What are the flotation technologies for bauxite?

Bauxite is an important aluminum-containing mineral aggregate, mainly composed of aluminum hydroxides such as diaspore, boehmite and gibbsite, and also contains a small amount of impurity elements such as iron, silicon, and titanium. Bauxite is a key raw material for the production of metallic aluminum and various aluminum products. Purification and impurity removal are particularly important, and flotation is one of the important methods for impurity removal in bauxite beneficiation. In this article, we will learn about the bauxite flotation methods?

Bauxite flotation is mainly based on the differences in the surface physical and chemical properties of aluminum minerals and gangue minerals. Aluminum minerals and gangue minerals are different in surface wettability, electrical properties, etc., and flotation is achieved by adding reagents to change their hydrophobicity. At present, the available flotation methods include positive flotation, reverse flotation and selective flocculation flotation.

1. Bauxite positive flotation

Positive flotation is to use the difference in the surface properties of aluminum minerals and gangue minerals to make aluminum minerals selectively attach to bubbles and float up, while gangue minerals remain in the slurry. In the process of bauxite positive flotation, collectors are usually added to enhance the hydrophobicity of aluminum minerals so that they can better combine with bubbles. During flotation, commonly used collectors include fatty acids, which can chemically react or physically adsorb with aluminum ions on the surface of aluminum minerals to make the surface of aluminum minerals hydrophobic. At the same time, in order to control the properties of the slurry and the flotation process, adjusters such as pH adjusters are added to adjust the pH of the slurry so that flotation is carried out within an appropriate pH range; inhibitors are used to inhibit the flotation of gangue minerals and improve the selectivity of aluminum mineral flotation.

The positive flotation process is relatively mature, with low requirements for equipment and relatively simple operation. When processing bauxite with coarse aluminum minerals and relatively large differences in floatability from gangue minerals, better flotation effects can be obtained to obtain higher-grade aluminum concentrates. However, due to the similar surface properties of aluminum minerals and some gangue minerals in bauxite, the selectivity of positive flotation is limited, and there are often more gangue minerals remaining in the concentrate, especially silicon-containing minerals, which makes it difficult to further improve the grade of the concentrate.

2. Bauxite reverse flotation

Reverse flotation is the opposite of forward flotation. It makes the gangue minerals attach to the bubbles and float up, while the aluminum minerals remain in the slurry. In the process of bauxite reverse flotation, the appropriate collector is selected according to the characteristics of the gangue minerals. For example, for silicon-containing gangue minerals, commonly used collectors are amine collectors (such as dodecylamine, etc.). Amine collectors can react with the surface of silicon minerals under alkaline conditions, making the surface hydrophobic and floating. At the same time, in order to inhibit the flotation of aluminum minerals, aluminum mineral inhibitors such as starch, dextrin and other natural polymers are added. They can be adsorbed on the surface of aluminum minerals, prevent the collector from interacting with aluminum minerals, and improve the selectivity of reverse flotation.

Reverse flotation can effectively remove silicon-containing gangue minerals in aluminum concentrate and improve the grade of aluminum concentrate, especially for bauxite with high silicon content and difficult to handle by direct flotation. Reverse flotation has obvious advantages. At the same time, the reagent system of reverse flotation is relatively flexible and can be adjusted according to the type and content of gangue minerals, with strong adaptability.

Amine collectors have certain pollution to the environment, and environmental protection issues need to be paid attention to during use and treatment. The reverse flotation process is more complicated than direct flotation, and has higher requirements for operating technology and equipment. It is necessary to accurately control the pH value of the slurry, the dosage of reagents and the flotation time, otherwise it is easy to affect the flotation effect. Moreover, the use of aluminum mineral inhibitors in the reverse flotation process may have a certain impact on the subsequent alumina extraction process, which requires further research and optimization.

3. Selective flocculation flotation of bauxite

Selective flocculation flotation is to use the selective flocculation effect of flocculants on aluminum minerals or gangue minerals to form larger flocs of the target minerals, and then flotation separation. For bauxite, flocculants are usually used to flocculate aluminum minerals first, while gangue minerals are in a dispersed state. Commonly used flocculants include high molecular polymers such as polyacrylamide derivatives. Under appropriate pH values and stirring conditions, flocculant molecules can be adsorbed on the surface of aluminum minerals, and aluminum mineral particles are connected to each other through bridging to form flocs. Then, through flotation, the flocculent aluminum minerals float up, while the dispersed gangue minerals remain in the slurry.

Selective flocculation flotation can reduce the difficulty of separating aluminum minerals from gangue minerals to a certain extent and improve the selectivity of flotation. For some bauxite ores with very fine embedded particles and serious mutual wrapping between minerals, this method can effectively achieve the enrichment of aluminum minerals. At the same time, this method can reduce the amount of flotation reagents used, reduce production costs, and has relatively little impact on the environment.

The process control requirements of selective flocculation flotation are very strict, and it is highly sensitive to parameters such as the type, amount, and stirring conditions of flocculants. If the parameters are not properly controlled, it is easy to lead to poor flocculation effect and affect the flotation separation effect. Moreover, the floating speed and stability of the flocs formed during the flocculation process during the flotation process also need to be further optimized to improve the flotation efficiency. In addition, the industrial application of this method is relatively small, and more practical experience accumulation and technical improvements are needed.

In addition to the above-mentioned flotation methods, some difficult-to-select bauxite can be combined with other beneficiation methods to form a joint process, giving full play to the advantages of each method and making up for the shortcomings of a single method, so as to achieve efficient recovery of bauxite and improve the quality of concentrate. However, no matter what kind of bauxite, the ore properties are different. It is recommended to conduct ore dressing tests and design suitable process plans through experimental analysis.