Physical and acidification processes solve magnesite beneficiation challenges

Magnesium is a trigonal carbonate mineral with a calcite-type structure. Common crystal forms include hexagonal prisms, rhombohedrons, parallelepipeds, and trigonal scalenohedrons. It is often associated with minerals such as talc, quartz, and dolomite. Its chemical composition is primarily magnesium, with associated silicon, calcium, aluminum, iron, and other trace impurities.

 1. Physical Impurity Removal Processes for Magnesite

 01 Desiliconization and Calcification Reduction Methods

 Calcium-containing carbonate impurities are difficult to separate by flotation due to their low floatability. To remove large amounts of calcium-containing impurities such as silica and dolomite from magnesite, traditional magnesite desiliconization typically uses reverse flotation, while decalcification uses direct flotation. Reverse flotation typically uses amine collectors to capture silicate minerals and metal oxides. Direct flotation uses inhibitors such as water glass and sodium hexametaphosphate to reduce collector adsorption on the dolomite, thereby achieving magnesium-calcium separation.

 02 Iron Removal Methods

Magnetic separation is commonly used to remove iron impurities from magnesite. First, the mass content of iron and its isomorphs in the magnesite must be determined. Magnetic separation can only reduce the Fe₂O₃ content to 0.3% to 0.5% by weight. If the Fe₂O₃ content in the magnesite falls below this range, separation of MgO becomes more difficult, and the iron impurities are unevenly interbedded and finely divided within the magnesite, necessitating fine grinding to separate them.

 Low-grade magnesite is typically processed using a combination of direct and reverse flotation and magnetic separation to remove impurities such as calcium, silicon, and iron. This method is relatively cost-effective. However, when processing ultrafine and low-grade magnesite, chemical methods are more commonly used for impurity removal due to high flotation reagent consumption, lengthy processes, and high energy consumption. Although traditional mineral processing methods using a combined reverse flotation-direct flotation-magnetic separation process can improve the grade of magnesite, flotation requires a higher grinding fineness to effectively remove fine calcium and iron impurities from ores. Otherwise, only surface impurities are removed, which weakens internal capture and limits the separation of magnesium oxide.

 2. Magnesite Ore Acidification and Impurity Removal Process

Magnesium oxide has a wide range of uses. The hydration of activated magnesium oxide to produce magnesium hydroxide is a simple, environmentally friendly process, resulting in a uniform, controllable product morphology. Currently, there are two main methods for producing activated magnesium oxide from magnesite: chemical leaching and calcination, including acid leaching, ammonium leaching, and carbonization; and direct calcination.

 01 Sulfuric Acid Acidification Method

 The sulfuric acid acidification method for producing magnesium oxide primarily uses magnesite and other ores as raw materials. These are calcined and then chemically reacted with sulfuric acid. The resulting magnesium sulfate solution is filtered and then reacted with ammonium bicarbonate. The resulting solution is then thermally decomposed, filtered, and precipitated to obtain basic magnesium carbonate. The resulting product is then dried and calcined to obtain the final activated magnesium oxide product.

 02 Hydrochloric Acid Acidification Method

The hydrochloric acid acidification method generally uses light-burned powder, produced by calcining magnesite, as raw material. Compared to the sulfuric acid method, the hydrochloric acid acidification method uses less ammonium bicarbonate and has lower impurity requirements for the hydrochloric acid. Industrial hydrochloric acid can also be used as the raw material for production. Furthermore, the hydrogen chloride gas generated by the volatilization of basic magnesium chloride during the calcination process can be recycled, increasing acid utilization and offering the advantages of low cost and high efficiency.