay particlesdispersed in solution. Nevertheless, the morphology (shape,diameter, thickness) of single clay particles in our K-mont-morillonite is comparable to the morphology of the smec-tites studied by Tournassat et al. (2003), Metz et al.(2005b) and Yokoyama et al. (2005). Therefore, it is reason-able to use the average ESA of 6.5 m2 g�1 estimated in thesestudies to roughly approximate the ESA of our sample.Dissolution rates of smectites normalized to edge surfacearea are plotted in Fig. 10c, assuming that the ESA forthe other 2:1 phyllosilicates is similar (e.g., these mineralspresent similar structure, chemistry and grain size) andclearly group more tightly than BET-normalized rates.

Our experimental results do not allow us to suggest asingle procedure to normalize dissolutions rates. BET sur-face area normalization is a common practice, and is de-rived from an apparently simple measurement. Sampledegassing may produce different results and there is no cor-relation between reactive surface area in smectites and BET

surface area (Tournassat et al., 2003; Metz et al., 2005b).The direct observation of the dissolution reaction on thecrystal edges on phyllosilicates (Bosbach et al., 2000;Bickmore et al., 2001; Yokoyama et al., 2005; Kuwahara,2006) highlights the importance of normalizing dissolutionrates to edge surface area, determined by AFM (Tournassatet al., 2003; Metz et al., 2005b; Yokoyama et al., 2005).Alternatively, mass normalization—as shown in Fig.10b—can be used to compare kinetic results. Until the sur-face area controls over clay dissolution are more unambig-uously defined it is important that reports of claydissolution kinetics include all possible surface area mea-surements—BET, ESA, and mass.

5. CONCLUSIONS

In the present study the effect of pH on K-montmoril-lonite dissolution rate was investigated at 25 �C, using bothstirred flow-through cells and batch reactors. Results fromthese experiments support the following conclusions:

(1) After a period of initial rapid dissolution, ratesbecome congruent and stoichiometric except betweenpH 5 and 10, where adsorption/precipitation of Aland Fe occurs.

(2) Despite the differences in concentrations of Si and Alin batch and flow-through experiments, far fromequilibrium rates are similar at 4.2 < pH < 12. Exper-iments conducted near neutral pH are unavoidablymuch closer to equilibrium.

(3) Dissolution can be described by a rate law to linkingdissolution rates to the concentrations of dissolvedprotons/hydroxyls.

(4) Dissolution rates of smectite and other phyllosili-cates—illite, micas and chlorites—are similar whennormalized to the mass of solid or edge surface area.The effect of pH on the dissolution rate is likewisesimilar.

(5) The reactive surface area is the critical parameter incomparing dissolution rates of clays. While the bestmethod for quantifying reactive surface area remainsa subject of debate, to facilitate comparison by anymethod, the available surface parameters should beprovided with the kinetic data. This would allowkinetic data from different dissolution studies to becorrelated to derive an overall mechanism ofdissolution.

ACKNOWLEDGMENTS

This investigation obtained financial support from SpanishNational Research Program (CGL2001-0255), EC (Febex IIFIKW-CT-2000-00016 and Ecoclay II FIKW-CT-2000-00028),and ENRESA (EN 0770043). M.L.R. and S.G.P. were grantedby Ministerio de Educacion y Ciencia. We also thank Ph.Vieillard and J. Cuevas for helpful discussions. Useful commentsand suggestions from S. Kohler and two anonymous reviewers,as well as from the associated editor E.H. Oelkers are acknowl-edged. F.J.H. dedicates this paper to the memory of Prof.Roland Wollast.

4238

APPENDIX A. CHEMICAL ANALYSIS AND SATURATION STATE WITH RESPECT TO A SELECTED GROUP OF MINERALS OF THE SOLUTIONS

WITHDRAWN FROM EXPERIMENTS IN BATCH REACTORS SERIES A

A-R01

Solution 0.05 M KNO3, 0.1 MHCl

pH average = 1.10 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R01-1 0 1.11 29 2.6A-R01-2 2 1.10 48 22.6A-R01-3 6 1.03 59 17.8 17.5 3.7 �38.868 �1.949 �14.210 �27.865 �46.942 �26.504 �12.402 �5.441A-R01-4 9 1.14 72 30.1A-R01-5 14 1.15 78 22.1 17.9 4.7A-R01-6 17 1.12 86 36.9A-R01-7 20 1.16 94 41.3 18.6 7.4A-R01-8 24 1.17 101 36.1A-R01-9 27 1.15 99 46.2 20.4 6.5 �35.708 �1.642 �13.146 �25.124 �42.663 �26.928 �11.577 �4.615A-R01-10 30 1.08 106 49.1 22.0 7.5 �36.066 �1.601 �13.407 �25.563 �43.419 �26.231 �11.782 �4.821A-R01-11 34 1.08 113 50.5 21.6 7.4 �35.920 �1.568 �13.391 �25.465 �43.272 �26.241 �11.790 �4.829A-R01-12 37 1.16 127 53.2 22.5 8.1 �34.866 �1.497 �13.445 �24.587 �41.843 �25.994 �11.407 �4.445A-R01-13 41 1.09 130 55.2 23.1 9.3 �35.388 �1.485 �13.296 �25.111 �42.726 �26.174 �11.618 �4.657A-R01-14 44 1.11 136 62.2 23.4 8.7 �34.999 �1.457 �13.142 �24.746 �42.152 �26.111 �11.573 �4.612A-R01-15 48 1.09 136 64.5 24.3 8.4 �35.139 �1.456 �13.206 �24.872 �42.369 �26.144 �11.680 �4.718A-R01-16 51 1.10 147 64.8 24.3 9.3 �34.850 �1.411 �13.461 �24.691 �42.084 �26.115 �11.578 �4.616A-R01-17 57 1.08 151 67.3 25.7 9.3 �34.928 �1.398 �13.224 �24.791 �42.262 �26.141 �11.660 �4.699A-R01-18 59 1.12 154 71.2 25.5 10.0 �34.469 �1.385 �13.021 �24.359 �41.558 �26.032 �11.453 �4.492A-R01-19 62 1.07 160 71.2 27.4 10.2 �34.795 �1.363 �13.233 �24.740 �42.198 �26.130 �11.646 �4.685A-R01-20 65 1.18 165 76.2 26.2 10.5 �33.732 �1.346 �12.728 �23.698 �40.483 �25.850 �11.177 �4.216A-R01-21 69 1.08 170 73.3 28.2 12.1 �34.518 �1.329 �13.174 �24.554 �41.906 �26.086 �11.507 �4.546A-R01-22 72 1.06 170 78.2 27.1 11.0 �34.662 �1.327 �13.221 �24.645 �42.070 �26.165 �11.644 �4.683A-R01-23 76 1.09 184 77.2 28.7 11.2 �34.233 �4.551A-R01-24 79 1.08 188 78.6 28.1 11.6 �34.380 �1.270 �13.134 �24.355 �41.608 �26.089 �11.530 �4.569A-R01-25 83 1.05 192 84.5 28.3 12.1 �34.199 �1.257 �13.219 �24.500 �41.866 �26.167 �11.632 �4.671A-R01-26 86 1.02 195 81.6 29.0 12.2 �34.625 �4.791A-R01-27 91 1.03 198 85.9 28.8 12.1 �34.467 �1.239 �13.294 �24.615 �42.066 �26.213 �11.716 �4.755A-R01-28 97 1.04 207 85.5 30.0 13.1 �34.369 �1.213 �13.255 �24.484 �41.857 �26.161 �11.627 �4.666A-R01-29 106 1.01 214 87.4 30.6 13.0A-R01-30 113 1.17 223 90.6 31.2 12.1 �32.890 �1.171 �12.670 �23.229 �39.793 �25.775 �11.133 �4.172A-R01-31 120 1.14 215 95.7 31.5 14.9A-R01-32 128 1.05 212 94.6 32.1 14.0A-R01-33 134 1.08 215 97.0 32.3 14.9A-R01-34 154 1.08 234 100.5 33.6 14.0 �33.452 �1.142 �12.990 �23.814 �40.796 �25.984 �11.424 �4.463

