Dephosphorization and Desulfurization of Acid Oxide Melts and Produced Iron

Abstract

Experimental data are given for a study of dephosphorization and desulfurization of acid oxide melts. Results are provided for determination of phosphorus distribution between phases within acid melts. It is shown that diffusion mass transfer is a limiting stage for phosphorus removal into a gas phase. A two-stage preparation scheme is proposed for iron preparation from ore materials: melting a charge with low basicity (less than 0.9) without adding reducing agents, then oxide melt reduction with preparation of fi nished metal. The fundamental possibility of preparing iron with a low phosphorus and sulfur content by the suggested scheme is confi rmed by experiment.Phosphorus behavior in various processes. Currently, production increasingly involves ore with a greater phosphorus and sulfur content. Removal of phosphorus from steel to standard concentration values is diffi cult in some cases, especially for steels alloyed with chromium and manganese. Existing methods for phosphorus removal do not entirely meet the main specifi cations for the process: a high degree of dephosphorization and low cost of performing the process. Phosphorus removal from slags makes it possible to provide more complete steel refi ning from phosphorus [1-3]. Methods have been proposed with which carbon material is added to slag (or another reducing agent, for example, Al) in order to reduce phosphorus from slag with transfer of it into a gas phase [4,5]. However, the possibility remains of metal rephosphorization, since phosphorus reduced from slag may be transferred both into a gas and also into metal, which reduces process effi ciency.In the agglomerate-blast furnace process, there are almost no conditions for removing phosphorus added with charge materials, up to 90% of which is transferred into iron. However, there are extra-blast furnace methods of iron production such as liquid-phase processes of the Romelt, Hismelt, Ausriron type, etc. Within these, due to the absence of a shaft, a considerable oxidizing capacity of slag, and the potential to maintain greater basicity compared with the blast furnace process, it is possible to provide transfer of a considerable part of phosphorus into slag, and as a result of the absence of a shaft up to 30% of phosphorus is transferred into a gas phase [6].In industry, phosphorus is prepared by reducing calcium phosphate with carbon in the presence of silicon with preparation of technical grade phosphorus. Subsidiary products of this process are slag and ferro-phosphorus containing up to 30% of phosphorus, 60% iron, and balance vanadium, chromium, silicon, titanium, nickel, and other impurities [7]. A typical composition of phosphate-silica melt formed during melting of Karatau phosphorite with addition of quartzite to a charge is, wt.%: 24.0 P 2 O 5 ; 37.3 CaO; 3.11 MgO; 33.0 SiO 2 ; 1.32 Al 2 O 3 ; 0.9 FeO [8]. Quartzite in a charge is added for more complete occurrence of transfer of phosphorus into gas (up to 90%) [9].In ferroalloy furnaces, there may be phosphorus removal into a gas phase in s...