ELSEV]ER Applied Clay Science 11 (1996)55-67

Treatment of sugar beet juice with bentonite, sepiolite, diatomite and quartamin to remove color

and turbidity

Baki Erdo~an a, ~ahinde Demirci b,*, Yener Akay c a Department of Chemistry, Gazi University, Ankara, Turkey

b Department of Chemistry, Middle East Technical University, 06531, Ankara, Turkey c Sugar Institute, Ankara, Turkey

Received 11 December 1995; revised 30 May 1996; accepted 30 May 1996

Abstract

We investigate the efficiency of five Turkish bentonites (Sama§, ~anbensan, Karakaya- Re~adiye, Karakaya-~ankm and Karakaya-Beyaz), a sepiolite, a diatomite and dioctade- cyldimethyl ammonium chloride (Quartamin D86) at removing color and turbidity from sugar beet juice. These minerals were added directly as a solid or as a suspension in water. The addition of bentonites was carried out after acid activation or without pretreatment. Bentonites, sepiolite and diatomite were added separately or with a certain amount of quartamin (600 ppm). The decolorization produced by quartamin with bentonites was about 34%, for quartamin with sepiolite the decolorization was 44.0% and for quartamin with diatomite 31.5%. Since diatomite is already used as tilter aid, its application, with quartamin requires almost no change in the process, and is therefore recommended.

I . Introduction

Color is one of the measures of the white sugar quality. Color of the sugar depends upon the color of juice from which sugar is produced. The other important property of the juice is turbidity which comes from undissolved or suspended constituents. Groups of colorants developed in sugar beet technology are given in Table 1.

In spite of researches aiming at using clays, particularly bentonites to remove color and turbidity of juice in sugar technology, this was never widely realized. Besides, there

* Corresponding author.

0169-1317/96/$15.00 Copyright © 1996 Elsevier Science B.V. All fights reserved. PII S01~,9-1 31 7(96)0001 2-9

56 B. Erdo~,an et al.

Table 1 Colorants formed in sugar beet technology

/Applied Clay Science 11 (1996) 55-67

Madsen et al., 1978)

Name of the process Melanins Melanoidins Caramels Colored iron compounds

Diffusion + a - - _ _ +

Purification of juice - - + + + Evaporation - - + + - - Crystallization - - + + - -

a ( + ) sign shows the formation of the colorant.

was no unanimous opinion about the common properties of clays required for their industrial use in this respect (Decker, 1953). Rather recently ion-exchange resins have also been introduced instead of clay. Nevertheless studies on clays, especially ben- tonites, still continue (Preverzeva et al., 1978; Bazhal et al., 1980).

In fact, high construction cost of ion-exchanger units, problems encountered in their use and environmental problems made us to find alternatives in color and turbidity removing processes (Novotny, 1985).

Other research revealed that quaternary ammonium salts can be used as an alternative (Bennett, 1982), but the flocks formed with these salts and colorants become too small to be effectively filtered out. In sugarcane technology flocks may be removed by flotation, whereas in sugar beet technology flotation is not a part of present technology.

In this study five different bentonites, sepiolite, diatomite and quaternary ammonium salt (Quartamin D86) were applied, both separately aand in combination with clay or diatomite plus Quartamin D86. Their efficiency in the removal of color and turbidity of sugar juice was tested. The bentonites under study were formed by hydrothermal alteration of andesitic volcanic tuff of Miocene age (I§can, 1989).

2. Experimental

In the study five commercial Turkish bentonites (Karakaya-Re§adiye, Karakaya- ~ankarl, Karakaya-Beyaz, ~anbensan and Sama~) were used with sepiolite, diatomite and quaternary ammonium chloride, Quartamin D86. The locations and producing companies of bentonites, sepiolite and diatomite are given in Fig. 1. The chemical compositions of the samples were determined by X-ray fluorescence spectrometry (XRF) using a Philips PV 1480 spectrometer with lithium tetraborate fused discs. Mineralogical composition of bentonites, sepiolite and diatomite was determined by X-ray diffraction analysis (XRD). The XRD patterns of random powder samples were obtained with a Jeol JDX-80 diffractometer using Ni-filtered CoK, radiation. Surface area of bentonites was determined by using methylene blue method (Kipling and Wilson, 1960). Quaternary ammonium salt, dioctadecyldimethyl ammonium chloride (Quartamin D86) was obtained from Kao. Some characteristic properties of the sub- stance are as follows; Approximate alkyl chain composition C14 5%, C15 32%, C18 64%; active matter: 76-78%; solvent: H20 and isopropyl alcohol; molar weight 570.

