Extraction Of Metals And Oxygen From Lunar Soil Simulant And Mixed Oxides

In the future,we will build a lunar base on the Moon to develop resources or use the Moon as a frontline post to explore the Mars.Oxygen is required for human activities on the moon.Silicon is required to utilize solar power energy,while structure metals such as Al,Fe and Ti are also indispensable.On the other hand,transporting materials between the Earth and the Moon is costly.Besides,there is abundant mineral and energy resources on the Moon.Therefore,it is important to prepare metals and oxygen by in-situ utilization of lunar resources.In this thesis,coal fly ash,volcanic rocks,and NEU-1 lunar soil simulant,which have similar chemical composition and phase component as lunar soil,are selected as raw materials for preparation of metal and oxygen by aluminum reduction and molten salt electrolysis in cryolite melts.The following conclusions are obtained based on experimental studies.(1)Al-Si alloy containing 8.56%silicon and alumina-rich cryolite were obtained by aluminothermic reduction of silica in 52.7%NaF-47.3%AlF3 melts at 980?.Besides,AI-Si alloy containing 94.01%aluminum and 5.55%silicon were obtained by electrolysis of the alumina-rich cryolite melts using the inert anode at 960?,while the anode product is oxygen.The recovery rate of silicon element was 83.43%.(2)Graphite was used as anode during the electrolysis of silica in 52.7%NaF-47.3%AlF3 melts.When the anode current density increased from 0.5A/cm2 to 0.9A/cm2,the mass concentration of silicon in the cathode products increased from 0.75%to 15.17%,while the current efficiency increased from 2.58%to 38.06%.Then,56%Fe-44%Ni alloy was used as anode.The cathodic product contains Al,Si and Al-Si alloy,and elements aluminum and silicon in the product were uniformly distributed.When the mass concentration of silica in the melts increased from 2%to 6%,the mass concentration of silicon in the cathode products increased from 3.19%to 19.86%,while the current efficiency increased from 12.43%to 70.48%.(3)The apparent activation energy and the reaction order of the aluminothermic reduction of Al6Si2O13,Fe2O3,and TiO2 in coal fly ash were calculated,and the results were described as follows:EAl-Si-O=89.38kJ/mol,nAl-Si-O=2.4;EFe-O=73.77kJ/mol,nFe-O=1.4;ETi-O=380.16 kJ/mol,nTi-O=0.9.The aluminothermic reduction of coal fly ash is a heterogeneous reaction,which is controlled by chemical reactions.When the reaction temperature was 1300?,the phase compositions of the products were Al2O3,Al6Si2O13,Al,and Si.When the reaction temperature was 1500?,the phase compositions of the products were Al2O3 and Al-Si alloy including 86.81%aluminum and 13.19%silicon.(4)Cyclic voltammetry for the melts of 50.3%NaF-43.3%AlF3-4.0%CaF2 dissolved with coal fly ash at 960? showed that Si(?)was reduced to Si(?)at potential of-1.05 V(vs.Pt),while aluminum and silicon co-deposited at potential more negative than-1.18V.The cathodic products obtained by electrolysis of coal fly ash contained 65.57%?75.93%aluminum,14.91%?19.76%silicon,1.74%?6.09%iron,and 1.06%?8.42%titanium.The current efficiency reached a maximum value of 40.7%when the anode current density was 0.9A/cm2.(5)Aluminothermic reduction of coal fly ash was carried out in 52.7%NaF-47.3%AlF3 melts at 960?.When the reaction time increased from 1h to 4h,the mass concentration of silicon in the alloys increased from 4.43%to 7.47%.As the amount of reductant increased from 1 to 5,the mass concentration of silicon in the alloy products decreased from 10.50%to 1.97%.When the amount of aluminum reductant was 3 times than the theoretical amount,the reduction efficiencies of silicon,iron,and titanium were 84.59%,78.51%,and 84.15%,respectively.The reaction mechanism of aluminothermic reduction coal fly ash in 52.7%NaF-47.3%AlF3 melts is described as follows:coal fly ash dissolved in molten salt and formed complex ions such as Si2O76-,Si2O5F24-,TiOFx2-x,and AlFeOF94-.At the same time,aluminum dissolved in molten salt and formed aluminum metal fog(Al0,AlF or AlF2-).When aluminum metal fog was in contact with metal complex ions,aluminothermic reduction occurred,generating metals(silicon,iron,and titanium)and alumina,in which alumina dissolved in the molten salt.Due to the density difference between metals and the molten salt,metals eventually sank to the bottom of the cell and form Al-based alloy.After the aluminothermic reduction process,the alloy products were separated from the alumina-rich cryolite melts.When the alumina-rich cryolite melts was electrolyzed using 56%Fe-44%Ni alloy,aluminum with purity in an interval of 97.94%?99.43%was obtained at the cathode,while oxygen with purity of 96.83%was obtained at the anode.The cathode current efficiency was 62.24%.(6)Cyclic voltammetry for the melts of 52.7%NaF-47.3%AlF3 dissolved with volcanic rock at 960? showed that Si(?)was reduced to Si(?)at-1.05V(vs.Pt),while aluminum and silicon co-deposited and formed Al-Si alloy at potential more negative than-1.18V.The electrochemical reduction of Si(?)ions on tungsten electrode is controlled by diffusion,and the value of diffusion coefficient is calculated to be 2.0×10-6cm2/s.After electrolysis of volcanic rocks in 52.7%NaF-47.3%AlF3 molten salt at 960? for 4h,the cathodic product is composed of 90.5%aluminum,4.4%silicon,1.9%iron,and 0.2%titanium when the current density is 0.9A/cm2 with liquid aluminum as the cathode,and the phase compositions were Al,Si,and Al5FeSi.(7)The NEU-1 lunar soil simulant was prepared from volcanic slag and basalt which were collected in Huinan county of Jilin province.The phase compositions of NEU-1 lunar soil simulant are anorthite,pyroxene and olivine.The median particle size was 177.56?m,and the particle size distribution basically accorded with the upper and lower grading curves of real lunar soil.Cyclic voltammetry for the melts of 52.7%NaF-47.3%AlF3 dissolved with NEU-1 lunar simulant at 960? showed that the order of cation reduction was Ti,Si,Al,and Na.The electrochemical reduction of Ti(?)was carried out by three steps,while Si(?)was electrochemically reduced by two steps.The co-deposition of aluminum and silicon occurred at potential more negative than-1.35 V(vs.Pt).When the NEU-1 lunar simulant was electrolyzed in 52.7%NaF-47.3%AlF3 molten salt at 960? using 56%Fe-44%Ni alloy as anode,the mass concentrations of metal Al,Si,Fe,and Ti in the cathodic product were 56.70%,40.80%,2.25%,and 0.25%,respectively.The phase compositions of the cathodic product were Al and Si.The gas collected around the anode contained O2 with purity of 97.10%,while the anode current efficiency was 61.17%.