為了達到鹽酸酸洗廢水零排放的要求,采用單陰膜動態(tài)電滲析技術(shù),進行回收酸洗廢水中的鐵的試驗研究。在動態(tài)試驗中采用經(jīng)擴散滲析和中和預處理的實際廢水,考察電壓、電流和流量對鐵回收率及電流效率的影響,并用電壓-電流法測定系統(tǒng)的極限電流密度。結(jié)果表明,用不銹鋼作陰極,Ti/SnO2-Sb2O3作陽極,采用DF120型均相陰離子交換膜,在試驗條件下,陰極液pH值為2.50~3.00,Fe2+質(zhì)量濃度為1 000~1 300 mg/L,陽極液pH值為3.00,控制陰陽極液進水流量均為60 mL/h,采用恒壓輸出方式,動態(tài)電滲析系統(tǒng)的極限電流密度為33.3 A/m2,對應的極限電壓為11 V。在試驗條件下,鹽酸酸洗廢水中的鐵回收率可達到91.8%,電流效率達到70.3%,陰極室出水pH值可達6.00,Fe2+質(zhì)量濃度小于60 mg/L,陽極室出水pH值達到1.00,Fe2+質(zhì)量濃度小于25 mg/L。鐵回收率隨著流量的增加而逐漸降低,電流效率隨著流量的增加而增高。陰極室出水pH值隨著流量的增加而降低,陽極室出水pH值隨著流量的增加而上升。
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.