Research On Optimization Of Granulation And Sintering Process Of Chromite Ores

Chromium is an essential element for the production of stainless steel, while thechromium is mainly extracted from the chromite ores. In recent decade, the rapidincrease of stainless steel in China has led to a great demand for chromite ores, whichare nearly all imported from overseas because of the reserves of chromium in Chinaaccounts for only0.15%in the whole world. Moreover, with the continuous depletionof lump ores, the agglomeration of fine ores and concentrates becomes very importantin order to avoid causing the increase of production expenditures.Generally, the main technic for chromite agglomeration is sintering process;however, the granulation and sintering itself still need improvement. Hence, based onthe theory of granulation and sintering, the researches on optimization were carried outby using chemical analysis, thermo analysis, XRD and SEM analysis, etc. The rawmaterials were supplied by a ferrochrome alloy plant, and the chromite ores were SouthAfrica chromite concentrate （UG2）, which is beneficiated from the tailings of platinumore, Turkey fine ore （TC） and South Africa fine ore （LG6） respectively.Firstly, according to the analysis on raw materials, it was found that the poorgranulation was largely created by the following two reasons: on the one hand, the smalland smooth UG2ore is hydrophobic, and is difficult to adhere to others; on the otherhand, the returns is nearly the same to the raw UG2ore, which result in lack of adequatenuclear particle and make the granulation worse. Therefore, it is necessary to add morenuclear particles and strengthen the adherence. LG6and TC ores are proper forgranulation improvement due to their good hydrophilicity and size distribution. Inaddition, the mineral phase of all three chromite ores are the spinel （Fe,Mg）（Cr,Al）₂O₄,the differences are there are more silicon and magnesium oxides in TC ore, which hasthe similar phase to the chlorite, i.e., the TC ore is probably favorable for the generationof liquid phase during sintering process.Secondly, the optimization experiments on granulation process showed that, theproper water content is in range of11¹3%. It is possible to make the granulation withonly TC and UG2ores, and more TC ore can bring out better granulation result. Besides,the damp milling method is unsuitable for the granulation of UG2ore.Finally, the sintering results proved that the proper carbon dosage is8.14%. Thesinter of TC and UG2can meet the requirement of quality, and the silicon and magnesium oxides in TC is indeed beneficial for reducing the addition of flux, hence, interms of its profit for granulation and the decrease of bentonite and chlotite, it is fairlyeconomical to use the UG2and TC together for sintering. When the UG2was sinteredwith LG6, only7.2%carbon and lower flux can achieve a very satisfied result, whichmeans higher chromium grade and more economical for the melting in electricityfurnace. As for the sinter, its mineral phases are spinel and iron silicon silicate, and thequality mainly depends on the recrystallization of spinel and solidification of silicateliquid phase. Furthermore, it is better to choose the simatic flux to modify the content ofsilicon and magnesium oxides simultaneously so as to promote the generation of lowmelting phases. And the water quenched slag from nickel laterite production is a verygood choice to be as the flux, due to its proper chemical composition and goodself-fluxing nature without extra energy consumption for reaction; under the samecondition, both the yield and the shatter strength of sinter can reach approximate90%.