Sorption of Chromate and Arsenate by Surfactant Modified Zeolite

 

Vandana Swarnkar*, Radha tomar and Nishi Agarwal

School of Studies in Chemistry, Jiwaji University, Gwalior. M.P.

*Corresponding Author E-mail: soni.vandana7@gmail.com

 

ABSTRACT:

In recent years growth of industries has led to introduction of pollutants in nature, especially the heavy metal ions like Cr(III) and As(V) usually present in many waste water. Heavy metal containing waste is generated from industries like metallurgical, mining, chemical, leather, distilleries, sugar, battery, electroplating and pigments. Chromium is found in natural water in oxidation states Cr(III) and Cr(VI). The former is essential elements for mammals where as the later is reported to be toxic. Same as arsenic is an ubiquitous contaminant which can be found at high concentrations in natural waters and wastewaters. Arsenic containing waste streams are generated mainly by the microelectronic industry and by pesticide and pharmaceutical facilities. It occurs in two oxidation states that form oxyanions, arsenate As(V), and arsenite As(III); arsenite is more mobile and toxic than AsO₄^-3. As arsenic is a major hazardous contaminant for the human health, its removal is an issue of increasing concern. Zeolite are crystalline, hydrated aluminosilicate containing exchangeable alkaline and alkaline earth cations in their structural frameworks. Since zeolite have permanent negative charge on their surfaces, they have no affinity for anions. However recent studies have shown that modification of zeolite with certain surfactants or metal cations yield sorbents with a strong affinity for many anions. Zeolite has high internal and external surface areas and high internal and external cation exchange capacities suitable for the surface modification by cationic surfactant (HDTMA). When the initial surfactant concentration is less than the critical micellar concentration (CMC), the sorted surfactant molecules primarily form a monolayer, limited chromate and arsenate sorption indicates that the patchy bilayer may also be formed. When the surfactant concentration is greater than the critical micellar concentration and enough surfactant exist in the system, the sorbed surfactant molecules form bilayer, producing maximum chromate and arsenate sorption. Quantitative sorption of chromate and arsenate and desorption of bromide ions indicate that the sorption of oxoanions is primarily due to surface anion exchange. 

 

1. INTRODUCTION:

 

Water is one of the most important natural resource essential for all forms of life. The natural being contaminated every day by various anthropogenic activities such as rapid growth of populations, urbanization and industrialization that ultimately make the environment polluted since recent years, sewage water have been used for irrigation purposes¹. There are greater concerns about heavy metal contamination ^(2,3) in the receiving water system and land. High levels of heavy metals can damage soil fertility and may affect productivity ^(4,5).Cr(VI) and As(V) are most common stable and abundant forms of metal contaminants. They are both a mutagen and carcinogen at low sub ppm levels⁶. Chromium is one of the transitions metals that can exist in oxidation states +2, +3, +4, +5 and +6. The most common stable and abundant forms are trivalent chromium [Cr (III] and hexavalent chromium [Cr (VI)].

 

The Cr (VI) species is more toxic and carcinogenic than Cr (III), however, it is possible that Cr (III) may be oxidized to Cr (VI) in the appropriate conditions hence the toxicity of Cr (VI) takes place usually, Cr (III) is readily oxidized to hexavalent state at high pH⁷. It is highly soluble in aquatic environment and can be readily absorbed by living organism. Once it accumulates in living organism beyond the allowable concentration, it can cause severe health problems⁸. Prolonged exposure to even small concentrations can cause lung cancer, liver and kidney damage and reproductive problem⁹. Leather and chromium planting industries are the major causes for environmental influx of chromium^(10,11). Same as Arsenic is a ubiquitous element that ranks 20^th abundance in the earth’s crust. It is a carcinogen and it toxic to humans and other organisms¹². The most common valence states of arsenic in water are the oxidized As (V) and As (III) forms. As (III) is more mobile and more toxic (25-60 times) than As(V)¹³. The chronic toxicity of arsenic in drinking water is known to cause black foot disease and various types of cancer¹⁴.Therefore, removal of arsenic and chromium is one of the most important water treatment issues. The most commonly used technologies to remove As include oxidation. Co-precipitation, and adsorption on to coagulated flocs and other sorption media, lime treatment, ion exchange and membrane techniques^(15-17). There are a number of methods employed^(18-22) for removal of hexavalent chromium from industrial waste water such as the use of various types of adsorbents. Recently the ion exchange resin in the cationic from²³, Zeolite ²⁴ betonies²⁵ and activated carbon²⁶ have been used to remove Cr. (III) from water. Since zeolite have a permanent negative charge on their surface, they have no affinity for anions. However, recent studies have shown that modification of zeolites with certain surfactants or metal cations yield sorbents with a strong affinity for many anions²⁷. In order to sorb anions, the modified surface must either possess positively charged exchanged sites, or there should be replacement of weakly held counter ions of the surf cement by more strongly held counter ions. Cationic exchanged forms of zeolites showed high uptake of iodide and molybdate from solution²⁸.

