| In recent years, Chinese alumina production scale and technology level have been canstantly improved with strong demand of aluminum. However, Chinese bauxite resource, especial high grade bauxite reserves decreases greatly. There are about 500 million ton high-sulfur bauxite in China, but it can’t be used for alumina production because of the harmfulness of sulfur in Bayer process. So it is necessary to find economic desulphurization methods of high-sulfur bauxite in order to relief resource tension of Chinese alumina industry.In this paper, pre-roasting method was employed for desulfurization process and a new environmental process of producing alumina from high-sulfur bauxite was presented, on basis of amount of open literature about sulphid ore and pretreatment of bauxite process at home and abroad. The systematical research on the key technologies of the new process gave the innovation results as following.Firstly, thermodynamics of digestion and preroasting reactions under different conditions were studied. The calculation results preliminarily estimated the necessity of desulfurized pretreatment process and determined the parameter range of pre-roasting process.Secondly, effect of roasting parameters on high-sulfur bauxite desulphurization regularity were studied by using muffle furnace, rotary tube furnace and fludized bed. Changes of microscopic appearance and crystal structure were analyzed with SEM and XRD. The experimental results indicate that sulfur element was successfully discharged as gas form and the sulfur content in high-sulfur bauxite met the industrial standard through roasting. Reasonable conditions of roasting pretreatment by using muffle furnace and rotary tube furnace are 750℃for 30 minutes, and those by using fluidized bed are 800℃for 10 minutes.Thirdly, digestion performance of raw ore and roasted ore were investigated. The results indicate that the digestion performance of roasted ore is better than that of raw ore. The alumina digestion rate of raw ore was 82.79%, when the digestion conditions were temperature 220℃,lime addition 15%, time 60 minutes, Nk 240 g·L-1 and molecular ratio 1.5. Under the same condition, the digestion rates of the ores roasted at 750℃for 30 minutes in muffle and rotary tube furnace were 95.35% and 94.40%, respectively, while the rate of the fluidized bed roasted ore produced under 800℃and 10 minutes was 94.15%.Fourthly, effects of different roasting parameters on settling performances of digested slurry were studied. The results show that the settling performance of digested slurry of roasted ores is better than that of raw ore, and the slurry of the ore roasted by rotary tube performed the best of all.Fifthly, main process material flow of raw ore and roasted ore for alumina production were estimated. Calculation results indicate that digestion molecular ratio affected material flow greatly. For 1 ton alumina products, material flow of digestion, settlement, seed precipitation and evaporation are decreased by 19.98%,5.38%,8.86% and 24.48% respectively with digestion parameters of Nk 240 g·L-1, digestion temperature 220℃and molecular ratio 1.3.Finally, main process energy consumptions of raw ore and roasted ore for alumina production were assessed. The calculation results display that the feasible conditions of roasting by fluidized bed were temperature 800℃and time 10 minutes, and the condition for digesting the roasted ore were optimized at Nk 240 g·L-1, temperature 220℃and molecular ratio 1.3. Under the above condition where the digestion temperature might decrease by 20℃to 40℃, alumina digestion rate was up to 94.15%. Meanwhile, the general energy consumption will be reduced by 14kg standard coal/t-Al2O3 and the general product cost will decrease by RMB11 yuan/t-Al2O3 with the comparison to the consumption by the same-grade diaspore. |
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