Extraction Of Lithium By Vacuum Thermal Reduction With Metal Reductant

The lightest of all metals, lithium is used extensively in the fields of ultra light alloy, aerospace, electric battery and nuclear-generated power. It is called energetic metal of the21st century. At present, the demand of lithium increases rapidly all over the world, especially in China. The production capacity of lithium industry needs to be expanded hurriedly. Nowadays, there are two chief kinds of lithium production method, which are molten salt electrolysis and vacuum thermal reduction. The development of the former method will be effected by some factors:expensive high-purity raw material, anode gas chlorine polluting environment and high percentage composition of sodium and potassium in products. Vacuum thermal reduction may be used extensively in future because of short-cycle, low-cost, and without harmful gas pruduced. In this thesis, extraction of lithium by vacuum thermal reduction with metal reductants such as ferro-silicon, coarse ferrosilicon-aluminum alloy and aluminum powder were investigated comprehensively. Industrial scale extraction lithium tests were reasearched in an internal resistance furnace which was designed by writer.The decomposition temperatures of Li2CO3were calculated based on metallurgical thermodynamic analysis at different conditions such as atatmospheric pressure, vacuum conditions and with addition of Al2O3. The principles of Lithia reduction by aluminum and silicon are analysed roundly. The reaction temperature will be decreased by adding CaO and reducing the system pressure. According to analysis comparison of vapor pressure of lithium and chief impurities, lithium can be condensed in the different position separated from Na, K and Mg.In the Li2CO3decomposition process, the contradictory that Li2CO3volatilized easily at high temperature was resolved by adding CaO or mixture of CaO and Al2O3. In the Li2CO3decomposition experiments with CaO addition agent, according to effects of addition agent ratio, calcination temperature and calcination time on decomposition rate, the L9(43) orthogonal experiment was designed. The results of orthogonal experiment showed that the optimal technological conditions were obtained, that was mol ratio of Li2CO3and CaO1:2, calcinition temperature1173K, time100min; briquetting pressure30MPa and vacuum degree4Pa. Under this condition, the decomposition rate of Li2CO3was99.71%, the volatility was0.29%.In the Li2CO3decomposition experiments with Al2O3-CaO mixture addition agent, the effects of briquetting pressure, calcination temperature and time on decomposition rate were investigated. The decomposition rate was98.21%when the briquetting pressure was50MPa, calcinition temperature was1073K, and calcinition time was120min. The calcined product mainly contained LiAlO2and CaO.In the experiments of extracting lithium using ferro-silicon alloy as reductant, lithium carbonate calcinate with calcium oxide addition agent as raw material, the effects of reduction temperature, time, briquetting pressure, particle size and reductant excess coefficient on reduction rate of Lithia were studied. By L16(54) orthogonal experiment and range analysis, the optimal conditions to extract lithium by vacuum thermal reduction with ferro-silicon alloy were obtained, that was reduction temperature1293K, reduction time180min, briquetting pressure30MPa, particle size-80μm and reductant excess coefficient50%. The average reduction rate of Li2O was97.83%. The lithium purity is99.24%. The process of reducing Lithia with silicon follows solid-solid reaction kinetic model, the reaction is controlled by diffusion that silicon pass solid product when the temperature is above1223K.In the experiments of extracting lithium by vacuum thermal reduction using coarse ferrosilicon-aluminum alloy as reductant, the effects of reduction temperature, time and reductant excess coefficient on reduction rate were investigated. The reduction rate of Lithia was97.62%when reduction temperature was1273K, time was180min and reduction excess coefficient was30%. The main components of reduction slag were Ca2SiO4,3CaO·Al2O3and12CaO·7Al2O3.In the experiments of extracting lithium using aluminum as reductant, calcinate of Li2CO3and Al2O3-CaO mixture addition agent as raw material, the effects of reduction temperature, time, briquetting pressure, particle size and aluminum excess coefficient on reduction rate were researched. Under the conditions of1423K,180min and aluminum excess coefficient20%, the reduction rate was95.50%, the lithium purity was98.64%. The process of reducing Lithia with aluminum follows liquid-solid reaction kinetic model, the reaction is controlled by diffusion that aluminum liquid pass solid product during the temperature is between1323K～1423K.The residue of vacuum aluminothermic reduction lithium that maily contained CaO·Al2O3and12CaO·7Al2O3were leached with a mixture of sodium carbonate and sodium hydroxide. The results showed that alumina leaching rate of calcium aluminate was84.89%while that of reduction residue was68.60%when the Na2Oc concentration was244g/L, Na2Ok concentration was8.89g/L, L/S was6:1, leaching temperature was95℃, and leaching time was180min. The chief phase of leaching slag was CaCO3.Industrial scale internal thermal resistance furnace was designed and completed, which capacity was7.5kg lithium each furnace. Industrial scale silicon thermal extraction lithium tests were researched in the internal resistance furnace with ferro-silicon as reductant, lithium carbonate calcinate with calcium oxide addition agent as raw material. The lithium reduction rate was63.86%which was below the reduction rate of basis experiments, so the design of condenser and technological process should be improved.