Recovery of Precious Metals from Electronic Scrap
Electronic waste includes electronic components and component manufacturing waste, residual materials, waste printed circuit boards, and scrapped computers, electrical appliances, and mobile phones. We have about millions of computers, TVs and other household appliances and tens of millions of mobile phones that are obsolete every year, which contain a lot of precious metals. According to rough statistics, about 5 million computers contain Au4.2t, Ag30t, and Pd1.5t. 50 million mobile phones contain about Au140kg, Ag1t, Pd50kg. A total of Au4.34t, Ag31t, Pd1.55t and a small amount of Pt. This is a great wealth, and many small businesses and workshops in China have been recycling. Electronic waste is mainly recovered from Au, Ag, Pd, and Pt, which only account for a small proportion of the total recycling of all secondary resources.
The amount of electronic waste is large, the grade of precious metals is low, and it contains a large amount of Cu, Sn, Pb, bakelite and plastic, and its composition is very complicated. Workshop-style treatment mainly uses incineration to decompose bakelite and plastics, and dissolves the cinder with aqua regia or aqua regia, and then separates and recovers precious metals from the solution. The material utilization rate and precious metal recovery rate of this method are low, and the environmental pollution is serious. The comprehensive law suggests that professional dismantling plants should be established in different areas to dismantle and classify them:
1. Recyclable components and easily recyclable plastics, wires, etc.;
2. Materials that are likely to cause environmental pollution;
3. Waste components, circuit boards, etc. containing ferrous metals and precious metals. For the latter, the most effective treatment process is roasting in a closed rotary furnace → smelting in a blast furnace or an electric arc furnace → obtaining a metal phase mainly composed of copper that has captured precious metals for electrolysis, and recovering Au, Ag, and Pd from copper anode slime , Pt.
The method studied by Yao Hong is: electronic waste → crushing, grinding, sieving → coarse material magnetic separation to separate iron-containing components → fine powder less than 40 mesh is dissolved twice with HCl + H2O2 → the solution containing precious metals is added with appropriate amount of Na2SO4 to precipitate lead →Iron powder replacement→Precious mud containing Cu>50% and precious metal 2% is heated to 65°C with HCI+NaCIO3 and leached twice→Pt, Pd, Au, Cu, Pb, Sn, Fe mixed solution→Separation and refining into precious metal products . 35 tons of waste components were processed, and the output of metal Pd was 28.18 kg, Pt 5.2 kg, and Au 150 kg. The purity of P and Pd was 99.95%, and the recoveries reached 97.4% and 96.5% respectively.
A method for recovering gold, palladium and silver from waste mobile phones. After separating the shell and the battery, the main board was broken, and the light bakelite powder was rinsed with water to obtain a deposit containing 0.92% Au, 0.38% Pd, and 1.67% Ag. Firstly, the non-metal components are separated by calcination at 600°C, Ag and Pd are dissolved with 25% HNO3 solution at a temperature of 60-80°C, and the dissolution rate is >98.5%. Add NaCl to the solution to precipitate AgCl, and recover palladium from the heavy silver mother liquor. Use aqua regia to dissolve gold in nitric acid insoluble residue, and sodium sulfite is reduced to crude gold. The recovery rates of gold, palladium and silver in the whole process are all >95%.
A special gold leaching technology was studied, that is, adding MnO2 and NaSCN solution, leaching gold at pH=1~2 at room temperature, and the leaching rate was 96%. The material must be fully and comprehensively utilized, but the direction behavior of other metals has not been examined.
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