 

In this paper, modifications of zeolite Erionite(ERI) were performed by exchange of cations bromide ion. Zeolite is an aluminosilicate with a framework structure enclosing cavities occupied by large ion and water molecules, both of which have considerable freedom of movement permitting ion exchange and reversible dehydration ²⁹.

 

Surfactant Modified Zeolite Erionite (ERI-SMZ) is synthesized zeolite Erionite (ERI) of which the HDTMA (Hexadecyltrimethyl ammonium) cations forms primarily a monolayer or hemimicelle or at higher concentration it form bilayer or "admicelle" on zeolite surface.

 

The preliminary objective and scopes of this study is to synthesized Erionite SMZ (Surfactant Modified Zeolite) by using HDTMA (Hexadecyl trimethyl ammonium). Subsequently characterized it by X-Ray diffraction (XRD) technique, FTIR technique, TGA technique, and the physicochemical properties which are related to the use of surfactant modified zeolite- Erionite as sorbent. The second objective is to investigate the kinetics parameter and the efficiency of the removal of Cr (III)  and As (V) from aqueous solution by the synthesized zeolite surfactant  modified zeolite – Erionite.

 

2. MATERIAL AND METHODS:

2.1 Chemicals and Reagents

The chemicals used for the zeolite synthesis and its modifications include Sodium nitrate, potassium nitrate, surfactant–modifier (HDTMA) and sulphuric acid were supplied by Qualigens. Calcium nitrate, aluminium nitrate and Diphenyl Carbazide were purchased by renkeM, CDH and HIMEDIA respectively. All reagents were analytical grade and the solution was prepared in DDIW.

 

2.2 Preparation of Zeolite (Erionite) 

Analogue of zeolite has been synthesized by hydorthermal method. Zeolite, Erionite was synthesized as follows: 0.1 gm potassium nitrate, 0.7 gm of sodium nitrate, 3.4 gm of aluminium nitrate, 0.5 gm calcium nitrate and 2.8 gm of sodium tetra silicate as a silica source were mixed with 100ml of distill water. The resulting solution was stirred for 1 hrs at room temp to obtain a common and homogenous solution. The solution was transferred to a stainless steel autoclave and placed in an oven of 175ºC for the required length of time (72 hrs).

 

2.3 Preparation of Surfactant Modified Zeolite (SMZ)

The synthesized zeolite ERI 5.0 gm were loaded with cationic surfactant i.e. HDTMA (0.25gm). These mixture were equilibrated on a shaker at 25ºC for 24 hrs. Than the mixture was centrifuged at 150 rpm and the supernatant solution is removed and SMZ were prepared.

 

2.4 Characterization of Erionite and Erionite SMZ

The ERI and ERI- SMZ were characterized by XRD, TGA and FTIR techniques. The crystalline structures was analyzed by XRD to identify the type of the zeolite form and the zeolite crystalinity. The thermal stability and the number of water molecules bound with the hydrothermally synthesized zeolite were ascertained by DTA/ TGA. [Perkin Elmer (Pyris diamond)]. FTIR technique was used to investigate a typical infrared spectroscopic pattern of zeolite.

 

3. RESULTS AND DISCUSSION:

3.1 Characterization of ERI and ERI-SMZ

X-ray diffractogram of synthetic gel has been recorded using Cu Kα radiation in a range 2q = 5º to 120º at a scanning speed of 1 step/second. Powder X-ray diffraction pattern of hydrothermally synthesized material ERI and ERI- SMZ are represented in Fig 1(a) and Fig 1 (b). These pattern show maxima at 2θ = 35.194^o, 101.703º, therefore, spacing between the plane is found to be d = 2.54794, d = 0.99328. In both the cases the XRD patterns indicate that the material is amorphous in nature.

