FACTORS INFLUENCING METALS RECOVERY FROM WASTEWATERS

BY ION EXCHANGE

 

Mohamed Ragaei Lasheen, Azza Ashmawy and Hanan Ibrahim

(Department of Water Pollution, National Research Center, Cairo, Egypt)

E-mail: ragaei24@intouch.com.

 

ABSTRACT

 

Ion exchange has received considerable attention for separation and concentration of a variety of metals from waste effluent. Heavy metal ions typically present in waste streams (Cd, Cr, Ni, Zn, Cu) can be removed by ion exchange processes. Strong acid, weak acid, or chelating ion exchange resins can be used to remove soluble metals. Reuse of treated electroplating rinse waters after ion exchange treatment is strong economic driving force even in cases when discharge limitations can be met by precipitation. The main objective of this study to use bench scale column runs to assess the effectiveness of ion exchange resin for metal recovery at different operating conditions. The results indicate that IRA 900 is highly efficient for Cr (VI) removal. Chelating resins showed great capacity and selectively for metal removal in the following order: Cu > Ni > Cd

This evaluation address the product quality, pollution prevention potential, and the factors involved in the use of ion exchange to recover Cd, Cu, Cr (VI), Ni from industrial wastewater.

INTRODUCTION

 

Industry is a major contributor to the Egyptian economy, representing 26% of Gross Domestic product. Industrial wastewater is a major contributor to Egypt’s pollution. It is estimated that the industrial complexes in Cairo produced about 127 million cubic meters of wastewater per year, about 80 million cubic meters is discharged into the Nile, the rest being discharged through the sewage. Small-scale industries are often responsible for disproportionately large contribution to overall pollution loads. Examples of this are the electroplating and painting industries, which are primary sources of heavy metals discharges to water. The heavy metals pollution load is 1.65 ton/d mainly from industrial wastewater’s (ref 1).

The main objective of this study is: to assess the effectiveness of ion exchange resins on removing Cd, Cu, Cr (VI) and Ni from wastewater in presence of competing anions and chelating agent.

METHODS AND MATERIALS

 

Four commercially available resins were used in this study: Two strongly basic anion exchange resins Sty–DVB matrix, with a quaternary ammonium functional group
a) Dowex 1x8 (Dow chemical company), b) Amberlite IRA 900 ( Rohm and Hans co.) and two chelating exchanger with iminodiacetate c) IRC-718 ( Rohm and Hans co.),
d) Lewatit TP 207 ( Bayer Ltd.).

A standard solution of cadmium, chromium (VI), copper and nickel was prepared by dissolving specific quantities of CdCl2.2.5H2O, K2Cr2O7, CuSO4.5H2O and NiCl2.6H2O respectively in double distilled water. EDTA was added based on the stoichiometric requirement for metals, considering that one mole of metal required one mole of EDTA.

A glass column having a diameter of (1.3cm) was used, the layer of the ion exchange was (9.5cm) and the flow rate of 2 L/h was applied using dosing pump. Effluent samples were manually collected at every 250 ml. Regeneration for anion exchanger was done by using 1.5M NaOH or alkaline brine (0.5% NaOH and 5% NaCl).

An atomic absorption spectrophotometer was used for metals analysis. Samples were digested and analyzed according to Standard Method (ref. 2).

 

RESULTS AND DISCUSSION

 

Effect of flow rate, column diameter and competing anions on chromate removal: Figure (1) shows that higher loading resulted in earlier breakthrough. This due to the fact that the higher flow rates, the shorter contact time between the resins and the liquid phases. In addition, Figure (2) indicates that at same bed volume with flow rate 2 L/hr, the treated bed volume is higher at (1.3cm) column diameter than that of (2 cm) diameter. Hwang and Lu (ref 3) obtained similar results. IRA 900 shows (Figure (3)) high selectivity for Cr (VI), the presence of sulfates and chlorides lead to early, gradual breakthrough at pH 4. Our results substantiated by that of Sengupta and Clifford (refs. 4&5). Regeneration was very effective as demonstrated in Figure (4). Newman and Reed (ref. 6) indicated that alkaline brine is the most suitable one for regeneration of anion resin.

Treatment of chelated metals: The results Figure (5) revealed that IRA-900 was very effective in removing metals in presence of EDTA. Metals removal increases in the following order: Cu> Ni> Cd. However, metal removal do not corresponds to the published formation constants for the EDTA complexes (ref.7). Inczedy, (ref. 8) showed that the steric effect of the octahedral of metal-EDTA chelates plays a certain role in ion exchange processes.

Treatment of electroplating rinsing Water: Electroplating rinsing water from an electro- plating plant located at 6th of October City (a new industrial city near Cairo) was used in this study. The average wastewater is 40 m3/d discharged without treatment into the sewer system. Rinsing water was collected from two plating processes (a) copper cyanide complexes and cyanide and (b) chromium (VI). Figure (6) showed that IRA-900 is highly efficient for chromium removal. In addition, the breakthrough curve is steeper for copper cyanide complexes. Additional studies have demonstrated the effectiveness of an ion exchange resin for removal of metal cyanide complexes (ref. 9).

Treatment of metals mixture: Figures (7 a & b) demonstrate that under identical operational conditions IRC-718 offers high efficiency for metal removal than TP 207 and both of them showed the same order of selectivity: Cu > Ni > Cd. Sengupta (ref. 10), obtained similar results.

Conclusions: Reducing the generation of metal finishing waste at the source or recycling the wastes on or off site will benefit the metal finishing industry in Egypt.

 

REFERENCES

 

1.       Environmental Action Plan of Egypt (1992), Egyptian Environmental Affairs Agency, Cairo Egypt.

2.       Standard Methods for the Examination of Water and Wastewater (1995), 19th Edition American Public Health Association, Washington D.C.

3.       Hwang S.J. and Lu W.J. (1995), Ind. Eng. Chem. 34, 1434-1439

4.       Sengupta A.K. and Clifford D. (1986), Ind. Eng. Chem. Fundam., 25, 249.

5.       Sengupta A.K. and Clifford D. (1986), Envir. Sci. Technol., 20, 149.

6.       Newman J. and Reed L.W. (1980), AICHE Symp. Ser. 197, 76.

7.       Principles of Aquatic Chemistry (1983) Morel, F.M.M., John Wily and Sons. Inc.

8.       Analytical Applications of Complex Equilibria (1976), Inczedy J., Ellis Horwood: Chichester, U.K., 67-74.

9.       Hassan S.Q. Vitello M.P., Kupferle M.J. and Grosse D.W. (1991), J.Air Waste Mgmt. Assoc. 41, 710-715.

10.   Ion Exchange Technology (1995), Sengupta A.K.(ed.), Technomic Pub. Com. Inc.

 

 

 

 

 

 

 

 

 

 

 

Text Box: Fig. (7) Treatment of Metals Mixture Using Chelating Resin.