B. Erdoff, an et al. /Applied Clay Science 11 (1996) 55-67 57

,s,oobo, f Kursuntu

O • • •

P01 h (~anktru I I

~o . t

n ~ ~ 0 n

'4..¢,

Fig. 1. Map showing locations of bentonites, sepiolite and diatomite studied. Sama~ bentonite: Re§adiye and Tokat; Sama§ Co. ~anbensan bentonite: Kur]unlu and ~anlan; ~anbensan Co. Karakaya-Beyaz and Karakaya--~ankan bentonites: (~ankan; Karakaya Co. Karakaya-Re§adiye bentonite: Tokat; Karakaya Co. Sepiolite: Tiirktaciri, Polath and Ankara; Mineral Research and Exploration Institute. Diatomite: Tinaztepe and Afyon; Sugar Institute.

Bentonites were used with and without pretreatment. Sepiolite was used preheated to 60°C. Diatomite and Quartamin D86 were not pretreated.

In be:ntonites the term pretreatment means acid activation. For this purpose a dry activatic,n process was applied (~akiclo~lu et al., 1985). In the process clay powder (size < 0.095 mm) was dried for 2 h at 110°C, and then mixed with HC1 solution (1:4) in the ac:id/clay ratio of 0.4. This mixture was kept at 150°C for 4 h and washed until the pH value of the filtrate reaches 3-3.5. The resulting material was dried overnight at 90°C, ground to pass through 95 /zm sieve and stored in a closed glass bottle.

The sepiolite sample, after crushing was dried for 5 h at 60°C, ground to pass through 0.100 mm sieve and stored in a closed glass bottle. The dry matter of sugar juice was determined by using a special Abbe Refractometer (Carl-Zeiss model). In the instrument there are', two scales, one for refractive index and the other one for percent dry matter as Brix, Bx, or refractometer dry substance, rds, units. Color of the solutions was measured by using a Uvidec-4 Model Jasco spectrophotometer. The working wavelength of the instrument is in the range of 220-850 nm. Percent transmittance of sugar juices increases regularly with wavelength. Transmittance becomes a maximum at about 560 nm (Chen, 1985). For sugar technology the optimum wavelength of 420 nm was recomm,~nded by International Commission for Uniform Methods of Sugar Analysis (ICUMSA, 1978). Study on this wavelength is called ICUMSA method 4, which is used in most countries for the measurement of color of molasses raw sugar, white sugar, sugar juice and all other sugar solutions related to the sugar industry. The working temperature should not exceed 30°C. In the process the sample is filtered through a 0.45

58 B. Erdoff, an et al. /Applied Clay Science 11 (1996) 55-67

Ixm membrane filter, pH is adjusted to 7 __+ 0.1. By application of a vacuum, air bubbles present in the solution are discarded, and absorbance is measured using water as a reference. Transmittance of the sample should be 20-80%. If necessary concentration of the sample is adjusted, to meet these requirements.

Finally, ICUMSA color is calculated by using the following equation:

ICUMSA 4 = 1000 X ( A / b C ) or 1000( - l o g T ) / b C ,

where A is absorbance, T is transmittance, C is solid (or dry substance) content in g /ml , b is the path length of light in cm.

C is determined by measuring the index of refraction of the sample and using the tabulated values in g /ml . Turbidity is determined by measuring ICUMSA color of the juice before and after filtration process. The difference in color measurements gives the turbidity value. A given additive may be effective in removing both color and turbidity. Therefore in this study color measurement was done without filtration. The sugar beet juice sample having 60% rds and 92% purity was prepared by mixing molasse, water and crystalline sugar in the appropriate ratio and dissolving them. The juice obtained had a color of 2650 ICUMSA unit (ICU). In the sugar technology this type of juice is called thick juice which is the phase right before the state of crystallization. In this study, first, bentonite, sepiolite, diatomite and Quartamin D86 were added separately. Next, each bentonite, sepiolite and diatomite were added with Quartamin D86.

