Research On The Recovery Of Gold From Waste Printed Circuit Board

A new technics of gold recovering from the waste printed circuit board ( PCB ) is put forward in this article. This technics is basis on the analysis of more than 20 kinds of metal ultimate in a certain waste PCB with Atomic Absorption Spectrometry (AAS) . In this PCB, the content of low-priced metal is very high, such as copper, aluminium and iron etc. So the oxidizing-acid soaking pretreatment technique is used to lixiviate these low-priced metals, and the gold left in the dregs is by soaked out with low toxicity drug. The result of the test shows : under certain terms, this pretreatment craft can soak effectively out such elements as the lowpriced metal copper , aluminium , iron and zinc , etc;the recovery rate of gold is more than 90% with the low and toxic durg as sulphur urea , sodium thiosulphate and chloric acid sodium ; at the same time, through treating properly with the waste water and waste residue produced in gold recovering course, will not cause the secondary pollution to the environment, achieve resource recovery and in-noxious double purpose .Oxidizing-acid soaking pretreatment technique is superior to calcine - acid soaking pretreatment technique for no gas contamination produced through out the reaction. Without improving density of sulphuric acid and response temperature, such metal as copper , aluminium , iron inside waste PCB can be effective lixiviated out just increasing the time of reaction. The best response terms of oxidizing-acid soaking pretreatment technique: Sulphuric acid density 5M, response of 60 degrees Centigrade in temperature, soaking time 2h, the recovering rate of copper may up to 86%, the aluminium , iron and zinc recovering rate is more than 95% .Sulphur urea recovering- gold test indicate the reaction to be very sensitive to PH , PH is too small, the sulphur urea is easy oxidized , PH> 2 , the sulphur urea is hydrolyzed, unfavorable to gold soaking out. In addition, the increase of sulphur urea density , Fe + density and response of time is help to creating Au[SCN₂H₄ ] and improve the gold recovering rate. Under the normal atmospheric temperature, density 10g/l of sulphur urea , 0.5% of density of sulphuric acid , 3% of density of FeCl₃, the gold recovering rate can be up to 92. 3%.In the sodium thiosulphate soaking gold course, under the condition of the existing of Cu2+and ammonia water, soaking- reaction speed can raise a dozen , its cause to Cu2+and ammonia water forms Cu(NH3)42+ that has played a catalysis role. This reaction goes on in the alkaline system, having the advantages of low requiring to the equipment, fast reaction speed, the defect is that the sodium thiosulphate is apt to oxidizing- decompose , excessively sensitive to temperature change, and fail to the reaction mechanism totally clear up.The best response condition of gold recovery with sodium thiosulphate : Response time 2h, temperature 60 °C, the density of sodium thiosulphate is 0. 25M, Cu2+ 0. 3M, ammonia 0. 45M, PH =9. 5, adding 0. 2% of the SO32", the gold recovering rate can be up to 93. 2%.Strictly Control PH , A lime neutralization ways to treat with the including heavy metal acid waste water which produced in the soaking- course, it can reach the request of discharge standard of sewage. The harmful waste residue is collected and sealed. The whole course will not cause danger to the environment.Innovate to some extent on the technological process, feasiblely and simple , this gold-recovering technics have double benefit of economy and environment.Wei JinXiu (Environmental Engineering) Supervised by professor Wang YongHui...