The mainland is rich in magnesite resources, with proven reserves of 3.4 billion tons, accounting for 26% of the world's total, mainly distributed in Liaoning, Shandong and other places. With the decreasing of high-grade easy-to-select magnesite resources year by year, low-grade magnesite and tailings left by extensive mining methods in the early years have become the main sources of magnesia materials in recent years.
magnesite
Magnesite is a trigonal carbonate mineral with magnesium as the main chemical component, and associated with silicon, calcium, aluminum, iron and other trace impurities. The process of magnesite beneficiation and purification is the process of increasing magnesium content and reducing impurity content. So what are the common methods of magnesite purification and impurity?
1. The occurrence form of impurities in magnesite
1. The occurrence form of calcium
The impurity calcium in magnesite is mainly in the form of the independent mineral dolomite, which is present in magnesite in the form of inclusions or intergranular gaps. The dolomite mostly presents granular, irregular and aggregate shapes, and is interspersed with vein-like filling along the magnesite fractures.
2. The occurrence form of silicon
The silicon content in magnesite is usually ≤3% (w), which is mainly found in siliceous inclusions and intergranular gaps, which affect the physical properties of magnesite, such as hardness and acid solubility. Whereas, less silicon is present in solid solutions.
Silicon is mainly found in minerals such as quartz, talc, clinochlorite, scapolite, tremolite, and sericite.
3. The occurrence form of iron
The occurrence forms of iron in magnesite mainly include pyrite, limonite, pyrrhotite, magnetite and hematite. In addition, there is also an iron in the form of magnesium carbonate homogeneous structure in magnesite, which cannot be separated by physical beneficiation methods, but when the grinding fineness is 0.074mm, FeCO3 in magnetite, limonite and chlorite embedded with magnesite particles can be basically separated.
Magnesite flotation
2. Physical method of magnesite purification and impurity removal
1. Desiliconization and calcium reduction method
Flotation method is a common and mature beneficiation process in magnesite beneficiation, in which magnesite desilica generally adopts reverse flotation, and decalcification often adopts positive flotation.
- Reverse flotation refers to the use of amine collectors to capture electronegative silicate minerals and metal oxide minerals by means of cationic-NH3+ groups with hydrophobic hydroxyl groups.
- Positive flotation refers to the use of inhibitors such as sodium silicate and sodium hexametaphosphate to reduce the adsorption of collectors on dolomite, so that magnesite and dolomite can be effectively separated, so as to achieve the purification effect.
In addition to flotation method, electric separation, thermal separation and gravity separation can also achieve the purpose of desiliconization and calcium reduction to a certain extent.
2. Iron removal method
Magnetic separation is a commonly used method to remove iron impurities from magnesite. Magnetic separation is often required in combination with other beneficiation processes to reduce Fe2O3 content. Strong magnetic separation, wet strong magnetic separation, and dry magnetic separation methods can be used to find a suitable magnetic separation method by adjusting the magnetic separation intensity.
However, the magnetic separation method is mainly aimed at magnesite with high iron content and is suitable for use in combination with other beneficiation methods.
Magnetic separation
3. Chemical method for magnesite purification and impurity removal
Common chemical methods include ammonium salt method, hydration method, acid leaching method, and carbonization method. The chemical treatment method generally needs to roast magnesite at a temperature of 700~900 °C to obtain active 6 After lightly burning magnesium oxide, different agents are added to separate magnesium ions in different forms of magnesium salts, and then pyrolysis, calcination and other treatments are carried out to obtain high-purity magnesium oxide products.
In addition, the researchers also remove impurities in magnesite by heating, such as chlorination roasting. The advantages of chlorination roasting are its low energy consumption, high purification efficiency, high recovery rate, and no waste generation.
Although the chlorinated roasting method has many of the above advantages, it is rarely used in magnesite purification. The reason why it has not been widely used is that this method still has some problems that are difficult to overcome, such as the strong corrosiveness and toxicity of gaseous chlorinating agents, and the high requirements for anti-corrosion sealing of equipment; Although solid chlorinating agents are less corrosive, they are less effective.
Fourth, the future development direction of magnesite purification and purification
1. The development direction of flotation method should focus on the development of environmentally friendly and recyclable flotation reagents, so as to improve flotation efficiency and reduce energy consumption;
2. The development direction of chemical purification method is to develop recyclable leaching agents;
3. The chlorination roasting method is expected to become a breakthrough in the innovation of magnesite purification technology, as long as the technical problems are overcome, it is possible to replace the flotation method as a widely used magnesite purification method in the future.