The extraction of gold from e-waste by hydrometallurgy

Abstract

E-waste production in great amounts and its problems, which challenge the field of Waste and Environment Management, stem from the increase in the production of electronic appliances, diversity-seeking consumers, and perishable products. To solve the problems and extract valuable metals by hydrometallurgy, leaching and organic solvent are used. To do this, after a specific amount of electrical and electronic waste was crushed, ground, and refined, it was sampled. Then, the sample was washed with water, and its remaining was leached into nitric acid. As a result, copper and silver were dissolved in it, and considering chemical features, gold remained in solid objects. To dissolve gold, the leached sludge is leached into the mixture of 1 mole nitric acid and 3 moles choric acid. More than 99.92 percent of the dissolved gold with some impurities entered the aqueous phase. The effect of three factors- the proportion of acid, time, and temperature- on the extraction of gold were observed and analyzed: they have no specific impact on the proportion of gold dissolution. Desirable conditions for the test, 60 minutes time, a 1:1 proportion of Hcl/HNO3, and a temperature of 60 degrees Celsius were used to purify the leached solution with gold and to transfer it to aqueous phase. The achievement of gold, with a result of 98.47 %, from waste happened during a single extraction in an aqueous to organic phases with a ratio of 1:10. In other words, less than 2 % of the gold remained in the gold leach solution. Then, the organic phase, which is charged with 2 M ammonium hydroxide solution and 0.5 M sodium thiosulfate, was transferred. The results were not positive, and 3.13 and 15.26 % of gold was transferred from organic to aqueous phase. It is worth mentioning that in case of copper anode sludge in similar situations, 3 and 15 % were achieved, respectively.