Water Air Soil Pollut (2010) 210:43–50 DOI 10.1007/s11270-009-0221-7
Kinetics of Chromium Ion Removal from Tannery Wastes Using Amberlite IRA-400 Cl− and its Hybrids Syed Mustafa & Tauqeer Ahmad & Abdul Naeem & Khizar Hussain Shah & Muhammad Waseem
Received: 29 April 2009 / Accepted: 14 September 2009 / Published online: 9 October 2009 # Springer Science + Business Media B.V. 2009
Abstract A strong base anion exchange resin Amberlite IRA-400 Cl− and its hybrids with Mn(OH)2 and Cu(OH)2 are used for the removal of chromium from the synthetic spent tannery bath. The recovery is examined by varying the experimental conditions, viz., resin dosage, stirring speed, and temperature. The rate of chromium removal by Amberlite IRA-400 Cl− increased almost four times when the resin dosage was increased from 0.2 to 1.0 g. Furthermore, the rate of chromium sorption almost doubled when the stirring speed was increased from 100 to 1,000 rpm, suggesting that the sorption is a diffusionally controlled process. The chromium removal capacity also increased with the rise of temperature, showing the endothermic nature of the process. The results are explained with the help of film diffusion, particle diffusion, and Lagergren pseudo-first-order kinetic models. The kinetics results of the Amberlite IRA400 Cl− are compared with its hybrid anion exchange resins IRA-400 Mn(OH)2 and IRA-400 Cu(OH)2. It is found that the hybrid ion exchangers have greater removal ability and fast kinetics as compared to the parent exchanger.
S. Mustafa (*) : T. Ahmad : A. Naeem : K. H. Shah : M. Waseem National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar 25120, Pakistan e-mail:
[email protected]
Keywords Amberlite IRA-400 Cl− . Chromium removal . Hybrid ion exchangers . Ion exchange . Kinetics . Spent tannery bath
1 Introduction The use of heavy metals and their compounds are essential for the economic growth of any nation. Like many other metallic species, chromium has variety of applications in leather tanning, explosives, ceramics, paint pigments, photography, and wood preservation. These industrial processes discharge large quantities of chromium into the environment, which has significant undesirable biological and ecological effects (Herrmann 1994; Mustafa et al. 1997; Tadesse et al. 2006). Chromium can exist in several chemical forms displaying oxidation numbers from 0 to VI. Only two of them, trivalent and hexavalent chromium, are, however, stable enough to occur in the environment. Chromium(III) is much less toxic than chromium(VI) and is seldom found in potable water. Evidences show that the presence of MnO2 and other oxidizing agents in soil favor the oxidation of chromium(III) to chromium(VI) even under ambient conditions in natural systems (Eary and Ray 1987; Nakayama et al. 1981). Chromium(VI) is able to traverse cell membranes and is the source of deleterious health problems like headache, skin rashes, upset stomachs and ulcers, respiratory problems, weakened immune systems, kidney and liver damage, lung cancer, etc.
