Study On Preparation Of Al-Ca Alloy With Liquid Aluminum By Microthermal Reduction In Molten Salt

Microthermal reduction in molten salt,as a method of preparing Al-Ca alloy,using directly electrolytic liquid aluminium,has some advantages,such as simple experimental equipment,low deoxidation temperature and production cost.The optimum technological parameters of preparation of Al-Ca alloy by thermal reduction in CaCl2-CaF2 system have been studied.Although the content of the prepared alloy is higher,the generated waste slag contains fluoride,resulting in fluoride wastewater and environmental pollution when the waste slag is treated.Meanwhile,the particle size of waste slag,almost scattering in the molten salt,is greatly tiny,which would lead to deterioration of viscosity and density of the molten salt,terrible conduct of reduction process and discontinuous production,even cause the floating of the alloy.According to the above problems,this research covers the preparation of Al-Ca alloy by thermal reduction in CaCl2 molten salt,the separation between slag with molten salt in CaCl2-CaF2 and CaCl2 and comprehensive recycling utilization of waste slag.The main experimental results are as follows:The preparation of the calcium aluminum alloy using electrolytic liquid aluminium in CaCl2 molten salt was studied.The appropriate technique parameters of preparing of Al-Ca alloy in CaCl2 molten salt by by microthermal reduction are as follows:deoxidation temperature of 950?,reduction time of 2 h,and m(CaO):m(Al)of 2:3,which results in the content of Ca of alloy reachs 14.7%.XRD,SEM and EDS tests show that the main phase compositions of prepared Al-Ca alloy are Al and Al4Ca,and well distributed.The main phase compositions of molten salt after the reaction in CaCl2-CaF2 system by X-ray diffraction are calcium aluminate slag series consisting mainly of C11A7·CaF2 and C12A7.The solubilities of CA,C12A7 and C3A in CaCl2-CaF2 system were measured using isothermal saturation method.The result indicates that the solubility of CA,C12A7 and C3 A in CaCl2-CaF2 system are greatly small,generally not more than 0.25%.The separation technology between slag and molten salt was investigated.The result shows that the effect of separation was great using alumina filter plate.When using 50PPI alumina ceramic filter plate in the separation process,the content of calcium aluminate of slag decreases by 99.0%.The melting point and density of molten salt after the filtration process were studied by the method of step cooling curve and Archimedes' method.The result indicates that the density of molten salt increases with the increase pore size of the ceramic foam filter plate and.the melting point is the opposite.The molten salt after filtration can continue to prepare Al-Ca alloy.The main phase compositions of molten salt after the reaction in CaCl2 molten salt by X-ray diffraction are calcium aluminate slag series consisting mainly of C12A7.The solubility of CA,C12A7 and C3A in CaCl2 molten salt was measured by isothermal saturation method.The result indicates that the solubilities of calcium aluminate in CaCl2 molten salt are very small,generally not more than 0.05%.The effect of separation between molten salt and slag by alumina ceramic filter plate is remarkable.When doing separation process using 50 PPI alumina ceramic filter plate,the content of calcium aluminate of slag decreases by 96.1%.For the recyclable slag from deoxidation process in CaCl2-CaF2 system,the research about recycle of aluminium oxide leached by mixed lye was investigated.The optimum experimental result shows that with 5 g/L of NaOH,40 g/L of Na2CO3,leaching at 85? for 90 mins,liquid-to-solid ratio of 6,the leaching rates of Al2O3 reached 93.2%.The inorganic water treatment flocculant PAC was prepared with slag after the reaction in CaCl2 molten salt,and the feasible conditions of acid leaching and curing conditions were determined.The results shows that the optimum technological conditions are as follows:acid material ratio of 4:1,leaching temperature of 90?,leaching time of 2 h,which results in the leaching rates of Al2O3 reachs 92.3%.The feasible experimental conditions of curing conditions preparing PAC were also determined.The results shows that when 2.5 g slag is added to pickle liquor,reacting for 4 h at 95?,the liquid product is obtained with the Al2O3 content of 6.29%and basicity of 71.2%.