Stainless Steel Dust Reduction Mechanism Of Study

Stainless steelmaking dust has been classified as a hazardous waste, while there are many metals in it, especially rare metals such as chromium and nickel. In order to recover these metals and protect the environment,a new process direct recycling of stainless steelmaking dust was introduced. And in order to study the reduction process and mechanism of dust/carbon pellet, particularly chromium oxide, pure Cr₂O₃ and dust powder were mixed with carbon and CaO, to form the pellets, then the reduction process was investigated by using an electric furnace. Some basic information of direct reduction was also investigated by using an induction furnace. The interfacial tension formula was studied in theory.In the reduction of the pellets with Cr₂O₃ and carbon, reduction extent increases with temperature rising, but the phenomena are not obvious when temperature is over 1530℃. The size of pellet hardly influences reduction extent, but the diameter of particles largely, especially at 0.080mm. Carbon content mostly influences reduction extent, but the effect is little when it exceeds certain amount. The initial stage of reduction is controlled by the chemical reaction and the kinetic equation of the process can be expressed as g(f) = (0.29Cn - 0.01)e ^-60370/RTt.The following stage is controlled by the diffusion of reduced products and the kinetic equation of this stage can be expressed as g(f) = (-0.17 Cn +0.31)e^-99435/RTt.The volatilization of lead is controlled by reduction and the volatilization speed k(Pb) can be expressed as k(Pb)=8E-08x³-0.0003x²+0.2667x-92.2 at 1500℃. The volatilization of zinc is controlled by reduction and diathermancy and its volatilization speed k(Zn) can be expressed k(Zn)=4E-10x³-7E-07x²+0.0004x at this temperature.The reduction extent and rate increase with temperature, however the temperature is lower at the same reduction extent in pure Cr₂O₃ reduction. Reduction extent is relativity low when carbon content isbelow 15%, while reduction extent increase little when it over 20%. Additive Fe powder can improve largely reduction rate. The initial stage is controlled by the chemical reaction and the kinetic equation of the reduction process can be expressed as g(f) = ( 3.44Cn+0.638 ) e¹6770/RTt.The following stage is controlled by the diffusion of reducedproducts and the kinetic equation of this stage can be expressed as g(f)= O288e-.46io/RTtAfter carbon pellet added to the furnace in the stainless steelmaking, it will present in the interface of slag and steel, 10 volume percent of it will exist in steel and the others in slag. The reduced metals mainly travel in slag. The rate of reduction is much quicker than that of melting and the slag will enhance both rates. The recovery of metals will be much high when the pellets are added in the end of the first reduction stage of smelting practice, especially Cr reduction degree could reach 95%.The carbon in the pellets that do not react in the reduction will move into slag, and the carbon in steel will not increase when its content is lower 20% in pellets. The viscosity of slag is 2.54Pa ? s and the surface tension is 490 mN ? m"1.The approximately formula of interfacial tension at 1560°C can be expressed as Y=0.668c (Cao) +3.728 c cMgo> -2.338 c (Mn0) -4.608 c (Feo> -9.89 c (Fe2O3) +4.182 C(Ai203) -8.928 c (Sj02> + 918.83.The process of direct reduction to recover metals is feasible in theory affter analyzing the slag and the simulation experiment in induction furnace.