Study On Removal Sulfur In Bayan-Obo Niobium-containing Iron Ore Gas Based Reduction Process

At present, with rapid development of iron and steel production in our nation, steeldemand for niobium and its compounds increase. However, the utilization of the metalniobium cannot meet the needs of national economic development. Moreover, there aresome harmful elements existing in niobium rich slag, such as S, P, C, Si and other elements,which to some extent limits the further development of the niobium iron smelting.In order to solve this problem, obtain the purer rich slag of niobium, and achieve thecomprehensive utilization of special iron ore resources of niobium in Baotou Bayan Obo,the both experiments directly reducing the Bayan Obo iron ore by gas and slag and metalseparating by melting method were undergone. The behavior of sulfur migration wasinvestigated under different conditions (including in feed flow of hydrogen, reducing time,and reducing temperature) in gas-based reduction process. And the behavior of residualsulfur migration was also studied in the slag and metal separation processes. When thesulfur content ran up to the lowest in the niobium-rich slag, that the iron oxides werereduced to the metal iron’s ratio and the ratio of niobium element distributed inniobium-rich slag were examined.The main contents and results of this paper are:Thermodynamic Study: To know the possibility of each reaction and the degree ofreduction in gas-based reduction process in the hydrogen reducing niobium-containing orefines process, the degree of difficulty of each response was determined with thethermodynamic analysis way. When the experiment temperature was the range of850to1050℃, the sulfur existed by formation of FeS2in the niobium-containing iron ore fineswas mostly reduced to the formation of H2S and escaped. The small part of FeS2firstly wasdecomposed into FeS and S2, then FeS was easier to be reduced to H2S which is wiped out.CaSO4which was a little exists in the iron ore fines was easily reduced by H2into CaS, butwas not removed from niobium containing slag. Gas base reduction experiment: There were several experimental factors, includingthe reduction temperature, the reduction time, the hydrogen feedstock rate, which affectedgasification desulfurization ratio. In the previous optimization results studied metallizationrate: in reduction temperature (950℃) and residence time (2h), the gasificationdesulfurization ratio increased with the hydrogen feedstock rate increased when thehydrogen feedstock rate was less than60L/h, but the gasification desulfurization ratedecreased with the hydrogen feedstock rate when hydrogen feedstock rate was greater than60L/h. When the hydrogen feedstock rate was60L/h, the gasification desulfurization rateran up to95.91%. Under the hydrogen feedstock rate maintained60L/h and the reductiontemperature maintained950℃, the gasification desulfurization rate increased with thereaction time increased. And the reaction time increased from1.5h to2h, the sulfuricgasification removal ratio of niobium-containing ore fines increased significantly, at thereduction time of2h, the desulfurization ratio of the niobium ore fines reached95.91%,continuing to increase the residence time from2h to3h, desulfurization ratio only going up1.62%. Similarly, in the hydrogen feedstock rate maintained60L/h and the reduction timemaintained2h, below950℃the gasification desulfurization ratio of niobium ore finesincreased with the temperature, but over950℃this ratio decreased with the temperature,and at950℃the gasification desulfurization ratio reached95.91%.The separation experiments of slag and metal: According to the experiment, theoptimum conditions for the separation of slag and metal was the melting temperatureholding to1550℃, the melting time maintaining25min, the heating rate reaching at14℃/min. In the vacuum melting separating section there was the portion remained sulfurremoved in the ore. This desulfurization capacity depends on the gasificationdesulfurization ratio of reduction process. That is, the gasification desulfurization ratio ofthe reduction process increased (decreased) as the desulfurization ratio in the meltingprocess decreased (increased). When the gasification desulfurization ratio of the reductionprocess was the highest, the desulfurization ratio in the melting process was only3.88%, correspondingly the total desulfurization ratio reached99.79%, the iron metallization ratioreached96.80%, the niobium yielding rate in the slag ran up to94.55%, the sulfur in theslag was less than0.043%.