Preliminary Research On Selective Extraction Of Chromium From Stainless Steel Slag By Pressurized Oxidation

Stainless steel slag is a byproduct of stainless steel smelting,which would cause serious environmental pollution in the process of open stacking.EAF slag was taken as the research object,the existing forms of typical elements in EAF slag in solution were simulated by thermodynamic software such as Factage 7.0 and HSC Chemistry 5.0,and the possible oxidation reaction of chromium containing substances in EAF slag in alkaline solution was calculated by thermodynamics.The best experimental conditions of extracting chromium from EAF slag were studied by single factor and orthogonal experiment.XRD and SEM-EDS were used to analyze the ore phase composition,micro morphology and micro area element composition of EAF slag and chromium extraction residue.The micro kinetics of chromium dissolution from EAF slag was established by using unreacted nuclear model.The results of thermodynamic calculation show that chromium in the leaching solution mainly exists in the form of chromium oxide,Fe Cr₂O₄,Fe Cr O₄,Mg Cr₂O₄,Mg Cr O₄ and Ca Cr O₄.At room temperature,Cr₂O₃,Fe Cr₂O₄ and Mg Cr₂O₄ can be oxidized in Na OH solution.The results of single factor combined with orthogonal experiment show that the best conditions of extracting chromium by pressurized oxidation in EAF slag are as follows:temperature 170°C,Na OH concentration 40 wt.%,oxygen pressure 1.6 Mpa,reaction time4 h,at this time,the extraction rate of chromium can reach 60.04%.The order of influence on chromium extraction rate is:temperature>time>Na OH concentration>oxygen pressure.XRD results show that the main ore phases of EAF slag include wollastonite,diopside and pyroxene.The chromium in EAF slag is mainly Fe-Cr spinel,and there is a small amount of magnetite in EAF slag.SEM-EDS results show that in the process of extracting chromium by pressurized oxidation,silicate minerals in slag are easy to dissolve,which makes the coated Fe-Cr spinel exposed and oxidized.The results of the unreacted nuclear model show that the activation energy of the reaction is 51.74 k J/mol,and the dissolution of chromium is mainly controlled by the diffusion of solid product layer.Figure 23;Table 14;Reference 56...