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Water Air Soil Pollut (2010) 210:43–50
(Kotas and Stasicka 2000; Rengaraj et al. 2001; van Heerden et al. 1994). Owing to the toxicity of chromium in water, its removal from wastewater is of wider interest. The National Environmental Quality Standards of Pakistan has set the maximum level of total chromium to 1.0 mg L−1 in the effluents (The Gazette of Pakistan 2000), while the Environmental Protection Agency of the USA has set the maximum level of total chromium concentration of 0.1 mg L−1 for drinking water (Narin et al. 2008). Tannery effluents containing chromium thus have to be treated to reduce the chromium concentration in the discharge below the tolerable limits. A number of methods like precipitation, coagulation, electrolysis, and biological treatment have been described for purifying wastewater from chromium (Mohan and Pittman 2006; Sengupta and Lim 1988). The main disadvantages of these processes, apart from the difficulties with sludge thickening, are that the resulting semi-solid waste cannot be recycled under economic conditions. However, ion exchange is the most rapid, cheap, effective, and versatile technique which demands less skill than those of the others. Furthermore, chromium can be easily regenerated from the exchanger to be utilized again (Kocaoba and Akcin 2002; Mustafa et al. 2008; Rengaraj et al. 2001; Tenório and Espinosa 2001). In recent years, a new class of ion exchangers known as hybrid ion exchangers (HIX) is developed. These ion exchangers comprise spherical macroporous polymeric ion exchanger beads within which submicron particles of polyvalent metal oxides have been uniformly and irreversibly dispersed. These hybrid ion exchangers are very selective and efficient as compared to the ordinary ion exchangers and have been used successfully for the removal of arsenic and phosphates (Cumbal et al. 2003; Cumbal and SenGupta 2005; DeMarco et al. 2003). Furthermore, to our Table 1 The composition of the spent tanning bath (Petruzzelli et al. 1991)
Items Cr(III)
knowledge, the hybrid ion exchange resins have not yet been employed for the removal of chromium. In the present report, a strong basic anion exchange resin, Amberlite IRA-400 Cl−, is used for the removal of chromium from synthetic spent tannery solutions. A non-conventional way of removing chromium is used in which chromium(III) is first oxidized to chromium(VI) by hydrogen peroxide in alkaline media. Kinetics of chromium ion removal from synthetic spent tanning bath solution is studied and the results are compared with its two hybrid forms containing Mn(OH)2 and Cu(OH)2.
2 Experimental All chemicals used in the present work were of analytical reagent grade. All the solutions were prepared in doubly distilled water using Pyrex glass apparatus. 2.1 Preparation of Synthetic Spent Tanning Bath The composition of the synthetic spent tanning bath prepared in the laboratory is given in Table 1 (Petruzzelli et al. 1991). 2.2 Amberlite IRA-400 Amberlite IRA-400 is a macroporous strong basic anion exchange resin with main characteristics given in Table 2. 2.3 Preparation of Hybrid Ion Exchange Resin Hybrid anion exchangers were prepared using Amberlite IRA-400 Cl− as a parent resin, and metal hydroxide particles were dispersed in it. The procedure for the preparation of hybrid ion exchangers has been reported elsewhere (Cumbal and SenGupta Real spent tanning bath 3,500–4,500 (mg L−1)
Synthetic spent tanning bath 4,400 (mg L−1)
Fe(III)
40–100
45
Al(III)
80–150
110
SO42−
10,000–12,000
Total (organic carbon) NaCl pH
1,200–1,800 50,000–70,000 3.0–3.5
11,000 1,300 (as CH3COOH) 58,000 3.0
Water Air Soil Pollut (2010) 210:43–50
45
Table 2 Characteristics of Amberlite IRA-400 ion exchange resin
0.4
Parameter
Remarks
0.3
Polymer matrix
Polystyrene DVB
Functional group
–N+R3
Ionic form
Cl−
Exchange capacity
2.6–3 eq kg−1 (dry mass)
Effective size
0.3–0.9 mm
Operating temperature
80°C (maximum)
pH range
0–14
X (mmolg-1)
293K 303K 313K
0.2
323K 0.1
0 0
10
20
30
40
50
60
Time (min)
2005; DeMarco et al. 2003). In short, ion exchange resin was transferred to a 100 mL burette used as a column. The loading of Cu(II) onto the quaternary ammonium sites of the exchanger was achieved by passing 4% CuCl2 solution at an approximate pH of 2.0 through the column. Afterwards, Cu(II) hydroxide was precipitated within the gel of the exchanger by passing a solution containing both NaCl and NaOH, each at 5% (w/v) concentration through the column. At the end column, contents were rinsed and washed with a 50:50 ethanol–water solution followed by a mild thermal treatment (50–60°C) for 60 min. Similarly, Mn(OH)2 hybrid resin was prepared using 4% MnCl2; the rest of the procedure was the same as described for Cu(II). 2.4 Procedure for Determination of Chromium The concentration of chromium in solution was determined by spectrophotometer Vis-1100, Canada
Fig. 2 Kinetic curves of the chromium sorption on Amberlite IRA-400 Cl− at different temperatures
using a method described elsewhere (Awan et al. 2003). In this method, chromium(III) is first oxidized to chromium(VI). For this purpose; 5.0 mL of chromium(III) of concentration below 25 mg L−1 and 5.0 mL of 0.1 M NaOH solutions were mixed in a test tube to which three drops of 3% solution of hydrogen peroxide were added. After addition of H2O2, the test tube mixture was heated until boiling. The color of the solution became bright yellow and was left in the tube for 1 h. The absorbance of this solution was read on visible spectrophotometer at 372 nm. A standard curve showing absorbance versus concentration was plotted and is shown in Fig. 1. The concentration of solutions after sorption was read from this standard curve.
