| With the gradual implementation of the carbon peaking and carbon neutrality goals,the photovoltaic industry has developed rapidly.Limited service life makes the polycrystalline silicon solar panels that remain rich in resources,becomes a large number of solid waste,which may pollute the environment.Polycrystalline silicon solar cell is a whole formed by multi-component bonding,for comprehensive treatment of polycrystalline silicon solar panels,the encapsulation material ethylene-vinyl acetate copolymer(EVA)should be removed first.Common methods include heat treatment,mechanical treatment,organic solvent treatment,etc.The organic solvent method is widely used to remove EVA due to milder reaction conditions and higher degree of resource utilization,etc.For the peeling of EVA,the predecessors often focus more on destroying the EVA to achieve the purpose of separating each component,mostly using solvents such as o-dichlorobenzene and trichloroethylene,Volatile gas escapes from these organic solvents during processing,the odor is extremely pungent,with strong toxicity,so industrial applications are difficult or require increased costs for off-gas treatment.Therefore,the development of green EVA stripping solvent,has some practical value.Waste solar panels are mainly composed of EVA,cover glass,polycrystalline silicon solar cells(PSSC)and backsheets,etc.The resourceful disposal of them is mostly focused on purifying single substances or reusing high-value elements.A large number of scholars had widely used glass powder,aluminum powder and transition metal catalyst to decolorize dye wastewater.The main body of the cell is polysilicon containing trace impurities such as transition metal elements,the back electrode of the cell is aluminum electrode,and the cover of the cell is glass.It is worth exploring whether the various components and integral components of these polycrystalline silicon solar cells can be used as decolorizing materials,which lays the foundation for realizing the goals of waste treatment,energy saving and carbon reduction.In this paper,the encapsulation material EVA(simulating single and double-sided photovoltaic modules)is peeled off by n-hexanol-coupling potassium hydroxide saponification and dissolution method.After the reaction,EVA can be separated and recovered only by centrifugation.After optimizing the experimental conditions,it was applied to the actual single-and double-sided modules,and the EVA was successfully peeled off,and the glass sheets and PSSC were separated.Further,for PSSC and removing the encapsulant and backsheet of the solar panels,the main components are the mixed powder(PSSP)of cover glass and PSSC,which are respectively used to simulate the decolorization of printing and dyeing wastewater.The main research conclusions are as follows:(1)Hexanol coupled with potassium hydroxide was used to successfully saponify and dissolve the exfoliated EVA from simulated and actual cell plates,which led to the successful separation of the components.The experimental results showed that the increase of liquid-to-solid ratio,reaction temperature,additive concentration,and reaction time could promote the increase of dissolution rate to some extent.The dissolution rate of EVA was98.67% under the conditions of reaction temperature of 145 ?,liquid-solid ratio(the ratio of solvent volume to the number of components in m L/each)of 30:4,stirring speed of 400 r/min,potassium hydroxide concentration of 6 g/L,and reaction time of 70 min.The order of the influencing factors was reaction time > liquid to solid ratio > reaction temperature > stirring speed > additive concentration.The product saponified EVA could be separated by centrifugation after the reaction,and the main functional groups of n-hexanol did not change before and after the reaction,which could be recycled.The optimal reaction conditions for the simulated double-sided assembly were 155 ?,liquid-solid ratio 40:2 m L/pc,stirring speed 800 r/min,potassium hydroxide concentration 4g/L,and reaction time 3.5 h,and the dissolution rate of EVA was 99.47%.For the actual single-sided module,EVA was completely exfoliated at 145 ? with a liquid-solid ratio of40:2 m L/pc,stirring speed of 800 r/min,potassium hydroxide concentration of 4 g/L,and reaction time of 3.5 h.For the actual double-sided module,EVA was completely exfoliated at155 ? with a liquid-solid ratio of 40:2 m L/pc,stirring speed of 800 r/min,potassium hydroxide concentration of 4 g/L,and reaction time of 5h.The reaction separated PSSC surface was almost free of EVA,not oxidized or corroded,and no new impurities were introduced.(2)The PSSC powder separated from the solar cell panel induces dissolved oxygen to generate hydroxyl radicals with the help of transition metal substances such as aluminum and iron,so as to realize the decolorization of printing and dyeing wastewater.The results of decolorization of activated black 5 simulated wastewater show that the aluminum back electrode induces the solution to generate hydroxyl radicals in an acidic solution,and some transition metals such as iron contained in the PSSC powder also play the role of generating hydroxyl radicals,To promote decolorization,the azo bond of active black 5 is broken and finally small molecular organics are generated.The effect of pH on decolorization is significant.The alumina film on the surface of aluminum electrode is easily removed under acidic conditions,and the reaction continuously consumes hydrogen ions,and the acidic conditions are favorable for hydroxyl radical generation.The optimum conditions for decolorization were pH 3,temperature 40?,particle size 74 ?m,reaction time 90 min,PSSC powder addition 0.2 g,and active black 5 concentration 100 mg/L.The decolorization rate could reach 98.59%.The kinetic fitting was carried out,and the process conformed to the pseudo-second-order kinetic equation.The process was an endothermic reaction with an activation energy of 98.01 k J/mol.(3)The PSSP powder with the removal of EVA and the backsheet from waste polysilicon solar panels is used to decolorize the printing and dyeing wastewater by means of the oxidation of hydroxyl radicals and glass adsorption induced by transition metal substances such as aluminum and iron.The decolorization pathway and products are similar to those in Chapter 3.The study of its treatment effect on reactive black 5 simulated printing and dyeing wastewater shows that the glass powder has a good adsorption effect under acidic conditions.The optimum conditions for decolorization of PSSP powder are: pH 2,temperature 35 ?,particle size 74 ?m,reaction time 300 min,dosage 4 g,the decolorization rate can reach99.02%.After 7 times cycles,the decolorization rate is still more than 91.27%.It also has good decolorization effect on Reactive Red 2 and Rhodamine B.The decolorization rate of PSSP powder is slightly lower than that of PSSC powder,but PSSC have high value and are generally not selected as decolorizing materials.The PSSP powder can decolorize azo dye wastewater,and it is a feasible way to comprehensively treat printing and dyeing wastewater with waste treatment. |
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