Effect Of Iron-rich Minerals And Impurities On Formation Mechanism Of Andradite

The national "Thirteenth Five-Year Plan" and "Non-ferrous Metal Industry Development Plan" listed "Efficient and energy-saving technology of low-grade bauxite producting alumina" and "Comprehensive utilization technology of red mud" as "Focus on technical innovation" and "green development project" at the same time.And put forward the main goal of non-ferrous metal industry development during the "Thirteenth Five-Year Plan" period is to increase the comprehensive utilization rate of red mud from the current 4%to 10%.China has abundant low grade bauxite reserves,and the red mud piles of Bayer process are huge.Therefore,the economically reasonable,technically feasible,green and efficient process to treat low grade aluminum resources is important for the sustainable development of China’s alumina industry.Based on a new process of treating low grade aluminum resources with one-step alkali digestion method of andradite,this paper systematically studied the effects of impurity phases of low grade aluminum resources and impurity ions of sodium aluminate solution on the behavior of andradite.The evolution of the phase and micro structure of different iron minerals on the conversion of sodium aluminosilicate hydrate to andradite were discussed.The main conclusions of the paper are as follows:The effect of titanium minerals and magnesium minerals in low grade aluminum resources as the impurity phase on the formation of andradite were studied.Anatase and rutile can enter andradite to replace SiO2 in it,which reduces the lattice constants,particle size and crystallization of andradite,and forms obvious crack on the surface of andradite.Rutile can generate andradite with a high substitution rate of TiO2,3CaO·(0.25Al2O3·0.75Fe2O3)·(1.15TiO2·0.65SiO2)·2.4H2O.Periclase can replace CaO of andradite and form(2.85CaO·0.15MgO)·(0.35Al2O3·0.65Fe2O3)·nSiO2·(6-2n)H2O,which reduces the lattice constants and the crystallinity of andradite,periclase has little effect on the content and SiO2 saturation coefficient of andradite.Hydromagnesite can react with sodium hydroxide and lime to generate insoluble magnesium hydroxide and calcium carbonate,which affects the conversion of hydrated garnet to andradite and reduces the crystallinity of DSP,while agglomerating into large solid makes the particle size of DSP larger.The effect of impurities sodium carbonate and sodium sulfate in sodium aluminate solution on the behavior of andradite was studied.Sodium carbonate can react with lime to form calcium carbonate,which adheres to the surface of hydrated garnet and andradite,hinders the formation of andradite,decreases the crystallization of DSP.At the same time,calcium carbonate agglomerates into large lumps with the reaction going on,which increases the particle size of DSP.Sodium sulfate mainly presents in the liquid phase after the reaction,which significantly increases the content of hydrated garnet in DSP,while the content of andradite is only about 40%.The crystallinity of andradite is greatly reduced,and the particle size of DSP gradually increased.The dissolving ability of different iron ore phases in sodium aluminate solution and their effects on the conversion of sodium aluminosilicate hydrate to andradite were studied.The solubility of sodium ferrite in sodium aluminate solution is much greater than that of goethite,while the solubility of hematite in sodium aluminate solution is very low.The conversion effect of goethite on sodium aluminosilicate hydrate to andradite is similar to that of sodium ferrite.The alumina extraction rate of sodium aluminosilicate hydrate can reach 55%,hematite is slightly worse,the extraction rate of alumina is 39.8%,and the Na2O residue in the solid phase is high,magnetite and iron powder are the worst,the alumina extraction rate is only about 30%.Goethite can be converted into hematite in sodium aluminate solution,and it is used to conduct the conversion of sodium aluminosilicate hydrate to andradite,the alumina extraction rate is less than 40%.Finally,the mechanism on the formation of andradite with the presence of goethite in sodium aluminate solution was studied.After the reaction,the main phase of DSP is andradite and a small amount of hydrated garnet.When the reaction time is 2 min,andradite is rapidly formed,and its content reaches 76.70%.With the extension of time,the content of andradite gradually increases,the lattice constants decreases,the crystallinity increases,and its SiO2 saturation coefficient increases.Compared with sodium ferrite,when goethite is used as an additive,the morphology of the crystallized andradite has changed from spherical particles to octahedral structure,with a regular shape and dense structure,and its surface has tiny ripples.