Recovery Of Nickel And Water From Nickel Containing Wastewater Using Electrochemical Combination Process

In this paper, the combination techniques of electrolysis (EL), electrodialysis (ED), and electro deionization (EDI) for nickel containing wastewater were studied in order to investigate nickel recovery as well as water reuse. As we know, EL is suitable for treating the high concentrations of heavy metals containing wastewater with the ability of heavy metal recovery in its solid form; however, the EL outlet discharge dose not satisfies with the accepted standard regulation. ED usually does well in low concentrations of heavy metals containing wastewater. EDI can produce high quality water, which is widely used for the production of ultrapure water. Recently, large number of researcher focused on treatment of heavy metal containing wastewater by EDI.The proposed combination techniques were investigated at different operating parameters including voltage, initial concentration of nickel, pH and H3BO3additives on electrolysis performance. On the other hand, the effects of voltage, initial concentration of nickel, and flow rate were investigated on the performance of ED and EDI performance. The effects of these parameters were discussed in terms of nickel recovery, energy consumption, and outlet Ni2+concentration, respectively.In EL experiments, Ni2+recovery increased obviously with the increases of voltage. The boric acid additives were favorable to Ni2+electro-deposition. The initial Ni2+concentration and pH has no obvious effect on Ni2+recovery. Increasing the amounts of H3BO3and initial Ni2+concentration increased the reduction of energy consumption. The most influential factors controlled outlet Ni2+concentration were:initial Ni2+concentration> voltage> boric acid> pH. A confirmation experiment was carried out under the optimized parameters (boric acid18g/L, nickel concentration1000mg/L, cell voltage4.0V, and pH4). The recovery of Ni2+yielded88%, whereas the outlet Ni2+concentration was as low as119mg/L. The energy consumption was49.9kW h/kg Ni2+. Also, the dynamic system showed that after90min, the outlet nickel concentration was about350mg L-1that reflected nickel recovery about65%which consumed energy25.7kW h/kgNi2+The ED experiments showed that the influential factors for nickel recovery were: voltage applied> flow rate> initial nickel concentration, and for energy consumption: voltage applied> flow rate> nickel concentration. The optimal levels for Ni2+separation were:voltage applied30-45V, initial nickel concentration<400mg/L, and flow rate4～6L/h. Under the optimized conditions, the average nickel recovery was91.65%, diluted water<10mg/L Ni2+, and concentrate water>1000mg/L. The dilute water should be further treated and Ni2+in concentrate water can be recovered by electrolysis.The EDI experiments showed that the outlet Ni2+concentration was stable after1h run. Under the optimum voltage25V, the Ni2+concentration in the dilute stream was5.14mg/L and the concentrated stream142.64mg/L. The outlet Ni2+concentration of both diluted water and concentrated water increased as flow rate increased. Under voltage25V and flow rate10L/h, the wastewater containing less than45mg/L Ni2+can be reduced to0-0.9mg/L, which can meet the outlet discharge standards.The combined process of EL, ED and EDI could achieve the recovery of nickel and water simultaneously from both high and low Ni2+concentrations. Almost99%of nickel (the purity of nickel is93%) and100%of water can be recovered, with outlet discharge containing less than0.9mg L-1Ni2+, which complies with international restriction levels of1mg L-1.The combination technique can treat either low concentration of nickel containing wastewater, or high concentration of nickel containing wastewater, or both of them at the same time, achieving save discharge. The combination technique can achieve nickel recovery and water reuse simultaneously without further pollution, which reflects environmental benefit as well as economic outcomes. However, nickel containing wastewater in this study was prepared with tap water and NiSO4·6H2O, the composition of which is simple. Generally, the components of real nickel containing wastewater are variable and complex, which is more difficult to treat. Improving nickel recovery and the rest of heavy metals using electrochemical combination process is still necessary to improve the overall performance.