07-The Removal of Textile Dyes by Diatomite Earth

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Journal of Colloid and Interface Science 282 (2005) 314–319

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The removal of textile dyes by diatomite earth

Emin Erdem ∗, Gülay Çölgeçen, Ramazan Donat

Department of Chemistry, Faculty of Science and Arts, Pamukkale University, Denizli, Turkey

Received 27 May 2004; accepted 18 August 2004

Available online 11 November 2004

Abstract

The adsorption of some textile dyes by diatomite was investigated using Sıf Blau BRF (SB), Everzol Brill Red 3BS (EBR), and Int Yellow5GF (IY). Adsorption of these textile dyes onto diatomite earth samples was studied by batch adsorption techniques at 30 ◦C. The adsorptionbehavior of textile dyes on diatomite samples was investigated using a UV–vis spectrophotometric technique. The effect of particle sizeof diatomite, diatomite concentration, the effect of initial dye concentrations, and shaking time on adsorption was investigated. Adsorptioncoverage over the surface of diatomite was studied using two well-known isotherm models: Langmuir’s and Freundlich’s. These resultssuggest that the dye uptake process mediated by diatomite has a potential for large-scale treatment of textile mill discharges. According tothe equilibrium studies, the selectivity sequence can be given as IY > SB > EBR. Values of the removal efficiency of the dyes ranged from28.60 to 99.23%. These results show that natural diatomite holds great potential to remove textile dyes from wastewater.© 2004 Elsevier Inc. All rights reserved.

Keywords: Adsorption; Textile dyes; Diatomite; Clay; Isotherm

1. Introduction

The presence of color in many industrial effluent streamsis aesthetically undesirable. Colored organic effluent is pro-duced in the textile, paper, plastic, leather, food, and min-eral processing industries [1]. Water contamination fromdyeing and finishing in the textile industry is a major con-cern. Discharging large amount of dyes into water resources,accompanied by organics, bleaches, and salts, can affectthe physical and chemical properties of fresh water. In ad-dition to their unwanted colors, some dyes may degradeto produce carcinogens and toxic products. Consequently,their treatment does not depend on biological degradationalone [2]. Traditionally both biological and chemical meth-ods have been employed for dye removal, but these tech-niques have not been very successful due to the essentiallynonbiodegradable nature of most dyes.

One of the powerful treatment processes for the removalof dyes from water at low cost is adsorption. Adsorption

* Corresponding author. Fax: +90-258-2125546. E-mail address: [email protected] (E. Erdem).

techniques have proven successful in removing colored or-ganics [1–3]. Several adsorbents are eligible for such a pur-pose. Activated carbon is the most popular adsorbent andhas been used with great success [4]. However, due to itsdifficulty and expense of regeneration, clays are being con-sidered as alternative low-cost adsorbents [3–5]. A largenumber of low-cost adsorbents have been treated for dyeremoval. For example, Asfour et al. have studied the ad-sorption of basic dye Astrazone blue FRR 69 on hardwood(Beech) sawdust [6]. The use of diatomaceous earth forthe adsorption of methylene blue, Cibacron reactive blackC-NN, and reactive golden yellow MI-2RN has been re-ported [7]. Dogan and Alkan have investigated the kineticsof methyl violet adsorption onto perlite [8]. Liversidge et al.have studied the removal of Basic blue 41 dyes by linseedcake [9]. Annadurai et al. have studied the adsorption of various dyes onto cellulose-based wastes [10]. Gupta et al.have studied the removal of Metomega Chrome Orange GLby fly ash [11]. The use of acid-activated clay for the re-moval of basic, acidic, disperse, direct, and reactive dyes hasalso been reported. The highest adsorption capacity was ob-served for basic dyes and the support was proposed as an

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doi:10.1016/j.jcis.2004.08.166


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E. Erdem et al. / Journal of Colloid and Interface Science 282 (2005) 314–319 315

efficient adsorption medium for their removal from aqueoussolution [12].

