| In 2015,more than 21 million tons of stainless steel were generated in China.That will produce a ton of chromium steel slag when producing three tons of stainless steel,So,Only 2015,there're produced about 7 million tons of chromium steel slag by produced stainless steel in China.At present,the treatment of stainless steel slag mainly in the storage of the slag field,However the stainless steel slag contains chromium elements,the surrounding environment is a potential hazard that in the long-term process of stacking.Therefore,create economic benefits by recycling valuable resources in stainless steel slag and play an effective role in environmental protection,to prevent secondary pollution,is an important issue that we need to face,has important theoretical and practical value.At present for the treatment of stainless steel slag mainly two categories both dry and wet,for wet leaching of stainless steel slag,at home and abroad have a certain degree of research,but the leaching effect is not very good,and the lack of leaching mechanism.It is mainly studied in this paper that mechanism of chromium in stainless steel slag during acid leaching under high temperature and high pressure is studied,and a comprehensive treatment scheme for stainless steel slag is proposed.The existence of chromium in stainless steel slag was determined by the analysis of composition and phase of stainless steel slag:mainly Cr(?)in complex oxide form in spinel phase and chromite in calcium,and a small amount of acid-soluble Cr(?)was dispersed in slag,To determine the leaching program,and proposed by screening,magnetic separation of the initial recovery of stainless steel slag in the iron program.By using the hydrothermal reaction of acid leaching experiment under high temperature and high pressure of different kinds of acid,extracts the initial H+ concentration,solid-liquid ratio,leaching temperature,leaching time and other factors on the leaching effect,the optimal condition of chromium leaching was determined by hydrothermal reaction at high temperature and high pressure:2.5 g of initial slag samples,50 ml of H2SO4 solution with a H+concentration of 5 mol/L,and a slag ratio of 1:20(g/ml),the leaching temperature was 250?,and the leaching time was 12 h.Under the optimum leaching conditions,the leaching reaction reached equilibrium at about 12 h,and the leaching rate was about 90%.The kinetic model of the leaching process of chromium in stainless steel slag is discussed.The results show that the dynamic model of the leaching process belongs to the pore diffusion model.There was a small amount of acid soluble Cr6+ in the original slag samples,but the Cr6+ was not detected in the leaching solution,which showed that the Cr6+was completely reduced by Fe2+.Analysis of electron microscope and X ray diffraction on the leaching residue after leaching,There were three kinds of ore-forming phases:CaSO4 long-striped particles with lamellar structure;dark gray irregular globular structure composed of SiO2,the surface was loose and porous;porous spinel(MgCr2O4)composed of bright white surface of the dense spherical structure,this ore is not involved in the reaction of the original sample of spinel ore phase.The residual Cr in the leaching residue is collected in the spinel phase and is not leached under various toxicity tests.The leaching residue is in accordance with the main components of the leaching residue and cement curing effect of Cr. |
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