In the former, bentonites were added either directly to the juice or as suspension in water (5 g /100 ml H20). In the case of direct addition various amounts of bentonite were added to 200 ml sugar juice and mixed at the rate of 1000 rpm for 10 min. Then the mixture was heated in the water bath to 85°C and filtered using filter paper under vacuum. The filtrate was diluted with distilled water to the extent that dry substance content becomes 15-20%. Absorbance of the filtrate was measured at 420 nm and the corresponding ICUMSA unit (ICU) was determined.

Amounts of bentonites added were in the range of 0.25-1.5 g per 100 ml sugar juice. Experiments were repeated with activated bentonites. Sepiolite and diatomite were

added directly to the juice, since they were dispersed readily in both water and juice without forming flocks. Amounts of additives were again in the range of 0.25-1.5 g per 100 ml juice.

Addition of Quartamin D86 was done from stock solution of 2 g /100 ml H20 to obtain 200-1200 ppm quartamin in 200 ml juice. After heating to 85°C in a water bath the solution was filtered. But on cooling the filtrate became turbid. Thus it was filtered by adding diatomite in the ratio of 0.75 g /100 ml juice.

In another series of experiments bentonite, sepiolite and diatomite were mixed with quartamin and were used for color and turbidity removal.

In order to determine the amount of quartamin to be added and the effect of addition sequence, two sets of experiments were carried out. In one set, first quartamin was added in the concentration of 200-1200 ppm, mixed for 5 min. Then one of the additives in concentration of 0.5 g /100 ml juice was added and mixed for 10 min, heated to 85°C, filtered and absorbance of the filtrate was measured at 420 nm and ICU color unit was calculated.

B. Erdo~,an et al. /Applied Clay Science 11 (1996) 55-67 59

In the other set, first bentonite, sepiolite or diatomite was added in the concentration of 2 g /200 ml juice and mixed for 10 min. Then quartamin was added in the concentration range of 200-1200 ppm, mixed for 5 min, heated to 85°C and the process was completed as before.

3. Resul[ts and discussion

Mineralogical analysis of bentonites showed that all samples are mainly composed of smectites (Fig. 2a-e) and feldspar, quartz, crystobalite, calcite, zeolite and opal-CT were identified as impurities. Feldspar appears in all five samples. Calcite, zeolite and opal-CT appear only in Sama§ bentonite (Fig. 2d). Crystobalite is absent in Sama§ and Karakaya-~ankln (Fig. 2b) and quartz is absent in Sama§ bentonite (Fig. 2d).

According to XRF data CaO content of Karakaya-Re§adiye bentonite is significantly higher than that of the others, whereas Karakaya-~ankln bentonite has the highest magnesia (4.81%). Iron oxide shows significant variations between the samples with highest value of 5.38% in ~anbensan and lowest value of 2.81% in Karakaya-~ankln bentonites (Table 2).

Mineralogical analysis of sepiolite showed that it is almost pure sepiolite and quartz and dolomite were identified as impurities (Fig. 3a). In the XRD trace of diatomite peaks corresponding to crystobalite were observed. Feldspar was identified as impurity. (Fig. 3b). X-ray studies indicate that, although diatomite is essentially amorphous, it contains crystalline aggregates of cristobalite (Hurlbut, 1971).

Upon addition of bentonites color of the sugar beet juice decreased from the feed color of 2650 ICU first rather steeply up to 0.5 g bentonite/100 ml juice, then slowly to give color levels of 2100-1900 ICU for 1.5 g bentonite/100 ml sugar juice.

Efficiency of bentonites on color reduction was found to be dependent upon the way of application of bentonite. The direct addition of bentonite decreases the color a little more than that of addition from stock solution of bentonite in water (5 g /100 ml). Besides, activated bentonites reduced color more than unactivated ones. For comparison, results obtained with Karakaya-~ankln bentonite is given in Fig. 4.