Cationic dye molecules also have a very high affinity forclay surfaces and are readily adsorbed when added to claysuspensions. Because of their high molar absorptivity, dyemolecules and their aggregates are easily detected by spec-

trophotometric and photophysical techniques, even at rela-tively low concentrations [13]. The rigid nature of the dye–clay organiccoverage provides a finite surface for adsorptionorganic compounds from aqueous solutions. Borisover et al.found that such dye-based organoclay complexes are effec-tive in reducing aqueous concentrations of nonionic organiccompounds such as atrazine, naphthalene, and phenol [14].

Biosorption is defined as the accumulation and concen-tration of pollutants from aqueous solutions by the use of biological materials, thus allowing the recovery and/or envi-ronmentally acceptable disposal of the pollutants. Biosorp-tion of various organic pollutants in wastewaters has been

investigated by various workers [15–17]. Biosorption fordyes could be also adopted for the treatment of textile efflu-ents [18,19]. Textile dyes vary greatly in their chemistries,and their interactions with microorganisms depend on thechemistry of a particular dye and the specific chemistry of microbial biomass.

Diatomite is a siliceous rock made up largely from theskeletons of aquatic plants called diatoms. Apart from beingmade of fossil skeletons, diatomite is essentially opaline hy-drous silica. It is used as an absorber of hazardous chemicalsin handling and storage and refining various acids [20]. Di-atomaceous earth—otherwise known as diatomite—found inabundance in the Middle East has been used in a number of applications, especially in the removal of heavy metals [21].It has a unique combination of physical and chemical prop-erties, which make it applicable as a substrate for adsorptionof organic pollutants as a filtration medium in a number of industrial uses [22]. Its high permeability and high porositymake it a cheap alternative to activated carbon. It is againstthis background that the feasibility of using diatomite for re-moval of color from textile wastewaters was attempted.

The aim of this study is to produce a satisfactory effluentfor discharge into receiving waters or for reuse as a watersupply from different concentrated textile dye solutions (SB,EBR, and IY), using diatomite earth samples. The adsorption

properties and adsorption isotherms of natural diatomite forsome textile dyes in solution were investigated.

2. Experimental

2.1. Materials

Three commercial dyes were chosen for this study. SB,EBR, and IY dyes were provided as gift samples by CEPATextile Fabrics (Denizli, Turkey). The molecular structurediagrams and formulae of SB, EBR, and IY were not pro-

vided for commercial reasons. IY represents an indanthrene

dye, while EBR and SB are examples of the reactive type,which is characterized by the presence of nitrogen–nitrogenazo bonds.

Diatomite earth was supplied as a natural resource fromthe Sarayköy basin, Denizli. Sample of 1 kg was washedseveral times with deionized water until neutralization of

the decantant was achieved. Finally, the sample was filtered,dried in an oven at 100 ◦C, sieved, and stored in closed con-tainers for further tests. Major oxide analysis by XRF canbe carried out on as little as 0.5 g of diatomite. The sam-ple material analyzed as a pressed powder was fused into aglass disk using a suitable flux, such as lithium tetraborate.Using fused samples produces an evenly dispersed solid so-lution, which enables a wide range of matrix compositions tobe accurately determined through the normalization of bothparticle size and interelement (matrix) effects.

All the chemicals were analytical grades obtained fromMerck.

2.2. Adsorptions

A standard stock solution of the dyes was prepared byappropriate dilution with deionized water to a final concen-tration of 1000 mg/L. Dyes were hydrolyzed by Na2CO3and Na2SO4 solutions at the start of the experiment. In thedyeing of cellulosic fibers with reactive dyes, the addition of alkali to the dye bath not only promotes formation of a co-valent bond between the dye and the cellulosic substitute butalso causes the hydrolysis of the reactive groups in the dye.Hence, the reactions necessary to introduce the substancesonto the fiber do not run to total completion, and residual re-

active hydrolyzed dyes remain in the process water. As a re-sult, the hydrolyzed form of these dyes is found in the textilefactory’s discharge wastewater [7]. Thus a study of the hy-drolyzedformsof these dyes was carried out. Thestock solu-tion was diluted to prepare working solutions. More dilutedsolutions were prepared daily as required. The buffer solu-tions (pH 4, 7, and 9) were used to calibrate the pH meter.

