Research On The Phase Compositions And Leaching Properties Of Sintering Products In CaO-Al₂O₃-SiO₂System

In China, the bauxite mainly exists in the form of diaspore bauxite, with high aluminum, high silicon, low iron and low Al/Si ratio. Most of the current domestic enterprises are using bauxite less than5grade to product alumina. The rapidly depleted bauxite resources lead to the urgently requirement of innovation which can make most of the bauxite of low quality (A/S is about4).Bayer process, lime-Bayer process and ore-dressing Bayer process are three traditional methods in alumina production, the alumina recovery rate is too low and the consumption of alkali is too high that will not only affects the costs and resource utilization but also failing to meet the national requirements to develop sustainably. In the sintering step of the traditional soda-lime sintering process, mixed combining method process and series process, the sintering clinker are sprayed into the kiln when it is still wet, so it consumes a lot of energy. In addition, the evaporation of carbonization precipitation also need abundant of energy. Therefore, research on the phase compositions and leaching properties of sintering products in CaO-Al2O3-SiO2system, for the further improvement and innovation lime sintering has important theoretical significance.In this paper, the writer use pure chemicals as raw materials to study the CaO-Al2O3-SiO2system (Al-Si ratio from1to5) at different sintering temperature. Through the research in the compositions of the sintered products, self-disintegrating and alumina digestion property, the condition and forming rules of12CaO·7Al2O3(with good dissolution properties) and γ-2CaO·SiO2(with self-disintegrating behavior) is made clear. The main test results are as follows:When the A/S is3-5, the best sintering temperature of the CaO-Al2O3-SiO2system is1350℃, the best ratio of added calcium amount and the alumina amount(C/A) is around1.4, the main sintering phase is12CaO·7Al2O3and y-2CaOSiO2,the leaching rate of alumina reaches90%or even higher. When A/S=1, the best sintering temperature of CaO-Al2O3-SiO2system is1350℃, the main phase is12CaO·7Al2O3with small amount of CaO·Al2O3and γ-2CaO·SiO2, the best ratio of added calcium amount and the alumina amount (C/A) is1.6, and self-disintegrating ratio reaches95%, alumina leaching rate is90%or more.Adding a small amount of Na2O to the clinker can improve the leaching rate of alumina, and reduce the sintering temperature and amount of calcium to add. Na2O added when C/A is low (about1.0) will enter the C12A7lattice instead of the missing CaO. With the increasing N/A, C2AS、CA and CA2in clinker will constantly change into C12A7, which can significantly improve the leaching properties of clinker. During the sintering process, adding impurities like Fe2O3, FeO and TiO2can not significantly influence the leaching property and the formation of calcium aluminate.Finally, for the analog bauxite and practical research, the mian phase is12CaO·7Al2O3and γ-2CaO·SiO2, aluminum oxlide leaching rate higher than90%, in low calcinm (C/A=1.0), increasing N/A can improve the dissolubility of actual ore clinker.