Fundamental Research On The Wet Reduction Of Sulfur Removal In The Alumina Production Process

Due to the scarcity of high quality bauxite resources in China,the dependence on foreign countries is becoming more and more serious.which restricts the development of alumina industry in China.However,China's high-sulfur bauxite resources are very rich,accounting for about 11%of total bauxite reserves,but limited by the technology and economic factors,the current can't be a large-scale rational development and utilization.Moreover,high-sulfur bauxite in the digestion process of sulfur enrichment corrosion of steel equipment,resulting in the digestion of the evaporator inside and inside the evaporators,reducing the heat transfer coefficient,resulting in increased energy consumption,but also lead to the decline of alumina digestion,affecting the normal production of alumina and so on.Therefore,it is of great significance to use the Bayer method to treat the high-sulfur bauxite and to remove the sulfur in sodium aluminate solution by wet reduction in the process of digestion.In this paper,sulfur removal from wet reduction method in alumina production is studied.The optimum conditions of digestion of high-sulfur bauxite,the effect of different reducing agents on the removal of sulfur in the process of digestion of high-sulfur bauxite,and the optimum process of alumina digestion rate and sulfur digestion rate when adding reducing agent were clarified.The kinetic model of alumina digestion rate,the kinetic model of sulfur digestion rate and the kinetic model of sulfur removal in the process of digestion of high-sulfur bauxite were established.The main findings of the paper are as follows:(1)The reaction kinetic equation of alumina in the digestion process can be described by 1-(1-x)1/3 = kt,and the apparent activation energy of the reaction is 41.907 kJ/mol.and the digesting process of high-sulfur bauxite The reaction kinetic model of alumina digestion belongs to the particle size shrinking nucleation model in the shrinking nuclear membrane type controlled by interfacial chemical reaction.The kinetic equation of sulfur reaction in the process of digestion can be described by 1-(1-x)1/3 = kt.The apparent activation energy of the reaction is 41.463 kJ/mol,in the process of digestion of high-sulfur bauxite,the reaction kinetic model of sulfur digestion belongs to the particle size shrinking nucleation model in the shrinking nuclear membrane type controlled by interfacial chemical reaction.The kinetic equation of the reduction reaction in the digestion process is as follows:1-2/3x-(1-x)2/3 = kt,the apparent activation energy of the reaction is 10.546 kJ/mol,and the reaction kinetics model of the process of digesting sulfur removal in the process of digestion of high-sulfur bauxite is the solid film diffusion control of the shrinking nuclear model.(2)The digestion rate of alumina can be improved by adding calcium oxide(CaO)to the digestion process of high-sulfur bauxite.The optimum digestion conditions of high-sulfur bauxite are as follows:CaO is added 13%,digestion temperature is 260?,and digestion time is 60min.At this time,the digestion rate of alumina is 79.54%and the digestion rate of sulfur is 55.88%.(3)The addition of reductant(Aluminum sheet,Zinc granule and Iron powder)in the digestion process can reduce the sulfur ions such as S2O32-,SO32-and SO42-in sodium a lu min ate solution,and decrease the concentration of S2O32-,SO32-and SO42-plasma in sodium aluminate solution.The addition of zinc can decrease the concentration of S2-in sodium aluminate solution and decrease the sulfur content in sodium aluminate solution.The addition of aluminum sheet and iron powder can't effectively remove the S2-in sodium aluminate solution,so it can't reduce the content of sulfur in sodium aluminate solution.The digestion effect was best when the amount of zinc was 15%,digestion temperature was 260 0C and digestion time was 80min.At this time,the removal rate of S2-was 96.55%,alumina digestion rate and sulfur digestion rate were 73.14%and 29.03%respectively.(4)After adding reducing agent in the digestion process,the most influential factors of alumina digestion rate is:temperature.the most influential factor of sulfur digestion rate is:the amount of zinc particles.The order of degree of influence on alumina digestion rate is:temperature,time,Zn dosage.The order of the sulfur digestion rate is:Zn dosage,temperature and time.