Applied Basic Research On Pre-Desiliconization Of Middle And Low Grade Bauxite Ore By Alkaline Medium Under Atmospheric Pressure

A new process of pre-desiliconization of bauxite ore through leaching by high-concentratied NaOH solution under atmospheric pressure was basically investigated and optimized, which was especially developed to resolve the key problems of great investment of equipments, high energy consumption and pollution of red mud with high alkaline content existing in the alumina industry of China, whose most of bauxite resources with high silica content. Creative points of the study are as follows:1. In oder to increase the grade of bauxite ore, pre-desiliconization of bauxite ore through leaching by high-concentratied NaOH solution under atmospheric pressure was proposed in the first time. The dissolving characters and treatment effects of this system was basically studied. The result showed that pre-desiliconization of bauxite ore by this method was speediness, the time of leaching was about 5～20 min, far more quickly than any other method of pre-desiliconizition. The effect was good enough to meet the need of the requirement of the Bayer process on the grade of bauxite ore.2. The effects of primary factors on this new process were investigated. The results shoued that the leaching rate of Al₂O₃ and SiO₂ were increased with the accretion of temperature, initial concentration of alkali and mass ratio of alkali to ore , and the affect of temperature on the leaching rate of Al₂O₃ was great than initial concentration of alkali did.3. The kinetic characters of this process was studied, apparent activation energy of bauxite ore was 23.4kJ/mol, reaction order of desilicization for it was 0.9,the kinetic equation was obtained as4. The basic research were also carried out about dissolving character and stability of Al₂O₃ and SiO₂ in sodium aluminate solution. The result was that sodium alumnate solution with SiO₂ in it was very steady, stable period of metastable was very long, it was uneasily for sodium aluminosilicate hydrate to separate out as crystal, and the concentration of SiO₂ was decreased slowly. However, through desiliconizition treatment , the leaching solution can be cyclic used, but the treatment would last a long time.5. Based on the research results above, the principle flowsheet on the pre-desiliconizition of bauxite are by high-concentratied NaOH solution under atmospheric pressure was proposed, and the primary technical parameters of the pre-desiliconizition of bauxite by high-concentratied NaOH solution was optimized.Pre-desiliconization of middle and low grade bauxite ore through leaching by high-concentratied NaOH solution under atmospheric pressure has the advantagements of low ratio of solution to bauxite, low consumption of alkali, and without pressure in production process, may provide technical support for the expliotage of our typical middle and low grade bauxite ore.