为了达到盐酸酸洗废水零排放的要求,采用单阴膜动态电渗析技术,进行回收酸洗废水中的铁的试验研究。在动态试验中采用经扩散渗析和中和预处理的实际废水,考察电压、电流和流量对铁回收率及电流效率的影响,并用电压-电流法测定系统的极限电流密度。结果表明,用不锈钢作阴极,Ti/SnO2-Sb2O3作阳极,采用DF120型均相阴离子交换膜,在试验条件下,阴极液pH值为2.50~3.00,Fe2+质量浓度为1 000~1 300 mg/L,阳极液pH值为3.00,控制阴阳极液进水流量均为60 mL/h,采用恒压输出方式,动态电渗析系统的极限电流密度为33.3 A/m2,对应的极限电压为11 V。在试验条件下,盐酸酸洗废水中的铁回收率可达到91.8%,电流效率达到70.3%,阴极室出水pH值可达6.00,Fe2+质量浓度小于60 mg/L,阳极室出水pH值达到1.00,Fe2+质量浓度小于25 mg/L。铁回收率随着流量的增加而逐渐降低,电流效率随着流量的增加而增高。阴极室出水pH值随着流量的增加而降低,阳极室出水pH值随着流量的增加而上升。
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 rate. 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 Fe2+ 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/SnO2-Sb2O3), 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/m2 corresponding to a limiting voltage of 11 V. 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 Fe2+ concentration less than 60 mg/L and the pH of the effluent from the anode chamber reached 1.00 with a Fe2+ concentration less than 25 mg/L. The other operating conditions are shown as follows: cell voltage =10 V, reaction time =240 min, pH of the cathode electrolyte solution =2.50-3.00, Fe2+ concentration of the cathode electrolyte solution =1 000-1 300 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.