Color reduction must be related to adsorption of colorants by the clay particles. Colorants in the sugar beet juice have various sized complex structures with mainly nonpol~tr and somewhat polar characters, Many clay minerals especially montmoril- lonites :readily adsorb organic molecules. Adsorption depends upon various factors including molecular size of the adsorbate, its concentration in the medium, effect of van der Waals forces, chain length, CH activity and entropy effect (Theng, 1974, Theng, 1982).

Adsorption is usually increased by raising the solute (organic) concentrations, or in the extreme case, by elimination of water from the system. This was also the case in our study. Adsorption of colorants increased or more color reduction was observed at adding bentonites, which means that water is eliminated.

Becwase of the above mentioned restrictions color reduction with bentonites was not complete. Within the bentonites it varied somewhat but the overall percentage decol- orization was about 25%.

60 B. Erdoff, an et al. / Applied Clay Science 11 (1996) 55-67

100

9 0

80

70

60

5 0

4 0

F

Sm,

'°f I0

g I , 45 0 55 50

(a) 02e Co K~

Sm Cr

KARAKAYA- RE~ADIYE

$m

5 I t I 2 20 15 I0

I 00

90

80

70

=•'60 '-= 50 .=>

40 n-

30

20

I0

KARAKAYA- (;ANKIR!

F

Sm

Q Sm

45

(b)

40 3 30 2 2 15 I0 6

*2e Co Kc~

Fig. 2. X- ray diffract ion traces o f unoriented samples o f Turkish bentonites (a) Ka rakaya -Re~ad iye , (b)

K a r a k a y a - ~ a n k m , (c) K a r a k a y a - B e y a z , (d) Sama§ and (e) ~anbensan (Sm = smectite. F = feldspar, Q = quartz, C = calcite, Cr = cristobalite, Z = zeolite, 0 = opal-CT).

B. Erdo~an et al. /Applied Clay Science 11 (1996) 55-67 61

I00

..=_

90

80

70

EO

50

40

30

2 0 '

I0

Cr Cr

4 0 3 30

(c)

Cr

KARAKAYA- BEYAZ

S m

i I 115 I ;)5 20 I0 6

e 2 0 CO Ko

I00

90

EtO

TO

E;O

_~ 40

30

;!0

IO

Sm

F

F 0

3m C

I i i 4 35 30 25

{d) *20 Co Ko

Fig. 2 (continued).

SAMAS

I I I

Sm

1 20 15 I0

Upon activation, the extent of decolorization increased and reached a value of about 29% (Fig. 5). This is an expected result. In acid activation the adsorption capacity of the clays increases with increasing acid/clay ratio up to about 0.50 and then decreases due

62 B. Erdo~an et al. /'Applied Clay Science 11 (1996) 55-67

,°° I 90

80

70

60 >,

~ 50 P t

~ 30

2O

I0

Cr

$m

Cr F 0 Sm

J

Sm ~ANBENSAN

(e)

l I0 I I O I I I I

4 35 3 25 2 0 15 I0 6

* 2e co Kc~

Fig. 2 (continued).

to the breakdown in the crystal structure and micropore structure (Sarlkaya et al., 1989). Among the bentonites Sama~ is most effective having 29% decolorization and Karakaya-~anlon is the least effective one with 20% decolorization.

Surface areas of the bentonites were found to be in range of 116.0-100.0 m2/g. Sama§ bentonite has highest surface area (being 116.0 m2/g), Karakaya-~ankln has the lowest surface area (being 100.0 m2/g). This difference might be due to the mineral composition of the samples. Karakaya-~ankln bentonite has a considerable amount of quartz (Fig. 2c).

Results obtained with sepiolite were similar to that of bentonite. The ICU decreased steeply up to the concentration of 0.4 g sepiolite/100 ml juice, then slowly reached the final value of about 1800 ICU or 33% (Fig. 5).

