Details of the recovery of precious metals from electronic scrap

Electronic scrap includes electronic components and components manufactured in the production of waste mouth, residual materials, waste printed circuit boards to end-of-life computers, appliances, cell phones and so on. Every year we have about millions of computers, TVs and other household appliances, tens of millions of cell phones are eliminated, which contains a large number of precious metals. Rough statistics, 5 million computers contain about Au4.2t, Ag30t, Pd1.5t. 50 million cell phones contain about Au140kg, Ag1t, Pd50kg. total of Au4.34t, Ag31t, Pd1.55t and a small amount of Pt. This is a great wealth, many small enterprises and workshops in China have been recycling. Electronic waste is mainly recycled Au, Ag, Pd, Pt recovery in the total amount of all secondary resources recycling only a small percentage of the total recycling.
Electronic scrap volume, low grade precious metals, containing a large number of Cu, Sn, Pb and rubber and plastic, the composition is very complex. Workshop-type treatment is mainly used to incinerate the decomposition of wood and plastic, burning slag with pin acid or aqua regia dissolved, and then separated from the solution and recovery of precious metals. This method of material utilization and precious metal recovery rate is low, and serious environmental pollution. Zhou Quanfa suggested that a professional dismantling plant should be established in the area to dismantle and classify them:
1, can be returned to the use of components and easy to reuse plastic, wire, etc.;
2, easy to cause environmental pollution of the material;
3, waste components containing non-ferrous metals and precious metals, circuit boards, etc. For the latter, the most effective treatment process is a closed rotary furnace roasting → blast furnace or electric arc furnace in the free refining → get trapped precious metals, copper-based metal phase for electrolysis, from the copper anode sludge to recover Au, Ag, Pd, Pt. Yao Hong research method is: electronic waste → crushing, grinding, sieving → coarse material magnetic separation of iron-containing components → less than 40 mesh fine powder with HCl + H2O2 dissolved twice → containing precious metal solution with an appropriate amount of Na2SO4 precipitation of lead → iron powder replacement → containing Cu>50%, precious metal 2% of the precious mud with HCI + NaCIO3 temperature to 65 ℃ leaching twice → Pt, Pd, Au, Cu, Pb, Sn, Fe mixed solution → separation and refining for precious metal products. The treatment of 35 t of waste components yielded 28.18 kg of Pd, 5.2 kg of Pt and 150 kg of Au. 99. 95% purity of P and Pd, and 97.4% and 96.5% recovery, respectively. Recovery of gold, palladium and silver from used cell phones. After separating the casing and battery and crushing the main board, water rinsed light gum wood powder chips to obtain a deposit containing Au 0.92%, Pd 0.38%, Ag l.67%. Firstly, the non-metallic components were separated by calcination at 600 ℃, and Ag and Pd were dissolved by 25% HNO3 solution at 60-80 ℃, and the dissolution rate was >98.5%. The AgCl was precipitated by adding NaCl to the solution, and the palladium was recovered from the silver precipitated mother liquor. Nitric acid insoluble residue with aqua regia dissolved gold, sodium sulfite reduction for crude gold. The recovery rate of gold, palladium and silver is >95% in the whole process. A special leaching technology was studied, namely, adding MnO2 and NaSCN solution, leaching gold at pH=1~2 at room temperature, leaching rate of 96%. The material had to be fully synthesized, but the orientation behavior of other metals was not investigated.