Alumina production requirements for bauxite quality

Quality bauxite direct impact on technical and economic indicators of alumina production process and selection of alumina production. The quality of bauxite is generally considered in terms of aluminum to silicon ratio, alumina content and aluminum mineral type. The dissolution properties of bauxite of different aluminum mineral types are quite different. However, due to the fact that China's bauxite mine is different from other countries in the world, 99% of the reserves are diaspore-type bauxite, most of which are sedimentary bauxite, with high aluminum, high silicon and low iron . Characteristics, therefore, the aluminum to silicon ratio of bauxite is the most important quality indicator.

The ratio of aluminum to silicon of bauxite which is suitable for different alumina production methods is shown in Table 1. Among the three alumina production methods, the Bayer process has obvious advantages such as simple process, low energy consumption, good product quality and low production cost. However, since SiO ₂ in the ore enters the red mud in the form of hydrated sodium aluminosilicate (Na ₂ O·Al ₂ O ₃ ·1.7SiO ₂ ·nH ₂ O), the loss of Al ₂ O ₃ and Na ₂ O is caused. Therefore, the Bayer process is suitable for the treatment of bauxite with a high aluminum to silicon ratio. More than 80% of the bauxite aluminum-silicon ratio in China is <9. Therefore, the domestic alumina production process based on domestic bauxite is mainly the sintering method and the combined method. Since both methods require sintering, a series of problems are caused by a complicated production system, a relatively large capital investment, and high energy consumption. Table 2 compares the main consumption of alumina plants at home and abroad. It can be seen that the consumption of bauxite and alkali consumption in alumina production in China is significantly lower than that in foreign alumina plants, but the energy consumption is much higher than them. In the composition of alumina production cost, China's energy cost accounts for 43%, which is 1.65 times of the corresponding foreign cost. This is the most important reason why China's alumina production cost is higher than foreign advanced indicators. With the shortage of bauxite resources and the deterioration of quality, China's alumina industry has to face the problem of large-scale utilization of low-grade bauxite. If the aluminum-to-silicon ratio of bauxite cannot be increased, and the energy price continues to rise, the technical and economic indicators of alumina production in China will definitely deteriorate further, which will have a serious impact on the production cost and competitiveness of China's alumina industry.

Table 1 Aluminum-silicon ratio of bauxite suitable for treatment of various alumina production methods

Table 2 Comparison of main consumption indicators of alumina plants at home and abroad (2003)

Chinalco Zhongzhou Branch improves the ratio of aluminum to silicon in bauxite by demineralizing by beneficiation . The use of beneficiation-Bayer process to produce alumina can reduce energy consumption by 50% and production cost by 20%. The cost of alumina production is basically the same as that of traditional Bayer. Flat. With the advancement of technology in the alumina industry, it has become possible to treat aluminum-silica with a ratio of aluminum to silicon of >9 by intensive sintering. Therefore, the high aluminum-silicon ratio raw material is the most important requirement of the alumina industry for the quality of bauxite. The main purpose of bauxite ore dressing in China is to demineralize the ore, obtain high-aluminum-silicon ratio concentrate, and simultaneously increase the content of Al ₂ O ₃ in the concentrate.