 

(a)

 

(b)

Fig.1(a) (b) XRD diffractogram of hydrothermally synthesised ERI and ERI-SMZ

DTA/ TGA thermograms obtained for ERI and ERI- SMZ are shown in Fig 2 (a) and 2 (b). Where it can be seen that both exhibit a continuous weight loss of 13.4 % and 10.4% respectively upon heating from room temp to 200ºC. This weight loss is associated with the dehydration of physically adsorbed water. Further weight loss in the temperature range of 200°C-700ºC is attributed to desorption of remaining water enclosed in the material matrix. The negligible weight loss is observed beyond 800ºC temperature may be either due to high temperature solid state transformation or due to oxide formation, Both the materials are found to be structurally stable up to 1000ºC. The total weight loss estimated by TGA is 21.8% and 20.0% for ERI and ERI-SMZ.

 

(a)

 

(b)

Fig. 2(a) (b).TGA graph of ERI and ERI-SMZ

 

The FTIR (NICOLET-410 Spectrometer) spectra of ERI and ERI-SMZ are presented in Fig.3 (a) and 3 (b). It is found in the range 950-1250 cm^-1 and 420-500cm^-1 strongest vibration at 950-1250 cm^-1 is assigned to T-O stretching and the next strongest band at 420-500 cm^-1 is assigned to T-O bending mode (T= Si or Al).

 

The Hydroxylbond –OH stretch near 3550 cm^-1 in Spectra indicates the bimodal absorbance the water molecules attached to zeolite frame work shows strong characteristic structure sensitive bands due to water (H₂O) bending vibration at 1630 cm^-1 The peaks below 550 cm^-1 indicates (O-T-O) bending of rotation mode. The peaks between 700-850cm^-1 and 1000-1150 cm^-1 are assigned to symmetric and antisymmetric T-O-T stretching vibration. Two bands around 3300 cm^-1 and 2800-2900 cm^-1 appeared in the ERI-SMZ indicate asymmetric and symmetric stretching vibration of –CH₂ of Alkyl chain and band at about 1477.47 cm^-1 was assigned to vibration of trimethyl ammonium quaternary group CN (CH₃)₃^{+ .}

 

(a)

 

(b)

Fig.3(a) (b) FTIR spectra o hydrothermaly synthesize ERI and ERI-SMZ

 

3.2 Effect of contact time

Results of kinetic study for the sorption of Chromate and Arsenate on ERI (SMZ) are given in Table (1). The data suggest that the Kd values for the oxoanion (CrO₄^-2 and AsO₄^-3) increases with the increasing equilibration time (1-24) between solid and liquid phase. It is observed that the equilibration time of around 5 hour is sufficient, since maximum sorption is attained in this period. The plots of sorption percentage V/s time are shown in Fig.4 indicate that the sorption become asymptotic to the time axis representing nearly an equilibrium pattern.

 

Table 1- Effect of time on sorption of metal oxoanions by an analogues of surfactant modified ERI.

 

Metal oxo-anions	Contact time Hrs.	Metal oxoanion concn solid phase meq	Metal oxoanion concn at equilibrium meq	Kd ml/gm	Sorpn %
CrO4 2-	1 3 5 7 24	0.0625 0.1330 0.1991 0.2980 0.3040	0.4374 0.3674 0.3008 0.2020 0.1960	71.500 81.190 331.10 737.62 775.50	12.5 26.6 39.8 59.6 60.8
ASO4 3-	1 3 5 7 24	0.053 0.1225 0.1635 0.2405 0.2570	0.4770 0.3775 0.3365 0.2595 0.2490	992.66 116.22 124.29 463.39 1504.0	10.6 24.5 32.7 48.1 50.2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weight of ion exchanger = 100mg; Temp. = 25⁰C; pH of the solution = 7

 

 

Fig. 4. Kinetics of Cr (VI) and As (V) on ERI-SMZ (pH= 7)

 

3.3 Effect of pH

 

The sorption behavior of CrO₄^-2 and AsO₄^-3 on ERI- SMZ were checked at different pH of the solution viz. pH 1, 3, 5, 7, 9. Table 2 and Fig. 5 shows the effect of pH on sorption of CrO₄^-2 and AsO₄^-3 on ERI- SMZ. The data shows maximum sorption at pH 7, for ERI–SMZ. The results show that the sorption percentage increases up to pH 7 with increase in pH of the solution and thereafter sorption percentage decreases.