Aqueous solutions of SB was prepared at a final con-centration of 10–90 mg/L with 10 mg/L intervals. Adsorp-tion isotherm experiments were carried out in 100-ml Er-lenmeyer flasks to which 5 g of diatomite (63 µm) and 50 mlof the appropriate concentration of the test dye solution wereadded. The samples were subsequently capped and shaken at125 rpm in a GFL Type 1083 shaker for 3 min at 30 ◦C. Af-ter phase separation by centrifugation (2 min at 2000 rpm),the residual dyes in aqueous solutions were determined us-ing a UV–vis spectrophotometer (Shimadzu 1100). The finaldye concentrations were determined using λmax of each dye.

SB, EBR, and IY textile dyes solutions showed maxi-mum absorbance at wavelengths of 612, 544, and 441 nm.The concentrations were calculated using the Beer–Lambertequation,

(1)absorbance= εCsl,

where ε is the molar absorptivity, Cs the concentration of

sample, and l the thickness of the absorbing medium (1 cm).


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The amount of adsorbed dye was calculated from the dif-ference between initial and final concentrations.

Adsorption of these textile dyes on natural diatomite wasdetermined in terms of distribution coefficients, Kd, percent-age adsorption, %, or amount sorbed per unit weight of thesorbent. The percent adsorption and distribution ratio (Kd)

were estimated using the equations [23]

(2)dye removal (%) =C j − Cf

Ci× 100,

where Ci and Cf are the concentrations of the textile dye ininitial and final solutions, respectively, and

(3)Kd =amount of dye in adsorbent

amount of dye in solution ×

V

m[ml/g],

where V is the volume of the dye solution (ml) and m is theweight of the adsorbent (g).

The pH was adjusted to pH 11 by adding sodium carbon-ate. The flasks were then removed from the shaker and the

final concentration of textile dyes in the solution was mea-sured using the spectrophotometer. Similar procedures wereperformed at a solution temperature of 30 ◦C.

2.3. Adsorption isotherm

Equilibrium isotherms are very important in designingadsorption systems. To estimate the adsorption characteris-tics of an adsorbent, the adsorption isotherms with a spe-cific adsorbate are carried out. The concentration variationmethod is used to calculate the adsorption characteristic of the adsorbent and the process.

Adsorption coverage over the surface of diatomite wasstudied using the two well-known isotherm models: Lang-muir’s and Freundlich’s. The experimental results have beenfitted to the Langmuir model and to the Freundlich model.

The equilibrium data for textile dyes over the concentra-tion range from 10 to 90 mg/L at 30 ◦C has been correlatedwith the Langmuir isotherm,

(4)Ce/Cads = 1/Qb+Ce/Q,

where Ce is the equilibrium concentration textile dyes in so-lution (M) and Cads is the amount of textile dyes sorbed ontodiatomite, Q and b are Langmuir constants related to sorp-tion capacity and sorption energy, respectively. A linear plot

is obtained when Ce/Cads is plotted against Ce over the en-tire concentration range of textile dyes investigated

The Freundlich sorption isotherm, one of the most widelyused mathematical descriptions, usually fits the experimentaldata over a wide range of concentrations. This isotherm givesan expression encompassing the surface heterogeneity andthe exponential distribution of active sites and their energies.The Freundlich adsorption isotherms were also applied forthe removal of textile dyes on diatomite,

(5)log Cads = log K + 1/n log Ce.

