| A large amount of chromium-containing slags has been produced in the production process of stainless steel,which has caused serious pollution problems and attracted wide attention.Under the dual pressure of the "Paris Agreement" and the environment-friendly transformation of the steel industry,research and development of a low-cost,large-scale,high-efficiency process for metallurgical waste is of vital important.Through the analysis of the composition and the exploration of harmless treatment of stainless steel slag,it was found that the enrichment of chromium in the stable phase can be achieved by the modification,and the leachable phase of calcium and magnesium contained in the slag has great potential in the mineralization and storage of carbon dioxide.In addition,the pickling waste liquid is acidic and difficult to handle.Using the solution as a mother liquor for selective leaching of calcium and magnesium from stainless steel slag can greatly reduce the process cost and promote the mutual digestion of various wastes.In this thesis,the stabilization of chromium in stainless steel slag and the highefficiency extraction of calcium and magnesium in slag were both considered.The precipitation characteristics of typical phase and the crystallization behavior of the target phases in slag during modification were studied.The enrichment of chromium in the stabilized phase and the crystallization enhancement of targeted phases were investigated.On this basis,the acid leaching of the modified slag was carried out.The release behavior of calcium and magnesium in the acidic system and the stability of the chromium or magnesium-bearing phase were studied.Combined with carbon dioxide mineralization and storage technology,carbonation product with industrial application value was prepared.The harmless treatment and resource utilization of the stainless steel slag were both achieved in this work.The main conclusions of this study are as follows:(1)The stability of typical phases of stainless steel slag was investigated.In the neutral and acidic solution system,the dicalcium silicate,merwinite and RO phase are easily leached phases followed by the akermanite.The glass,gehlenite and spinel are stable phase.(2)The effect of MnO content on the chromium distribution in stainless steel slag was investigated.Moderate amount of MnO reduced the content of chromium in the merwinite,dicalcium silicate and RO phase,and promoted the enrichment of chromium in spinel phase,realizing the stabilization of chromium in stainless steel slag.When the mass fraction of MnO in the slag was too high,? 8%in this study,a small amount of chromium was detected in the RO phase.(3)The precipitation behavior and crystallization enhancement of targeted phases in stainless steel slag were investigated.Adjusting the MnO content promoted the crystallization of merwinite,and improved the enrichment of calcium and magnesium in the merwinite and dicalcium silicate phases.The achievement is beneficial to the leaching of the calcium and the magnesium in the acidic solution system.(4)The effects of conditions on the leaching behavior of stainless steel slag in acidic solution system were investigated.In the nitric acid-based solution system,normal temperature,high acidity and long duration are conducive to the extracting of calcium and magnesium from stainless steel slag and the reduction of slag quantity.Prediction models of calcium and magnesium leaching yields and slag amount reduce was established and checked.(5)The practical potential of the proposed resource utilization process was clarified.On the basis of the achievement of modification and acid-based leaching,high purity calcium carbonate with calcite and vaterite as the main crystalline forms was successfully prepared by carbon dioxide mineralization storage method.Results proved that the new resource utilization process of stainless steel slag is feasible in the stabilization of chromium and the resources utilization of calcium and magnesium. |
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