Basic Study On Bauxite With High Iron Content By Acid Process

With the rapid development in alumina industry and dramatical increasing demands of bauxite, new technologies to take full utilization of the untraditional bauxite resources must be developed to sustain a continuous supply of bauxite resources. There are varity of bauxite resources with high iron content in China, depositing as much as 1.5 billion tons, which has been a widespread concern in academia and industry.At present, the main precedure of producing alumina using bauxite with high iron content is alkaline process, the disadvantages of which are the low utilizations of aluminum and iron, the time-consuming production process and the high energy consumption. The acid method shows tremendous advantages in treating such bauxite resources. Therefore, this thesis proposed two new technologies, the two-cycle method and the substep acid-leaching process of bauxite with high iron content, to produce alumina.In this thesis, the key technologies of the two processes above were studied, and the innovative achievements were obtained as follows:First of all, the hydrochloric acid leaching process was studied systematically in the two-cycle method. Thermodynamics of the main chemical reactions during the leaching process were studied; effects of certain factors (the ratio of liquid to solid, ore granularity, leaching temperature and leaching time) on the leaching performance of the hydrochloric acid leaching process and kinetics of this process were also studied.Secondly, the separation process of iron and aluminum in the leaching solution by the two-cycle method was researched. In the TOA and TBP extraction system, extraction separation of iron and aluminum in the non-saturated hydrochloric acid solution was studied. Influences of certain factors (TBP concentration, extraction time, acid concentration, the phase ratio of TBP/A, etc.) on the separation performance of iron and aluminum were investigated. And effects of certain factors (back extraction time, TBP concentration, acid concentration, the phase ratio of A/O, etc.) on the back extraction rate in organic phase containing iron were also investigated.Thirdly, the critical aspect in the two-cycle method, direct pyrolysis preparation of alumina with aluminum chloride solution was studied. The thermodynamics and differential scanning caloric analyses of the reaction system were studied. The results of direct pyrolysis of the crystalline aluminum chloride and of the pyrolysis process in the water vapor atmosphere showed that the suitable pyrolysis conditions in the water vapor atmosphere were the pyrolysis temperature of 800?, the pyrolysis time of 30min. Under the status above, the chlorine content of the product can be reduced to 0.14%. The chlorine content of the products in the pyrolysis process of AICI3 solution for 150min at 800? was 0.72%. In contrast, the spray pyrolysis at 750?850? with the solution concentration 15% of AlCl3 solution for 15min, the chlorine content of the products could be reduced to 0.31%.Fourthly, the two-step acid-leaching process was mainly studied in the substep acid-leaching method. Influences of certain factors (sulfuric acid concentration, leaching temperature, leaching time and the ratio of liquid to solid) on the first-step acid-leaching performance were examined. Effects of sulfuric acid concentration, leaching temperature and the ratio of liquid to solid on the second-step leaching performance were studied, also, the kinetics of first-step leaching process was considered. The results showed that the best leaching conditions in the first-step acid-leaching process were:the leaching time of 60 min, the leaching temperature of 100?, the ratio of liquid to solid of 5:1, and the sulfuric acid concentration of 20%. Under these conditions, leaching rate of iron was 98.68%, and leaching rate of aluminum was 3.02%. The dissolution ratio was 32.68, realizing the step-by-step dissolution of iron and aluminum. The kinetic analysis of the leaching process showed that the leaching process was controlled by chemical reaction. And the reaction activation energy was 35.11kJ/mol. Optimum leaching conditions for the second-step acid-leaching were:the leaching time of 60min, the leaching temperature of 180?, the ratio of liquid to solid of 10:1, and the sulfuric acid concentration of 60%. Under the conditions above, the leaching rate of aluminum could reach 95.86%.