Experimental Methods Research Of Gold Leaching From Electronic Waste

The electronic wastes contained various metals, such as gold, silver and copper except for some pollutants. If the electronic wastes are directly disposed as garbage, this would not only be a waste of amount of metals, but also result in serious damage to environment. The waste circuit boards were digested, the gold contents of waste computer circuit boards and waste phone boards were 0.043 mg/g and 0.165 mg/g, respectively. Gold recovery from circuit boards may not only bring forth considerable economic benefit, but also avoid harm to environment.Taking 5.00 g waste circuit boards for example, they were pretreatmented using nitric acid, and dried the residue after pretreatment, then four gold leaching methods were choosen to leach gold, and leaching schemes were designed according to different methods. Gold leaching rate of iodinate method was the lowest among the four methods, and the best gold leaching condition of other three methods were: (1) thiosulfate leaching gold with copper and ammonia existed: solid/liquid ratio of 1:5, thiosulfate concentration of 0.30 mol/L, ammonia concentration of 0.40 mol/L, copper ions concentration of 0.03 mol/L, leaching temperature of 40℃, leaching time of 2.5 h, pH value of 9 10, adding 5.00 mL 0.2% SO₃^2- and air flow rate of 1.2 L/min,and the highest leaching rate of gold reached 93.36%; (2) thiosulfate leaching gold adding sodium chloride: thiosulfate concentration of 1.0 mol/L, ammonia concentration of 0.8 mol/L, sodium chloride concentration of 0.8 mol/L, leaching temperature of 30℃, leaching time of 2 h, pH value of 9 10, adding 5mL 0.2% SO₃^2- and air flow rate of 1.2 L/min, and the highest leaching rate reached 91.79%; (3) thiourea leaching gold: under the conditions of pH value of 1.00, thiourea concentration of 24 g/L, Fe³⁺ concentration of 0.6%, react temperature of 25℃, leaching time of 2 h, and material particle size of less than 100 meshes.Thiourea leaching gold and thiosulfate leaching gold were selected to calculate the cost, comparing the three methrods, thiosulfate leaching gold with the exists of copper and ammonia involved the lowest cost. Taking this method for economic benefit analysis, it was concluded that the profit gained from a ton of WPCB by this method was 3090 yuan. Thiosulfate leaching gold with the exists of copper and ammonia had the advantages of quick leaching speed, small toxicity, simple operation, low cost, etc. Besides, it happened in the alkaline condition of pH= 9 10, had weak corrosion to equipment and good environmental benefits, meeting the current win-win economic and environmental requirements of the modern times.