Phosphate rock is a fundamental raw material in various fields such as agriculture, chemical industry, and new energy. Its mineral composition is complex and contains many impurities, mainly including silicates, carbonates, iron and aluminum oxides, rare earth elements, etc. The methods chosen for processing vary depending on the impurities present in the phosphorus. Scientific and reasonable mineral processing techniques that effectively enrich phosphorus minerals and remove impurities are key to the efficient utilization of phosphate rock resources. So, what are the different processes? Let's explore together!

1. Beneficiation process of siliceous phosphate ore

The main impurity in siliceous phosphate ore is silicate. In this type of ore, phosphate minerals are closely associated with siliceous gangue, making mineral processing challenging. Given its characteristics, mineral processing plants often employ reverse flotation to separate phosphate minerals from gangue. The process generally follows the sequence of crushing, grinding, and separation (reverse flotation).

Crushing: The process of coarse crushing followed by medium crushing or coarse crushing followed by fine crushing is commonly adopted to gradually reduce large pieces of phosphate ore to a suitable particle size, with a maximum size of no more than 15mm, to facilitate subsequent grinding operations.

Ore grinding: Fine grinding is performed on crushed minerals to facilitate the thorough dissociation of phosphate minerals from siliceous gangue. Typically, equipment such as ball mills and rod mills are employed, coupled with spiral classifiers or hydrocyclones to form a closed-loop grinding system. During the grinding process, the particle size is usually controlled to achieve a -200 mesh (0.074mm) content of 70-80%.

Reverse flotation: After grinding, the slurry enters the reverse flotation process, where inhibitors such as water glass are added. Water glass can selectively adsorb onto the surface of phosphate minerals, forming a hydrophilic film that inhibits the floatation of phosphate minerals. At the same time, amine or modified fatty acid collectors are added, which can interact with the surface of silicate gangue, making it hydrophobic. Under agitation and aeration conditions, the hydrophobic silicate gangue adheres to the surface of bubbles and floats to the surface of the slurry, forming a foam layer, while the inhibited phosphate minerals remain in the slurry. To further improve the grade of phosphate concentrate, multiple stages of roughing, cleaning, and scavenging operations are usually set up. Through multiple flotation separations, silicate impurities are removed to the greatest extent possible.

Concentrate dewatering: The post-dewatering phosphate concentrate contains a large amount of water, which needs to be reduced through dewatering and filtration to facilitate subsequent processing. Generally, a thickener is first used to concentrate the concentrate, increasing its concentration from 20%-30% to 50%-60%. Then, a filter is employed to further reduce the water content of the concentrate, bringing the final product's water content down to below 12%, thus obtaining phosphate ore products that meet quality requirements.

2. Beneficiation process of calcareous phosphate ore

The main impurities in calcareous phosphate ore are carbonate minerals, such as calcite and dolomite. For this type of phosphate ore, the positive flotation process or the roasting-digestion process is usually used for beneficiation and impurity removal.

Direct flotation: During the direct flotation process, sodium carbonate is added to the slurry as an adjuster to adjust the pH value of the slurry to 8-10, creating a suitable alkaline environment for the action of reagents. At the same time, fatty acid (oleic acid, sodium oleate) collectors are added, which can chemically react with the metal ions on the surface of phosphate minerals to form a hydrophobic film, allowing the phosphate minerals to adhere to the bubbles and float up. After roughing, cleaning, and scavenging processes to enrich the phosphate concentrate, the final phosphate concentrate product is obtained through concentration and filtration operations.

Roasting-digestion process: It involves directly roasting the crushed product at high temperatures (800-1000°C). During the process, carbonate impurities undergo decomposition reactions, with calcium carbonate decomposing into calcium oxide and carbon dioxide, and magnesium carbonate decomposing into magnesium oxide and carbon dioxide. After cooling, the roasted ore is digested using water or dilute acid to dissolve the alkaline oxides such as calcium oxide and magnesium oxide produced by decomposition into the solution. Then, through processes such as water washing and filtration, impurities are removed, and the filter cake is dried to obtain phosphate ore products.

3. Mixed phosphate ore beneficiation process

Mixed phosphate ore contains various impurities such as carbonates and silicates, and the ore properties are complex. A single mineral processing method is difficult to achieve ideal separation results, so the stage grinding-classification-combined flotation process is usually adopted.

Stage grinding and classification: It is generally divided into two or three stages of grinding. In the first stage, the ore is ground to a certain particle size, allowing some phosphate minerals to undergo preliminary dissociation from gangue. Then, qualified particle size of ore pulp is separated out through classification equipment, and the coarse particles are returned for re-grinding. Through stage grinding, the phenomenon of over-grinding caused by grinding too finely at once is avoided, reducing the loss of fine-grained phosphate minerals and improving grinding efficiency.

Combined flotation: Based on the content ratio and properties of carbonate and silicate impurities in the ore, positive flotation or double reverse flotation can be used initially to remove carbonate impurities. After removing carbonate, the grade of phosphate ore can be gradually improved through multi-stage grinding and multiple flotation operations, effectively removing various impurities.

The above is an introduction to several different beneficiation process flows for phosphate ore. In actual beneficiation plants, different types of phosphate ore, such as siliceous phosphate ore, calcareous phosphate ore, and mixed phosphate ore, require targeted beneficiation process flows due to differences in impurity types, mineral composition, dissemination characteristics, and grade levels. At the same time, various factors such as production costs, environmental protection requirements, and equipment selection need to be comprehensively considered. Through continuous experimental research and process optimization, an economical, efficient, green, and environmentally friendly beneficiation process flow for phosphate ore can be formulated, thereby achieving effective utilization and sustainable development of phosphate ore resources.