Knowledge Management System Of Institute of process engineering,CAS
|导师||曹宏斌 ; 任彥萍|
|关键词||钢铁工业 六价铬 总铬 三价铬 产污节点 流向分析|
A potent carcinogen and mutagen which can lead to distortion to humans announced by the World Health Organization and one of the five major heavy metal pollutants strictly controlled by our country, hexavalent chromium [Cr(VI)] is the major associated harmful element in the iron and steel smelting process. It is usually discharged together with the “three waste” (waste water, waste gas and waste residue) of the smelting process, and as a result, it will cause heavy environmental pollution and put a great threat to the health of living beings. However, for a long time, not having a clear-cut background for the sources of hexavalent chromium pollution in the steel industry of our country, together with the decentralization of pollutions and the insufficiency of the effective statistics has prevented the industry from forming a technical basis for effectively controlling and coping with the hexavalent chromium pollution. By analyzing the evolution of the morphology and concentration of chromium in the production process of steel through the material flow analysis (MFA) approach, this paper, in the three fields—waste residue, waste water and waste gas—where hexavalent chromium goes, aims to thoroughly present the directions the hexavalent chromium flows and its paths in the production process of steel, therefore, provide an important basis for the analysis of the pollution sources of hexavalent chromium in steel industry, and provide a reference for the further cuts and controls of hexavalent chromium in steel industry. The main content and results of the research are as follows:(1) Through literature research and consulting experts, analysed the manufacturing technique and process of the long steel-making process; by selecting the overall process of mining, carbonizing, sintering, iron-making, steel-making and steel rolling, and the two key sub-sectors of stainless steel and titanium alloy as the research system, systematically sorted out related procedures and the pollution node of sub-sectors, and the emission of waste water, waste gas and waste residue.(2) On the basis of different directions and paths hexavalent chromium goes to, clarified its inflow and outflow in the production process, and clarified the main procedures polluted by chromium in the production process of steel. And the result shows that chromium widely exist in the production process of steel, and hexavalent chromium involves in all five procedures: mining, chromium slag sintering, iron-making, steel-making and steel rolling, and mainly in the procedure of chromium slag sintering and steel rolling.(3) In production process of steel, chromium comes from such sources as minerals, the Cr2O3, the chromate and the dichromate produced by eliminating chromium slag; besides, passivation solution in process of passivation and the Cr2O3, chromic anhydride and chromate in the oxide scale of stainless steel can also bring chromium. Finished products containing hexavalent chromium are mainly the concentrates and tailings at the stage of mining and dressing, the sinters using sintered chromium slag, the hot metal and the molten steel in the procedure of iron- and steel-making, and the passivation films on the surface of the passivated steel plate. Respectively, the chromium in the minerals in the process of mining and dressing takes up 95.9% of the general input, the chromium in the hot metal and the molten steel in the process of iron- and steel-making 99.9% and 82.44%, and the chromium in steel plates in the process of passivation 98.8%. And the main production points of hexavalent chromium come down to two parts: the process of passivation and the process of stainless steel pickling.(4) Clarified the main points where the hexavalent chromium lies in the emissions of the terminal “three wastes” (waste gas, waste water and waste residue). The waste gas containing hexavalent chromium mainly consists of the dust produced when taking chromium slag as the raw material for sintering, of the mist of chromic acid produced in steel-making and in the passivation of steel rolling. The waste water containing hexavalent mainly comes from the waste water in mining and dressing concentrates and tailings, the effluent in the water sealing zipper sewage reservoir after applying chromium slag in sintering process, the effluent containing Cr6+ produced in passivation in steel-making and in the process of electroplating, and the effluent of stainless steel pickling. The waste residue containing hexavalent chromium mainly comes from the slag produced in sintering, iron- and steel-making, and from the sludge containing chromium produced in the process of passivation of steel rolling and stainless steel.(5) The flow diagram and flow summary graph of hexavalent chromium in steel production the main process Through literature, experimental data and the production process node, and by means of mass balance model, achieved the mass balance among the process of inflow, generation and diffusion of hexavalent chromium and the associated pollutants in five processes and two key sub-sectors.(6) Based on the terminal emission of the “three wastes” of hexavalent chromium in steel industry, proposed the treatment principles and trend. The waster residue ranks the highest proportion in the three wastes of hexavalent chromium, waster water takes the second place, and waste gas takes a less proportion. Besides a certain quantity of chromium element, there is also a large quantity of valuable metal in waste residue, such as iron, zinc and nickel, which should be recycled and reused as the raw material for other techniques. At present, what the steel industry applies in dealing with waste water remains the chemical methods, which should be optimized and improved; therefore, the research and promotion of a physical and biological way to deal with waste water should be accelerated, and waste gas should be purified and trapped. In terms of raw material substitution, low-chromium and free-chromium passivation technique should be developed so that the inflow of hexavalent chromium can be reduced from the source.
|王妍. 钢铁行业六价铬元素流向分析[D]. 北京. 中国科学院研究生院,2015.|
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