1.2
11.4 11.2
1
11
0.8
pH
Absorbance at 372 nm
293k 303k 313k 323k
0.6
10.8 10.6
0.4
10.4
0.2
10.2 10 0
0 0
5
10
15
20
25
30
10
20
30
40
50
60
Time (min)
Concentration of Cr (mg/L)
Fig. 1 Calibration curve for the determination of chromium
Fig. 3 Effect of temperature on pH during chromate sorption. Effect of temperature on the pH of the adsorbate solution
46
Water Air Soil Pollut (2010) 210:43–50 10
different time intervals, 1.0 mL solution was drawn into test tubes and analyzed for the total chromium concentration. pH of the solutions during sorption process were measured with a pH meter BOECO BT600, Germany using a combination glass electrode.
293K 303K
8
-ln(1-F)
313K 6
323K
4
3 Results and Discussion
2
0 0
10
20
30
40
Time (min)
Fig. 4 Film diffusion plots for the chromium removal by Amberlite IRA-400 Cl− at different temperatures
The same method was employed for the oxidation of chromium in the synthetic spent tannery bath solution. The solution (22.73 mL) was taken in a 1,000 mL beaker to which 10 mL of 30% hydrogen peroxide, 385 mg of sodium hydroxide, and 500 mL of water were added. The mixture was boiled for 5 min and allowed to cool. It was then transferred to a 1,000 mL volumetric flask and diluted to 1,000 mL with water. This solution was used for the exchange studies. 2.5 Kinetic Studies For kinetic studies, synthetic spent tanning bath solution after oxidation to chromium(VI) was diluted to (1.923 mmol L−1). Of this diluted solution, 100 mL was transferred to a double-walled glass cell attached to the water-circulating bath WiseCircu WCB-6, Korea. After attaining the desired temperature, 0.5 g of resin was added in it, while the stirring speed of magnetic bar was adjusted to 1,000 rpm. After Table 3 Kinetic parameters for the chromium removal by Amberlite IRA-400 Cl−
Temperature (K)
The results for chromium removal from synthetic spent tanning bath solution by anion exchange resin Amberlite IRA-400 Cl− are shown in Fig. 2. It can be observed that the equilibrium is attained approximately within 50, 40, 35, and 30 min at 293, 303, 313, and 323 K respectively, indicating that the rate of reaction increases with the rise of temperature. However, the rate is the fastest during the first 20 min of contact. Furthermore, it is observed that the maximum amount sorbed at equilibrium is 0.32 mmol g−1 at all the temperatures under investigation. The maximum sorption capacity observed here is almost the same as observed for chromium(III) on two different ion exchangers Chelex-100 and Liwatit TP-207 by Gode and Pehlivan (2003). This shows that the resin Amberlite IRA-400 in the Cl− form is highly selective toward the uptake of chromium(VI) as the synthetic spent tannery bath used in the present investigation also contains a very high concentration of SO4−2 anions. Thus, it can be concluded that the removal of chromium in the form of chromium(VI) by the anion exchange resin is more feasible as compared to the chromium(III) by the cation exchangers. Dabrowski et al. (2004) had also pointed toward the difficulties in removing the chromium(III) from the industrial wastewaters due to the presence of sulfates. The pH of the solution is noted after different time intervals during the exchange process. The results are
Rat constants (min−1) Film diffusion model (ku)
Particle diffusion model (B)
First-order Lagergren model (kL)
293
0.118
0.109
0.107
303
0.138
0.129
0.140
313
0.167
