Pretreatment Of Electronic Wastes And Preparing Copper By Electrodeposition

ABSTRACTThe electronic wastes still contained various metals, such as gold, copper and silver except for some pollutants, such as halogen flame retardants, mercury, selenium, nickel, lead and chrome. If the electronic wastes are directly disposed as garbage, this would not only be a waste of amount of metals, but result in serious damage to environment. How to deal with these electronic wastes has become a universal subject faced by the humankind.In this paper, the author took the circuit board of the discarded computer as example, summaried the characteristics of electronic wastes and the technology of recovering copper from electronic wastes at home and abroad. On the basis of determining element component and content in circuit board, the way of recovering high-quality copper from discarded circuit board had been studied, and the preliminary processing design and benefit analysis about the entire process had been carried out. There were three main steps in this process: the pretreatment of electronic wastes, selective extraction of copper from the pretreated solution, and preparing copper from copper sulfate solution which had been extracted and condensed.The element component and content in circuit board were deter-mined by IGP-AES and AAS methods, respectively. Result indicated that there were many type of elements in circuit board, and the element content varied widely. The main metals contained in circuit board were copper, aurum, silver, magnesium, lead, zinc, manganese, aluminum, iron, stannum, platinum, palladium, chrome, nickel, titanium etc. Because copper content was 90%, recovering copper from circuit board may not only bring forth considerable economic benefit, but avoid resulting in harm to environment.The pretreatment on circuit board was carried out on the basis of determining the component and content of element in circuit board. There were two alternative schemes for pretreatment process. The first was HSO-HNO-HO-NaOH system, and the second was HSO-HNO-HO-O-NOx System, which was on the basis of the first system. oxygen was added into the entire system, together with the gas absorption setup which was used for turning nitrogen oxide produced by metal-oxidized reactions into nitric acid for recycling. The best operating conditions of pretreat-ment process had been found out through experiment: Raw material, 20g; sulfuric acid, 35ml; nitric acid, 18ml; water, 200ml; flow rate of oxygen, 3L/h; temperature, 60(?); time of reaction ,2 hours. The dissolution rate of metal mixture was over 93%, and that of copper was also over 99%. At the same time, the recycling rate of nitric acid was at least 94% with the use of the equipment available.By the pretreatment, the original copper sulfate could be gained. The pure copper sulfate solution which meet the need of electrodeposition could be prepared through tri-stage extraction and single stage re-extraction. The best operating conditions of single stage extraction were: temperature, 20(?); pH, 2．0; O/A, 2:1; extraction time, 3min; stirring velocity, 910r/min; extractant concentration, 80%. The extraction efficiency was high to 99．2% provided that the tri-stage extraction was carried out to the original solution under the optimized condition (extractant concentration, 30%). The re-extraction efficiency could be higher than 99% by single re-extraction with the operating parameter (O/A, 3:1) .High-quality copper could be prepared by electrodeposition of copper sulfate solution. The effect of pH, temperature, current density, cell voltage, reaction time, stirring velocity and concentration of copper sulfate on current efficiency was studied, the result of experiment demonstrated that high current efficiency, low electricity consumption, good surface characteristic and high purity of copper could be gained under the following operating conditions:pH,4;temperature,60(?);currentdensity,200A/m; cell voltage,2．2V; concentration copper sulfate, 18g/L;stirring velocity,600r/min. Based on the experiment, the preliminary precessing design and theeconomic benefit analysis about the entire process had been carried out.The result demonstrated that this process of preparing high-quality copperhad both economic and environmental benefit.Name: Zhangwuxue (environmental engineering) Supervised by: Lidengxin(professor)...