Study On New Process Of Valuable Metals Leaching Of Electronic Circuit Board Materials

With the advancement of electronic technology,the speed of electronic products is becoming more intelligent and updated,resulting in the rapid elimination of many electronic products and the production of a large amount of electronic waste.Waste Printed Circuit Boards(WPCB)is the most economical part of e-waste.WPCB contains high levels of base metals and precious metals.However,it also contains many harmful components,such as heavy metals,plastics,brominated or chlorinated flame retardants.These materials can cause irreversible damage to the human body and the environment if not handled properly.Therefore,it is of great significance to select a suitable method for recovering valuable metals from electronic waste.In this paper,by using XRD,AAS,SEM-EDS and other analytical methods,based on the determination of metal composition and main material formation process in WPCB,the water potential-pH diagrams of copper,gold and silver were drawn,and the region where the relevant substances are stably present in the aqueous solution in different states was indicated;the potential-pH diagram of gold(silver)-thiourea-water system was also drawn,and the thermodynamic analysis showed that thiourea dissolved silver is easier than gold dissolution,Only when the pH of the solution is less than 1.78(6.17),the oxidant can dissolve gold(silver).During the experiment,copper in the WPCB was leached by two different gold extraction pretreatment methods of hydrogen peroxide-sulfuric acid system and biological system.In the hydrogen peroxide-sulfuric acid system,the optimal conditions for copper leaching were obtained by single factor analysis:hydrogen peroxide addition amount 20 mL,sulfuric acid concentration 1 mol/L,55?,3 h,liquid-solid ratio 1:10,300 rpm.Under this condition,the leaching rate of copper can reach 99.14%;in the bio-impregnated copper system,the optimal conditions for copper leaching are obtained by orthogonal experiment:pH=2.0,sulfur addition amount 0 g/L,ferrous sulfate addition amount 30 g/L and the concentration of pulp is 2%.Under this condition,the leaching rate of copper can reach 99.73%.Through the comparative study of oxidizing acid leaching and bioleaching,the oxidizing acid leaching was selected as the gold extraction pretreatment method,and the optimal conditions for the copper extraction of the LIX984N extractant after leaching were discussed:LIX984N 20%,ratio of O/A(VO/VA)2:1,pH 3.0,oscillation time 10 min,room temperature,the single stage extraction rate can reach 98.25%,and the stripping reaction was carried out with 3 mol·L-1 sulfuric acid solution,and the stripping rate is 83.6%.On the basis of oxidizing acid leaching,the optimum conditions for the soild filtrate obtained after oxidative leaching step were determined by single factor condition experiment and orthogonal experiment.The optimum conditions for gold leaching are:leaching temperature 45?,pH 0.8,ferric sulfate mass fraction 1.0%,thiourea mass concentration 22 g/L,leaching time 2.5 h;optimal leaching temperature for silver leaching is:leaching temperature 50?,pH 0.5,leaching time 2.5 h,ferric sulfate mass fraction 0.8%,thiourea mass concentration 22 g/L.Under the optimal conditions,the gold leaching rate is greater than 90%,and the silver leaching rate is greater than 95%.The high-efficiency leaching of gold and silver in WPCB is achieved,and the results are satisfactory.The kinetic study of the acid thiourea leaching process of gold and silver was carried out in combination with the process research.The results show that the leaching process accords with the liquid-solid unreacted shrinkage nucleus model and belongs to the diffusion control of solid product layer.The activation energy of gold leaching reaction is 9.699 kJ·mol-1,the reaction order of thiourea to gold is 1.2555,the activation energy of silver leaching reaction is 11.457 kJ·mol-1,and the reaction order of thiourea to silver is 0.8509.