Study On Gold Leaching From Waste Circuited Boards By Bioleaching Process

Electronic waste not only contains lead, mercury, chromium and other heavy metal pollutants, but also contains gold, silver, platinum and other precious metals. If these waste equipments can be used scientifically, which not only can reduce the environmental pressure, but also can make up for the shortage of resources.The leaching of gold from waste circuited boards by using microorganisms is an environmentally friendly method. Firstly, the growth and metabolism of the bacteria were obtained by culturing the Chromobacterium violaceum, and the pH was adapted to 7-11. In order to achieve the maximum generation of cyanide, respectively, the factors were carried out by comparing the contrast before and after via oxygen, add nutrients and adjust the pH, and the optimal conditions for the generation of cyanide were obtained. Gold leaching experiments were conducted under optimum conditions of cyanide generation. In order to obtain a higher leaching rate of gold, the optimum leaching conditions were obtained by comparing the leaching rate of gold with before and after pretreatment, different powder additions and different pH conditions.Through experiments, the content of gold increased from 0.082 mg/g to 0.188mg/g, and the leaching rate of gold raised from 20.49% to 31.84% after pretreatment.After oxygen supplement, the amount of cyanide increased from almost zero up to 36mg/L. The addition of metal ions and nutrients can significantly improve the production of cyanide, with the addition of 4.0× 10-3 mol/L MgSO4 and 1.0×10-2mol/L K2HPO4, amount of cyanide increased from 36 mg/L to 59 mg/L. At the range of pH 7 to 9, with the increase of pH, cyanide generation also increases. But when pH>10, cyanide generation is reduced. The leaching rate of gold decreased with the increase of the powder additions. In the phase of leaching gold, the leaching rate of gold was greatly influenced by the pH. When the pH was adjusted to 10.5, the leachingrate of gold reached a maximum value of 68.14%. Considering the factors in cyanogenic stage and leaching gold phase, the optimal conditions for leaching gold with Chromobacterium violaceum are: via oxygen, add 4.0×10-3 mol/L MgSO4 and1.0×10-2 mol/L K2HPO4 and adjust pH to 9.0 in cyanogenic stage; pretreatment of powder, powder addition of 0.5 g and adjust pH to 10.5.Gold leaching by Chromobacterium violaceum not only has a good environmental benefits, but also can get 1452 yuan of benefits through treating 1t waste circuited boards according to the analysis of economic benefits.