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A-R02

Solution 0.05 M KNO3, 0.01 MHCl

pH average = 1.98 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) G bsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R02-1 0 1.92 0.2 0.1A-R02-2 2 2.02 14.7 11.3A-R02-3 6 1.98 24.7 14.1 10.9 3.7 �32.722 �2.452 �A-R02-4 9 2.07 29.4 15.6A-R02-5 14 1.99 36.7 18.4 14.4 3.7A-R02-6 17 2.05 39.0 19.2A-R02-7 20 2.05 43.8 20.2 12.7 3.7 �30.266 �2.082A-R02-8 24 2.02 46.6 21.3A-R02-9 27 2.03 49.6 22.5 15.3 5.6 �30.136 �2.046A-R02-10 30 1.99 52.1 23.0 15.4 5.6 �30.151 �2.017A-R02-11 34 2.01 59.0 24.2 15.9 5.6 �29.649 �1.944A-R02-12 37 1.99 60.6 25.5 16.2 5.6 �29.727 �1.929A-R02-13 41 2.01 63.5 25.5 16.5 5.6 �29.429 �1.902A-R02-14 44 2.00 65.7 26.3 16.9 5.6 �29.408 �1.882A-R02-15 48 1.96 66.9 27.0 16.9 5.6 �29.695 �1.872A-R02-16 51 2.02 70.4 27.6 17.6 5.6 �29.030 �1.842A-R02-17 57 2.00 73.1 28.9 17.8 5.6 �29.086 �1.819A-R02-18 59 2.01 73.6 29.3 18.4 5.6 �28.956 �1.816A-R02-19 62 1.96 75.1 30.3 19.2 5.6 �29.284 �1.804A-R02-20 65 2.03 77.3 31.0 19.0 5.6 �28.629 �1.787A-R02-21 69 2.01 79.6 31.5 19.3 5.6 �28.711 �1.770A-R02-22 72 1.99 82.2 31.5 19.7 5.6 �28.788 �1.751A-R02-23 76 2.00 81.1 31.8 20.2 3.7 �28.711 �1.759A-R02-24 79 1.97 82.1 32.7 19.7A-R02-25 83 1.92 84.1 33.4 19.0 6.5A-R02-26 86 1.91 83.7 33.7 19.1A-R02-27 91 1.97 85.8 36.4 19.1 5.6 �28.831 �1.726A-R02-28 97 1.94 88.7 37.1 19.9 6.5A-R02-29 106 1.93 90.3 38.6 20.4 7.4A-R02-30 113 2.06 91.1 39.8 20.1 7.4 �27.825 �1.691A-R02-31 120 2.02 88.8 40.8 20.4 6.5A-R02-32 128 1.90 91.7 40.2 20.5 5.6A-R02-33 134 1.99 89.3 40.8 20.6 6.5A-R02-34 154 1.98 92.8 42.4 20.6 6.5 �28.436 �1.681

ib

10.259 �20.972 �35.269 �24.043 �8.390 �1.430

�9.854 �19.421 �32.889 �23.794 �8.239 �1.279

�9.783 �19.208 �32.556 �23.749 �7.965 �1.005�9.932 �19.449 �32.971 �23.852 �8.116 �1.156�9.823 �19.085 �32.397 �23.780 �8.040 �1.081�9.872 �19.153 �32.527 �23.826 �8.116 �1.156�9.791 �18.935 �32.173 �23.758 �8.040 �1.081�9.814 �18.942 �32.197 �23.774 �8.078 �1.119�9.962 �19.217 �32.664 �23.880 �8.230 �1.270�9.705 �18.643 �31.722 �23.696 �8.003 �1.043�9.760 �18.709 �31.847 �23.743 �8.078 �1.119�9.710 �18.602 �31.674 �23.697 �8.040 �1.081�9.896 �18.949 �32.262 �23.807 �8.230 �1.270�9.597 �18.319 �32.222 �23.623 �7.965 �1.005�9.668 �18.427 �31.411 �23.669 �8.040 �1.081�9.750 �18.552 �31.625 �23.711 �8.116 �1.156�9.704 �18.475 �31.497 �23.669 �8.078 �1.119

�9.747 �18.497 �31.570 �23.782 �8.192 �1.232

�9.328 �17.588 �30.085 �23.510 �7.685 �0.726

�9.618 �18.148 �31.035 �23.712 �8.064 �1.105(continued on next page)

Sm

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4240

A-R03

Solution 0.05 M KNO3,0.001 M HCl

pH average = 3.04 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R03-1 0 3.00 0.0 0.0 —A-R03-2 2 3.04 8.4 7.0 —A-R03-3 6 3.03 14.6 8.7 6.2 — �26.365 �2.896 �5.965 �13.253 �22.252 �21.487 �5.465 1.523A-R03-4 9 3.11 17.2 9.4 —A-R03-5 14 3.09 21.8 10.6 8.8 —A-R03-6 17 3.08 23.4 11.0 —A-R03-7 20 3.09 25.3 11.8 9.0 — �24.142 �2.519 �5.596 �11.761 �19.960 �21.101 �4.971 2.016A-R03-8 24 3.07 27.6 12.3 —A-R03-9 27 3.07 29.9 12.6 10.0 — �23.935 �2.471 �5.582 �11.637 �19.774 �21.092 �4.923 2.065A-R03-10 30 3.03 30.9 11.9 10.3 — �24.187 �2.450 �5.778 �11.987 �20.354 �21.184 �5.013 1.975A-R03-11 34 3.05 31.9 13.4 10.7 — �23.863 �2.432 �5.628 �11.652 �19.823 �21.106 �4.939 2.048A-R03-12 37 3.05 32.9 13.5 10.9 — �23.779 �2.413 �5.623 �11.604 �19.751 �21.102 �4.918 2.070A-R03-13 41 3.05 35.7 14.2 11.2 — �23.534 �2.365 �5.590 �11.441 �19.507 �21.082 �4.872 2.116A-R03-14 44 3.06 36.5 15.6 23.3 — �23.331 �2.352 �5.496 �11.227 �19.173 �21.046 �4.829 2.158A-R03-15 48 3.03 37.1 15.0 11.6 — �23.545 �2.343 �5.642 �11.502 �19.625 �21.114 �4.905 2.083A-R03-16 51 3.05 37.3 15.3 11.7 — �23.356 �2.339 �5.548 �11.305 �19.303 �21.048 �4.848 2.140A-R03-17 57 2.98 39.5 15.6 11.9 — �23.726 �2.305 �5.821 �11.782 �20.114 �21.233 �5.013 1.975A-R03-18 59 3.06 39.9 15.7 12.3 — �23.087 �2.299 �5.491 �11.111 �18.998 �20.994 �4.779 2.209A-R03-19 62 3.02 40.0 16.1 12.8 — �23.350 �2.297 �5.641 �11.407 �19.497 �21.082 �4.889 2.099A-R03-20 65 3.07 41.0 16.0 12.7 — �22.923 �2.283 �5.439 �10.976 �18.782 �20.946 �4.733 2.254A-R03-21 69 3.05 42.1 16.4 12.7 — �22.998 �2.268 �5.506 �11.080 �18.966 �21.006 �4.777 2.210A-R03-22 72 3.04 42.2 16.3 12.8 —A-R03-23 76 3.04 43.5 16.8 12.9 —A-R03-24 79 3.05 43.6 17.0 12.6 —A-R03-25 83 3.00 46.1 17.3 12.1 —A-R03-26 86 2.99 45.2 17.3 12.2 —A-R03-27 91 3.05 51.0 17.6 12.3 — �22.502 �2.30 �5.777 �11.164 �19.113 �21.114 �4.916 2.043A-R03-28 97 3.02 47.4 17.6 12.4 —A-R03-29 106 2.85 47.1 17.9 12.5 — —A-R03-30 113 3.10 47.8 17.7 13.1 — �22.418 �2.192 �5.256 �10.427 �17.917 �20.850 �4.559 2.429A-R03-31 120 3.04 49.5 18.4 12.5 —A-R03-32 128 2.97 47.5 17.6 12.8 —A-R03-33 134 3.07 50.9 18.9 12.9 —A-R03-34 154 3.09 51.8 19.2 13.0 — �22.161 �2.145 �5.246 �10.319 �17.770 �20.881 �4.541 2.447

