Physicochemical Properties And Applied Research Of Pickling Sludge As Slagging Flux In Electric Furnace

For existence of polluted components such as F^-,Cr⁶⁺,stainless steel pickling sludge?PS?,a hazardous waste,is treated by landfill after solidification.This treatment cannot eliminate the risk of contamination of soil and groundwater.Applying PS as slagging flux?SF?in EAF process probably not only recycles the valuable metal element including Fe,Cr,and Ni,but also reutilizes the CaO and CaF₂ as slag forming constituent,which is a potential resource utilization method for PS.In present research,the thermodynamic condition for preforming the fluxing effect of PS was calculated;evolution of sulfur in smelting process with/without oxygen blowing as various ratio of PS/hot metal,as well as recycling of Fe,Cr and Ni were investigated;the feasibility of using PS as slagging flux was also discussed based on kinetic analysis.The thermodynamic calculation related on fluxing effect of PS was carried out using FactSage thermodynamics software and the results are elaborated as follows.Under the condition that adoption of full-scrap as smelting substance with ratio of 10:1for scrap to composite slagging flux?CSF,mixing the PS into the conventional SF of EAF process?at 1600°C accompanied by oxygen blowing,the recovery rate of Ni element has reached 90%,part of Fe and Cr entered the slag in the form of oxides resulting in a lower recovery rate.The sulfur content in the molten steel is less than that in the original scrap and the maximum value was 0.014%.Using the raw materials with ratio of pig iron to scrap as 9:1,the nickel recovery rate was increased to more than98%with the maximum iron recovery rate of 98.63%.Furthermore,with the addition of PS the chromium recovery decreased,and the sulfur content in molten steel increased with a maximum value 0.035%,which is also less than the value of sulfur under the meaning of mixing scrap into original hot metal.The recycling rate of metal elements was higher under the ratio of CF and PS as 1:1 in CSF.Effects of factors including proportions of PS blending into CSF?the ratios of SF:PS are 3:1,2:1,1:1,1:2,1:3,respectively?,treatment methods of molten steel?with/without oxygen blowing?,sulfur content in PS on evolution of sulfur and valuable elements in process were investigated according to multiple-conditions of experiments.The results shown that the low sulfur PS has little effect on sulfur content in steel ingot.Without oxygen blowing,the recovery rate of Cr,Ni?Cr<0.01%,Ni<0.1%?was low.When the oxygen was blown and the ratio of SF/PS as 1:1 was employed,the recovery efficiency of Cr,Ni?Cr 66.04%,Ni 97.9%?was improved significantly,which is correspondent with thermodynamic calculation.However,utilization of high sulfur PS increased the sulfur content in steel ingot to the value of more than 0.2%,which is obviously higher than that in the steel ingot prepared from raw materials without PS addition?S 0.018%?,and simultaneously the recovery efficiency is also lower under this process.Consequently,the high sulfur PS must be processed and transformed to a low sulfur PS by pretreatment to satisfy the EAF operation.The desulphurization kinetics of the PS as the SF in the EAF was analyzed and the results show that under the condition that temperature at 800¹ 000?,heating rate as10?/min is favour of desulphurization.The internal-diffusion is the restriction in this reaction.This process is in accordance with a random nucleation and subsequent growth model,and the activation energy is 171.707 kJ·mol^-1,and the kinetic equation can be expressed as following:???.