Single Crystal Aluminum-Based Energy Storage Materials Were Prepared By Using The Effective Components Of Secondary Aluminum Ash

Secondary aluminum ash is a solid hazardous waste produced in the process of alumina electrolysis,casting,processing and regenerated aluminum production.The content of aluminum is 10%～80%.Due to the low recycling efficiency and high energy consumption of secondary aluminum ash,the recycling process is complicated,which causes resource waste and environmental pollution.Low temperature alkaline smelting is one of the methods to extract aluminum elemental,alumina,aluminum nitride and other active components of secondary aluminum ash,which can realize the reuse of secondary aluminum ash resources.The main steps of low temperature alkaline melting process are low temperature alkaline melting-water leaching-seed decomposition,and the refined alumina products can be used to prepare high temperature phase change latent heat energy storage materials.As the base material of energy storage material,alumina extracted by secondary alumina ash low temperature alkaline smelting can not only reduce the corrosion of the container during the metal phase transformation process,but also maintain the stability of the material.This paper focuses on the above contents as follows:（1）Optimize the process flow of low temperature alkaline smelting method.The step of"adjustingαk-seed decomposition"in the process of low temperature alkaline smelting process is changed to"acid leaching".XRD and XRF were used to analyze the main components and element proportion of secondary aluminum ash.The main reactions involved in low temperature alkaline melting-acid leaching process were analyzed by thermodynamic analysis.The influence of the main factors on the purity of alumina and the extraction rate of aluminum was investigated by single factor experiment.The optimal conditions were determined as 1 mol/L hydrochloric acid concentration,30 min reaction time and 80℃leaching temperature.The response surface method was used to further optimize the acid leaching conditions,and a response model was established.With alumina purity and aluminum extraction rate as response values,the influence of three influencing factors,hydrochloric acid concentration,reaction time and leaching temperature,on the acid leaching results was explored.The optimum conditions under the theoretical model were substituted into the experimental process to verify the reliability of the model.The errors between the experimental values and the predicted values of alumina purity and aluminum extraction rate were only 0.5%and 0.29%.The model has a good fit for the acid leaching process.（2）Optimize the process flow of low temperature alkaline smelting.Considering the complexity of the process and the extraction rate of active components,the step of"adjustingαk-seed decomposition"in the process of low temperature alkaline smelting was adjusted to"acid leaching".Control sintering temperature of 550℃,750℃,950℃,1100℃,respectively,to obtainγ-Al₂O₃,δ-Al₂O₃,θ-Al₂O₃,α-Al₂O₃.XRD analysis,SEM analysis and FTIR analysis were carried out on the four crystal types of alumina.（3）Preparation of high temperature composite energy storage materials.Four kinds of energy storage materials,Al/γ-Al₂O₃ type PCM material,Al/δ-Al₂O₃type PCM material,Al/θ-Al₂O₃ type PCM material and Al/α-Al₂O₃ type PCM material,were obtained by using Al as the main material of phase transformation,and the optimal pressing conditions were determined as 10 MPa and 10 min respectively.The optimal energy storage material is Al/δ-Al₂O₃ PCM material with950.33 k J/kg heat storage capacity.After 30 cycles of endothermic and exothermic heat,the heat storage capacity remains at 485 k J/kg and the heat storage capacity remains 54%.The weight loss rate of the material is less than 15%,and the material has no leakage and cracking problems.In summary,the effective components in secondary aluminum ash were extracted by alkaline melting and acid leaching method and calcined,which wereγ-Al₂O₃,δ-Al₂O₃,θ-Al₂O₃ andα-Al₂O₃,respectively.Al/δ-Al₂O₃ PCM materials had the best energy storage effect,with a heat storage capacity of 950.33 k J/kg and heat storage capacity of 54%.The weight loss rate of the material is within 15%.