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A-R04

Solution 0.05 M KNO3, 0.01 M HAcO, 0.0015 M KAcO

pH average = 3.97 DGr (kcal/mol)

Sample Time(d) pH Si(LM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolin

A-R04-1 0 3.85 0 0.1 <dlA-R04-2 2 3.87 6.1 3.6 <dlA-R04-3 6 3.87 10.0 4.4 4.7 <dl �21.637 �2.978 �3.394 �8.29A-R04-4 9 3.92 11.8 4.8 <dlA-R04-5 14 3.90 14.5 5.0 7.0 <dlA-R04-6 17 3.92 15.2 5.2 <dlA-R04-7 20 3.93 16.3 5.4 6.3 <dlA-R04-8 24 3.91 18.8 5.4 <dl �19.571 �2.611 �3.110 �6.99A-R04-9 27 3.92 19.1 5.7 7.3 <dl �19.409 �2.601 �3.049 �6.84A-R04-10 30 3.89 20.2 5.7 7.5 <dl �19.482 �2.568 �3.157 �7.00A-R04-11 34 3.91 21.1 5.8 7.6 <dl �18.440A-R04-12 37 3.92 21.6 6.0 8.2 <dl �18.276 �2.512 �2.989 �6.55A-R04-13 41 3.92 22.3 6.3 8.9 <dl �18.131 �2.486 �2.986 �6.49A-R04-14 44 3.92 23.3 6.3 8.7 <dl �18.031 �2.461 �2.997 �6.46A-R04-15 48 3.92 24.3 6.2 8.6 <dl �17.948 �2.462 �2.930 �6.33A-R04-16 51 3.93 24.3 6.5 8.7 <dl �17.813A-R04-17 57 3.92 25.5 6.5 9.1 <dl �17.780 �2.367 �2.858 �6.00A-R04-18 59 3.95 25.6 6.5 9.7 <dl �17.515 �2.367 �2.826 �5.93A-R04-19 62 3.95 26.2 6.4 10.5 <dl �17.253 �2.405 �2.818 �5.99A-R04-20 65 3.95 26.2 6.8 10.6 <dl �17.214 �2.358 �2.603 �5.47A-R04-21 69 3.95 26.8 6.9 10.9 <dl �17.341 �2.405 �2.818 �5.99A-R04-22 72 3.95 27.6 6.9 10.8 <dlA-R04-23 76 3.95 27.1 6.9 10.8 <dlA-R04-24 79 3.99 27.6 7.0 10.5 <dlA-R04-25 83 3.96 28.6 6.9 10.0 <dlA-R04-26 86 3.96 28.6 7.1 10.0 <dlA-R04-27 91 4.00 29.0 7.1 10.0 <dl �16.789 �2.358 �2.604 �5.47A-R04-28 97 4.01 29.4 7.0 10.2 <dlA-R04-29 106 4.00 30.0 7.9 10.4 <dlA-R04-30 113 4.10 30.6 8.3 10.9 <dl �15.793 �2.328 �2.132 �4.46A-R04-31 120 4.03 30.6 8.4 10.6 <dlA-R04-32 128 4.10 31.1 8.5 10.7 <dlA-R04-33 134 4.12 31.3 8.5 10.9 <dlA-R04-34 154 4.16 32.6 8.7 11.0 <dl �15.171 �2.290 �1.875 �3.88

ite Muscovite Brucite Fe(OH)3 Goethite

3 �13.560 �19.504 EQ 6.960

2 �11.556 �19.170 EQ 6.9609 �11.328 �19.113 EQ 6.9602 �11.597 �19.183 EQ 6.960

2 �10.882 �19.000 EQ 6.9604 �10.795 �19.016 EQ 6.9605 �10.752 �19.022 EQ 6.9602 �10.539 �18.952 EQ 6.960

0 �10.014 �18.823 EQ 6.9606 �9.918 �18.830 EQ 6.9606 �10.007 �18.803 EQ 6.9604 �9.158 �18.717 EQ 6.9606 �10.007 �18.803 EQ 6.960

4 �9.158 �18.717 EQ 6.960

9 �7.516 �18.400 EQ 6.960

1 �6.554 �18.236 EQ 6.960(continued on next page)

