Reaction Mechanism And Condensation Process Optimization Of Lithium Extraction By Vacuum Aluminothermic Reduction

Due to excellent properties,lithium metal and compounds are not only used in traditional industrial fields such as medicine,metallurgy,glass ceramics,petrochemicals and synthetic rubber,but also are favored in advanced defense fields such as energy batteries,atomic energy,and aerospace.At present,there are two production methods of metallic lithium:one is the traditional method-molten salt electrolytic method;the other is the most promising process method-vacuum thermal reduction method.The corrosive gas chlorine is produced during the molten salt electrolytic production process;the raw material high-purity lithium chloride is expence;the content of impurities such as potassium and sodium in the product is high.The vacuum thermal reduction method is relatively easy to obtain the raw materials,the process is clean,and the product purity is high compared to the molten salt electrolysis method.This thesis mainly studies the reaction mechanism of lithium-containing clinker preparation and vacuum aluminothermic reduction in the new process of extraction lithium by vacuum aluminothermic reduction,which use lithium hydroxide as raw materia.(1)During the process of synthesizing lithium-rich clinker Li5AlO4 at atmospheric pressure,as the temperature increases and the time prolongs,the burning loss rate gradually increases and then stabilizes.Based on the theoretical loss rate and clinker phase composition analysis,it is concluded that the preferred calcination conditions are a calcination temperature of 750? and a calcination time of 120 min.(2)The reaction mechanism and kinetics of Li5AlO4 preparation were studied.The reaction mechanism of the process Li5AlO4 clinker synthesized from lithium hydroxide,calcium oxide,and alumina was as follow at 100?,lithium hydroxide monohydrate dehydrates the crystal water,at the same time as the crystal water is removed,calcium oxide in the raw material absorbs water to generate calcium hydroxide,at 375?,calcium hydroxide is decomposed into calcium oxide and water,at 425?,lithium hydroxide and alumina react to form LiAlO2,at 475?,lithium hydroxide is thermally decomposed into lithium oxide and water.At 500?,Li2O reacts with LiAlO2 to form Li5AlO4:The kinetics of Li5AlO4 was studied by Flynn-Wall-Ozawa(FWO)method and Kissinger method,the activation energies of the five endothermic peaks during the preparation of Li5AlO4 are 198.65 kJ/mol,369.6 kJ/mol,510.15 kJ/mol,487.0 kJ/mol,and 510.5 kJ/mol,respectively.(3)During the aluminothermic reduction of Li5AlO4,as the reduction temperature increases,the reduction rate of lithium gradually increases,at 1200?,the reduction rate is reduced because Li5AlO4 melts;with the increasing of the reduction time,the reduction rate gradually increased,and the reaction was basically complete when the reduction time exceeded 100 minutes,and the reduction rate didn't increase significantly;as the excess coefficient of aluminum powder increases,the reduction rate increases firstly and then decreases.The reduction rate is highest at 15%.The preferred reduction conditions are 1150?,the reduction time of 120 minutes,excess coefficient of aluminum powder of 15%,the reduction rate 90.7%under the condition.The phase composition of the reducing slag is LiAlO2?CaO and calcium-aluminum compounds mainly composed of 12CaO·7Al2O3,with different reactions.There will be 3CaO·Al2O3?CaO·Al2O3?CaO·2Al2O3.(4)The mechanism and kinetics of aluminothermic reduction of Li5AlO4 were studied,during the reduction process,firstly Li5AlO4 is decomposed into LiA1O2 and Li2O,and they are reduced to lithium and alumina.The alumina produced is combined with calcium oxide in the raw materials to form different calcium aluminum compounds.Which mainly contain 12CaO·7Al2O3,and a bit of 3CaO·Al2O3?CaO·Al2O3 and CaO·2Al2O3.The kinetic analysis of the reduction process is performed,the vacuum aluminothermic reduction of Li5AlO4 is a liquid-solid reaction,It belongs to chemical reaction control from 1373 to 1473K,the activation energy is 33.06 kJ/mol.(5)The condensation collection process in the vacuum aluminum thermal reduction lithium smelting process was optimized.The condensing area of metallic lithium was gradually moved up with the increase of the reaction temperature;A new condensing device was designed,and a lithium collection tank was added on the basis of the original to make it easier to collect metallic lithium intensively,It is proved that the expected effect can be achieved.