Research On Treatment Of Highly Concentrated Heavy Metal Waste Liquid Containing Zinc And Nickle By Membrane Distillation Crystallization Technology

Highly concentrated heave metal waste liquid is produced in electroplating and other industries.These waste liquid is characterized by high acidity,high concentration,strong corrosion and so on.Crystallization is one of the common methods to deal with this kind of waste liquid.The equipment used in tradition crystallization needs a good resistance of corrosion and MVR method costs a lot.Aiming at these problems,membrane distillation crystallization?MDC?by PTFE tube membrane was proposed to treat highly concentrated heave metal waste liquid.In the study of membrane distillation treating highly concentrated solutions,the performance differences of dilute and concentrated ZnSO₄ solution in membrane distillation under different flow rates,temperatures and pH values were investigated firstly.The results showed that high concentration didn't have a special effect on the membrane distillation performance.Then,the effect of saturation and ion species on membrane distillation performance of highly concentrated solutions was investigated.The results showed that when saturation of the ZnSO₄ solution was 1.3,the membrane flux dropped from 2.60 to 2.07 kg·m-2·h-1,with a acceptable decline.It is feasible to treat highly concentrated heave metal solutions to supersaturation state by tube membrane distillation.In addition,highly concentrated Zn²⁺ or Ni²⁺ did not have a special effect on membrane distillation performance.In the study of MDC treating sulfuric acid system heave metal solutions,MDC of ZnSO₄ solutions was firstly invested.The results showed that it was feasible to produce crystal products by tube MDC from treating sulfuric acid system heave metal solutions.The higher the supersaturation,the higher the quality of the product.Then the treatment of Zn²⁺ and Ni²⁺ mixed sulfuric acid system solutions by MDC were studied.The results showed that the methods of preferred crystallization and mixed crystallization could be selected for the treatment of solutions with different radios of ZnSO₄ and NiSO₄.In the study of MDC treating hydrochloric acid system heave metal solutions,the effects of temperature on membrane flux and Cl retention rate were investigated,and the MDC performance of 48.19wt%ZnCl₂ solution was studied under the optimized conditions.The results showed that the higher the temperature was,the greater the flux was,but the rejection rate of Cl was always above 99.98%.Under the optimized conditions,the membrane flux was maintained at 1.86?1.38 kg·m-2·h-1,the retention rate of Cl reached 99.96%.After cooling at 10?,crystal product was obtained.In this work,the treatment of heavy metal waste liquid whose pH value was 1.5 and concentration of Ni was 93.73 g·L-1 was studied.The results showed that membrane flux was maintained at 1.95?1.7 kg·m-2·h-1 and the retention rate of Ni reached 99.99%.Part of Cl entered permeate side as HCl morphology,thus removing some acidity of the original solution.At the end,the concentration of Ni was 281.2 g·L-1.In this process,the tubular PTFE hydrophobic membrane had a good tolerance to highly acid and concentrated waste liquid.It could be expected that the process to deal with the actual waste liquid to obtain crystal products was feasible after a long period operation.The surface morphology and membrane fouling,pore size and porosity,hydrophobicity,mechanical properties of hydrophobic membranes used in this paper were studied.The results show that there were membrane fouling in the surface of membranes.The pore size and porosity of membranes increased.The contact angles decreased caused by the decrease of roughness.But the mechanical properties kept well.The membrane distillation properties and stability of hydrophobic membranes were not affected.PTFE tube membrane had a good tolerance to highly concentrated heavy metal solutions.