| Waste printed circuit boards(WPCBs)is a kind of electronic waste with large quantity used in a very wide range,which has the dual characteristics of high-quality resources and environmental hazards.At present,the main method of recycling metals from WPCBs consists of physical and mechanical pretreatment and further hydrometallurgical or pyrometallurgical treatment,which with high energy consumptions,too long technological processes and serious environmental pollution issue.In this work,the copper alloy powders with high added value was recovered by physical method,and application examples was studied.The main results are as follow:(1)A new technology for the fabrication of copper alloy powders via physical treatment of metal rich particles of WPCB was developed.The main process includes: pretreatment to removal impurity,ball milling and sieving treatment,and powder refining of copper alloy particles,as well as preparing copper matrix composites using the recycled copper alloy powders by powder metallurgy.The process was short,and pyrometallurgical and hydrometallurgical processes was avodied,and therefore environmental pollution could be reduced significantly.(2)Magnetic separation,crushing and shaking table separation were selected as pretreatment and impurity removal processes with the aim to remove Fe impurities and nonmetals in metal-rich WPCBs particles.The removal rates of Fe and nonmetal were 95.93% and 76.11%,respectively.The grade of Cu was increased from 51.80 wt.% to 72.23 wt.%.(3)Cu has good ductility,which is evidently different from that of Sn and Pb,which can be easily grinded.In addition,non-metallic particles are brittle.The ball milling and sieving process were proposed to further remove non-metallic materials.Meanwhile,the fine powders of Sn and Pb with soft characteristics were sieved out in time,which was conducive to the enrichment of Cu and the refinement of powder particles.After ball milling and sieving,the grade of Cu was increased from 72.23 wt.% to 94.72 wt.%,and the nonmetallic materials was decreased to 0.11 wt.%.(4)A new technology of refining copper alloy particles by ball milling using self-made medium as milling medium was developed.Copper and copper alloy powders were usually fabricated by electrolysis,atomization and redox methods due to its good plasticity and difficulty in mechanical comminution.After mechanical impact crushing,ball milling and sieving treatment,a large number of defects such as stress,crack,vacancy,dislocations,etc.,could be accumulated in the copper particles.Using self-made medium as milling medium could hinder the cold-welding behavior between copper particles in the ball milling process,and therefore mechanical milling refinement of copper particles was realized.Using self-made medium as milling medium,the ratio of ball to powder was 20:1,and the rotating speed was 400 rpm.The ball milling time was 10 h.After ball milling,the particle size was 5?45 ?m(average particle size was 13 ?m).TEM results showed that the grains of the powder particles were mostly nanocrystals(5?100 nm).(5)Under the optimal process conditions,the metal grade of the copper-rich alloy powder was 99.89 wt.%,in which the grade of Cu was 94.72 wt.%.In the meantime,the direct yield of Cu was 82.85%.The Sn-Pb rich alloy powders could be used as the raw material for powder metallurgy after removing non-metallic by further treatment.The particle size of copper rich alloy powder and tin rich lead alloy powder were less than 200 mesh.The direct yield of total metals(Cu,Sn,Pb)could reach 88.20%.A small amount of tailings containing valuable metals produced in the process of treatment could be recovered by pyrometallurgical or hydrometallurgical process.The recycled copper alloy powder was used to fabricate copper-based friction materials by powder metallurgy,it could meet the performance requirements of copper-based friction material fabricated by powder metallurgy. |
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