Removal Of Nickel(?) From Aqueous Solution By Complexation-Ultrafiltration-Electrodeposition Technique

The removal of nickel(?)from aqueous solution by complexation-ultrafiltration-electrodeposition technique with water-soluble polymer polyvinyl pyrrolidone(PVP)and carboxymethyl cellulose(CMC)was studied in this study.The whole experiment process includes six parts: pre-treatment,complexation-ultrafiltration(CP-UF),concentration,decomplexation,regeneration of polymer and electrodeposition.In the CP-UF process,numerous factors affecting the retention rate of nickel(?)(RNi)and permeate flux(J),such as pH,loading ratio,transmembrane pressure(TMP),complexation time and added salt have been investigated.Electrodeposition method could be adopted for recovering the nickel(?)from nickel-containing concentrated solution on the basis of complexation-ultrafitration process.In electrodeposition process,effects of current density,pH,electrolysis time,temperature,polar distance and stirring on current efficiency and nickel(?)recovery efficiency were investigated.In the pre-treatment of PVP,permeate flux decreases slightly as the time varies from 5 min to 50 min,while it tends to keep stable after 50 min under different transmembrane pressure.But in the pre-treatment of CMC,permeate flux has a similar trend as time increases from 5 min to 40 min.Both of PVP and CMC,permeate flux increases with increasing TMP.The steady permeate flux(Js)are not influenced by pH.The phenomenon may be explained as: a change of the conformation of PVP and CMC molecules do not occur while membrane fouling does not change with pH.The retention rate obtained in the pH range 3-10 are almost equal.This means that R is not influenced by pH.In the CP-UF process: pH value is an important parameter,R value increases to a maximum of 97% as pH value increases from 3.0 to 10.0.The optimal pH to complex PVP is 7,but pH of 7 is much more suitable to complex CMC.The loading ratio is one of the most important parameters for the CP-UF process.RNi value increases with loading ratio in the range 1-4,and then remains unchanged when loading ratio is beyond 4.The optimum loading ratio of 4 was chosen for PVP,but loading ratio of 2 is much more suitable for CMC.Both of PVP and CMC,the steady permeate flux increases linearly as TMP increases,but steady permeate flux are not influenced by TMP.With increasing complexation time,RNi increases rapidly in the early time,and then keeps steady.The optimal time to complex PVP is 30 min,but 20 min is much more suitable to complex CMC.RNi value decreases with increasing the concentration of added salt(sodium chloride),and then changes little.In the process of concentration,decomplexation and regeneration of polymer: concentration process of PVP-Ni is underpH=7,TMP=1.0 bar,L=4,VCF=10.Finally,nickel concentrations in the retentate is 192.3 mg/L,nickel concentrations in the permeate almost keeps a steady value and is approximately 1.5 mg/L.The equilibrium nickel concentrations in the retentate and the permeate are 192.3 mg/L and 80.7 mg/L respectively,which means that about 42% of PVP-Ni(?)complexes are dissociated.Concentration process of CMC-Ni is under pH=8?TMP=1.0 bar?L=2,Finally,nickel concentrations in the retentate is 196.6 mg/L,nickel concentrations in the permeate almost keeps a steady value and is approximately 0.6 mg/L.The result indicate that about 56% of CMC-Ni(?)complexes are dissociated which is higher than PVP-Ni.In electrodeposition process:as the current density and electrolysis time increase,current efficiency decreases but Ni(?)recovery efficiency increase;with the increase of pH and polar distance,both of current efficiency and Ni(?)recovery efficiency increase at first then decrease;as temperature rises and stirring was added,current efficiency and Ni(?)recovery efficiency increase accordingly.Current efficiency and Ni(?)recovery efficiency could be reached to 42% and 52% respectively under the following optimum condition: current density was 3.5 mA/cm2,pH=4,temperature at 50 oC,polar distance was 10 cm,electrolysis time was 130 minutes and stirring was added.