What Are the Roles of Coagulants in Mineral Processing?

Coagulant, also known as coagulant and flocculant, is a substance that causes sols to coagulate. It is mainly electrolytes such as salts, whose ions can neutralize the opposite charge of colloidal particles and cause coagulation. It is a substance used to clarify turbid water and purify sewage. Common coagulants include aluminum sulfate and alum, which, when added to ice, undergo a chemical reaction and form flocs through stirring, promoting the precipitation of suspended impurities and thus purifying water.

Classification of coagulants

Organic coagulants can be divided into: first strong coagulants, which coagulate rapidly, such as ammonium acetate and acetic acid solutions, calcium nitrate solutions in alcohols (methanol or ethanol); second slow coagulants, which coagulate slowly, such as sodium fluorosilicate solutions, bentonite and aluminum hydroxide suspensions in water; third thermal coagulants, which are substances that can coagulate latex at a certain temperature. The most widely used substance is zinc ammonia complex ion, which can be prepared from zinc oxide or zinc chloride and ammonia water. In recent years, various synthetic polymers such as polyethylene glycol methyl ether and polyoxypropylene glycol have also been used.

Additionally, coagulants such as alum and aluminum sulfate used to purify water, gypsum used to coagulate tofu, and acetic acid used to precipitate casein from milk are all considered coagulants. Partially hydrolyzed sodium polyacrylonitrile or apple acid polymer hydroxylated with acetic acid, when added to soil, can prevent soil erosion and enhance soil conservation. Water molecule coagulants can react quickly with water molecules and expand by up to 30 times when mixed in a ratio of 1:4 to 1:12, forming a porous gel-like substance after 5 to 15 seconds. They are widely used to handle various water leakage situations encountered in construction, such as large holes of water seepage, crack seepage, point seepage, surface seepage, and rock fissure water infiltration.

The functional role of coagulants in mineral processing

In the mineral processing process, it is difficult to separate fine mineral particles using flotation or other mineral processing methods, but some minerals can be effectively separated by adding coagulants to coagulate and settle fine mineral particles (or useless ore slurry). The zeta potential carried on the surface of suspended particles of different minerals is not the same. Particles carrying the same charge repel each other and remain in a dispersed state, making it difficult to coagulate, while particles carrying different charges attract each other, causing coagulation. The main function of coagulants is to change the electrical properties and interaction forces between suspended particles in the mineral slurry, reduce the collision of particles with the same charge, or make the particle surface lose its charge, resulting in the coagulation and precipitation of fine mineral particles. In mineral processing, inorganic compounds (including inorganic macromolecules) are used as coagulants for fine mineral aggregation. Commonly used coagulants include basic aluminum chloride, iron sulfate, polymeric iron sulfate, ferrous sulfate, iron chloride, zinc chloride, titanium tetrachloride, sulfuric acid, hydrochloric acid, carbon dioxide, sodium carbonate, lime, active silica, and bentonite. Coagulants can be used to separate iron minerals and clay minerals. Lime can be added as a coagulant into the concentrator to concentrate the finely dispersed ore, improving the efficiency of concentration and filtration.

Coagulants also have important uses in environmental protection and soil science. For example, alum can be used to purify drinking water, industrial water or factory wastewater containing suspended particles. It can also be used to coagulate solid powders, such as dust control and other applications.