Research On Treatment Of Heavy Metal Wastewater With Spouted Bed Electro-deposition Approach

Wastewater containing heavy metal ions which cause environmental issues have endangered the sustainable economic development and human's health seriously.With wide attention to heavy metal wastewater,domestic and foreign researchers have researched heavy metal wastewater treatment for a long time.Electro-deposition is a common heavy metal wastewater treatment method which decreases concentration of heavy metal ion and environment stress,recycling metal resource in wastewater.For this reason,it is meaningful to research electro-deposition on treatment of heavy metal wastewater.It is difficult to ensure high removal rate and current efficiency of heavy metal wastewater treatment under low concentration,so the application of electro-deposition has been confined to high concentration of wastewater such as electroplating wastewater.To solve this problem,based on previous studies,a Spouted Bed Electro-deposition(SBE)system which spraying conductive particulate electrode circularly instead of simple fluidized particulate electrode had been designed,significantly reducing the requirement of metal ions concentration in wastewater and broadening the application of electro-deposition.Through the experimental research on typical single electro-deposition of copper/nickel ion and co-electro-deposition of copper and nickel/copper and zinc ions,the influence on metal ion recovery ratio of different conditions hand been studied.Meanwhile,based on Tafel,Nernst and Butler-Volmer classic electrochemical quation,doing mathematical simulation on single electro-deposition and co-electro-deposition,the main reaction mechanism of electro-deposition process had been discussed.The results of single electro-deposition of copper and nickel showed that the optimum pH of copper ion and nickel ion was 3 and 4.5 respectively,DO increased as pH increased.With increasing of current value,recovery ratio of nickel/copper ion and DO increased,but current efficiency decreased.The optimum temperature of copper ion and nickel ion was 40? and 35?.With increasing of temperature,DO decreased.While the particle electrodes had the same quality,the smaller the particle size was,the bigger the specific surface area was,the higher the recovery ratio was.Sparging nitrogen into the solution reduced the DO concentration in wastewater apparently,restraining metal redissolve rate,which increased the recovery ratio of copper/nickel ion.Under different pH and temperature,metal redissolve rate performed good linear dependence,which was similar to a concentration function of zero order.Under the condition that the constant current was 10 A,the temperature was 40?,pH was 3,the diameter of cathode particle was 1.8 mm,the initial copper ion concentration was 1000 mg·L-1,with nitrogen sparging to the electrolyte solution,after 300 min of electro-deposition,copper ion removal rate could reach 90.64%,increased by 12.21%than without N2,and average current efficiency was 81.14%,increased by 8.33%than without N2.Under the condition that the constant current was 15 A,the temperature was 35?,pH was 4.5,the diameter of cathode particle was 1.8 mm,the initial nickel ion concentration was 1000 mg·L-1,with nitrogen sparging to the electrolyte solution,after 180 min of electro-deposition,nickel ion removal rate could reach 66.77%,increased by 31%than without N2,and average current efficiency was 64.61%,increased by 13.97%than without N2.The results of co-electro-deposition of copper and nickel/copper and zinc ions showed that while co-electro-deposition of two metals,the optimum pH of copper ion nickel ion and zinc ion was 3,4.5 and 3.5,respectively.DO increased as pH increased.The net corrosion rate of nickel and zinc was higher than copper due to the existance of replacement reaction.If the pH was greater than 4,the replacement reaction between zinc and copper/nickel and copper would be superior to corrosion reaction.With increasing of current value,electrochemical reaction rate,recovery ratio of nickel/copper/zinc ion and DO all increased,but current efficieny decreased.As the solution temperature increased,DO gradually decreased,increasing electro-deposition rate,redissolve rate and replacement reaction rate,but total recovery ratio of nickel and copper/zinc and copper decreased.Sparging nitrogen into the solution reduced the DO concentration in wastewater apparently,restraining metal redissolve rate and stirring the solution,which increased the co-recovery ratio of copper and nickel/copper and zinc ions.Under different pH and temperature,except assumption that redissolve rate was a concentration function of zero order,the co-electro-deposition rate of copper and nickel/copper and zinc ions were nearly constant,meanwhile,two metals in electro-deposition process performed certain succession.For copper and nickel,under the condition that constant current was 15 A,the temperature was 25?,pH was 3 in the first 210 min and 4.5 in the last 270 min,with nitrogen sparging to the electrolyte solution,after 480 min of electro-deposition,copper ion removal rate could reach 99.88%,nickel ion removal rate could reach 85.12%which was 17.69%higher than without nitrogen sparging,the average current efficiency was 68.89%which was 17.72%higher than without nitrogen sparging.Under the condition of sparging nitrogen,the total deposition rate of copper and nickel ions was 90.42%,increased by 10.86%than without nitrogen,the average current efficiency was 68.89%,17.72%higher than without nitrogen.For copper and zinc,under the condition that constant current was 15 A,the temperature of wastewater was 25?,pH was 3.5,with nitrogen sparging,after 210 min electro-deposition,copper ion removal rate could exceed 99%,after 480 min electro-deposition,zinc ion removal rate was 75.64%,which was 15%higher than without nitrogen sparging.Under the condition of sparging nitrogen,the total deposition rate of copper and zinc ions were 87.19%,increased by 8.6%than without nitrogen,the average current efficiency was 65.59%,11.85%higher than without nitrogen.Based on electrochemical principles of electro-deposition process,differential equations had been set up which have relation between copper ion concentration/nickel ion concentration/zinc ion concentration/the electrochemical reaction rate constant,redis-solution rate constant,replacement reaction rate constant,mass transfer coefficient and electro-deposition time in single and coelectro-deposition process and current closing,getting the general solution of the differential equations.Analyzing the equation parameters,the consistency between experimental results and numerical simulation conclusion had been verified,which provided a scientific basis for further research about Spouted Bed Electro-deposition approach from theory and practice.