Extraction Mechanism Of Enrichment And Vacuum Separation,and Technology Of Scattered Metal Germanium,Gallium And Indium From Solid Wastes

In recent years,with the development of electronic communications,photovoltaic?PV?,new energy,aerospace technology,scattered metal germanium,gallium and indium play important role in these fields,and their use increases year by year.However,in worldwide,germanium,gallium and indium resources are scarce.Recycling of germanium,gallium and indium from solid wastes are one of the important ways to alleviate the contradiction between supply and demand of them.Scattered metals in wastes have different chemical forms,dispersed distribution and low concentrations.In addition,some poisonous and harmful substances also exist in solid wastes,such as organic matter,heavy metal etc.These features increase some difficulties for recycling of germanium,gallium and indium.Therefore,recycling process of scattered metals in wastes is different from mineral metallurgy process.The three typical wastes----coal fly ash,waste solar cell moduel,and waste liquid crystal panels containing different chemical forms of germanium,gallium and indium were used as the research object.According to the distribution characteristics of germanium,gallium and indium,an idea of recycling of“enrichment-vacuum separation”was proposed.By the study of principle and laws of enrichment and vacuum separation,and optimizing conditions,we proposed environment-friendly recycling process,including vacuum reduction-chlorination distillation process to recover germanium in coal fly ash,the process of combining pyrolysis-vacuum decomposition to gallium in waste solar cell moduel and the process of mechanical stripping-pyrolysis with controlling carbon-vacuum in situ reduction to recover indium from waste LCD panels.For the study of containing GeO₂ coal fly ash inorganic waste system,this research proposed the vacuum reduction-chlorination distillation process,and optimizated corresponding single factors and surface analysis method of vacuum reduction process,and parameters of chlorination distillation process.The results showed optimal parameters was the reaction temperature of 1173 K,system pressure of 10 Pa,reaction time of 40 min,recovery rate of germanium was 93.96%.Results of pilot tests were also verified the actual effect.When reaction temperature was1473 K,system pressure of 1-10 Pa and reaction time of 40 min,94.64%of germanium can be recovered.According to the TCLP results,the residues after vacuum reaction were not hazardous wastes.By vacuum separation technology,we realized the enrichment of germanium from coal fly ash,and then by the chlorination distillation process,the condensated products enriched germanium can be distilled and reducted to prepare pure metal germanium.In the study of complex system of waste GaAs solar cell module,by thermogravimetric-mass spectrometry experiments,we firstly determined the composition of plastic in solar cell panels and the organic matter of panel materials from solar cell module was mainly EVA.Pyrolysis experiments showed that when the pyrolysis temperature,carrier gas flow of N₂ and pyrolysis time was 773 K,0.5L/min,30 min respectively,removal rate of organics closed to 100%.And then through the calculation of thermodynamic and saturated vapor pressure,separation rule were discussed in detail.The optimal condition of vacuum decomposition process to recover gallium was 1173 K of temperature,1 Pa of system pressure and<0.3 mm of particle size.For the study of complex system of In₂O₃-organic matters from waste LCD panels,we firstly adopted mechanical stripping process to enrich indium and liquid crystals.Using GC-MS and thermogravimetric analysis,the type of liquid crystals from waste LCD panels was identified and was mainly TFT type of liquid crystals.In the experiment of contrasting of carrier gas pyrolysis and vacuum pyrolysis,we confirmed that the vacuum pyrolysis was better than carrier gas pyrolysis.Hence,vacuum pyrolysis was chose to remove liquid crystals.By vacuum chlorination of PVC experiments,indium can be successfully recovered in the form of InCl₃,and carbon fiber can be preparated.Based on this process,we firstly put forward the concept of element cycle in the solid waste.The concept and implementation of element cycle were elaborated.In addition,we illustrated using element cycle to achieve waste recycling.And then,according to the idea of element cycle in waste,we put forward a process of controling carbon in situ reduction to recover indium.The mechanism of vacuum pyrolysis-controlling carbon in situ reduction to decompose organic matter and form carbon fiber in control was illuminated.The optimal conditions of pyrolysis with controlling carbon and vacuum in situ reduction was<0.3 mm of molecular sieve size,773 K of pyrolytic temperature,5000 Pa of system pressure,and added 30%molecular sieve,pyrolytic carbon fiber can well formed and were mainly inorganic carbon.In the process,recovery rate of indium can reach 86%.Under the mild reduction conditions,reduction ability of carbon fiber was better than coke.On the basis of above research,industrial recycling process of vacuum reduction-chlorination distillation to recover germanium from coal fly ash,combined pyrolysis-vacuum decomposition process to recover gallium from waste solar cell moduel and mechanical stripping-pyrolysis with controlling carbon-vacuum in situ reduction to recycle indium from waste LCD panels was proposed.Comparing with enrichement-vacuum separation process and traditional recycling process from recycling technology and environmental aspects,it was concluded that the enrichement-vacuum separation process had advantages for recycling of germanium,gallium and indium from typical solid wastes.This study can promote industrialization of recycling secondary wastes and provides theoretical basis and technical support for sustainable development of related industries.