Research On The Recovery Of Valuable Metals In Scrap Material With Tin And Nickel Coating And Relative Fundamental Theory Study

Scrap circuit boards are major components of e-waste,which contain abundant valuable metals.Hydrometallurgical and pyrometallurgical technologies are the major methods to recover metals from scrap circuit boards at present.Although pyrometallurgical treatment is effective,it faces multiple difficulties such as high energy-consuming and strict pollution regulations.At present,the pyrometallurgical technologiy is more and more popular and widely used in the leaching of the circuit board.However,the existing pyrometallurgical technology is not perfect.Therefore,it is critical to develop a new process in leaching metals from scrap circuit boards.In this study,raw material is the scrap material with tin and nickel coating which removed from scrap circuit boards.The thermodynamic and dynamic analysis of hydrochloric acid and hydrogen peroxide leaching process on the basis of determining the composition of metals were studied,and the process conditions of the leaching of scrap plating and the recovery of valuable metals from the leaching liquid were optimized.The main conclusions are as follows:First,the thermodynamics analysis of leaching process is studied.The results indicated that:tin,nickel and copper occurred spontaneously react in hydrochloric acid and hydrogen peroxide solution;the sequence of leaching is nickel,tin and copper;and Eh-pH diagrams for Sn-H2O,Ni-H2O and Cu-H2O system at the temperature of 25? had been plotted by FactSage.Obviously,when voltage between-136?136 mV,pH less than 0.2,tin and nickel can be leach selectively without copper.However,increasing the oxidation potential will improve the probability of leaching of tin and nickel.Second,the leaching results indicated that hydrochloric acid was better than sulfuric acid;the optimal conditions for leaching the scrap plate are HCl 1 mol·L-1,H2O2 0.15 mol·L-1,liquid-solid ratio 20 mL·g-1,temperature 25? and reaction time 20 min.Reducing the loss of copper while leaching tin and nickel under the optimal condition,the leaching efficiencies of tin and nickel are 99.99%and 96.2%,but copper is 16.2%.The phase analysis of leaching process showed that order of removal is tin,nickel and then Cu-Sn alloy;The content of tin,nickel and copper in after-leaching liquid was analyzed,obtained tin oxide by adding sodium hydroxide,the optimum conditions for separation of copper by solvent extraction were as follows:LIX984N 20%,ratio of O/A 2:1,pH 2.6,temperature 25?,reaction time 10 min.Under the conditions,the extraction ratio of copper was 97.40%,the reverse extraction ratio of copper was up to 98.12%with 300 g·L-1 sulfuric acid.In the end,the leaching kinetics of scrap plates showed that the leaching rate was practically independent of stirring speed,while dependent on temperature and the concentrations of H2O2 and HCl.The nickel leaching kinetics studies indicated that:two stages of the leaching of nickel were found.When activation energy was 103.5 kJ·mol-1,the chemical reaction was the rate controlling step.For the first stage,the empirical reaction order with respect to H2O2 and HCl were 1.3703 and 1.2355.For the second stage,the empirical reaction order iuwith respect to H2O2 and HC1 were 1.2355 and 0.4803,it indicated that hydrochloric acid was ineffective on the leaching of nickel in the second stage.The copper leaching kinetics studies showed that,the activation energy for copper leaching was 56.67 kJ·mol-1,chemical reaction was the rate controlling step.The empirical reaction order with respect to H2O2 and HCl were 1.6097 and 1.9575,it indicated that hydrochloric acid enormous impact on the leaching of copper.