The Freundlich constants of n and K were calculated

from the slope and interception of the Freundlich plots, re-

Table 1Chemical composition properties of diatomite earth sample

Constituent Diatomite (% by weight)

SiO2 49.82Al2O3 1.01Fe2O3 0.67

CaO 18.71MgO 1.34Na2O 0.15SO3 23.19LOIa 4.87pH 4.85

a Loss on ignition.

spectively, by using the equation. Where Ce is the equilib-rium concentration in mg/L and Cads shows that the adsorp-tion seems to follow the Freundlich isotherm model as wellas the Langmuir isotherm, where K roughly represents theadsorption capacity and can be related to the surface energy

as K = RT nbeH/RT and 1/n is the adsorption intensity.The value of n is usually greater than 1 and must reach somelimit when the surface is fully covered.

3. Results and discussion

The chemical composition of diatomite determined byX-ray fluorescence (XRF) is shown in Table 1. This ta-ble shows that the main constituent of diatomite samples isSiO2 (49.82%). It is not pure hydrous silica but rather con-tains other associated elements: inorganic matter, principally

calcium, and to a lesser extent ions, metals, alkaline earthmetals, alkali metals, and other minor constituents such aschlorite and potassium.

3.1. Adsorption of textile dyes

3.1.1. Effect of diatomite concentration

The dependence of SB dye adsorption on diatomite(300 µm) concentration was studied at 30 ◦C by varying theadsorbent amount from 1 to 9 g while keeping the volume,50 ml, of the dye solution constant (100 mg/L). The results,shown in Fig. 1, indicate that the percentage adsorption in-

creases with increasing amount of adsorbent. The increasein the percentage adsorption with increasing amount of thesorbent is due to the greater availability of the exchange-able/adsorption sites at higher concentrations of the adsor-bent. On the basis of these results 5 g of the diatomite wasused for the further studies.

3.1.2. Effect of particle size of diatomite

Fig. 2 shows the effect of size for a fixed mass of the di-atomite particles. It is clear that decreasing the particle sizeof diatomite from 300 to 63 µm has increased the adsorptionrate of SB. This is because increasing the external surface

area of the diatomite particle exposes more active sites to


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Fig. 1. Dependence of SB dyes adsorption on diatomite percentage adsorp-tion. (SB conc.: 100 mg/L, particle size of diatomite: 300 µm, V : 50 ml,t : 10 min, T : 30 ◦C.)

Fig. 2. Effect of particle size of diatomite on the adsorption of SB. (SBconc.: 100 mg/L, m: 5 g, V : 50 ml, t : 10 min, T : 30 ◦C.)

SB molecules. There is a slight effect of particle size of di-atomite on adsorption of textile dyes. Therefore, particle size63 µm was found to be appropriate for maximum adsorptionand was used in all subsequent measurements.

3.1.3. The effect of initial dye concentrationAs generally expected, a change in the inlet dye concen-

tration of the feed affects the adsorption. The adsorptionof SB was studied as a function of dye concentration. Dyeconcentration was varied from 10 to 100 mg/ml. Fig. 3 il-lustrates the effect of initial dye concentration on adsorption.Dye adsorption increased in the initial concentration rangefrom10 to100mg/ml and slightly decreased after 10 mg/mlfor SB.

3.1.4. Effect of shaking time

The effect of shaking contact time was studied using a

constant concentration (10 mg/ml) of dye solution at 30◦

C.

Fig. 3. Variations of adsorption (%) versus initial SB concentration (m: 5 g,particle size of diatomite: 63 µm, V : 50 ml, t : 10 min, T : 30 ◦C).

Fig. 4. Variation in adsorption of SB onto diatomite as a function of shak-ing time. (SB conc.: 10 mg/L, m : 5 g, particle size of diatomite: 63 µm,V : 50 ml, T : 30 ◦C.)

The adsorption of SB dye onto composite adsorber has beeninvestigated as a function of time in the range of 1–30 min.Fig. 4 shows percentage adsorption with shaking time fortextile dyes. As seen from Fig. 4, a higher removal per-centage of textile dyes is obtained at the beginning of the

adsorption. Percent adsorption decreases sharply with in-creasing shaking time. Quantitative adsorption of dye fromsolution was determined within minutes. Therefore, 3 minshaking time was found to be appropriate for maximum ad-sorption and was used in all subsequent measurements. Itis interesting to note that percentage adsorption later on de-crease with longer periods of shaking. The uptake of dyeby diatomite adsorbent is very rapid; percentage adsorptionreaches a maximum almost immediately after mixing of ad-sorbent and dye solution.