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�C4241

A-R05

Solution 0.05 M KNO3,0.0013 M HAcO, 0.0005MKAcO

pH average = 7.01 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R05-1 0 4.98 0 0.09 <dlA-R05-2 2 5.01 2.6 0.37 <dlA-R05-3 6 5.23 4.4 1.15 3.2 <dl �13.445 �3.607 1.347 �0.050 0.568 �15.893 EQ 6.988A-R05-4 9 5.60 5.3 1.23 3.4 <dlA-R05-5 14 5.94 7.9 1.10 3.8 <dlA-R05-6 17 6.05 8.3 0.94 3.5 <dlA-R05-7 20 6.28 11.0 0.78 3.3 <dlA-R05-8 24 6.37 8.9 0.63 3.4 <dlA-R05-9 27 6.66 9.2 0.19 3.4 <dl �7.810 �3.171 1.991 2.109 5.757 �11.953 EQ 6.988A-R05-10 30 6.79 9.1 0.12 3.5 <dlA-R05-11 34 6.92 12.4 0.11 3.7 <dlA-R05-12 37 6.88 12.6 0.10 3.7 <dlA-R05-13 41 7.04 12.8 0.10 3.7 <dl �14.351 �2.972 1.270 1.065 4.710 �10.864 EQ 6.988A-R05-14 44 6.89 12.8 0.12 3.7 <dl �14.364 �2.972 1.505 1.533 5.207 �11.273 EQ 6.988A-R05-15 48 7.10 13.5 0.09 3.7 <dl �7.070 �2.943 1.337 0.855 4.477 �10.701 EQ 6.988A-R05-16 51 7.03 13.5 0.09 3.8 <dl �7.137 �2.942 1.190 0.964 4.544 �10.879 EQ 6.988A-R05-17 57 7.03 13.7 0.07 3.9 <dl �7.268 �2.932 1.051 0.706 4.158 �10.856 EQ 6.988A-R05-18 59 7.14 13.6 0.06 4.2 <dl �5.524 �2.937 0.827 0.249 3.622 �10.511 EQ 6.988A-R05-19 62 7.07 13.7 0.18 4.7 <dl �6.447 �2.934 1.569 1.739 5.762 �10.640 EQ 6.988A-R05-20 65 6.97 14.4 0.18 4.9 <dl �6.422 �2.904 1.652 1.964 5.962 �10.892 EQ 6.988A-R05-21 69 6.97 13.5 0.12 5.1 <dl �8.561 �2.942 1.124 0.832 4.293 �10.868 EQ 6.988A-R05-22 72 6.99 13.5 0.07 4.6 <dl �7.243 �2.940 0.768 0.126 3.301 �10.702 EQ 6.988A-R05-23 76 7.00 13.8 0.16 4.0 <dlA-R05-24 79 7.04 13.6 0.05 4.9 <dl �7.578 �2.940 0.623 �0.165 3.307 �10.386 EQ 6.988A-R05-25 83 7.21 13.8 0.00 6.0 <dlA-R05-26 86 7.20 13.7 0.00 5.3 <dlA-R05-27 91 7.19 13.6 0.05 4.2 <dl �5.705 �2.918 0.307 �0.737 2.773 �9.150 EQ 6.988A-R05-28 97 7.62 13.6 0.05 4.1 <dlA-R05-29 106 7.12 14.1 0.12 4.1 <dlA-R05-30 113 7.62 14.1 0.07 4.6 <dl �6.884 �2.922 �0.579 �2.534 0.443 �8.510 EQ 6.988A-R05-31 120 7.16 14.0 0.05 4.2 <dlA-R05-32 128 7.81 14.5 0.04 4.3 <dlA-R05-33 134 7.82 13.7 0.05 4.3 <dlA-R05-34 154 7.87 14.1 0.03 4.3 <dl �3.964

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A-R06

Solution 0.05 M KNO3, 0.004 MKHCO3, 0.006M K2CO3

pH average = 10.47 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R06-1 0 10.40 1.0 0.2 <dlA-R06-2 2 10.31 11.7 3.6 <dlA-R06-3 6 10.31 14.7 4.2 0.9 <dl �7.097 �3.684 �0.882 �4.663 0.670 �3.271 0.000 6.988A-R06-4 9 10.31 14.7 4.7 1.0 <dlA-R06-5 14 10.30 13.6 5.1 1.2 <dlA-R06-6 17 10.50 27.0 5.3 1.2 <dlA-R06-7 20 10.53 28.4 5.4 1.2 <dlA-R06-8 24 10.15 29.0 5.7 1.2 <dlA-R06-9 27 10.20 29.6 5.7 1.2 <dl �4.743 �3.161 �0.555 �2.964 3.069 �3.371 EQ 6.988A-R06-10 30 10.47 30.3 5.9 1.4 <dlA-R06-11 34 10.48 37.1 5.9 1.5 <dl �3.366 �2.865 �0.919 �3.098 3.249 �2.535 EQ 6.988A-R06-12 37 10.46 36.8 5.9 1.5 <dl �3.340 �2.849 �0.893 �3.015 3.345 �2.634 EQ 6.988A-R06-13 41 10.46 38.0 5.9 1.4 <dl �3.646 �2.830 �0.889 �2.969 3.414 �2.652 EQ 6.988A-R06-14 44 10.50 37.6 4.0 1.5 <dl �3.732 �2.880 �1.182 �3.655 2.439 �2.485 EQ 6.988A-R06-15 48 10.50 38.4 6.9 1.5 <dl �3.235 �2.867 �0.844 �2.954 3.491 �2.485 EQ 6.988A-R06-16 51 10.47 39.2 6.0 2.0 <dl �3.171 �2.822 �0.896 �2.966 3.432 �2.530 EQ 6.988A-R06-17 57 10.48 39.6 6.0 2.8 <dl �3.166 �2.827 �0.905 �2.995 3.402 �2.476 EQ 6.988A-R06-18 59 10.45 39.3 5.8 2.7 <dl �2.558 �2.799 �0.885 �2.898 3.507 �2.552 EQ 6.988A-R06-19 62 10.45 39.2 6.3 2.7 <dl �3.045 �2.800 �0.839 �2.809 3.641 �2.566 EQ 6.988A-R06-20 65 10.43 39.8 6.5 2.4 <dl �4.694 �3.221 �0.832 �3.635 2.374 �2.536 EQ 6.988A-R06-21 69 10.43 39.7 6.1 1.9 <dlA-R06-22 72 10.43 39.2 6.1 — <dlA-R06-23 76 10.48 39.0 5.9 — <dlA-R06-24 79 10.17 41.6 5.8 1.9 <dlA-R06-25 83 10.09 41.8 6.0 1.8 <dlA-R06-26 86 10.08 41.4 6.0 1.8 <dl �3.389 �2.855 �0.364 �1.969 4.399 �3.446 EQ 6.988A-R06-27 91 10.07 40.5 6.0 1.8 <dlA-R06-28 97 10.09 40.5 5.9 1.9 <dlA-R06-29 106 10.07 39.8 5.4 2.2 <dlA-R06-30 113 10.02 40.4 5.5 2.4 <dl �3.270 �2.819 �0.334 �1.837 4.515 �3.413 EQ 6.988A-R06-31 120 9.91 40.0 5.9 2.1 <dl

A-R06-32

128 9.98 38.55.5

2.4 <dlA-R06-33 134 10.02 40.0 5.1 2.2 <dlA-R06-34 154 9.96 39.2 4.9 2.2 <dl �3.292 �2.790 �0.322 �1.755 4.557 �3.597 EQ 6.988

