How Do You Get High-quality Raw Materials for Alumina Products?

Raw materials will be of great significance for the production of refractories, influencing its bulk density, porosity, impurity content, thermal shock resistance and so on. We have done researches on how to select the raw materials and here are the basic process for manufacturing upscale refractories or ceramic products. Beneficiation and homogenization are key steps!

(1) Beneficiation:

① When did beneficiation get popular in China?

The problem of bauxite beneficiation and purification was raised in China in the 1970s. From the 1980s to the 1990s, many achievements have been made in the research of bauxite beneficiation and purification. In recent years, some of the results have been applied in production.

② Beneficiation methods

There are many beneficiation methods of high alumina, such as washing, flotation, magnetic separation, biological separation, removing SIO2, TiO2 from high alumina clay by using aluminum fluoride. The alumina content was increased by the reaction of acid and alkali with the impurity in the high alumina soil. The bauxite clinker after combustion was ground and soaked with hydrochloric acid to remove iron, calcium and magnesium. Among them, the most widely used is the combined process beneficiation, such as washing--magnetic separation--flotation, etc. . Washing is the simplest method of mineral processing, can be used with a vibrating screen scrub machine, drum screen, slow rotation of the mixer and so on to wash away the surface of the minerals attached. Based on the characteristics of friability and argillation of silicon-containing minerals, the fine-grained material is washed off and the Al-Si ratio is increased. In order to further increase the content of alumina and reduce impurities, the washed ore can be ground for magnetic separation and flotation. For example, by flotation, we can obtain high aluminum products and low aluminum products, intermediate products and then through strong magnetic iron removal, flotation detitanium process, and finally obtain high aluminum products with a ratio of aluminum to silicon greater than 9, as raw materials for Bayer process to produce alumina, a low-alumina product with an Al-Si ratio of approximately 2.55, used as a refractory material for synthesis of mullite.

③ Sucessful practices in beneficiation

We also try to separate low-grade high-alumina ore with new technology of tailless separation, and select a large number of locally accumulated crushed ore, the main product is Al2O3≥75% , using rotary kiln with preheater to produce high-alumina homogenizing material; Another concentrate with an Al-Si ratio greater than 8 is used for the production of alumina; tailings are used for the synthesis of mullite to achieve tailings-free production.

④ Other methods availble

There are electric melting method: using the basic principle that the affinity of aluminum to oxygen is greater than that of iron, silicon, titanium, etc. . By controlling the amount of reducing agent (carbon) , the main impurities in high alumina bauxite are reduced by reduction smelting method, the ferro-silicon alloy is separated from corundum melt, and the brown corundum or sub-white corundum with the required crystallization can be obtained. When brown corundum is smelted, the AL2O3 content of high alumina is more than 76% . The higher the AL2O3 content is, the better the technical index of smelting corundum is. The content of Al2O3 in sub-white corundum is more than 98% to 98.5% by adding carbon materials in the process of smelting brown corundum. The former and middle stages of smelting are reduction smelting, the latter stage is oxidation refining, and decarbonization is carried out by adding decarbonizing agent. AL2O3 content ≥85% is required in high alumina bauxite for smelting sub-white corundum.

(2) homogenization:

①Why do we need homogenization?

In addition to Al2O3, there are SiO2, TiO2 in natural high-alumina rockfill. Refractory, Fe2O3 and other impurity components, often the same ore bed, the same section, the same piece of ore chemical composition fluctuations are of very uneven texture. According to international standard, the fluctuation range of Al2O3 content is 1% ~ 2%. To meet this index figure, homogenization treatment is a necessary step.

②How can we achieve raw material that is up to standards?

Basically, there are two kinds of homogenizing process: semi-dry process and wet process. Dry process is the direct grinding of dry materials. Wet process is the basic process of water grinding, according to the chemical composition of the ore, of batching grinding, fine composition, molding, drying, burning of high alumina clay. One of our partners have tried to use ball-forming disc semi-dry method ball, the heavy oil rotary kiln successfully calcined product with Al2O3 content ranging from 1% to 2%. Wet grinding can easily achieve 325 mesh or more, the specific surface area is large, the calcination temperature is 30-50 ℃ lower than dry method, the volume density is 0.1 ~ 0.3 g/cm³denser, the iron can be removed by high-pressure electromagnetic wet method, the working condition is good, and the environment is not polluted. To sum up, homogenization treatment does not change the chemical composition of raw materials, and by using high-grade raw materials and low-grade raw materials to produce a predetermined composition of homogenized materials, a large number of medium-and low-grade high bauxite and crushed ore can be fully utilized.

(3) Do you know the standard for alumina refractories?

	Al2O3	Fe2O3	TiO2	Bulk Density
GL-90	≥89.5	≤1.5	≤4.0	≥3.35
GL-88A	≥87.5	≤1.6	≤4.0	≥3.20
GL-88B	≥87.5	≤2.0	≤4.0	≥3.35
GL-70	70~80	≤2.0		≥3.35