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Dissolution of Copper from Waste Printed Circuit Boards

Author: CheJianZuo
Tutor: WangZhiKe
School: Henan Normal
Course: Environmental Science
Keywords: Waste Printed Circuit Boards(WPCB) Copper recycling Leaching Hydrometallurgical
CLC: X76
Type: Master's thesis
Year: 2011
Downloads: 96
Quote: 1
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Abstract


Copper is a kind of important non-ferrous metals, which is widely used in electrical, light industry, machinery manufacturing, construction industry, national defense industry and so on. Copper reserves are not adequate in our country, so it was necessary to recover copper from waste copper-containing materials. Waste Printed Circuit Boards （WPCB）, that contain much copper, are a kind of waste copper-containing materials. Technologies for recovering metals from Waste Printed Circuit Boards （WPCB） were reviewed in details in this paper. Compared with the three other technologies, hydrometallurgical technology has been the most widely used method for recovering metals because of its apparent advantages such as the lower handling cost and the high recovery percent of metals. It has been the common goal for scholars at home and abroad to develop a quick, effective and environmental friendly technology for leaching Cu from WPCB.Firstly, the dissolution behavior of metallic copper powder in acidic ferric chloride solutions and ammonium persulfate-sodium chloride system was respectively studied in this article, then based on the analysis of the metals in the WPCB with Atomic Absorption Spectrometry （AAS）, studies on the leaching of copper from WPCB was conducted in solutions that hydrogen peroxide and sodium persulfate was respectively used as the oxidant.In acidic ferric chloride solutions, Fe3+ is oxidant and Cl- is complexant, which would accelerate the dissolution of metallic copper. Based on the thermodynamic analysis, the dissolution of metallic copper in acidic solutions containing ferric chloride was investigated in detail. The related parameters such as pH, ferric chloride concentration, excess Cl- concentration, stirring speed, solid/liquid ratio and temperature were systematically studied. Under the optimized experimental conditions, the dissolution percent of Cu was 100%. The reaction mechanism was also discussed, and the mechanism was confirmed by testing the changes of the solution redox potentials. The copper dissolution rate in acidic solutions of FeCl3 fits the following conversion-time expression: 1-2/3R-（1-R）2/3=kt, where R is the fraction reacted of copper powder, k is the reaction rate constant, t is the dissolution time. The activation energy was found to be 24.9 kJ/mol and inward diffusion was considered to the rate-controlling step. In the study of using ammonium persulfate-sodium chloride solutions to dissolve metallic copper powder, the effects of the ammonium persulfate concentration, sodium chloride concentration, temperature, stirring speed, pH, and solid/liquid ratio were investigated. Finally, the reaction mechanism was proposed as that S2O82- and oxidized Cu2+ are oxidant, then the oxidized Cu+ complexed with the produced NH3 by the hydrolysis of NH4+ and the Cl-, thus accelerating the dissolution of copper powder.In the hydrogen peroxide leaching copper from WPCB course, the H2O2 is the oxidant which makes possible the leaching of metallic copper from waste PCBs in acidic chloride solutions. HCl is the main reagent, the leaching course proceeds in acidic solutions, and the copper extraction was almost 0 in the solution without HCl. The copper extraction increased significantly with the increase of HCl concentration and the H+ and Cl- ions both accelerated the leaching of copper from waste PCBs and had the synergetic effect on copper dissolution. The copper extraction also increased with the increase in stirring speed, temperature and solid/liquid ratio. Finally, a reaction mechanism was proposed. Under the best experimental conditions, the dissolution rate of Cu was more than 98%.The dissolution of copper from waste printed circuit boards using sodium persulfate as oxidant was investigated. In the range of our study, the copper dissolution rate increased with the increasing of the sodium persulfate concentration, sulfuric acid volume, stirring speed and temperature, while the solid/liquid ratio showed little influence on the copper extraction. The activation energy was found to be 18.23kJ/mol, the reaction order is 0.7, and the reaction rate constant is 0.095.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > Machinery, instruments and industrial waste treatment and comprehensive utilization
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