Research On New Process Of Lithium Extraction By Vacuum Aluminothermic Reduction

Lithium, with excellent properties, is used extensively in the fields of electric battery, light alloy, aerospace, and nuclear-generated power, etc. Lithium metal product is in short supply, while the demand of lithium is sharply increasing especially in China. At present, there are two chief methods of lithium extraction:molten salt electrolysis and vacuum thermal reduction. Restrictions on the development of the former method are high consumption of raw materials, polluting gas and high percentage composition of potassium and sodium in products. Vacuum thermal reduction may be used extensively in future because of short-cycle, low-cost, and without harmful gas produced. So, it is urgent necessary to develop a high efficient lithium extraction methode. In this thesis, a new efficient methode of lithium extraction was proposed based on the summary of metallurgical thermodynamic analysis and the theory of vacuum thermal reduction. In the process, LiOH·H2O and Al2O3were used to synthesize Li5AlO4by adding CaO as additives. Aluminum was used as reducing agent to extract lithium, and the reduction slag was suitable for the extraction of aluminium hydroxide.Sintering thermodynamics of lithium hydroxide monohydrate and alumina at high temperature was calculated and analyzed. The result show that Li5AlO4is easily synthesized with LiOH·H2O and Al2O3at normal pressure. The starting reduction temperature of Li5AlO4is1869K at atmospheric pressure used the aluminothermic reduction methode, but when the system pressure decreases to10Pa, the starting reduction temperature is1392.5K. The starting reaction temperature decreases from1869K to1694K by adding CaO at atmospheric pressure, and the temperature decreases from1694K to972.6K by adding CaO when system pressure decreases to10Pa. In process of synthesizing of Li5AlO4, the loss rate increased slightly and then decreased with the increase of temperature and time. The influence of briquetting pressure on loss rate was unconspicuous. The experimental results showed that the optimal technological conditions were that the calcinations temperature was1073K, calcinations time was90min and briquetting pressure was30MPa. In these conditions, the loss rate was34.74%. The main components of product were Li5AlO4and CaO, which were suitable for the next reduction process.In the experiment of lithium extraction by vacuum aluminothermic reduction, the reaction temperature was775℃when the pressure was about7Pa. The experimental results showed that the reduction rate increased with the increase of temperature, time and excess coefficient of aluminum, the influence of briquetting pressure on reduction rate was unconspicuous. There were two optimal conditions in which the reduction rates exceeded96%. The first condition was that the reduction temperature was1473K, reduction time was120min, briquetting pressure was35MPa and excess coefficient was0%, the reduction rate was97%and the main components of slag were12CaO·7Al203and CaO·Al2O3. Another condition was that the reduction temperature was1473K, reduction time was90min, briquetting pressure was35MPa, excess coefficient was6%, the reduction rate was96.5%and the main components of slag were CaO·2Al203and CaO·Al2O3. The calcium aluminate slag produced through the two optimal conditions can be leached with alkali liquor, and the aluminum hydroxide can be obtained by the methode of carbonation precipitation.