DYE (REACTIVE BLUE-19) ADSORPTION FROM AQUEOUS SOLUTIONS

USING ACTIVATED CARBON PREPARED FROM TROPICAL ALMOND

(TERMINALIA CATAPPA) FRUIT SHELL

Leni M. Armeroa1*, Ni Lar Wynnb2**

aM.S. in Environmental Engineering Student, Department ofChemical Engineering, College of Engineering University of the

Philippines Diliman QC 1101bPh.D. in Environmental Engineering Student, Department of

Chemical Engineering, College of Engineering University of thePhilippines Diliman QC 1101

*DOST-SEI ERDT Scholarship Program for Graduate Studies**AUN/SEED-Net JICA Graduate Scholarship Program

1leniarmero@yahoo.com, 2sengmonnal@gmail.com

ABSTRACT

In this study activated carbon derived from tropical almond(terminalia catappa) fruit shell treated with concentrated sulfuricacid was used to adsorb Reactive Blue 19 (RB 19) from aqueoussolutions. The effects of initial concentration, contact time andadsorbent dosage were investigated in batch experiments.Experimental runs were generated by using Design Expert 7.0Response surface methodology through central composite design.The experiment was conducted in batch process using 50 ml RB-19dye aqueous solution of different concentrations. The residualdye after adsorbent was determined using UV-vis spectrophotometer

(SP3000 Spectrophotometer). Overall, the results showedcomparable ability of tropical almond (TC) activated carbon tocommercially available adsorbent in adsorbing RB 19 from aqueoussolutions.

Keywords: Terminalia Catappa, Reactive Blue (RB 19), Adsorption

1. INTRODUCTION

In Philippines, textile industry has grown immensely for the pastdecades. However, textile industry poses environmental threatsdue to its high wastewater discharges. Synthetic dyes areextensively used in many industries. Approximately, 10,000different dyes and pigments are used industrially, and over 0.7-0.8 million tons of synthetic dyes are produced annuallyworldwide [1]. Nearly 10-15% of synthetic textile dyes, usedyearly are lost to waste streams and about 20% of these lossesenter the environment through effluent from waste water treatmentplant [2]. Synthetic dyes are potentially harmful to environmentand human health and pose need for suitable effective extractionmethodologies. The most commonly used to remove the dyes arecoagulation, electrocoagulation, flotation, chemical oxidation,filtration, ion-exchange, ozonation, membrane separation, aerobicor anaerobic microbial degradation and adsorption [3]. However,all such methods suffer from one or other limitations. Among themadsorption technique has got maximum potential for the removal ofdyes. Adsorption is a physical process, inexpensive, less timeconsuming and is widely accepted [4]. As synthetic dyes inwastewater cannot be efficiently decolorized by traditionalmethods, the adsorption of synthetic dyes on inexpensive andefficient solid supports was considered as a simple and

economical method for their removal from water and wastewater[5]. The high cost of removal of dyes from aqueous solutionsusing adsorption on commercial activated carbons though veryeffective has motivated the search for alternative adsorbents[6]. Many investigators have studied the feasibility of usinginexpensive alternative materials like pearl millet husk, datepits, saw dust, buffing dust of leather industry, coir pith,crude oil, residue tropical grass, olive stone and almond shells,pine bark, wool waste, coconut shell etc., as carbonaceousprecursors for the removal of dyes from water and wastewater [7].

One of the most effective and economical adsorbent is activatedcarbon derived from agricultural wastes. In Philippines, one ofthe abundant and potential source of activated carbon is tropicalalmond fruit shell (terminalia catappa), or locally known as “talisay”.Tropical-almond is a 30 to 55-foot-tall, deciduous tree whichforms a symmetrical, upright silhouette in youth with horizontalbranches reaching 35 feet in width. The inconspicuous, greenish-white, springtime blossoms appear in six-inch-long terminalclusters and are followed by the edible fruits. These drupes are2.5 inches long and mature from green to yellow or red during thesummer. The outside husk is corky fiber with an inner thin greenflesh. The inside holds the edible, almond-like kernel. The fruitis high in tannic acid and this could stain cars, pavement andsidewalks. It also causes significant litter on the ground andthus, waste disposal of the fruit shell has been a problem.

The almond tree belongs to the family called combretaceae(Combretum family). The botanical name of the tropical almondtree is Terminalia catappa L. The fruit is a sessile, laterallycompressed, ovoid to ovate, smooth-skinned drupe. Duringmaturation, it changes color from green through yellow to brightred or dark purplish-red at full maturity. Fruit size variesconsiderably, e.g., 3.5–7 x 2–5.5 cm (1.4–2.8 x 0.8–2.2 in), withextremes in length from 2.5 to 10 cm (1–4 in). This material was

chosen as a biosorbent for the present study because it isnatural, easily available, and thus a low-cost biomass foradsorption of dyes.