0.156
0.155
323 Activation energy (kJ mol−1)
0.201
0.188
0.182
14.059
14.394
13.367
Water Air Soil Pollut (2010) 210:43–50
47
2RCl þ CrO4 2 Ð R2 CrO4 þ 2Cl :
8
293K 303K 6
ð1Þ
0 0
Various kinetic models were applied to the data and are discussed below. 3.1.1 Film Diffusion Model The expression for film diffusion is written as (Rengaraj et al. 2003): lnð1 F Þ ¼ ku t
ð2Þ
where F is the ratio of amount adsorbed after time t to the amount adsorbed at equilibrium and ku is the rate constant. The values of ku are obtained from slope of the plot of −ln(1 − F) versus t, shown in Fig. 4 and are reported in Table 3. The energy of activation (Ea) is calculated using the Arrhenius equation: Ea ln ku ¼ ln A RT 0.0031
4
2
3.1 Application of Kinetic Models
0.003 -1.5
313K 323K
Bt
shown in Fig. 3. It can be observed from the plot that there is very small change in pH during the entire period of experiment. In the present system, the pH being greater than 9, therefore only CrO4−2 ions are expected to be present (Kotas and Stasicka 2000). These ions are sorbed on the resin (RCl) according to the following exchange reaction:
ð3Þ
10
20
30
Fig. 6 Particle diffusion plots for the chromium removal by Amberlite IRA-400 Cl− at different temperatures
where ku is the rate constant, A is the Arrhenius factor, R is the molar gas constant (JK−1 mol−1), and T is the absolute temperature. The plot of lnku versus 1/T according to the above equation is shown in Fig. 5. Energy of activation calculated from the slope of the straight line is found to be 14.059 kJ mol−1. 3.1.2 Particle Diffusion Model The expression for particle diffusion is: Bt ¼ 2:30258 log ð1 F Þ 0:4977 for F > 0:85 ð4Þ Bt ¼ 6:28318 3:2899F 6:28318ð1 1:047F Þ1=2
0.0032
0.0033
0.0034
40
Time (min)
for F < 0:85 ð5Þ
0.0035
-1 0
-1.7
-2
-1.8
-3 ln (qe-qt)
ln(Rate)
0 -1.6
-1.9 -2
lnku -2.1 -2.2
lnkL
-2.3
1/T (K-1)
Fig. 5 Arhenius plots for the chromium removal by Amberlite IRA-400 Cl−
20
30
40
50
-4 -5 -6
lnB
10
293K
-7
303K
-8
313K
-9
323K Time (min)
Fig. 7 Lagergren plots for the chromium removal by Amberlite IRA-400 Cl− at different temperatures
48 Table 4 Comparison of the equilibrium concentration values of the different kinetic model
Water Air Soil Pollut (2010) 210:43–50 Experimental qe (mmol g−1)
Film diffusion qe (mmol g−1)
Particle diffusion qe (mmol g−1)
Lagergren qe (mmol g−1)
293
0.3249
0.3258
0.3257
0.3264
303
0.3222
0.3235
0.3233
0.3234
313
0.3222
0.3231
0.3230
0.3236
323
0.3244
0.3251
0.3251
0.3257
Temperature (K)
2
where B is the rate constant and is equal to Dp =r2 , D is the particle diffusion coefficient, and r is the radius of the resin particle. Equation 5 is used for values of F from 0 to 0.85 and Eq. 4 for the values from 0.86 to 1 (Mustafa et al. 2008; Reichenberg 1953). Equations 4 and 5 are used to calculate the Bt values and are plotted versus t as shown in Fig. 6. The values of the rate constants (B) from the plots in Fig. 6 are reported in Table 3. Energy of activation calculated from the slope of Fig. 5 is found to be 14.394 kJ mol−1.
et al. 2008). The activation energies found here for the chromium sorption are less than 42 kJ mol−1, which is the limit for distinguishing between the diffusionally and chemically controlled reactions (Scheckel and Sparks 2001). Similar values of rate constants and activation energies were reported by Erdem et al. (2004) for the removal hexavalent chromium by heatactivated bauxite.
