Intermittent Microscopic Observation of Structure Change and Mineral Reactions of High Phosphorus Oolitic Hematite in Carbothermic Reduction

摘要

Change of the typical structure of high phosphorous oolitic hematite during carbothermic reduction process have been studied using intermittent observation. It indicated that there were four change stages, including crack formation and growth, mineral diffusion, mineral crystalization, mineral crystal migration and reaction. Eventually, inherent oolitic structure was completely destroyed. Mineral reactions were also investigated and discussed along the structural change, giving much understanding of thermal behavior of the oolitic hematite during reduction. The results showed a variety of mineral reactions occurred, such as decomposition of CaCO_3, reduction of iron oxide, dehydration and decomposition of chlorite, decomposition of fluorapatite, and transformation of gangues. SiO_2 and Al_2O_3 decomposed from chlorite can not only combine with FeO to form Fe_2SiO_4 and FeAl_2O_4, which hindered the reduction of iron oxide, but also promoted the decomposition of fluorapatite to form Ca_3(PO_4)_2 in the presence of SiO_2. Then, Ca_3(PO_4)_2 was reduced to form CaSiO_3 and P_2, which was the main process of dephosphorization. However, a small amount of fluorapatite diffused into iron oxides, which made it difficult to separate by mechanical crushing and screening.