Technical Research On Metallurgical Grade Alumina Production By Using High-sulfur Bauxite

The rapid development of China's aluminum output leads to the exhaustion of high quality bauxite resources in China.The non-traditional aluminum resources,represented by high sulfur bauxite,are causing more and more attraction in the industrial and academic circles.The feasible utilization of the high sulfur bauxite will relieve the burden of bauxite resources and ensure the sustainable development of alumina industry in China.This research mainly focuses on the roasting process in the preroasting-Bayer method for metallurgical grade alumina preparation by using high sulfur bauxite as raw material.The thermodynamics and kinetics of desulfurization process,effect of muffle furnace roasting parameters on the desulfurization performance and pattern of bauxite,the scattered roasting characteristics of high sulfur bauxite,the desulfurization performance of bauxite through suspension roasting and the dissolution activity of the roasting ore were systematically studied.The main contents and results are as follows:(1)The thermodynamics and kinetics analysis results of the roasting process illustrate that:the standard Gibbs free energy of the reactions are less than 0 except for the kaolinite dehydration reaction in the temperature range of 500??750 ?;the endothermic value of the high sulfur bauxite is between 442.5 kJ·kg-1?518.1 kJ·kg-1 when the main reaction ratios of roasting process are between 85%?100%;the first stage reaction of bauxite roasting desulfurization mainly includes two reaction processes of dehydration and desulphurization;the dehydration of diaspore and pyrite oxidation mainly concentrate between 428? and 593?;the desulfurization reaction is earlier than the bauxite dehydration,and the maximum desulfurization rate is appeared at 492.2?.(2)The muffle furnace roasting desulfurization process results indicate that:the roasting temperature for the muffle furnace roasting desulfurization is higher and the time is longer.The total sulfur content in the roasted ore is lower to 0.7%with the roasting temperature of 750? for 10 min.The main components of the roasted ore are alumina,metakaolinite and iron oxide,and the specific surface area of roasted ore increases firstly and then decreases with the increasing of roasting temperature.(3)Under the condition of disperse roasting,high desulfurization rate can be achieved with relatively high temperature in a short period of time.However,when the sulfur residue is lower than 0.25%,the removal of residual sulfur requires higher temperature or longer time;the sulfur contents in the form of sulfide in roasted ores are below 0.3%when the roasting time is longer than 60 s.(4)The optimal temperature of the pilot scale suspension roasting is 570±10?.The sulfur content in the form of sulfide type can be less than 0.05%through suspension roasting treatment.The energy consumption of the suspension roasting process is 23.20 kgce/t-bauxite.(5)The digestion performance and the settlement performance of the dissolving pulp of continuous suspension roasted ore were also studied.The results indicate tha the digestion ratio and the settlement performance of the dissolving pulp for the roastedore are all superior to the raw ore.Under the optimal digestion conditions,47.80%of the sulfur in the raw ore enters into the solution,while only 18.28%of the sulfur in the roasted ore is entered into the solution.The digested liquor of roasted ore meets the requirement of metallurgical grade alumina preparation.