3.1.3 Lagergren Kinetic Model
To observe the effect of different doses of adsorbent, the studies were carried out using 1.9231 mmol L−1 synthetic spent tanning bath solutions. The results are shown in Fig. 8. The removal efficiency was 44.82%, 72.98%, and 91.60% for the resin amounts of 0.2, 0.5, and 1.0 g, respectively. The rate constant ku values are reported in Table 5; it is observed that the rate constant of the sorption process is almost doubled when the resin dosage is increased from 0.2 to 0.5 g and doubled further when the resin amount is increased from 0.5 to 1.0 g. The sorption efficiency is therefore increased with increasing adsorbent dose
ð6Þ
where qe and qt are the equilibrium concentration and concentration at time t, while kL is the Lagergren rate constant. The results are graphically shown in Fig. 7, while the rate constant kL values are reported in Table 3. The plot of lnkL versus 1/T according to the Arrhenius equation is shown in Fig. 5. Energy of activation is found to be 13.367 kJ mol−1. The equilibrium sorption values calculated using the rate constants derived from the different kinetic models are compared with the experimental values in Table 4. It can be observed from this table that all the kinetic models fit to the exchange data reasonably well. The sorption process is thus controlled by both the film and particle diffusions and also follows the first-order kinetics. Rengaraj et al. (2001) also assumed that the sorption of chromium by ion exchange resins followed the first-order and film diffusion kinetics. The low values of activation energies calculated from the different models are in the range of 13.367–14.394 kJ mol−1 also point toward the diffusional nature of the process (Ayoob
0.8
0.2g 0.5g 0.6
1.0g
-1
Lnðqe qt Þ ¼ lnqe kL t
X (mmolg )
The pseudo-first-order rate expression derived by Lagergren (Rengaraj et al. 2003) was also applied to the data for the determination of rate constant values. Lagergren equation is written as:
3.2 Effect of Resin Dosage on Sorption Kinetics
0.4
0.2
0 0
10
20
30
40
50
Time (min)
Fig. 8 Chromium sorbed as a function of resin dosage
60
Water Air Soil Pollut (2010) 210:43–50
49 0.35
Table 5 Effect of resin dosage on rate constants for the removal of chromium
0.3
Rate constant (ku) (min−1)
0.2
0.064
0.5
0.123
1.0
0.211
Cl
0.25
X (mmolg-1)
Weight of resin (g)
Mn Cu
0.2 0.15 0.1
due to the increase in the number of sorption sites and greater surface area for a fixed adsorbate concentration. Similar effect of adsorbent dosage was observed elsewhere (Pehlivan and Cetin 2009).
0.05 0 0
10
20
30
40
50
60
Time (min)
Fig. 10 Comparison of different forms of Amberlite IRA-400 resin for chromium removal
3.3 Effect of Stirring Speed Figure 9 shows the effect of stirring speed on the removal of chromium. The studied speeds are 100 and 1,000 rpm. The removal efficiency increased from 73.667% to 83.896% with the increase of stirring speed from 100 to 1,000 rpm. The calculated rate constant ku values are almost doubled from 0.057 to 0.123 min−1 when the stirring speed is increased from 100 to 1,000 rpm. The sorption rate being stirring dependent also shows it to be a diffusionally controlled process. 3.4 Kinetic Comparison of Hybrid Resins The kinetic data of chromium removal by Amberlite IRA-400 Cl−, IRA-400 Mn(OH)2, and IRA-400 Cu (OH)2 are shown in Fig. 10. The rate constant values (ku) for each type of resin are reported in Table 6. It shows that the hybrid ion exchangers have not only
faster kinetics but also a higher capacity than the parent materials. It is observed that the rate of sorption for the chromium removal increases in the following order: IRA 400MnðOHÞ2 > IRA 400CuðOHÞ2 > IRA 400Cl : The increase in sorption by the hybrid ion exchanger is due to the presence of –OH groups on the oxides in addition to the fixed groups of the ion exchangers. Similar observations were reported for the removal of phosphate and arsenic by hybrid ion exchange resins (Blaney et al. 2007; Cumbal and SenGupta 2005).
