Combined RO And EDI For Treatment Of Rinse Water Of Nickel Electroplating

Nickel ions are very toxic.They can affect growth,bring about pathological changes in the brain,and even cause cancer after accumulated in organisms.The amount of industrial wastewater from nickel electroplating is huge,and rinse wastewater accounts for about 80 percent.The rinse wastewater can pose a severe threat to water environment and public health if discharged directly.In addition, nickel is expensive,so it is significant to develop a technique for reuse of the nickel from the rinse wastewater.Currently,there are many methods available for the treatment of wastewater laden with nickel.However,there exist various disadvantages.Concentration by vaporization is effective only for concentrated solution.Chemical treatment not only consumes chemicals,but also produces sludge.Moreover,it is difficult to reuse the effluent.Microbiological process usually demonstrates low efficiency due to slow propagation of bacterium,and the effluent is also difficult to reuse.Ion exchange needs chemicals for regeneration,resulting in complex operation and thus high operational cost.Multilevel nano-fitration(NF)/reverse osmosis(RO)technique cost so much that it can hard to be accepted by small electroplating factorys.This thesis systematically studied combined RO and electrodeionization(EDI)for treatment of rinse wastewater from nickel electroplating.In this combined process, RO is used for the primary separation to get concentrated liquid and dilute permeation liquid,whereas EDI is used for further separation of permeation liquid so that the effluent can be discharged directly or reused.The major objectives of this study are to examine the separation efficiency of RO under different conditions, to explore the main factors affecting separation efficiency of EDI,and to determine the appropriate parameters of RO and EDI.Experimental results show that the combined RO-EDI process can treat the rinse wastewater from nickel electroplating effectively and stably.Under a pressure of 1.5 Mpa,RO can reduce Ni²⁺from initial 200 mg/L to about 10mg/L.Meanwhile,a concentrated solution containing about 1600mg/L of Ni²⁺is obtained.The Ni²⁺ concentration of permeation liquid can be further reduced to 0.8mg/L using EDI, achieving the discharge standard.Experimental results also show that a complex factor,which is called charge-mass ratio(CMR),exits in the treatment of water containing low concentration nickel by EDI.The CMR includes factors like current,flow rate,and influent nickel concentration.The experimental date verified the good correlation between the effluent nickel concentration and CMR,indicating that EDI can be operated efficiently,economically and stably by adjusting CMR properly.