2. MATERIALS AND METHODS

2.1 Collection and preparation of terminalia catappa fruit shell

The adsorbent used in this study is fruit shell of tropicalalmond tree. The fruit shells were collected from University ofPhilippines – Diliman Campus, Quezon City, Philippines. The fruitshell collected was sorted and only mature fruits were selected.It was then washed several times with tap water to remove dust,soil and other materials adhering to the shell. Subsequently, theshells were dried in sunlight for 5 days to remove free water.The dried fruit shells were then crushed manually using hammerinto small pieces and the edible nuts inside were removed. Thecrushed fruit shells were then dried in hot air oven at 100 ᵒCfor 3 hours to remove residual moisture content. The driedcrushed fruit shells were milled in a Wiley mill to obtain finerparticle size and sieved through mesh of different sizes usingUSA Standard Testing Sieve. The particle size selected for theexperiment was between 100-150 µm.

2.2 Preparation of activated carbon

The resulted fine powder was then treated with concentratedsulphuric acid (Sp.gr.1.84) in the weight ratio of 1:0.98 (weightacid:weight of adsorbent) and soaked for 24 hours. The slurry wasthen washed and filtered. Heating for three hours in a hot airoven at 120°C has completed the carbonization and activation. Theresulting black carbon adsorbent sizes in a range of 100-150µmwas used for all adsorption experiment. The resultant activatedcarbon was kept in air tight container for further studies.

2.3 Adsorbate

Basic dye used in this study was Reactive Blue (RB 19) obtainedfrom Department of Chemical Engineering, College of Engineering,University of the Philippines Diliman, Quezon City. RB 19 hasmolecular formula C12H16O11N2S3Na2 (Mol. wt. 626.5 g/mol). Themaximum wavelength of this dye is 594 nm. The dye stock solutionwas prepared by dissolving accurately weighed dye in distilledwater to the concentration of 100 mg/L. The experimentalsolutions were obtained by diluting the dye stock solution inaccurate proportions to needed initial concentrations. TheReactive Blue RB19, also known as Remazol brilliant blue, is veryresistant to chemical oxidation due to its aromatic anthraquinonestructure highly stabilized by resonance. In case of RB 19, therelatively low fixation efficiency (75-80%) is due to thecompetition between the formation of the reactive form (vinylsulfone) and hydrolysis reactions.

2.3 Experimental Design

The different concentrations of synthetic reactive dye wastewaterwere prepared based on the experimental runs generated by theDesign Expert 7.0. It is a statistical tool for designingexperiments, making models, evaluating the effects of variablesand searching for optimum conditions of variables to predict thetargeted response [7]. It examines the responses of chosenfactors by varying them simultaneously with limited number ofexperiments [7]. Particularly, the central composite design (CCD)of RSM was the chosen experimental method providing significantand sufficient information for testing the lack of fit withlimited number of experiments [7]. Based on preliminary runsconducted prior to actual experiment, the maximum and minimumvalues of controlling parameters were estimated. The range and

level of three factors used in the experiment are shown in Table1.

Table 1 Experimental range and level of independent variablesfor CCD.

Factors Symbol Coded level-2 -1 0 +1 +2

Initial conc.(ppm)

A 20 40 60 80 100

Contact time(h)

B 0.3 0.6 0.9 1.2 1.5

Adsorbentdosage (g)

C 0.1 0.2 0.3 0.4 0.5

The adsorption experiments were carried out in a batch process atroom temperature. The known weight of adsorbent material wasadded to 50 ml of the dye solutions with an initial concentrationranging from 20 mg/L to 100 mg/L. The contents were reactedthoroughly using a magnetic stirrer rotating with a constantspeed of 200 rpm. The solution was then filtered at preset timeintervals and the residual dye concentration was measured usingUV-Vis Spectrophotometer.

3. RESULTS AND DISCUSSIONS

3.1 Experimental Design

Factor interactions were analyzed using the central compositedesign (CCD) of RSM. The generated 20 combinations ofexperimental runs with three determining variables such asinitial dye concentration, adsorbent dose and contact time wereobtained using the design. Result showed dye removal efficienciesin the aqueous solution ranging from 75% to 100% (Table 2). This

variation indicates that the variables used in the study havesignificant effects on the removal of RB 19 dye using activatedcarbon from tropical almond fruit shell.

Table 2. The RB 19 dye removal efficiency

RunInitialConcentration(ppm)

Contacttime(hr)

Adsorbentdose (g)

DyeRemoval

1 80 1.2 0.2 922 60 0.9 0.3 993 40 1.2 0.4 1004 40 0.6 0.2 965 60 0.9 0.3 996 80 0.6 0.4 997 80 0.6 0.2 818 80 1.2 0.4 989 60 0.9 0.3 9810 40 0.6 0.4 9811 40 1.2 0.2 10012 60 0.9 0.3 9713 20 0.9 0.3 9714 60 0.9 0.5 10015 100 0.9 0.3 9216 60 0.9 0.1 7617 60 0.9 0.3 10018 60 0.9 0.3 10019 60 1.5 0.3 10020 60 0.3 0.3 80

The result fitted to CCD Quadratic Model by using Natural Logtransform. Table 3 displayed the Analysis of Variance for the RB19 removal. Based on the results, significant factors affectingdye removal were initial concentration and time with a p-value of0.0499 and 0.0702 respectively. This means, varying initialconcentration and time greatly affects adsorption of dye onto thetropical almond activated carbon. The Model F-value was 3.11,

this implies that there is a 6.25% chance that a "Model F-Value"this large could occur due to noise. The "Lack of Fit F-value" of1.33 implies the Lack of Fit is not significant relative to thepure error. There is a 43.21% chance that a "Lack of Fit F-value" this large could occur due to noise.

