The Basic Research Of The Separation And Recovery Of Crystalline Silicon From Waste Photovoltaic Modules

With the development of society and technology,a large number of non-renewable fossil fuels are consumed,which results in serious energy crisis and environmental problems.Recently,the widely distributed solar energy has attracted more and more attention,since it is a kind of safe,clean,abundant and renewable energy.As the most important method of solar electrical energy generation,photovoltaic（PV）solar industry has be regarded as one of the most attractive sunrise industries.In general,the operating life of PV modules is 20 to 30 years in theory,in the foreseeable several years,a large number of PV modules will run out of their operating life and become waste.In addition,a situation usually happens during using is that the purity and operation performance of crystalline silicon are stable,while other components are easy to be damaged which make PV modules became waste due to the long-time exposure to the external environment.So the new solid waste of PV modules causes serious economic loss and badly hurt the environment,which become a serious problem in the sustainable development and environmental protect.Moreover,the PVC modules is hard to be disposal of,while the metal and crystalline silicon,which are the core of the PV modules,remain highly recycling value.Therefore,the new techonogly and methods need to develop to separate the metal and crystalline silicon from PV modules for recycling.Crystalline silicon usually maintain integrated mechanical structure and excellent photoelectric performance,and the high-cost crystalline silicon is exactly the most important factor that restricts the wide spread and use of PV solar panels.Once the recovery of integrated crystalline silicon can be achieved,we can not only realize the recycling of valuable resource and the protection of environment,but also reduce the cost of the production of PV modules and promoting the use of solar energy.Recently,the main recycling methods of waste PV modules divided into heat treatment,chemical treatment and physical treatment.However,all of these methods have inevitable disadvantages.The treatmental effect is unsatisfactory and the pollution and cost of the treatment is high.Moreover,the crystalline silicon,the most valuable component can not be recovered.We have developed a method that waste PV modules were treated with hydrothermal method in this research,and the separation and recovery of each component in the PV modules were explored in combination with organic solvent method.Eventually,the target materials were separated,individually,and the recovery of integrated crystalline silicon with excellent photoelectric performance was finally achieved.First of all,the separation conditions of waste PV modules in hydrothermal conditions was studied.It is proved that the organic glass can be completely separated under the appropriate conditions,and optimized the most suitable condition according to the complete separation results.The optimal conditions are follows:reaction temperature 270℃,reaction time 3 h,50%water filling.Secondly,the separation of EVA from PV modules with hydrothermal method was studied.It is proved that the separation of EVA can only be achieved when alkali was added into the reaction system.Na HCO₃ was selected as the appropriate additive.The optimum conditions for separation of EVA are follows:reaction temperature 270℃,reaction time 3h,1mol/L Na HCO₃,50%water filling.With these conditions,organic glass and the EVA layer,which exists between the glass and crystalline silicon（called the upper EVA）were completely separated.While the back sheet and the EVA layer,which exists between the crystalline silicon and back sheet（called the lower EVA）keep adhering with crystalline silicon.The result proves that the separation of organic glass and the upper EVA can be simultaneously completed with the addition of Na HCO₃ in hydrothermal reaction system.In addition,the separation of the lower EVA and the back sheet from PV modules was studied.It is shown that the separation can be achieved when combining organic solvent method and hydrothermal method.N-amyl alcohol was selected to be the appropriate solvent.The optimal conditions are follows:Reaction temperature 140℃,reaction time 12h,50%amyl alcohol filling.Finally,the influence of the reaction sequence of the above two-step separation process was studied on the separation of waste PV modules and the recovery of crystalline silicon.It shows that the separation of glass and upper EVA is completed firstly in the hydrothermal-Na HCO₃ system,then the separation of the lower EVA and the backsheet is finished in the hydrothermal-organic solvent system,finally the complete crystalline silicon can be obtained.