 

 

Table 2- Effect of pH of the solution on sorption of metal oxoanion by ERI-SMZ.

Metal oxo-anions	pH of the solution	Metal oxoanion concn in solid phase meq	Metal oxoanion concn at equilibrium meq	Kd ml/gm	Sorpn %
CrO4 2-	1 3 5 7 9	0.104 0.197 0.253 0.298 0.291	0.3954 0.3029 0.2469 0.2020 0.2090	132.19 325.20 512.35 737.00 696.17	20.91 39.41 50.61 59.60 58.20
ASO4 3-	1 3 5 7 9	0.095 0.147 0.153 0.240 0.213	0.4045 0.3525 0.3470 0.2595 0.2870	118.04 209.20 220.46 463.39 371.08	19.10 29.50 30.60 40.10 42.60

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weight of ion exchanger = 100mg; Temp. = 25⁰C; Equilibration time = 7 hrs

 

Fig. 5- Effect of Initial pH of the solution.

 

3.4 Effect of Sorbent dose

The Percentage of sorbed Chromate and Arsenate varying with amounts of sorbent is presented in Table 3 and Fig. 3 for ERI-SMZ with HDTMA. While changing the aqueous phase to exchange ratio 1:2 (ml/mg). It is found that Kd values and sorption percentage increases the data shows that with increases in weight of sorbents from 50-250mg, sorption percentage increases. The reason being as the weight of sorbent is increase it provides more number of active sites on the surface of ERI-SMZ.

 

Table 3- Effect of weight variation of ERI-SMZ on sorption of metal oxoanions

Metal oxo-anions	Amount of ex-changer (mg)	Metal oxo-anion concn solid phase (meq)	Metal oxo-anion concn in equilibrium (meq)	Kd ml/gm	Sorpn %
CrO4 2-	50 100 150 200 250	0.1665 0.2980 0.3040 0.3135 0.3170	0.3334 0.2020 0.1960 0.1865 0.1830	499.70 738.12 775.50 840.40 866.12	33.3 59.6 60.8 62.7 63.4
ASO4 3-	50 100 150 200 250	0.1230 0.2400 0.2490 0.2500 0.3010	0.3770 0.2590 0.2570 0.2490 0.1990	163.13 463.39 496.01 504.01 756.28	24.5 28.1 49.8 50.1 60.2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weight of ion exchanger = 100 mg; Temp. = 25⁰C; pH of the solution = 7 Equilibration time = 7 hrs.

Fig. 3 Effect of the dose of sorbent.

 

 

3.5 Effect Concentration on Sorption

Variation in metal oxoanion concentration has been recognized as an important factor in sorption. While changing the concentration from 0.01N - 0.05N, it is found that the Kd value and sorption percentage decreases. This sorption study was at pH 7 for Chromate and Arsenate.

 

The data [Table 4, 5, 6 and Fig. 7(a), (b), (c)] show that with increase in metal oxoanion concentration from 0.01 N to 0.05N sorption percentage decreases. The reason being availabilities of limited number of active sites of the sorbent.

 

Table 4- Effect of metal oxoanion concentration on ERI-SMZ.

Metal oxo-anion	Concn of metal oxo-anion in N	Initial metal oxo-anion concn meq	Metal oxo-anion concn solid phase meq	Metal oxo-anion concn at equilibrium meq	Kd ml/gm	Sorpn %
CrO4 2-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.298 0.366 0.441 0.388 0.252	0.202 0.634 1.059 1.612 2.248	737.62 288.64 208.21 120.34 056.00	95.6 36.6 29.4 19.4 10.1
ASO4 3-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.240 0.432 0.592 0.592 0.382.	0.260 0.568 0.908 1.408 2.118	461.53 380.28 325.99 210.22 090.17	48.1 43.2 39.5 29.6 15.3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

pH of the solution = 7; Temp. = 288K; Equilibration time = 7 hrs.

