Study On Crystallization And Leaching Behavior Of CaO-SiO₂-MgO-Al₂O₃-Fe₂O₃-Cr₂O₃ Slag System

Stainless steel slag is a by-product during the stainless steel smelting.Due to the technical inmature in recycling,most of the slag is dumped currently.Meanwhile,because it contains 1-5 wt%chromium oxide,the Cr?III?in the slag can be transformed into toxic Cr?VI?in the alkaline environment,which seriously pollutes the environment.Therefore,it is necessary to study the crystallization and leaching behavior of stainless steel slag if we try to handle or reuse it.In this paper,the crystallization behavior of CaO-MgO-SiO₂-Al₂O₃-Fe₂O₃-Cr₂O₃ slag system under different basicity and different content of Cr₂O₃ and the heat treatment process were studied.The crystallization behavior of additives CaF₂ and B₂O₃ was discussed.The leaching behavior of slag system before and after crystallization was also studied.The SiO₂ coated spinel powder was synthesized by sol-gel method and its magnetic properties were studied.The main research results are as follows:?1?Different basicity?0.8,1.0,1.25,1.5?and Cr₂O₃ content?0.0 wt%,2.0 wt%,3.0wt%,4.0 wt%,6.0 wt%,?were designed,prepared by chemical reagents and melted at high temperature to form CaO-MgO-SiO₂-Al₂O₃-Fe₂O₃-In the Cr₂O₃ system,studies have shown that when the basicity ranges from 0.8 to 1.25 and Cr₂O₃?2.0wt%,crystallization is promoted.When the basicity is 1.5,the system will crystallization with or without Cr₂O₃;when the basicity is 0.8 and the Cr₂O₃ content is 4.0%,the main crystal phase is the spinel phase and the calcium magnesium silicon phase;when the alkalinity is At 1.0,mainly chrome-containing spinel and aluminum-containing spinel;when the basicity is 1.25,spinel and magmatic sillimanite are the main crystal phases.Most of the chromium is present in the spinel phase.The heat treatment and crystallization behavior of the formed glass system were studied.It was found that the glass transition temperature and the crystallization temperature increased with the increase of the heating rate.Cr₂O₃ reduced the crystallization activation energy of the same basicity sample,which was beneficial to crystallization.?2?The effects of CaF₂ and B₂O₃ on the crystallization behavior of the slag system were studied.The slag system has a basicity of 1.0 and a Cr₂O₃ content of 4.0%.1.0 wt%CaF₂ is added,and the monticellite and spinel are precipitated in the quenched slag;when the CaF₂ is added at 2.0 wt%,the monticellite is precipitated in the quenched slag;When the CaF₂ content is 4.0%,the quenched slag basically exhibits amorphous glass.When the slag system is added with 1⁴ wt%B₂O₃,the tendency of the quenched slag to precipitate the spinel is weakened.?3?The slag sample with a basicity of 1.0 and a Cr₂O₃ content of 4.0%was selected.The fixed liquid-solid ratio was 10:1,the temperature was 40?,and the particle size was325 mesh,the leaching time?6 h,9 h,15 h,24 h?was studied for the leaching behavior of chromium.The results showed that the pH of the solution was maintained between 10¹1after leaching for a certain period of time.Before crystallization,the concentration of Cr?VI?did not change much before 9 h,and the concentration reached 0.32 mg/L.However,between 9¹5 h,the concentration of Cr?VI?changed rapidly and the concentration reached 3.32 mg/L.After crystallization,the concentration of Cr?VI?changed greatly before 9 h,and the concentration reached 4.95 mg/L,after which the Cr?VI?concentration changed slowly.In general,the concentration of Cr?VI?after crystallization is higher than that after quenching.It is indicated that after crystallization,the chromium portion of the spinel is released and exists in other forms.?4?Acid-decomposed electric furnace slag shows that the acid hydrolysis product contains spinel and amorphous SiO₂,which provides a new idea for the treatment of chrome-containing spinel.Silica-coated magnesium-aluminum-chromium spinel composites were prepared by sol-gel method using citric acid as surface modifier,ammonia as precipitant and tetraethyl orthosilicate?TEOS?as silicon source.The results show that the coated material is still in the spinel phase structure,and the characteristic peak of amorphous SiO₂ matrix was found at 30⁴0o.As the content of SiO₂ coating increases,SiO₂ hinders the growth of spinel grains to some extent.As the holding time increases,the spinel grows slowly.Magnetic analysis showed that the hysteresis loop of the sample was a curve and approached the paramagnetic state at room temperature.