4 Conclusions 0.4
On the basis of the above studies, it can be concluded that the efficient sorption of chromium from tannery wastes can be achieved by a strong basic anion exchange resin Amberlite IRA-400 Cl− and its hybrid forms. To find the mechanism of the sorption process,
X (mmolg-1)
0.3
100rpm
0.2
1000rpm
Table 6 Comparison of the rate constant values for the chromium removal by different forms of the resin
0.1
Resin type 0 0
10
20
30
40
50
Time (min)
Fig. 9 Chromium sorbed as a function of stirring rate
60
Rate constant (ku) (min−1)
Amberlite IRA-400 Cl−
0.123
HIX Mn(OH)2
0.135
HIX Cu(OH)2
0.132
50
kinetic experiments are performed at different temperatures, stirring rate, and resin dosage. Different kinetic models like film diffusion, particle diffusion, and Lagergren pseudo-first order are applied to the data. The low values of activation energy calculated using Arrhenius equation indicate that the process is diffusion-controlled and physical in nature. Increase in resin dosage, stirring speed, and precipitation of metal hydroxides in the resin matrix favor the chromium removal from the tannery wastes. References Awan, M. A., Baig, M. A., Iqbal, J., Aslam, M. R., & Ijaz, N. (2003). Recovery of chromium (III) from tannery wastewater. Journal of Applied Sciences and Environmental Management, 7, 5–8. Ayoob, S., Gupta, A. K., Bhakat, P. B., & Bhat, V. T. (2008). Investigations on the kinetics and mechanisms of sorptive removal of fluoride from water using alumina cement granules. Chemical Engineering Journal, 140, 6–14. Blaney, L. M., Cinar, S., & SenGupta, A. K. (2007). Hybrid anion exchanger for trace phosphate removal from water and wastewater. Water Research, 41, 1603–1613. Cumbal, L., & SenGupta, A. K. (2005). Arsenic removal using polymer-supported hydrated iron(III) oxide nanoparticles: Role of Donnan membrane effect. Environmental Science and Technology, 39, 6508–6515. Cumbal, L., Greenleaf, J., Leun, D., & SenGupta, A. K. (2003). Polymer supported inorganic nanoparticles: Characterization and environmental applications. Reactive and Functional Polymers, 54, 167–180. Dabrowski, A., Hubicki, Z., Podkoscielny, P., & Robens, E. (2004). Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere, 56, 91–106. DeMarco, M. J., SenGupta, A. K., & Greenleaf, J. E. (2003). Arsenic removal using a polymeric/inorganic hybrid sorbent. Water Research, 37, 164–176. Eary, L. E., & Ray, D. (1987). Kinetics of chromium(III) oxidation to chromium(VI) by reaction with manganese dioxide. Environmental Science and Technology, 21, 1187–1193. Erdem, M., Altundogan, H. S., & Tumen, F. (2004). Removal of hexavalent chromium by using heat-activated bauxite. Mineral Engineering, 17, 1045–1052. Gode, F., & Pehlivan, E. (2003). A comparative study of two chelating ion-exchange resins for the removal of chromium(III) from aqueous solution. Journal of Hazardous Materials, B100, 231–243. Herrmann, M. S. (1994). Testing the waters for chromium. Journal of Chemical Education, 71, 323–324. Kocaoba, S., & Akcin, G. (2002). Removal and recovery of chromium and chromium speciation with MINTEQA2. Talata, 57, 23–30. Kotas, J., & Stasicka, Z. (2000). Commentary: Chromium occurrence in the environment and methods of its speciation. Environmental Pollution, 107, 263–283.
