Dissertation
Dissertation > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Solid waste disposal and utilization

Research on Recycling Process of Cu from Scrap Printed Circuit Boards

Author ZhengYongYong
Tutor ZhengHuaJun
School Zhejiang University of Technology
Course Applied Chemistry
Keywords printed circuit boards electro-deposition indissolubility anode Cu(II)-NH3-NH4Cl-NH2(CH2)2NH2
CLC X705
Type Master's thesis
Year 2010
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The production of printed circuit boards (PCBs) is the basis of the electronic industry as it is the essential part of almost all electrical and electronic equipments. Both technological innovation and market expansion continue to accelerate the replacement of equipment leading to a significant increase of waste PCBs. The typical composition of PCBs is including heavy metal, precious metal, PVC plastic and brominated flame retardants, which is hazardous for environment. Therefore, recycling of PCBs is an important subject not only from the point of waste treatment but also from the recovery of valuable metal.Combined with physical process, hydrometallurgy process could recover metal and treat waste environmental friendly. Based on the difference between metal and non-metal, the metal concentration could be obtained through the step of mechanical crush-separation. Considering the advantages of Cu(II)-NH3-NH4Cl and Cu(II)-NH2(CH22NH2 system, a new Cu(II)-NH3- NH4Cl-NH2(CH22NH2 solution is proposed to recover copper.In this paper, the Cu(II)-NH3-NH4Cl-NH2(CH22NH2 solution was served as the electrolyte system of hydrometallurgical process to recovery of copper from scrap PCBs metal concentration. First, the RuO2-Ti anodic and cathodic process was studied by electrochemical tests. In addition, the influences of each component of the electrolyte were also investigated. Next, several factors: such as the proportion of the electrolyte, temperature, the solid-to-liquid ratio etc., their effects on the leaching stage were investigated. Meanwhile, the phosphate consumption on lead removal was also investigated. Effect of current density and temperature on the current efficiency and power consumption were investigated by a series of electrolysis test, and the optimal conditions for electrolysis process were primarily confirmed. At last, the economic efficiency of recycling process of copper was evaluated under the optimal conditions, and the quality of cathodic copper obtained was analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results of electrochemical tests showed the RuO2-Ti anode is nitrogen evolution reaction, and the apparent active energy was 30.28 KJ/mol and the exchange current density was 1.64×10-4 A/cm2.During the electrochemical test, the increment of concentration of NH4Cl could decrease the anode polarization. The copper was reduced in two steps leading to Cu(I) and Cu in this system, and its exchange current density was 1.2×10-5 A/cm2 and given the apparent activation energy of 15.39 KJ/mol. The surface morphology of electrodeposited copper from the Cu(II)-NH3-NH4Cl-NH2(CH2)2NH2 electrolyte was smooth. For the stage of leaching, solid-liquid ratio of 1:10, 5 hours leaching, hydrogen peroxide 10 mL, ammonia:ammonium chloride: ethylenediamine=4:4:1, by adding 0.01 M of ammonium phosphate, could extract 96.47% copper of metal concentration and remove of lead impurities more than 90%. Consider the condition of current density of 500 A/m2, 298 K, electrolysis 12 hours, the current efficiency can reach 98.8 % and the average energy consumption was 2090 KWh/t Cu. The purity of copper was 99.98 % analyzed by EDS. In conclusion, the Cu(II)-NH3-NH4Cl-NH2(CH22NH2 solution served as the electrolyte system of hydrometallurgical process to recovery of copper from scrap PCBs metal concentration, based on a combination of leaching, purification and electro-deposition. Furthermore, the whole process flow was quite short and with high recovery rate, which showed high economic benefit. The electrolyte of the whole process can be circularly utilized, and without no pollution to the environment.

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