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A-R07

Solution 0.05 M KNO3,0.0021 M KHCO3

pH average = 8.44 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R07-1 0 8.44 0.2 0.1 <dlA-R07-2 2 7.99 5.3 0.5 <dlA-R07-3 6 8.20 7.9 0.8 2.3 <dl �6.347 �3.273 1.021 �0.034 4.630 �7.984 0.000 6.988A-R07-4 9 8.20 8.5 0.8 2.4 <dlA-R07-5 14 8.19 9.5 1.1 2.6 <dlA-R07-6 17 7.95 10.0 1.2 2.5 <dlA-R07-7 20 8.07 10.3 1.1 2.4 <dlA-R07-8 24 8.05 10.8 1.2 2.5 <dlA-R07-9 27 7.94 10.8 1.2 2.6 <dl �5.319 �3.078 1.605 1.522 6.609 �8.613 0.000 6.988A-R07-10 30 8.01 11.2 1.2 2.5 <dl �5.225 �3.058 1.513 1.380 6.491 �8.450 0.000 6.988A-R07-11 34 8.21 11.2 1.2 2.8 <dl �5.142 �3.063 1.234 0.811 5.911 �7.823 0.000 6.988A-R07-12 37 8.04 11.6 1.2 2.8 <dl �5.117 �3.040 1.466 1.321 6.444 �8.303 0.000 6.988A-R07-13 41 8.13 12.0 1.3 2.9 <dl �4.933 �3.020 1.388 1.206 6.394 �8.032 0.000 6.988A-R07-14 44 8.02 11.9 1.2 3.1 <dl �5.054 �3.024 1.470 1.361 6.476 �8.210 0.000 6.988A-R07-15 48 8.15 12.0 1.1 3.0 <dl �4.974 �3.023 1.283 0.989 6.096 �7.955 0.000 6.988A-R07-16 51 8.03 12.5 1.1 3.4 <dl �4.916 �2.994 1.445 1.362 6.506 �8.210 0.000 6.988A-R07-17 57 8.18 12.5 1.1 3.2 <dl �4.912 �2.993 1.215 0.911 6.020 �7.824 0.000 6.988A-R07-18 59 8.03 12.6 1.0 3.7 <dl �4.966 �2.992 1.380 1.243 6.314 �8.155 0.000 6.988A-R07-19 62 8.19 12.8 1.3 4.4 <dl �4.658 �4.6 1.292 1.080 6.287 �7.612 0.000 6.988A-R07-20 65 8.05 12.9 1.2 4.2 <dl �4.715 �2.978 1.467 1.447 6.645 �8.033 0.000 6.988A-R07-21 69 8.18 12.6 1.1 4.0 <dl �4.842 �2.995 1.217 0.912 6.022 �7.655 0.000 6.988A-R07-22 72 8.07 12.5 1.0 4.3 <dlA-R07-23 76 8.15 12.8 1.1 4.7 <dlA-R07-24 79 7.98 12.7 1.0 4.1 <dlA-R07-25 83 8.07 12.7 1.0 3.2 <dlA-R07-26 86 7.77 12.6 0.9 3.3 <dl �5.133 �2.987 1.395 1.284 6.215 �8.439 0.000 6.988A-R07-27 91 7.95 12.6 0.9 3.3 <dlA-R07-28 97 8.20 12.9 0.9 3.3 <dlA-R07-29 106 7.85 13.3 0.9 3.4 <dlA-R07-30 113 8.24 13.3 0.9 4.0 <dl �4.853 �2.965 1.022 0.582 5.609 �7.532 0.000 6.988A-R07-31 120 7.85 13.7 0.8 3.5 <dlA-R07-32 128 8.24 13.2 0.7 3.5 <dlA-R07-33 134 8.33 13.5 0.7 3.6 <dlA-R07-34 154 8.25 13.7 0.7 3.6 <dl �5.018 �2.947 0.844 0.283 5.173 �7.567 0.000 6.988

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A-R08

Solution 0.005 M KOH pH average = 11.59 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R08-1 0 11.59 1.8 0.2 <dl <dlA-R08-2 2 11.45 19.3 5.6 <dl <dlA-R08-3 6 11.47 20.8 6.6 2.5 <dl �9.832 �4.832 �1.933 �9.063 �10.751 1.255 EQ 6.987A-R08-4 9 11.39 25.5 6.5 0 <dlA-R08-5 14 11.86 23.7 7.4 2.6 <dlA-R08-6 17 11.81 27.6 8.8 0 <dlA-R08-7 20 11.84 27.7 9.0 1.8 <dl �5.896 �5.196 �2.445 �10.814 �12.640 2.037 EQ 6.987A-R08-8 24 11.15 26.6 8.6 2.0 <dl �7.738 �4.254 �1.518 �7.076 �8.211 0.277 EQ 6.987A-R08-9 27 11.77 28.1 9.0 2.1 <dl �10.787 �5.082 �2.349 �10.395 �12.080 1.967 EQ 6.987A-R08-10 30 11.83 29.0 10.0 2.3 <dl �10.953 �5.153 �2.371 �10.598 �12.305 2.167 EQ 6.987A-R08-11 34 11.85 28.7 9.6 2.5 <dl �11.104 �5.189 �2.424 �10.759 �12.501 2.260 EQ 6.987A-R08-12 37 11.49 33.1 11.2 2.5 <dl �8.681 �4.586 �1.834 �8.372 �9.571 1.319 EQ 6.987A-R08-13 41 11.69 30.1 10.2 2.9 <dl �9.992 �4.926 �2.163 �9.709 �11.187 1.939 EQ 6.987A-R08-14 44 11.86 32.7 10.1 3.0 <dl �10.748 �5.127 �2.405 �10.596 �12.169 2.402 EQ 6.987A-R08-15 48 11.85 31.6 10.5 3.3 <dl �10.770 �5.132 �2.371 �10.540 �12.162 2.331 EQ 6.987A-R08-16 51 11.77 31.6 10.5 3.3 <dl �10.259 �5.014 �2.260 �10.080 �11.571 2.228 EQ 6.987A-R08-17 57 11.89 32.7 10.6 3.5 <dl �10.844 �5.172 �2.427 �10.731 �12.318 2.571 EQ 6.987A-R08-18 59 11.87 31.6 10.0 0.0 <dlA-R08-19 62 11.87 32.7 10.9 4.5 <dlA-R08-20 65 11.74 32.9 10.7 0.0 <dlA-R08-21 69 11.85 33.0 10.8 4.8 <dl �10.466 �5.106 �2.355 �10.455 �11.924 2.650 EQ 6.987A-R08-22 72 11.86 33.0 10.6 0.0 <dlA-R08-23 76 11.95 33.7 11.2 4.8 <dlA-R08-24 79 11.46 33.7 10.7 0.0 <dlA-R08-25 83 11.38 35.3 12.0 4.0 <dlA-R08-26 86 11.45 36.0 11.1 0.0 <dlA-R08-27 91 11.45 36.0 11.3 3.0 <dl �8.524 �4.479 �1.787 �8.065 �9.083 1.322 EQ 6.987A-R08-28 97 11.42 36.1 11.3 0.0 <dlA-R08-29 106 11.54 34.8 11.1 3.7 <dlA-R08-30 113 11.35 36.2 11.4 4.1 <dl �7.910 �4.339 �1.657 �7.524 �8.380 1.229 EQ 6.987A-R08-31 120 11.23 36.2 10.9 2.4 <dlA-R08-32 128 11.39 37.3 10.8 2.3 <dlA-R08-33 134 11.24 36.7 10.9 2.5 <dlA-R08-34 154 10.97 36.0 10.6 1.3 <dl

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A-R09

Solution 0.05 M KOH pH average = 12.77 DGr (kcal/mol)

