Research On Producing Iron Nuggets With Nickel And Chromium At High Temperature Directly From Self-reduction Of Stainless Steel Dust Coal Mixed Briquettes

This paper reviews the advanced technology of dealing with stainless steel dust at home andaboard, and summarizes the current situation of direct reduced iron in all over the world and theprospect of coal-based direct reduction process in China. Combined with the actual production ofsteel, the method of dust mixed coal with high basicity （Wcomet process） based on rotary hearthfurnaces recycling stainless steel dust containing with iron, chromium and nickel was proposed.The process parameters were researched.The direct reduction experiment was undertaken in carbon tube furnace with high-speedheating function. The effect of reduction temperature, C/O ratio, basicity and additives on thetechnique qualifications such as slag phase pulverization, iron phase aggregation and iron,chromium and nickel yield. The results are shown as follows:1) when the basicity （w（CaO）/w（SiO2）） of slag of briquettes is between2.3and2.5, the slagphase of self-reduced product could be separated from the iron nuggets naturally during theproduct cooling. But when the basicity of the slag phase is lower, more difficult the iron granulesgrow up, because of the bigger quantity of slag. when the basicity of the slag phase is high to2.8,the slag phase isn’t pulverizing after direct reduction, it may be because the slag phase isn’t in2CaO·SiO2area.2) Raised the C/O mole ratio of stainless steel dust coal mixed briquettes, the amount ofresidual carbon in the slag increases obviously and the excessive carbon in the slag wouldprevent the metallic phase diffused and aggregating growth. Iron granules aggregate and growwell as the C/O mole is1.1.3) As the temperature increases, the sponge structure of the direct reduction irondisintegrates and the iron nuggets easily form. The higher the reducing temperature is, the moreeasily to aggregate and grow the iron nuggets.4) CaF₂can make the surface tension of the molten slag decrease greatly, but if CaF₂quantity is too large, it will increase the slag quantity, which is bad for aggregation and growth ofthe iron nuggets.2%of CaF₂addition amount is suitable for the direct reduction of the stainlesssteel dust.5) Improve the metal content of briquettes, which will reduce slag quantity correspondingly,the iron nuggets aggregating and growing more easily. As the carbon is excessive more than10%,it will provide enough carbon as reducing agent to ensure the reduction of iron, chromium andnickel.6) The desulfurization and dephosphorization ability of reduction process of high basicitystainless steel dust coal mixed briquettes at high temperature are high. The desulfurization rate ismore than94%as the dephosphorization rate between45%and65%. Iron nuggets with lowsulfur and phosphorus content and high chromium and nickel content can be obtained throughthe direct reduction process.