Table 2 Composition of the studied bentonites, sepiolite and diatomite (%)

Sample SiO 2 AIzO 3 Fe203 CaO MgO NazO K20

Karakaya-Re§adiye 61.76 16.62 3.35 4.50 1.79 2.65 0.92 Karakaya-~ankln 60.98 17.76 2.81 2.81 4.81 2.70 0.72 Karakaya-Beyaz 60.11 19,14 3.83 2.87 2.49 2.47 0.36 Sama~ 61.43 17.32 3.73 3.16 1.98 1.49 1.01 Canbensan 61.83 17.36 4.38 1.39 2.64 2.24 0.95 Sepiolite 40.80 2.34 0.79 10.00 25.00 0.01 0.31 Ignition loss (21.36%) Diatomite 89.81 2.40 1.72 1.02 0.30 3.49 0.26

B. Erdo~an et al. /Applied Clay Science 11 (1996) 55-67 63

I00

90

80

70

60

50

__ 4o

3O

20

IO

SEPIOLITE

S

F S

S 0

Ca)

n I I I I I I

40 35 30 25 20 15 I0

*2e Co Kc~

IOO

9 { )

8 , : )

70

~,. 60

5 o

4o

3o

20

I0

n

40 35 30

(b)

Cf

DIATOMITE

5 i i I 20 1,5 I0

*20 Co Ko

Fig. 3. X-ray diffraction traces of sepiolite and diatomite. (a) Sepiolite and (b) diatomite (notation as in Fig. 2 and S = s,~piolite and D ~ dolomite).

Sepiolite is a good adsorbent for organic species, because it has a large specific surface area because of the existence of intracrystalline channels. Total surface area of the sepiolite is about 600 m2/g (Martin-Vivaldi and Fenall Hach-Ali, 1970). Penetration

64 B. Erdo~an et al. /Applied Clay Science 11 (1996) 55-67

2 7 0 0

2 6 0 0

2 5 0 0

2 4 0 0

2 3 0 0

2 2 0 0 ~D u 2 I 00

2000

1900

1800

1700

1600

1500 0

i i I I i i i

0.2 0.4 0.6 0.8 I 1.2 1.4

g / l O 0 ml

1.6

Fig. 4. C olor reduct ion e f f e c t o f K a r a k a y a - ~ a n k t n bentoni te under di f ferent appl icat ion condi t ions . ( 0 ) Inactivated, direct, (X) activated, direct, ( + ) inactivated suspension in water, ( [ ] ) activated suspension in water.

of organic molecules in the channels depends on their own properties, especially their shape and volume (Brindley, 1959). The adsorption of several molecules on sepiolite has been reported by Heller-Kallai et al. (1984); Singer and Huang (1989); Hoyo et al. (1993) and others.

The reason for reaching not enough color reduction may be due to the dependence of adsorption effect of sepiolite on the shape and volume of adsorbate organic species (colorant). It could not adsorb all types of colorant molecules. However, sepiolite has given the best result of color reduction (Fig. 5).

35

3O

~2~ .~ = 20 (~ X

o

.?_ is o "5 ÷ D

5

01 , ~ ~ ' '

0 0.2 0 .4 0 .6 0.8 I 1.2 1.4 1.6

g/100 ml

Fig. 5. Percent decolorization of activated bentoni tes , sepio l i te and diatomite. (~) Sepiolite, ( 0 ) Sama~, ( x ) Karakaya-Re§adiye, ( + ) ~ a n b e n s a n , ( [ ] ) Karakaya-Beyaz, ( * ) Karakaya-~ankm and ( zx ) diatomite.

B. Erdo~,an et al. /Applied Clay Science 11 (1996) 55-67 65

2400

~'.3 oo[

~:200

~lO0

~ooo

_o t900

1800

1700

'1600

~500 0 200 400 600 800 1000 1200 1400

pprn

Fig. 6. Effect of the addition sequence of quartamin and Karakaya-Re§adiye bentonite and sepiolite on sugar beet color. ( n ) Bentonite, ( × ) sepiolite, ( + ) first Quartamin, then bentonite, ( 0 ) first Quartamin, then sepiolite.

The cationic surfactant quartamin itself decreased color level to about 1600 ICU (39% decrease). The color reduction was rather steep to 400 ppm quartamin, then slowly raised to 1000 ppm. Addition of the cationic surfactant at high concentration might precipitate the anionic high molecular weight colorant which appeared as turbidity or flock formation (Tate and Lyle, 1972). Results showed that 600 ppm quartamin concentration is the optimum ratio which provides about 24% color reduction. Previous studies also showed that the optimum concentration of quartamin can be in the range of 100-700 ppm (Bennett, 1982; Frank et al., 1987).

