Research On The Pyrolysis Processing Of Non-metals And Gold Recycling Technology From Waste Printed Circuit Boards

At present,the processing and resource recycling of waste printed circuit boards(WPCBs)is one of research hotpots in the field of resources and environment,and it is the difficulty problem of secondary resources recycling.With the increasingly attention to the e-waste environment pollution,the relevant laws and regulations have been published.Stringent laws and regulations not only propose higher requirements for the e-waste processing and recycling,but also promote the research development of e-waste recycling technology.In this study,liquid-solid fluidization technique,catalytic pyrolysis technique and the efficiently and environmentally gold leaching technique were used to construct a set of comprehensive recycling process for WPCBs,and it can provide technical support and theoretical basis for the WPCBs recycling.The main contents are as follows:1.Based on the structure and interface characteristics of WPCBs,the electronic components were removed by the hot-air gun,and the micro high speed universal grinder was used to crush and dissociate the WPCBs.By means of screening analysis and scanning electron microscopy,the fragmentation and dissociation characteristics of WPCBs were discussed.When the particle size became smaller,the dissociation degree of metals increased.Based on the crushing and screening experiments,the variation of different particle size with crushing time was studied.The results showed that,when the single crushing time is 3-5 min,it can not only keep the good crushing efficiency,but also avoid the over-crushing phenomenon.The contents of major metals were analyzed by using X-ray fluorescence spectrometry and atomic absorption spectrophotometer.It indicated that the major metals were enriched effectively in the process of fragmentation and dissociation.2.The liquid-solid fluidization technique was used to separate the WPCBs particles,and the fluidization separation behavior of the particles with different particle size was also studied.The minimum fluidization velocity and terminal settling velocity of different WPCBs particles was calculated to explore the relationship between major metals and water velocity.The results showed that,in the fluidization separation process of the WPCBs particles,the particles with different particle size could be effectively separated.The minimum fluidization velocity and terminal settling velocity of different WPCBs particles predicted perfectly the separation behavior between the metallic particles and the non-metallic particles.Based on the liquid-solid fluidization separation experiments,effect of perforated rate and bed height on the metal grade and recovery rate was also discussed.It indicated that the variation of perforated rate had a little effect on the metal grade and recovery rate.However,the effect of bed height was remarkable.3.The catalytic pyrolysis technique was adopted to decompose the WPCBs particles,and the weight loss characteristics of the WPCBs catalytic pyrolysis process were discussed.The results showed that the effect of catalyst on the WPCBs particles pyrolysis was significance.Compared with the other combustion-supporting agents,the whole pyrolysis process was optimized when the catalyst ZSM-5 was added into the WPCBs particles.The distributed activation energy model(DAEM)was used to analyze the kinetic parameters of the WPCBs pyrolysis,and the range of activation energy values was 129.15-280.53 kJ/mol,the range of frequency factor was 9.02 × 1010-4.21 × 1022 s-1.Based on the thermal-degradation experiments in the fixed bed,the effect of the final pyrolysis temperature,final temperature duration and heating rate on the thermal-degradation process of the WPCBs particles was studied.The results showed that the thermal-degradation efficient was best when the final pyrolysis temperature was 700 ?,the final temperature duration was 30 min and the heating rate was 10 ?/min.The composition of the thermal-degradation products were characterized by FTIR and GC-MS.It was found that the generated major products for the catalytic pyrolysis of WPCBs were H2,CO2,CO,H2 O,aromatics and phenols.4.The DMSO anhydrous solution containing cuprous bromide and potassium bromide was used for the gold leaching of waste electronic components.The effect of temperature,concentration(Cu+,Br-),and stirring speed on the gold extraction rate was studied,and the mechanism of gold leaching was also explored.The results showed that temperature,concentration(Cu+,Br-),and stirring speed had a great influence on the gold extraction rate of waste electronic components.The best gold leaching condition was,respectively,75 ? of temperature,0.2 M of concentration(Cu+,Br-),and 600 rpm of stirring speed.Based on the EDS energy spectrum analysis,the elemental composition of the sediment by adding the water or sulfuric acid was analyzed.It indicated that the addition of sulfuric acid could effectively remove the impurity elements in the gold leaching solution,which greatly improved the purity of gold.