Sample Time(d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R09-1 0 12.93 2.0 0.0 <dl <dlA-R09-2 2 12.95 21.6 5.7 <dl <dlA-R09-3 6 12.78 27.2 7.1 <dl <dl �20.207 �6.950 �3.944 �17.319 �15.070 EQ EQ 6.988A-R09-4 9 12.78 29.2 8.3 <dl <dlA-R09-5 14 12.95 33.0 8.8 <dl <dlA-R09-6 17 12.94 33.8 9.7 <dl <dlA-R09-7 20 12.90 34.8 10.2 <dl <dlA-R09-8 24 13.01 38.4 9.8 <dl <dl �21.628 �7.296 �4.083 �18.287 �16.237 EQ EQ 6.989A-R09-9 27 13.03 39.0 12.1 <dl <dl �21.653 �7.338 �3.984 �18.173 �16.041 EQ EQ 6.989A-R09-10 30 13.01 41.9 12.3 <dl <dl �21.246 �7.244 �3.947 �17.913 �15.675 EQ EQ 6.989A-R09-11 34 12.93 42.9 13.2 <dl <dl �20.243 �7.031 �3.790 �17.174 �14.665 EQ EQ 6.989A-R09-12 37 12.95 45.0 13.0 <dl <dl �20.357 �7.051 �3.826 �17.285 �14.808 EQ EQ 6.989A-R09-13 41 12.78 46.5 13.7 <dl <dl �18.738 �6.632 �3.551 �15.897 �12.937 EQ EQ 6.989A-R09-14 44 12.78 48.1 14.2 <dl <dl �19.393 �6.611 �3.531 �15.815 �12.814 EQ EQ 6.989A-R09-15 48 12.95 49.4 14.2 <dl <dl �20.074 �6.996 �3.776 �17.075 �14.491 EQ EQ 6.989A-R09-16 51 12.94 50.4 14.7 <dl <dl �19.888 �6.960 �3.741 �16.932 �14.289 EQ EQ 6.989A-R09-17 57 12.90 52.3 15.3 <dl <dl �19.332 �6.841 �3.656 �16.526 �13.730 EQ EQ 6.989A-R09-18 59 13.01 53.2 15.4 <dl <dlA-R09-19 62 13.03 54.2 16.7 <dl <dlA-R09-20 65 13.01 55.1 16.2 <dl <dlA-R09-21 69 13.00 55.0 17.3 <dl <dl �20.229 �7.058 �3.730 �17.106 �14.476 EQ EQ 6.989A-R09-22 72 13.06 55.8 16.9 <dl <dlA-R09-23 76 13.13 57.1 17.2 <dl <dlA-R09-24 79 12.59 57.7 16.6 <dl <dlA-R09-25 83 12.54 58.3 17.5 <dl <dlA-R09-26 86 12.60 58.7 17.8 <dl <dlA-R09-27 91 12.66 58.8 18.3 <dl <dl �16.469 �6.231 �3.212 �14.417 �10.869 EQ EQ 6.989A-R09-28 97 12.63 60.6 18.3 <dl <dlA-R09-29 106 12.84 60.3 18.8 <dl <dlA-R09-30 113 12.65 63.2 19.5 <dl <dl �16.153 �6.167 �3.158 �14.182 �10.529 EQ EQ 6.989A-R09-31 120 12.65 63.5 19.9 <dl <dlA-R09-32 128 12.81 62.7 20.3 <dl <dlA-R09-33 134 12.72 61.7 20.5 <dl <dlA-R09-34 154 12.97 66.1 21.3 <dl <dl

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A-R010

Solution 0.5 M KOH pH average = 13.44 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe (lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

A-R10-1 0 13.44 0 0 <dl <dlA-R10-2 2 13.73 24.3 7.0 <dl <dlA-R10-3 6 13.37 33.0 8.8 <dl <dl �26.506 �8.525 �4.705 �21.985 �20.036 EQ EQ 6.995A-R10-4 9 13.32 33.8 9.7 <dl <dlA-R10-5 14 13.84 41.6 11.4 <dl <dl �31.722 �9.747 �5.220 �25.449 �24.661 EQ EQ 7.002A-R10-6 17 13.83 47.2 12.5 <dl <dl �31.223 �9.641 �5.151 �25.103 �24.152 EQ EQ 7.002A-R10-7 20 13.87 52.5 12.6 <dl <dl �31.492 �9.699 �5.204 �25.322 �24.433 EQ EQ 7.003A-R10-8 24 13.61 55.9 14.7 <dl <dl �27.858 �8.892 �4.741 �22.787 �20.943 EQ EQ 6.998A-R10-9 27 13.85 53.8 12.0 <dl <dl �31.212 �9.624 �5.205 �25.174 �24.236 EQ EQ 7.002A-R10-10 30 13.89 55.6 15.9 <dl <dl �31.444 �9.726 �5.096 �25.159 �24.165 EQ EQ 7.003A-R10-11 34 13.92 57.6 16.9 <dl <dl �31.712 �9.796 �5.105 �25.317 �24.367 EQ EQ 7.004A-R10-12 37 13.75 60.2 17.1 <dl <dl �29.366 �9.259 �4.852 �23.740 �22.204 EQ EQ 7.000A-R10-13 41 13.74 64.1 18.7 <dl <dl �29.017 �9.191 �4.783 �23.469 �21.808 EQ EQ 7.000A-R10-14 44 13.89 65.4 18.8 <dl <dl �30.929 �9.629 �4.996 �24.765 �23.575 EQ EQ 7.003A-R10-15 48 13.84 66.9 19.6 <dl <dl �30.188 �9.465 �4.899 �24.246 �22.855 EQ EQ 7.002A-R10-16 51 13.87 67.7 20.3 <dl <dlA-R10-17 57 13.97 72.9 20.8 <dl <dlA-R10-18 59 13.97 71.6 20.6 <dl <dlA-R10-19 62 13.97 72.2 22.4 <dl <dlA-R10-20 65 13.87 74.7 23.4 <dl <dlA-R10-21 69 13.90 73.9 22.9 <dl <dl �30.625 �9.587 �4.896 �24.482 �23.138 EQ EQ 7.004A-R10-22 72 14.02 75.6 23.3 <dl <dlA-R10-23 76 13.55 76.7 24.1 <dl <dlA-R10-24 79 13.51 77.9 28.6 <dl <dlA-R10-25 83 13.54 80.1 28.9 <dl <dlA-R10-26 86 13.55 79.9 30.1 <dl <dlA-R10-27 91 13.54 85.0 29.6 <dl <dl �25.444 �8.442 �4.225 �20.858 �18.134 EQ EQ 6.997A-R10-28 97 13.83 79.2 30.6 <dl <dlA-R10-29 106 13.62 82.3 32.4 <dl <dlA-R10-30 113 13.62 88.4 33.1 <dl <dl �26.278 �8.650 �4.275 �21.369 �18.804 EQ EQ 6.998A-R10-31 120 13.74 90.4 32.3 <dl <dlA-R10-32 128 13.67 88.7 33.3 <dl <dlA-R10-33 134 13.68 96.5 33.5 <dl <dlA-R10-34 154 13.68 100.3 34.2 <dl <dl

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APPENDIX B. CHEMICAL ANALYSIS AND SATURATION STATE WITH RESPECT TO A SELECTED GROUP OF MINERALS OF THE SOLUTIONS

