| In recent decade, the development of economy has led to a great demand for the stainless steel. However, the resources of laterite and chromite are nearly all imported from overseas because of the reserves of chromium in China are small relative to the whole world. Moreover, with the continuous depletion of high grade ores, the fine ores and concentrates becomes the main raw material for the preparation of stainless steel. In order to implement the transition from the big iron&steel nation to the strong iron&steel nation and reply to increasingly ardent competition of stainles steel market, It is neeessary to how to use the low grade ore and reduce production cost. The process of producing stainless steel master alloys by smelting reduction in a small blast furnace has been put forward in this thesis. And fruitful researeh have been carried out according to the main line of sintering processes and reduction separation mechanisms of Ni-Cr Composite Sinters.Firstly, the agglomeration of fine ores and concentrates becomes very important in order to avoid causing the increase of production expenditures. Generally, the main technic for fine ores and concentrates agglomeration is sintering process. However, the granulation and sintering itself still need improvement. According to the analysis on raw materials, the sintering processes of laterite nickel ore and chromite have the problems of high energy consumption and poor granulation. It was largely created by the following two reasons:on the one hand, the small and smooth South Africa chromite concentrate ore is hydrophobic, and is difficult to adhere to others; on the other hand, the nickel laterite is dried from original moisture content of30%to moisture content of2%, a great deal of energy is consumed. The holes due to wate was removed from the mixture lead to reduced quality of sinter. Hence, based on the theory of granulation and sintering, sintering processes of Ni-Cr composite sinters were carried out. As for the sinter, its mineral phases are spinel and iron silicon silicate, and the quality mainly depends on the recrystallization of spinel and solidification of silicate liquid phase whice was produced mainly from nickel laterite.Secondly, Factsage software was used to calculate the physical chemistry changes at different parts of blast furnace. So the whole mechanism about chromite has been obtained. The analysis showed that the reduction of mixed charge during the diopping in the blast furnace was found to occur in two stages. Firstly, mixed charge was reduced indirectly with CO. The iron oxides and nickel oxides in mixed charge would get reduced. The second stage was involved the dissolution of chromite ore into the slag, and direct smelting reduction was initiated by solid carbon. The melting point of alloy was increased with the increase of Cr content, but reduced with the increase of C content. Carburization of molten alloy is3%～6%.Finally, the smelting reduction of mixed charge during smelting was simulated in laboratory. The effects of temperature and fiux were studied. The results proved that the recovery rate of Ni、Fe、Cr increased with the roasting temperature increasing to1600℃. Most of Ni、Fe、Cr are reduced with adding35%CaO, and roasting for60min at1600℃. Then conventional magnetic separation was carried out. The content of Ni、Fe and Cr are1.82%、75.12%and19.33%in alloy nugget prepared by this method. And the recovery rate of Cr is84.46%, which indicates that a high recovery of chromium from mixed charge is achieved indeed. |
PDF Full Text Request