Recovery Of Nickel From Nickel Plating Wastewater And Sludge Using A Bipolar Membrane Electrodialysis

As a crucial metal raw material for electroplating and electroless plating industry,nickel is widely used in the surface processing of items such as aerospace hardware,electronic parts,textile machinery and auto parts due to its excellent wear resistance,anti-corrosion,anti-oxidation,electrical and thermal conductivity.However,the rinsing wastewater and waste plating solution from the nickel plating process contain heavy concentrations of nickel ions（Ni（II））,which can cause water and soil pollution via discharge.Besides,Ni（Ⅱ）is bioaccumulative and can be a threat to the growth of organisms through the food chain.Excessive intake of nickel for human will increase the risk of cancer and teratogenicity.In order to improve the quality of plating,complexing agent is added to the plating solution,such as ethylenediaminetetraacetic acid（EDTA）,citric acid,tartaric acid,etc.,which makes the Ni（Ⅱ）exist in complex state.It is difficult to remove nickel complex using the traditional chemical precipitation own to its stable structure and strong mobility.At present,the mainstream treatment of nickel plating wastewater is pretreatment-chemical precipitation.Fenton or hypochlorite is first used to destroy the structure of nickel complex,then the free Ni（Ⅱ）is precipitated using alkaline reagent.Nevertheless,this process generates a large number of electroplating sludge with metal.Electroplating sludge,hazardous waste,is disposed in landfill,which causes secondary pollution and huge waste of nickel.In this paper,H⁺produced by bipolar membrane（BPM）in BMED system was used to destroy the stable structure of nickel complex,and free Ni（Ⅱ）was obtained.In addition,electrodialysis was used to separate and enrich Ni（Ⅱ）.Therefore,BMED finally realized the treatment of nickel plating wastewater and sludge and recovery of nickel.The main contents and results in this study are listed as follows:（1）Recovery of nickel from nickel complex wastewater using a BMED systemThe nickel recovery performance of BMED system from Ni-EDTA wastewater was investigated.First,the effect of electrolyte（Na₂SO₄）concentration on BMED voltage was investigated,and the results showed that the voltage was lower when the concentration of Na₂SO₄ was 1 mol/L.Second,the effects of electrolyte（Na₂SO₄）concentration in wastewater,current density,initial concentration of Ni-EDTA and the number of wastewater compartments in BMED on p H,conductivity,cell voltage,Ni（Ⅱ）removal,specific energy consumption and current efficiency were investigated.The results showed that when the concentration of Na₂SO₄ in wastewater was 0.2 mol/L,the initial concentration of Ni-EDTA was 3000 mg/L and the current density was 16 m A/cm²,the removal rate of Ni（Ⅱ）reached 99.9%after 48 h.With the increase in the number of equipped wastewater compartments from one to two and three,the Ni（Ⅱ）removal specific energy consumption decreased from 0.388 k W·h/g to 0.224 k W·h/g and 0.193k W·h/g,and the current efficiency increased from 1.73%to 3.98%and 5.77%,respectively.BMED recovered 95.2%of Ni（Ⅱ）from actual nickel plating wastewater.The results of reaction kinetics showed that the removal of Ni（Ⅱ）was a zero-order reaction kinetics,which meaned that the removal rate was independent of the initial concentration and time required to reach a certain removal rate was proportional to the initial concentration.（2）Separation and recovery of Ni（Ⅱ）,NH₄⁺,HPO₃^2-,H₂PO₂^-and NO₃^-in electroless nickel plating wastewater using a BMED systemThe effects of current density on the separation and recovery of Ni（Ⅱ）,NH₄⁺,HPO₃^2-,H₂PO₂^-and NO₃^-in electroless nickel plating wastewater were investigated.Under the current density of 8.0 m A/cm²,12 m A/cm²,16 m A/cm²,20 m A/cm² and 24 m A/cm²,the removal of Ni（Ⅱ）,NH₄⁺,TP and NO₃^-,recovery of TP and NO₃^-,solution p H,conductivity,cell voltage,specific energy consumption and current efficiency were investigated.The results showed that when the current density was 20 m A/cm²,the removal rates of Ni（Ⅱ）,NH₄⁺,TP and NO₃^-reached 100%,98.6%,99.3%and 100%,respectively.The recovery rates of TP and NO₃^-were 94.5%and 90.6%,respectively.With the increase in the number of equipped wastewater compartments from one to two and three,the current efficiency increased from 42.5%to 77.9%and 113%,and the specific energy consumption decreased from 1.67 k W·h/mol to 1.38 k W·h/mol and 1.32k W·h/mol.The removal kinetics analysis results showed that the removal of Ni（Ⅱ）,NH₄⁺,TP and NO₃^-was most consistent with the zero-order kinetics process,which meaned that the ion removal rate was independent of the initial ion concentration,and the ion migration rate was proportional to the current density.The secondary phosphorus and phosphite recovered from BMED were completely oxidized,and the phosphorus was recovered in the form of struvite under the condition of p H 8.5.Struvite with similar physical and chemical properties to commercial struvite was obtained.（3）Recovery of nickel,zinc and copper from electroplating sludge using a BMED systemThe effects of current density,solid-liquid ratio,particle size of electroplating sludge and number of sludge compartment series on Ni,Zn and Cu recovery from electroplating sludge were investigated.The results showed that that the recovery of Ni,Zn and Cu reached 96.4%,85.8%and 86.7%,respectively,at the current density of 20 m A/cm²after60 h.When the solid-liquid ratio was 1:15 g/m L,the recovery rate of Ni,Zn and Cu were93.5%,79.9%and 81.6%,respectively,after 28 h.The results showed that particle size had little influence on the recovery of Ni,Zn and Cu.The increase in the number of equipped electroplating sludge compartments in series can increase the electroplating sludge capacity of a single BMED,improve the current efficiency and reduce the specific energy consumption.With the increase in the number of equipped electroplating sludge compartments from one to two and three,the current efficiency of Ni,Zn and Cu recovery increased from 13.0%to 25.3%and 38.4%,and the specific energy consumption decreased from 3.48 k W·h/mol to 2.63 k W·h/mol and 2.15 k W·h/mol.The recovery kinetics of Ni,Zn and Cu was zero-order reaction kinetics,which meaned that the recovery rate of Ni,Zn and Cu was independent of the initial concentration,and the time required to reach a certain recovery was proportional to the initial concentration.