Reduction Behavior of Panzhihua Titanomagnetite Concentrates with Coal
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MAGNETITE of Panzhihua, China, is a complex iron ore, containing elements of vanadium and titanium. It accounts for more than 90 pct of the titanium reserves in China.[1] By the beneficiation process of the ore, titanomagnetite concentrates and ilmenite concentrates are produced. The mineralogy of titanomagnetite concentrates has been studied extensively by geologists.[2,3] It consists of titanomagnetite in majority, with less magnetite and ilmenite. Titanomagnetite has a cubic spinel structure. The general formula can be written as AB2O4, where A is in tetrahedral coordination and B is in an octahedral site.[4,5] Titanomagnetite (Fe3–xTixO4) is a solid-solution of magnetite (Fe3O4) and ulvospinel (Fe2TiO4) in which Fe3+ in the B sub-lattice of magnetite are replaced by Ti4+, with the concurrent conversion of Fe3+ to Fe2+ to maintain charge balance.[6] Most of the titanomagnetite concentrates are used as the main materials for the blast furnace process in Panzhihua area now. Most of the iron and partly of vanadium can be reduced into the hot metal. However, almost all of the titanium still remains in the slag, forming TU HU, Ph.D. Student, XUEWEI LV and GUIBAO QIU, Associate Professors, CHENGUANG BAI, Professor, and ZHIGANG LUN, Postgraduate, are with the School of Materials Science and Engineering, Chongqing University, Chongqing 400044, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 15, 2012. Article published online January 15, 2013. 252—VOLUME 44B, APRIL 2013
the high-titanium slag in which the content of TiO2 varies from 22 pct to 25 pct.[1,3,7,8] There is no appropriate and economic method so far to deal with the slag.[3,7,8] In recent years, most of the studies focus on developing an alternative route to use the titanomagnetite concentrates. One potential choice is the rotary hearth furnace process, which involves the reduction step of composite briquette of titanomagnetite concentrates with noncoking coal and the smelting of the reduced sample in an electric-arc furnace. Direct reduction of titanomagnetite has been widely studied for many decades. It was found that the reduction of titanomagnetite is slower than that of magnetite because of the existence of titanium cations, resulting in a higher thermodynamic stability of titanomagnetite.[1,9–11] Desheng Chen et al.[1] studied the effect of preoxidation on the carbothermic reduction of titanomagnetite concentrates by isothermal experiments at 1273 K to 1473 K (1000 C to 1200 C) in nitrogen. It was found that the preoxidation processing accelerated the reduction rate of titanomagnetite concentrates due to the destruction of the crystal lattice of raw titanomagnetite concentrates and the formation of pore in the particles. Roshchin et al.[12] investigated the solid-state reduction of titanomagnetite concentrates with milled graphite electrodes as the reductant at temperature range 1273 K to 1773 K (1000 C to 1500 C). It was found that the metallic iron began to form at the temperature range 1353 K to 1383 K (1080 C to 1110 C) a
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