Study on Dissolution and Reduction Mechanism of Powdered Chromium Ore in Molten Slag.

Research Project

Project/Area Number	60550464
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	金属精錬・金属化学
Research Institution	Muroran Institute of Technology
Principal Investigator	KATAYAMA Hiroshi G. Faculty of Engineering, Muroran Institute of Technology, 工学部, 助教授 (90002881)
Project Period (FY)	1985 – 1986
Project Status	Completed (Fiscal Year 1986)
Budget Amount *help	¥1,700,000 (Direct Cost: ¥1,700,000) Fiscal Year 1986: ¥300,000 (Direct Cost: ¥300,000) Fiscal Year 1985: ¥1,400,000 (Direct Cost: ¥1,400,000)
Keywords	Chromium ore / Dissolution of chromite / Smelting reduction / Ferrochrome production / Chromium valence in slag / Temperature dependence of reduction rate / EPMA分析
Research Abstract	Experiments were conducted to elucidate smelting reduction behavior of powdered chromium ore in molten slag at the temperatures between 1550 and 1650゜C. The smelting reduction consists of the processes such as (1) dissolution of chromite grain into slag, (2) mass transfer in slag and (3) reduction at reacting interface. The process (1) may be classified into ( <I> ) the dissolution only from the surface of chromite grain and ( <II> ) the simultaneous dissolution from the surface and the inside, owing to the penetration of molten slag into the pore of chromite grain. Type <II> occurs in relatively fluid slags with MgO/CaO < 0.5 and the <SiO_2> concentration of 40-60% and type <I> in more viscous slags with the other composition. Chromite dissolves into slag first to form <Cr^3> +, which is then reduced to <Cr^2> +. In the slags with higher <SiO_2> concentration <Cr^3> + is more easily reduced to <Cr^2> +, whereas in the slags with higher basicity <Cr^3> + is more stable and its reduction retards. Since the rate of reduction is higher when chromite grain is dissolved into slag according to type <II> , it seems that the smelting reduction is mainly rate-determined by the dissolution of chromite grain into slag. Temperature dependence of reduction rate becomes smaller above 1600゜C. This may be attributed to the change in reduction mechanism, but the detail on it is unknown. Main reaction site is the interface between graphite grain and slag. Furthermore, the reduction of Fe proceeds to an appreciable extent at the surface and the inside of chromite grain. As above-mentioned, the aid intended beforehand could be almost attained. Hereafter, the author will continue his work concerning the following problems: Effect of chromite composition on dissolution behavior of chromite into slag, development of promoting agent for the dissolution of chromite, detailed mechanism of smelting reduction at different temperatures and so on.