Recover Gold From Waste Printed Wiring Board With Aqueous Two-phase System

A new technology of gold recovery from the waste printed circuit board (PCB) is putting forward in this article. The technology is based on the analysis of elements in a certain waste PCB which is disposed by microwave clearing up with Atomic Absorption Spectrometry (AAS) and Inductively Coupled Plasma-atomic Emission Spectrometry (ICP-AES). There is a high content of general metal and Pb that is baneful for the environmental. So the nitric acid leaching and thiosulphate leaching method is used for the pretreatment respectively, and the gold in the solution is extracted out with aqueoustwo-phase system (ATPS).Aqueous two-phase extraction (ATPE) that bases on the difference of distribution coefficient is a course of diffusion and separation. So it can make use of theory, equipment and operation of traditional liquid-liquid extraction. ATPE has an advantage for high extraction efficiency of gold, such as soft extraction conditions, easily magnified, fast and continuous operation, easy for automatic control and so on. The efficient and selectivity of ATPE can be improved by many methods.The results of acidic leaching indicate: in the leaching pretreatment of copper and plumbum with nitric acid and under certain conditions, the leaching rate is satisfied. When taking the waste circuit board 3g, the best pretreatment react condition is: 1:3 solid-liquid ratio, 80ml nitric (1:3), reaction time 2h, temperature 25℃. The leaching rate of Cu and Pb reaches 93.24% and 96.13%, respectively. Meanwhile it can take out Sn, Ni, Fe, and Zn about 86%, 99%, 97%, and 98%. Then the gold is resolved by aqua regia, the gold density is 3mg/L. The gold solution is extracted by ATPE of polyethylene glycol-ammonium sulphate. The functions of the concentration of acids and ammonium sulphate, the molecular weight and concentration of the PEG, the temperature are investigated. The best condition is: 30% PEG2000, PEG2000 solution/gold solution=1:1, pH=1, 20% ammonium sulphate, temperature 25℃. The extraction ratio of gold can arrive at 97.56%. The gold in the PEG phase need't to be stripped, it can be reduced by Zn powder and the reduction of AuCl^- can arrive at 95.16% under the best condition.The results of alkaline leaching indicate: When taking the waste circuit board 10g, the best pretreatment react condition is 1:4 solid-liquid ratio, 0.6mol/L (NH₄)₂S₂O₃,0.05mol/LCu²⁺,0.4mol/L(NH₄)₂SO₄,pH=9.0±0.5, reaction time 3h, temperature 50℃. The leaching rate of Au reaches 93%. Then the alkaline gold solution is extracted by ATPE of i-PrOH-ammonium sulphate. The functions of the pH, the concentration of i-PrOH and ammonium sulphate and the temperature are investigated. The best condition is: ph=9, 30% i-PrOH, 25% ammonium sulphate, temperature 25℃. The extraction ratio of gold can arrive at 97.56% under the best condition.