 

Table 5- Effect of metal oxoanion concentration on an analogue of surfactant modified mordenite

Metal oxoa-nion	Concn of metal oxo-anion in N	Initial metal oxoanion concn meq	Metal oxoanion concn solid phase meq	Metal oxoanion concn at equilibrium meq	Kd ml/gm	Sorpn %
CrO4 2-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.283 0.378 0.390 0.312 0.240	0.217 0.622 1.110 1.688 2.260	652.07 303.85 175.67 92.410 53.090	56.6 37.8 26.0 15.6 9.60
ASO4 3-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.213 0.399 0.324 0.312 0.212	0.287 0.601 1.176 1.688 2.288	371.08 331.94 137.75 92.41 46.32	42.7 39.9 21.6 15.6 8.50

pH of the solution = 7; Temp. = 288K; Equilibration time = 7 hrs.

 

Table 6- Effect of metal oxoanion concentration on ERI-SMZ.

 

Metal oxo-anion	Concn of metal oxo-anion in N	Initial metal oxo-anion Connmeq	Metal oxoanion Conn solid phase meq	Metal oxoanion Concn at equilibrium meq	Kd ml/gm	Sorpn %
CrO4 2-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.312 0.599 0.651 0.710 0.727	0.188 0.401 0.849 1.290 1.773	829.78 746.88 383.39 275.19 205.01	62.5 59.5 43.4 35.5 29.1
ASO4 3-	0.01 N 0.02 N 0.03 N 0.04 N 0.05 N	0.50 1.00 1.50 2.00 2.50	0.254 0.498 0.549 0.574 0.272	0.246 0.502 0.951 1.426 2.228	516.26 496.01 288.64 201.26 61.04	50.9 49.8 36.6 28.7 10.9

pH of the solution = 7; Temp. = 35⁰C; Equilibration time = 7 hrs.

 

 

3.6 Effect of Temperature

The effect of temperature on the adsorption of oxoanions of ERI-SMZ were also checked using the optimized conditions. The temperature was varied from 288 to 308K. The amounts of metal oxoanions adsorbed at various temperature is shown in Table 7 and Fig. 8 which reveals that the uptake of Cr (VI) and As (V). Increase with increase in temperature, indicating better adsorption at higher temperature. The enhancement amount of oxoanions adsorbed at equilibrium with the rise in temperature may be either due to creation of some new active sites on the adsorbent surface.

 

The amounts of oxoanions adsorbed at equilibrium at different temperatures have been utilized to evaluate the thermodynamically parameters for the sorption system. The van't Hoff plot of lnkc V/s 1/T was a straight line Fig. 10.

 

The estimated DH and DS values for the present system were 809.8762, 176.860 and 1639.6129, 949.18 JK^-1Mol^-1 for CrO₄^2- and AsO₄^3- respectively.

3.7 Sorption isotherm

Analysis of the isotherm data is necessary in order to develop an equation that can accurately represent the results and could be used for design purposes (Mahvi, et al 2004). The data obtained from the adsorption isotherm studies were fitted to the Langmuir and Freundlich Isotherms.

The Freundlich isotherm shown is above equation assumes that the uptake of metal ions occur on a heterogenous surface by multi-layer adsorption and the amount of adsorbate adsorbed increases with increasing concentration. The K and 1/n are the constants of the Freundlich isotherm that corresponds to the adsorption capacity and intensity respectively. The parameter C_eq correspondence to the remaining concentration of the adsorbate in the solution and C_ads is the amount adsorbed at equilibrium (Reynolds, et al. 1996).

 

Table 7 : Effect of Temperature

Metal oxoanions	Initial metal oxoanion concentration meq	288K				298K				308K
		A	B	Kd	Sorption %	A	B	Kd	Sorption %	A	B	Kd	Sorption %
CrO4 2-	0.50	0.283	0.217	652.07	56.6	0.298	0.202	737.62	59.6	0.312	0.188	928.78	62.5
ASO4 3-	0.50	0.283	0.287	371.08	42.7	0.240	0.260	461.53	48.1	0.254	0.246	516.26	50.9

A: Concentration of metal oxoanion in solid phase meq; B: Concentration of metal oxoanion in solution phase mq

pH of the solution = 7; Equilibration time = 7 hrs.