WITHDRAWN FROM EXPERIMENTS IN BATCH REACTORS SERIES B

B-R01

Solution 0.1 M HCl, 0.1 MKNO3

pH average = 1.09 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R01-0 0 1.04 0 0 0 0.0B-R01-1 3 0.95 439 268 181 28.4 �31.678 �0.7756 �13.048 �23.194 �39.660 �25.403 �11.685 �4.723B-R01-2 6 0.93 579 304 209 34.2 �31.037 �0.6145 �13.059 �22.895 �39.240 �25.376 �11.660 �4.698B-R01-3 10 1.07 728 314 230 41.1 �29.190 �0.4809 �12.450 �21.410 �36.818 �24.932 �10.972 �4.010B-R01-4 15 1.10 918 434 243 47.5 �28.096 �0.3453 �12.138 �20.515 �35.435 �28.819 �10.766 �3.803B-R01-5 20 1.08 1009 487 267 52.7 �27.915 �0.2905 �12.154 �20.438 �35.346 �24.817 �10.788 �3.825B-R01-6 22 1.08 1059 510 262 54.5 �27.769 �0.2623 �12.128 �20.329 �35.184 �24.828 �10.769 �3.807B-R01-7 24 1.11 1084 498 247 55.6 �27.448 �0.2485 �12.016 �20.077 �34.764 �24.734 �10.581 �3.619B-R01-8 30 1.10 1253 541 272 60.8 �27.130 �0.1645 �12.011 �19.898 �34.509 �24.753 �10.622 �3.660B-R01-9 35 1.11 1287 557 273 63.7 �26.949 �0.1488 �11.952 �19.749 �34.273 �24.722 �10.554 �3.592B-R01-10 41 1.10 1369 600 281 68.4 �26.814 �0.1127 �11.951 �19.674 �34.174 �24.733 �10.554 �3.592B-R01-11 45 1.04 1461 615 292 69.0 �27.152 �0.0747 �12.187 �20.074 �34.853 �24.877 �10.797 �3.835B-R01-12 50 1.07 1510 619 294 74.8 �26.792 �0.0554 �12.058 �19.774 �34.365 �24.790 �10.626 �3.664

B-R02

Solution 0.01 MHCl, 0.1 M KNO3

pH average = 2.11 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R02-0 0 2.05 0 0 0 0.0B-R02-1 3 2.05 195 142 110 10.6 �24.736 �1.248 �8.796 �15.637 �26.805 �22.632 �7.735 �0.774B-R02-2 6 2.05 279 139 97 12.2 �23.938 �1.040 �8.808 �15.246 �26.218 �22.704 �7.649 �0.689B-R02-3 10 2.10 366 137 98 12.8 �22.884 �0.026 �8.616 �14.544 �25.098 �22.563 �7.435 �0.475B-R02-4 15 2.10 425 136 99 12.8 �22.531 �0.794 �8.619 �14.375 �24.844 �22.556 �7.435 �0.475B-R02-5 20 2.10 484 137 100 10.6 �22.248 �0.718 �8.618 �14.221 �24.614 �22.552 �7.547 �0.586B-R02-6 22 2.11 504 210 101 10.0 �21.741 �0.695 �8.326 �13.592 �23.657 �22.521 �7.542 �0.581B-R02-7 24 2.14 498 214 100 10.0 �21.441 �0.686 �8.195 �13.312 �23.197 �22.442 �7.430 �0.469B-R02-8 30 2.10 583 275 102 10.0 �19.798 �0.243 �8.212 �12.461 �21.973 �22.541 �7.580 �0.619B-R02-9 35 2.13 594 277 101 10.6 �20.966 �0.600 �8.085 �12.918 �22.619 �22.467 �7.436 �0.476B-R02-10 41 2.15 628 285 101 10.0 �20.654 �0.567 �7.989 �12.661 �22.206 �22.413 �7.393 �0.433B-R02-11 45 2.07 664 287 100 9.4 �21.198 �0.534 �8.308 �13.234 �23.174 �22.631 �7.726 �0.765B-R02-12 50 2.09 693 289 101 10.0 �20.668 �0.509 �8.039 �12.645 �22.263 �22.576 �7.618 �0.658

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B-R03

Solution 0.001 M HCl,0.1 M KNO3

pH average = 3.63 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R03-0 0 3.05 0 0 0.0 >l.d.B-R03-1 3 3.39 118 52 1.4 <ld �16.764 �1.657 �3.650 �6.144 �10.734 �19.297 eq 6.989B-R03-2 6 3.79 135 61 1.4 <ld �13.330 �1.462 �2.279 �3.031 �5.556 �18.336 eq 6.960B-R03-3 10 3.60 190 77 1.5 <ld �13.712 �1.264 �2.891 �3.860 �7.057 �18.789 eq 6.960B-R03-4 15 2.99 216 81 1.7 <ld �17.900B-R03-5 20 3.68 241 80 2.0 <ld �12.420 �1.124 �2.540 �2.877 �5.474 �18.403 eq 6.960B-R03-6 22 3.67 252 83 1.9 <ld �12.181 �1.048 �2.559 �2.763 �5.317 �18.462 eq 6.960B-R03-7 24 3.66 257 85 1.8 <ld �12.417 �1.087 �2.587 �2.897 �5.531 �18.528 eq 6.960B-R03-8 30 3.69 286 83 1.9 <ld �11.938 �1.025 �2.477 �2.553 �4.975 �18.413 eq 6.960B-R03-9 35 3.76 295 84 2.0 <ld �11.319 �1.007 �2.186 �1.936 �3.955 �18.203 eq 6.960B-R03-10 41 3.76 312 85 2.1 <ld �11.167 �0.974 �2.181 �1.860 �3.841 �18.178 eq 6.960B-R03-11 45 3.76 323 67 2.1 <ld �11.257 �0.954 �2.319 �2.094 �4.191 �18.159 eq 6.960B-R03-12 50 3.75 260 80 2.2 <ld �11.147 �0.942 �2.259 �1.950 �3.989 �18.183 eq 6.960

B-R05

Solution 0.01 M AcOH,0.0005 M AcOK, 0. 1 M KNO3

pH average = 7.53 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R05-0 0 5.99 0 0 0 <l.d.B-R05-1 3 5.93 50 1 38 <l.d. �5.100 �2.161 2.572 5.293 9.890 �12.651 eq 6.989B-R05-2 6 5.95 69 1 40 <l.d. �5.979 �2.424 2.796 5.214 9.798 �12.564 eq 6.989B-R05-3 10 6.22 82 1 41 <l.d. �2.975 �1.872 2.898 6.523 12.130 �11.815 eq 6.989B-R05-4 15 6.40 97 1 44 <l.d. �2.025 �1.775 2.885 6.690 12.626 �11.281 eq 6.989B-R05-5 20 6.88 105 1 49 <l.d. �0.881 �1.728 2.387 5.787 11.926 �9.900 eq 6.989B-R05-6 24 6.20 109 0 46 <l.d. �2.728 �1.706 2.237 5.533 10.617 �11.800 eq 6.989B-R05-7 30 7.37 114 0 43 <l.d. �0.737 �1.679 1.560 4.231 10.250 �8.652 eq 6.989B-R05-8 35 7.49 119 0 48 <l.d. �0.350 �1.657 1.559 4.274 10.490 �8.259 eq 6.989B-R05-9 41 7.57 122 1 49 <l.d. �0.068 �1.523 1.861 5.127 11.748 �8.336 eq 6.989B-R05-10 45 7.36 123 0 48 <l.d. �0.400 �1.634 1.666 4.533 10.701 �8.609 eq 6.989B-R05-11 50 7.68 135 1 48 <l.d. 0.255 �1.582 1.482 4.270 10.742 �7.739 eq 6.989B-R05-12 55 7.68 133 1 47 <l.d. 0.534 �1.592 1.728 4.742 11.450 �7.749 eq 6.989

(continued on next page)

