Investigation On Direct Preparation Of Low Ni-Cr Alloy Cast Iron From Bayer Red Mud By Carbothermal Reduction Smelting

Bayer red mud is a strongly alkaline solid waste generated in the production of alumina.It has seriously hindered the sustainable development of aluminum industry for its characteristics of very fine particles,complex chemical composition,environmental pollution and low comprehensive utilization.Therefore,direct preparation of low Ni-Cr alloy cast iron from red mud by carbothermal reduction smelting was investigated in the present work.In the process,Bayer red mud of Guangxi Pingguo county was taken as main raw material,mixed with laterite nickel ore containing nickel and chromium elements,which had similar chemical composition to red mud,was added into electric arc furnace in order to explore the possibility of red mud reduction to the cast iron with low Ni and Cr.This paper was focused on the following:first,thermodynamic analysis of selective reduction of valence metals from the red mud was carried out,and the experimental simulation of carbothermal reduction smelting under vacuum was further explored;second,based on the results of experimental simulation,a single electrode DC submerged electric arc furnace was designed,with which the experiments of direct preparation of low Ni-Cr alloy cast iron from red mud and laterite nickel ore were studied by carbothermal reduction smelting;at last,some key problems of the application of the low Ni-Cr alloy cast iron were investigated.The main conclusions are as follow:1.It was first time to proposed that reduction of Fe and the other elements in red mud could be realized by adding laterite nickel ore or other ores using single electrode DC submerged electric arc furnace,and the reducted alloy could by easely separated from the slag.Combined with the downstream industry,the performance of the low Ni-Cr alloy cast iron was explored,and it was expected that in the actual production situation,the usability of the alloy cast iron was superior to the existing materials,which has provided an experimental basis for the utilization of high alkaline Bayer red mud in industry.2.The thermodynamic analysis on carbothermal reduction of the red mud without and with laterite nickel ore addition indicated that the reducing sequence of main metal oxides in red mud was Fe>V>Cr>Mn>Ti>Si>Zr when the reaction temperature was between 700 ?and 1800 ?,and the reduction products were metal/graphite or metal/carbides.Si,Zr,Al,Mg and Ca elements were difficult to be deoxidized,and they would interact with each other to generate complex oxide compounds to form slag.With the addition of laterite nickel ore to red mud,the Ni,Cr,Mn,V,Ti elements would be deoxidized with the Fe elements.3.The addition of laterite nickel ore to red mud could obtain suitable basicity for reducing smelting,promote the reduction of various oxides and further enrich the elemental composition of the alloy iron.The results of vacuum carbothermal reduction showed that only Cr,Ti,Si elements could be deoxidized with the Fe reduction when red mud as only raw materials,and the total recovery and the Fe,Cr,Ti recovery were 76.45%,78.03%,45.64%and 6.08%,respectively.While with laterite nickel ore addition,the effect of carbothermal reduction smelting improved.The total recovery and the Fe,Ni,Cr,Ti recovery were 84.86%,79.44%,83.72%,58.96%and 39.74%,respectively.The alloy iron was mainly consisted of ferrous matrix and flake graphite phases.4.It had been discovered that low Ni-Cr alloy cast iron coluld be prepared directly from red mud with laterite nickel ore by carbothermal reduction smelting and refining with single electrode DC submerged electric arc furnace and medium frequency induction furnace.The content of Ni and Cr of the alloy cast iron were 1.59-2.06%and 0.76-0.83%,respectively.In addition,Ni and Cr elements were very evenly distributed in the ledeburite matrix of the cast iron.With the increasing of Ni and Cr contents,the hardness and corrosion resistance of the low Ni-Cr alloy cast iron were improved.5.Low Ni-Cr alloy cast iron,which had similar chemical composition to HT250,RuT380 and QT450 cast irons,was prepared by carbothermal reduction smelting.It was found that with the increasing of Ni and Cr elements,the phases in the microstructures of the alloy cast irons were not changed compared with the standard cast irons which were consisted of graphite,pearlite and a small amount of ferrite.But the morphology of these phases changed,especially the pearlite was more refined and its distribution was more uniform and dense.From the aspect of mechanical properties,the cast iron containing Ni and Cr was better than the one only containing Ni because the pearlite of the former was finer and more uniform.Compared with the HT250,RuT380 and QT450 cast irons,the tensile strength of the developed low Ni-Cr alloy cast iron was increased by 14.8%,31.3%and 44.5%,respectively.Moreover,the corrosion resistance of the cast iron was better.