 

Table 8- Thermodynamic parameters for metal oxoanion sorption on ERI-SMZ

 

Metal Oxoanions	Temp. (K)	l/T (K)	Concn. sorbed meq L-1	Concn. in bulk meq L-1	KC	lnKc	DG (KJmol-1)	DH (KJmol-1)	DS (KJmol-1K-1)
CrO4 2-	288 298 308	0.00347 0.00336 0.00324	0.217 0.202 0.188	0.283 0.298 0.312	0.066 0.096 0.124	-2.7181 -2.3434 2.0874	-50.12 -0.52 -0.131	809.876	176.860
ASO4 3-	288 298 308	0.00347 0.00336 0.00324	0.287 0.260 0.246	0.213 0.240 0.254	0.074 0.02 0.008	-2.6036 -3.9120 -4.8283	-0.0059 -26.649 -27.594	1639.612	949.18

 

 

Fig. 7(a). Effect of concentration of Cr(VI) and As(V) oxoanion on ERI-SMZ (288K).

 

 

 

Fig.7(b). Effect of concentration of Cr(VI) and As(V) oxoanion on ERI-SMZ

 

Fig. 7(c). Effect of concentration of Cr(VI) and As(V) oxoanion on ERI-SMZ (308K). (298K).

Table 9- Sorption isotherm for metal oxoanions sorption on ERI-SMZ

Metal oxoanions	Concn of metal oxoanions N	250C
		logCads(meq/g)	logCeq(meq/l)
CrO42-	0.01 N	-0.5257	-0.6946
	0.02 N	-0.4365	-0.1979
	0.03 N	-0.3555	0.0248
	0.0 4 N	-0.4111	0.2073
	0.05 N	-0.5985	0.3517
AsO43-	0.01 N	-0.6197	-0.5850
	0.02 N	-0.3645	-0.2456
	0.03 N	-0.2276	-0.0419
	0.0 4 N	-0.2276	0.1486
	0.05 N	-0.4179	0.3259

Metal oxoanions

Fig. 8 : Effect of Temperature on Sorption of Metal Oxoanions by ERI-SMZ

 

Fig 9(a) and 9(b). Freundlich sorption isotherm of CrO₄^2- and AsO₄^3- on ERI-SMZ at 25⁰C

 

Fig. 10. Vant's Hoff Plot of lnkc Vs 1/T for metal oxoanions sorption of ERI-SMZ.

 

The constants of the isotherm equations can be computed from the intercept and slope of the linearized plot of the experimental :

                              [C_ads = K C_eq ^1/n ]

The isotherm constants were calculated from the slope and intercept of Fig.9 (a) and 9 (b) and are present in table. The values of correlation coefficient R² are 096163 and 0.9509 for CrO₄^2- and AsO₄^3- higher in the Freundlich isotherm which indicates that the adsorption process is well represented by the Freundlich equation.

 

4. CONCLUSION:

In the present work, Erionite material was synthesized hydrothenmally. This zeolite is treated with cationic surfactant HDTMA-Br, an organic coating is created on the external surface of zeolite and the charge is reversed. Anions are retained on SMZ Via anionexchanger and ERI-SMZ were synthesized. ERI and ERI-SMZ have been characterized by X-ray powder diffraction, FTIR, and TGA analysis. The studies were carried out at varying contact time, pH, sorbent dose and concentration of metal oxanions. For these experiments, at initial metal ion concentration of CrO₄^-2 and AsO₄^-3 are kept 0.01 N. The kd value and sorption %age for CrO₄^-2 and AsO₄^-3 and higher at pH=7. The increase in contact time, exchanger composition and temperature show sharp increase in kd value and sorption percentage with ERI-SMZ. It may be proven that the ERI-SMZ is a potential candidate for sequestration of CrO₄^-2 and ASO₄^-3 from waste water solution.

 

5. ACKNOWLEDGEMENT

The authors acknowledge to Head IIT, IIT Roorkee providing necessary instrumental facilities for XRD and TGA analysis.

 

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Received on 28.07.2010        Modified on 07.08.2010

Accepted on 11.08.2010        © AJRC All right reserved