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B-R09

Solution 0.0021 M KHCO3,0.1 M KNO3

pH average = 9.19 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R09-0 0 9.09 0.0 0.17 0.0 <ldB-R09-1 3 9.27 51.4 1.68 13.6 <ld 0.387 �2.287 �0.030 �0.165 6.264 �4.121 eq 6.989B-R09-2 6 9.25 58.1 0.58 13.7 <ld 0.647 �2.065 �0.306 �0.292 5.877 �4.542 eq 6.960B-R09-3 10 9.26 68.4 0.00 14.7 <ld 1.021 �1.972 �0.320 �0.134 6.128 �4.476 eq 7.960B-R09-4 15 9.19 78.0 0.27 15.9 <ld �0.239 �2.019 �1.001 �1.570 4.046 �4.264 eq 8.960B-R09-5 20 9.19 83.8 0.30 19.9 <ld 0.054 �1.977 �0.954 �1.382 4.314 �4.111 eq 9.960B-R09-6 24 9.19 85.2 0.29 15.9 <ld 0.037 �1.9661 �0.962 �1.386 4.322 �4.246 eq 10.960B-R09-7 30 9.14 84.0 0.27 16.1 <ld 0.019 �0.210 �0.941 �1.340 4.324 �4.372 eq 11.960B-R09-8 35 9.19 82.2 0.35 17.9 <ld 0.149 �1.988 �0.857 �1.221 4.570 �4.173 eq 12.960B-R09-9 41 9.16 85.3 0.13 17.7 <ld �0.705 �1.959 �1.413 �2.274 2.950 �4.261 eq 13.960B-R09-10 45 9.04 85.1 0.16 17.8 <ld �0.264 �1.935 �1.110 �1.189 3.765 �4.579 eq 14.960B-R09-11 50 9.02 89.0 0.22 18.1 <ld 0.173 �1.905 �0.906 �1.152 4.441 �4.625 eq 15.960B-R09-12 55 9.03 86.9 0.20 18.1 <ld 0.011 �1.921 �0.963 �1.319 4.206 �4.596 eq 16.960

B-R010

Solution 0.004 M KHCO3,0.0061 M K2CO3, 0.1 M KNO3

pH average = 10.10 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R10-0 0 10.33 0 0.02 0.0B-R10-1 3 10.21 86 1.61 6.7 <ld �3.045 �2.563 �1.3556 �3.367 2.708 �2.905 eq 6.989B-R10-2 6 10.11 95 1.36 6.6 <ld �2.932 �2.297 �0.9792 �2.102 4.285 �3.508 eq 6.961B-R10-3 10 10.11 106 1.10 6.9 <ld �2.514 �2.348 �1.4424 �3.111 2.957 �3.128 eq 6.989B-R10-4 15 10.04 114 1.51 8.4 <ld �1.803 �2.240 �1.1629 �2.337 4.025 �3.176 eq 6.989B-R10-5 20 10.02 110 0.91 11.8 <ld �2.118 �2.247 �1.4371 �2.898 3.156 �3.019 eq 6.989B-R10-6 24 9.99 111 0.97 7.4 <ld �2.099 �2.214 �1.3537 �2.666 3.464 �3.366 eq 6.989B-R10-7 30 9.94 108 1.11 6.4 <ld �1.975 �2.194 �1.2067 �2.332 3.898 �3.560 eq 6.989B-R10-8 35 10.02 112 0.87 6.4 <ld �2.315 �2.237 �1.4619 �2.929 3.110 �3.378 eq 6.989B-R10-9 41 9.96 118 0.73 7.0 <ld �2.125 �2.157 �1.4844 �2.813 3.203 �3.467 eq 6.989B-R10-10 45 9.60 122 1.03 9.2 <ld �1.676 �2.136 �1.2773 �2.356 3.888 �3.301 eq 6.989B-R10-11 50 9.57 122 0.47 9.5 <ld �1.406 �1.891 �1.2054 �1.724 4.312 �4.142 eq 6.989B-R10-12 55 9.63 105 0.38 10.2 <ld �2.003 �2.008 �1.4177 �2.381 3.407 �3.975 eq 6.989

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B-R12

Solution 0.05 M KOH pH average = 12.50 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R12-0 0 12.77 0 30 0.0 <ldB-R12-1 3 12.62 272 83 8.3 <ld �10.722 �5.196 �2.237 �10.398 �5.821 4.923 eq 6.987B-R12-2 5 12.57 294 115 <ld <ld �9.789 �4.661 �1.976 �8.806 �3.495 eq eq 6.987B-R12-3 8 12.41 310 127 <ld <ld �9.566 �4.709 �1.686 �8.322 �2.974 eq eq 6.987B-R12-4 13 12.43 323 135 <ld <ld �9.595 �4.722 �1.678 �8.331 �2.962 eq eq 6.987B-R12-5 17 12.44 343 157 <ld <ld �9.401 �4.705 �1.605 �8.152 �2.680 eq eq 6.987B-R12-6 25 12.38 368 169 <ld <ld �8.607 �4.554 �1.477 �7.593 �1.918 eq eq 6.987B-R12-7 29 12.48 370 187 <ld <ld �9.427 �4.735 �1.558 �8.118 �2.578 eq eq 6.987B-R12-8 34 12.50 385 179 <ld <ld �9.573 �4.751 �1.614 �8.261 �2.767 eq eq 6.987B-R12-9 38 12.27 382 179 <ld <ld �7.467 �4.336 �1.287 �6.779 �0.839 eq eq 6.987B-R12-10 42 12.27 396 194 <ld <ld �7.305 �4.316 �1.239 �6.641 �0.634 eq eq 6.987B-R12-11 46 12.20 406 194 <ld <ld �7.214 �4.326 �1.145 �6.466 �0.462 eq eq 6.987

B-R13

Solution 0.5 M KOH pH average = 13.58 DGr (kcal/mol)

Sample Time (d) pH Si (lM) Al (lM) Mg (lM) Fe(lM) K-Mtm SiO2(am) Gibbsite Kaolinite Muscovite Brucite Fe(OH)3 Goethite

B-R13-0 0 13.68 0 0 0 0B-R13-1 3 13.55 355 111 <ld <ld �22.831 �7.523 �3.432 �17.436 �13.920 eq eq 6.993B-R13-2 6 13.55 403 137 <ld <ld �22.323 �7.447 �3.310 �17.040 �13.325 eq eq 6.993B-R13-3 10 13.49 467 144 <ld <ld �21.082 �7.337 �3.192 �16.270 �12.240 eq eq 6.993B-R13-4 14 13.53 506 162 <ld <ld �21.333 �7.252 �3.178 �16.388 �12.371 eq eq 6.993B-R13-5 20 13.62 571 173 <ld <ld �22.257 �7.454 �3.994 �16.975 �13.147 eq eq 6.993B-R13-6 25 13.70 600 194 <ld <ld �23.176 �7.670 �3.322 �17.508 �13.856 eq eq 6.993B-R13-7 31 13.67 646 200 <ld <ld �22.800 �7.534 �3.260 �17.954 �13.297 eq eq 6.993B-R13-8 35 13.49 642 207 <ld <ld �19.968 �6.992 �2.976 �15.462 �11.028 eq eq 6.993B-R13-9 40 13.49 675 229 <ld <ld �19.752 �6.963 �2.916 �15.285 �10.762 eq eq 6.993B-R13-10 45 13.24 707 230 <ld <ld �16.256 �6.216 �2.551 �13.064 �7.726 eq eq 6.993B-R13-11 49 13.37 733 233 <ld <ld �17.889 �6.562 �2.732 �14.116 �9.150 eq eq 6.993B-R13-12 55 13.40 655 218 <ld <ld �18.628 �6.715 �2.814 �14.587 �9.820 eq eq 6.993

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Associate editor: Eric H. Oelkers