The adsorption of textile dyes on natural diatomite as afunction of their concentration was studied at 30 ◦C by vary-

ing SB and EBR concentrations from 10 to 90 mg/L and IY


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318 E. Erdem et al. / Journal of Colloid and Interface Science 282 (2005) 314–319

Fig. 5. Kd and adsorption of dyes (SB, EBR) by natural diatomite sample asa function of initial concentration (m: 5 g, particle size of diatomite: 63 µm,m: 5 g, V : 50 ml, t : 3 min, T : 30 ◦C).

Fig. 6. Kd and adsorption of IY dye by natural diatomite sample as a func-tion of initial concentration (m: 5 g, particle size of diatomite: 63 µm, m: 5 g ,V : 50 ml, t : 3 min, T : 30 ◦C).

concentrations from 70 to 630 mg/L while keeping all otherparameters constant. The adsorption and Kd results for dyesare shown in Figs. 5 and 6. The results show that the percent-age color removal of SB, EBR, and IY was decreased whenthe initial dye concentration was increased. The Kd valuesincrease with the decreasing concentration of dyes. In otherwords, the Kd values increase as dilution of dye ions in so-lution proceeds. The affinity of SB, EBR, and IY dyes to di-

atomite was as follows: IY > SB > EBR. The pH of the dyeis a very important parameter, since it affects the dye adsorp-tion capacity on diatomite. The content of silica in diatomitegives its structure credibility as a good adsorbent. The silanolgroup is a very active group, which can react with many po-lar organic compounds and various functional groups [7].Indanthrene dye and unhydrolyzed reactive dyes react withsilanol groups that spread over the surface of diatomite.

3.2. Equilibrium adsorptions isotherms

The pH of the aqueous solution is an important variable

for the adsorption of dyes on the adsorbents. The effect of the

Fig. 7. Dye adsorption Langmuir isotherms to diatomite.

Fig. 8. Langmuir plot for IY dye adsorption onto diatomite.

pH on dyeadsorptionby diatomite was studied at pH 11. Theequilibrium isotherm at 30 ◦C was fitted using a Langmuirmodel and compared with the proposed correlation. It ap-pears that Langmuir and Freundlich models were fitted thesedata at the solute concentrations in Figs. 7–9. All constantsobtained by both Langmuir and Freundlich models are listedin Table 2 with a high correlation coefficient (r2 > 0.97).For the Langmuir model, the linearity is well maintained

in the considered concentration range and this indicates thattemperature is the only factor that greatly affects the globalprocess [24]. It is important to recognize that the mechanismof dye adsorption on diatomite cannot be determined directlyfrom the Langmuir or Freundlich fitting. However, from Ta-ble 2, it can be concluded that the adsorption isotherms of SB, EBR, and IY exhibit Langmuir behavior, which indi-cates monolayer adsorption. The adsorbed dye anions forma monolayer with sulfonate groups as close as possible to theadsorbent surface [25].

The n values of SI, EBR, and IY are above 5, indicat-ing that the adsorption of more charged dyes was also more

favorable. Value of n between 2 and 10 show good adsorp-


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Fig. 9. Dye adsorption Freundlich isotherms to diatomite.

Table 2

Isotherm parameters of textile dye adsorption on diatomite sample

Dye sample Langmuir parameters Freundlich parameters

Q (mg/g) b (l/g) R2 1/n K (mg/g) R2

SB 10.11 0.33 0.9887 0.18 4.12 0.9809EBR 5.92 1.45 0.9915 0.20 3.55 0.9878IY 117.75 0.10 0.9770 0.18 3.84 0.9802

tion [26]. The Freundlich isotherm gives an expression en-compassing the surface heterogeneity and the exponentialdistribution of active sites and their energies [27]. The nu-merical value of 1/n

07-The Removal of Textile Dyes by Diatomite Earth

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