Water Air Soil Pollut (2010) 210:43–50 Mohan, D., & Pittman, C. U., Jr. (2006). Review: Activated carbons and low cost adsorbents for remediation of tri- and hexavalent chromium from water. Journal of Hazardous Materials, 137, 762–811. Mustafa, S., Bashir, H., Rehana, N., & Naeem, A. (1997). Selectivity reversal and dimerization of chromate in the exchanger Amberlite IRA-400. Reactive and Functional Polymers, 34, 135–144. Mustafa, S., Shah, K. H., Naeem, A., Waseem, M., & Tahir, M. (2008). Chromium (III) removal by weak acid exchanger Amberlite IRC-50 (Na). Journal of Hazardous Materials, 160, 1–5. Nakayama, E., Kuwamoto, T., Tsurubo, G., & Fujinaga, T. (1981). Chemical speciation of chromium in seawater: Part2. Effect of manganese oxides and reducible organic materials on the redox process of chromium. Analytica Chimica Acta, 130, 401–404. Narin, I., Kars, A., & Soylak, S. (2008). A novel solid phase extraction procedure on Amberlite XAD-1180 for speciation of Cr(III), Cr(VI) and total chromium in environmental and pharmaceutical samples. Journal of Hazardous Materials, 150, 453–458. Pehlivan, E., & Cetin, S. (2009). Sorption of Cr(VI) ions on two Lewatit-anion exchange resins and their quantitative determination using UV–visible spectrophotometer. Journal of Hazardous Materials, 163, 448–453. Petruzzelli, D., Santori, M., Passino, R., & Tiravanti, G. (1991). Cr (III) recovery and separation from spent tannery baths by carboxylic ion exchange resins “New Developments in Ion Exchange”. Proceedings of the International Conference on Ion Exchange Resins (pp. 383–388). Kodansha, Tokyo, Japan. Reichenberg, D. (1953). Properties of ion exchange resins in relation to their structure. III. Kinetics of exchange. Journal of American Chemical Society, 75, 589–597. Rengaraj, S., Yeon, K. H., & Moon, S. H. (2001). Removal of chromium from water and wastewater by ion exchange resins. Journal of Hazardous Materials, B87, 273–287. Rengaraj, S., Joo, C. K., Kim, Y., & Yi, J. (2003). Kinetics of removal of chromium from water and electronic process wastewater by ion exchange resins: 1200H, 1500H and IRN97H. Journal of Hazardous Materials, 102, 257–275. Scheckel, K. G., & Sparks, D. L. (2001). Temperature effects on nickel sorption kinetics at the mineral– water interface. Soil Science Society of America Journal, 65, 719–728. Sengupta, A. K., & Lim, L. (1988). Modeling chromate ionexchange processes. AIChE Journal, 34, 2019–2029. Tadesse, I., Isoaho, S. A., Green, F. B., & Puhakka, J. A. (2006). Lime enhanced chromium removal in advanced integrated wastewater pond system. Bioresource Technology, 97, 529–534. Tenório, J. A. S., & Espinosa, D. C. R. (2001). Treatment of chromium plating process effluents with ion exchange resins. Waste Management, 21, 637–642. The Gazette of Pakistan, Extra. (2000). Statutory notification (S.R.O). Government of Pakistan Ministry of Environment, Local Government and Rural Development Notification, Islamabad. S.R.O. 549 (1)/2000. van Heerden, P. V., Jenkins, I. R., Woods, W. P. D., Rossi, E., & Cameron, P. D. (1994). Death by tanning—A case of fatal basic chromium sulfate poisoning. Intensive Care Medicine, 20, 145–147.
