| The resources are becoming more and more important with the development of society, and the concept of recycling economy has been paid attention around the world. In the last decade, the recycling of secondary resources had become the subject of the world’s attention. Printed circuit board (PCB) waste is one of the typical secondary resources in the nonferrous scrap. Because of the gross production and high nonferrous metal content in the PCB waste, the recycling process could make a considerable economic and social benefit. The traditional processes of the cyanide, incineration and acid hydrolysis could cause the serious environmental pollution, which are not suitable for high-efficiency green recycling of PCB waste. Thus, in this thesis, the non-cyanogens hydrometallurgical recovery technology and mechanism of PCB waste were studied. The research is of important significance to the environment protection and the sustainability of nonferrous metals industry.The non-cyanogens hydrometallurgical recovery technology of PCB waste was proposed in this study. And the copper, gold, silver, lead, tin could be separated and recycled successively. The technology has the advantage of short flow, high-efficiency, environmental protection and none heavy metals emission. Therefore, the harmless recycling valuable metals from PCB waste could be are realized.The copper was obtained by medium-frequency melting and electrorefining from the scrap copper powders of PCB waste. The purity of copper cathode reached up to99.9%, which met the standard of GB/T467-2010. The copper in the anode slime was recycled by the heating leaching technique in the sulfuric acid solution, and the recovery rate of copper reached98.7%. In order to reduce the tin ion contents in the de-copper solution, the stepwise electrolytic technology was proposed. Based on the results of simulated experiments, the copper and tin were separated orderly by constant-voltage electrolysis and graphite anode material. The recovery rate of copper was up to100%at1.50V, while that of tin is80%at3.00V. The tail liquid could be recycled in the process of copper electrolysis.The leaching and depositing processes of gold by sodium chlorate and sodium sulfite were investigated. And the leaching and depositing processes of silver by sodium sulfite and formaldehyde were studied. This kind of technology eliminates the contamination to the environment by cyanide in traditional processes. The leaching efficiency rates of gold and silver were98.1%and97.1%. Fundamentally speaking, the initial concentration of sodium chlorate is the key factor for the recycling of anode slime. Specially, the concentration of sodium chlorate is recommended higher than5g/L for the lower gold content of anode slime.The lead was recycled by the solution of HCl-NaCl-CaCl2. The tail liquid could be recycled in the leaching process of lead. The recovery rate of lead was reached99%with the parameters as followed:solid-to-liquid ratio was20:1, leaching time was1h, leaching temperature was95℃and the concentration of lead chloride, sodium chloride, hydrochloric acid and calcium chloride were saturated,180g/L,75g/L and25g/L, respectively. The grade of recycled lead chloride could be up to industrial grade. The recovery rate of lead maintained97%after four times of leaching cycles. The tin was recycled by alkali fusion process in the condition of ball-milling for0.5h, roasting at500℃for2h. The recovery rate of tin reached91%. After calcium chloride disposed, the de-tin solution could be used for the process of dissolving tin.To improve the additional value of lead recycling, lead was separated and used to prepare BaPbO3conductive ceramics from the anode slime of PCB waste. The material compositions and PTC resistivity characteristics of the BaPbO3prepared from anoede slime were similar with the results obtained from the pure chemical reagents. It was helpful to reduce the pollution of lead, and improved the high-value utilization of anode slime as well. |
PDF Full Text Request