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Recovery of Fe from the HCI pickling wastewater by dynamic electrodialysis

ZHU Mao-sen~1,XIA Chun-mei~2,HU Xiao-min~1 (1 School of Resources and Civil Engineering,Northeastern University, Shenyang 110004,China;2 NEUSOFT Corporation,Shenyang 110179,China)  
Dynamic electrodialysis using an anion-exchange membrane was employed to recover Fe from the HCl pickling wastewater. Actual wastewater effluent which was pretreated by diffusion dialysis and neutralization was used in setting tests.In these tests,the HCl pickling wastewater was treated in a home-made dynamic electrodialysis reactor by adjusting the reaction parameters which included cell voltage,current density and flow rale.The effects of these factors on the Fe recovery rate and current efficiency were studied.The limiting current density of the dynamic electrodialysis system was measured by voltage-current plot method.The sample water reached the cathode chamber and anode chamber respectively when the electrodialysis reaction was completed.The pH value and Fe~(2+)concentration of each sample were then measured.In addition,the Fe recovery rate was calculated according to the experimental results.A stainless steel cathode,a titanium-based anode with metal oxide coatings of Sn and Sb(Ti/SnO_2-Sb_2O_3),and a DF120 anion-exchange membrane were employed in the dynamic electrodialysis system.It was found that the zero discharge of HCl pickling wastewater could be achieved through the dynamic electrodialysis system,which is a good separator for the mixture of HCl and ferrous chloride.The results of experiments on HCl pickling wastewater demonstrated that the limiting current density was 33.3 A/m~2 corresponding to a limiting voltage of 11V.The Fe recovery rate reached 91.8% and the current efficiency reached 70.3 %.In addition,the pH of the effluent from the cathode chamber reached 6.00 with a Fe~(2+)concentration less than 60 mg/L and the pH of the effluent from the anode chamber reached 1.00 with a Fe~(2+)concentration less than 25 mg/L.The other operating conditions are shown as follows:cell voltage=10 V,reaction time=240min, pH of the cathode electrolyte solution=2.50-3.00,Fe~(2+)concentration of the cathode electrolyte solution=1000-1 300 mg/L and pH of the anode electrolyte solution=3.00.The results have also revealed that both Fe recovery rate and the pH of effluent from cathode chamber decreased when the flow rate was increased.Meanwhile,the current density and the pH of effluent from anode chamber increased when the flow rate was increased.
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