Diatomite itself did not reduce color as expected. There are no available active adsorbing centers on the SiO 2 particles of diatomite.

Using Quartamin D86 in combination with each of bentonites, sepiolite and diatomite reduced color more than that obtained with additives alone. Applying first quartamin, then other additives gave better results (Fig. 6). When quartamin is added, it interacts with anionic colorants and reduce color to some extent. Upon addition of clay, adsorption still continues. Besides, cationic surfactant may interact with clay particles. This long chain quaternary ammonium cation is adsorbed on the clay and changes the nature of the surface from hydrophilic to hydrophobic. Thus adsorption of colorants can occur more easily by interacting with the hydrophobic alkyl group on the mineral surface (Mortland et al., 1986).

When bentonite is added first, adsorption of colorants on clay particles decreases color to some extent, addition of quartamin may not interact with anionic colorants which are already adsorbed on the clay particles by the possible bonding mode of ligand exchange by which the anionic species enters the inner coordination layer of edge alumimlm to form a coordination complex with it (Tate and Theng, 1980).

Similar effect was observed in the case of sepiolite (Fig. 6). In the case of diatomite, the addition sequence was not important. Here color

reduction was only related to the quartamin.

66 B. Erdo~an et al. /Applied Clay Science 11 (1996) 55-67

50

45

40

._~ 25

"~ 20

~ t5

" I0

5

O_ ~ 0

t ]

I I I I I

O.Z5 0.5 0.75 I 1.25 1.5

g /100 ml

Fig. 7. Percentage of decolorization of activated bentonite, sepiolite and diatomite in combination with 600 ppm quartamin. ( 0 ) Karakaya-Re§adiye, (X) Sama§, ( + ) Karakaya-(~anl~n, ( 0 ) ~anbensan, (*) Karakaya-Beyaz, ( zx ) sepiolite and (©) diatomite.

The degree of decolorization of all additives in combination with 600 ppm quartamin as a function of additive concentration is given in Fig. 7. As it is seen from the graph, with activated bentonites about 33%, with sepiolite 44% and with diatomite 31.5% color reduction was obtained.

Diatomite decolorization should be attributed to the quartamin. The increase of decolorization from 24% (for only quartamin) to 31.5% may be the result of the increase of the adsorbent surface and which provides quartamin cations to interact with colorants which may be gathered on the diatomite particles and removed from the medium.

4. Conclusion

In this study five Turkish bentonites (Karakaya-Re§adiye, Karakaya-~ankin, Karakaya-Beyaz, Sama§ and ~anbensan), a sepiolite and a diatomite were investigated in their effects of removing color and turbidity in sugar beet juice with and without quaternary ammonium salt (Quartamin D86). Without quartamin the percentage change in color and turbidity reached 29% with bentonites, 32.5% with sepiolite and 3% with diatomite. With quartamin, these values reached approximately 33% in bentonites, 44% in sepiolite and 31.5% in diatomite.

In sugar beet technology diatomite with quartamin seems to be more convenient, as it is already used as filter aid to remove turbidity causing suspended compounds. The convenient amount of quartamin (600 ppm) should be added to the sugar beet juice before filtration through a diatomite coated filtering medium which doesn't need too much investment.

In the case of bentonites, storing, transportation, mixing and removing of the clay mud are not easy and need quite large additional investment.

Sepiolite was found to be most efficient one in color and turbidity removal. However, finding pure and good quality sepiolite is not easy or even impossible in Turkey. It may

B. Erdo~an et al. /Applied Clay Science 11 (1996) 55-67 67

be imported. Besides, decreas ing its size into the required value need extra treatment,

therefore extra cost. Cons ider ing the approximate consumpt ion o f sepioli te per day for

an average sized sugar factory (3600 ton sugar per day process ing capaci ty) o f 11 tons,

the annual consumpt ion for Turkey may be about 30,000 tons o f sepiolite.

Compar ing all the results and possibil i t ies, using dia tomite with Quar tamin D86 can

be advisable in color and turbidity r emova l in the sugar beet juice.

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