The model equation in coded factors for RB 19 adsorptiongenerated using Design Expert 7.0 is shown in Eq. (1). The resultmodeled a surface quadratic polynomial equation to predict theamount of RB 19 dye that will be retained in the adsorptionprocess given other conditions of the independent variables suchas initial concentration, contact time and adsorbent dose.

Y = -1.23 + 0.90A - 1.29B - 0.81C + 0.57 AB - 0.45AC + 0.21BC +0.59A2

+ 0.11 B2 + 0.57C2 (Eq. 1)

where Y is the predicted residual RB 19 concentration retained inthe aqueous solution and A, B and C are the values of theindependent variables initial concentration, contact time andadsorbent dose, respectively.

Table 3. ANOVA for the Response Surface Quadratic Model for RB19 uptakeSource Sum of df Mean F p-value RemarksSquares Square Value Prob > F

Block 2.933099917 2 1.466549959

Model 67.8305511 9 7.5367279 3.107810

29 0.0625 notsignificant

A-initialconc

12.91003984 1 12.91003984 5.323524

371 0.0499 significant

B-time 26.49391208 1 26.49391208 10.92490

716 0.0108 significant

C-adsorbentdose

10.57905885 1 10.57905885 4.362331

822 0.0702

AB 2.564768363 1 2.564768363 1.057596

031 0.3339

AC 1.631220592 1 1.631220592 0.672642

585 0.4359

BC 0.345444489 1 0.345444489 0.142445

893 0.7157

A^2 8.42251465 1 8.42251465 3.473069

221 0.0994

B^2 0.312387192 1 0.312387192 0.128814

539 0.7290

C^2 7.741357397 1 7.741357397 3.192190

364 0.1118

Residual 19.40074122 8 2.425092652

Lack of Fit 13.38453293 5 2.676906587 1.334847

362 0.4321 notsignificant

Pure Error 6.016208285 3 2.005402762

Figure 1 Plot of actual response versus predicted RB 19 removal

Figure 2. Effect of (a) contact time and initial concentration, (b) adsorbent dose and initial concentration and (c) contact time and adsorbent dose

(a)

3.2 Effect of Parameters

In order to determine the effects of parameters, experiments wereconducted with different initial concentrations, adsorbent doseand contact time while keeping all other factors constant. Theeffects of controlling parameters in RB 19 adsorption weredetermined through a verification run. By setting two parametersconstant, the other parameter is varied to determine it effectsin dye removal.

(b)

(c)

3.2.1 Dosage of adsorbent

The various doses of the adsorbents are mixed with the dyesolutions and the mixture was agitated in a magnetic stirrer. Theadsorption capacities for different doses were determined atdefinite time intervals by keeping all other factors constant. At0.1 g dose, percent removal was 50% while at 0.3 and 0.5 g theremoval was 100%. Increasing adsorbent dose, dye removal is more

efficient.

3.2.2 Initial concentration of dye

Initial concentration were varied from 20 ppm to 100 ppm whileadsorbent dose (0.5 ppm) and contact time (1.5 h) were heldconstant. The percent removal results were very close rangingfrom 99.70% to 100%. Lower initial concentration, higher percentremoval of RB 19 dye.

3.2.3. Contact time

Figure 3. Effect of

Figure 4. Effect of initial concentration

0 0.1 0.2 0.3 0.4 0.5 0.60.00

Effect of adsorbent dose

Adsorbent dose (h)% Re

mova

l

10 20 30 40 50 60 70 80 90 100 11099.50

Effect of Initial Concentration

Initial concentration (ppm)% Re

mova

l

The effect of contact time ranging from 0.3 hours to 1.5 hours onthe removal of the dye was determined by setting initialconcentration at 100ppm and adsorbent dose at 0.5 g. Based on theresults, at 1.5 hours percent removal is 100%.

4. CONCLUSION

This study investigated the feasibility of tropical almond fruitshell activated carbon in removing RB 19 dye from aqueoussolutions. Based on the results, it showed great potential oftropical almond fruit shell as an alternative in RB 19adsorption. The factors which are significant in adsorptionprocess were initial concentration and time. Increasing thecontact time also increases removal of RB 19. At lower initialconcentration, the adsorption of RB 19 is more efficient.

5. RECOMMENDATION

For further studies, it is advised to conduct optimization andkinetic studies to determine extent of tropical almond fruitshell activated carbon adsorption capacity. Also, the activationmethod can be varied and studied as to see its effects inadsorption of reactive dyes.

Figure 5. Effect of

0.2 0.4 0.6 0.8 1 1.2 1.4 1.695.00100.00105.00

Effect of contact time

Contact time (h)

% Re

mova

l

6. REFERENCES

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