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Flotation is a crucial mineral separation technique that utilizes differences in surface properties to separate valuable minerals from gangue. It can be classified into positive and reverse flotation, depending on whether valuable or waste minerals are recovered. With a history dating back to ancient practices, modern flotation has evolved into a sophisticated process involving specialized chemicals and machinery, playing a vital role in mineral processing today.
Flotation can be divided into positive flotation and reverse flotation according to the separation of valuable components. The method of discharging useless minerals (i.e. gangue minerals) in the slurry as tailings is called positive flotation; the reverse is called reverse flotation. Commonly used flotation agents in flotation include collectors, frothers, inhibitors, activators, pH adjusters, dispersants, flocculants, etc. Common flotation machines include mechanical stirring, aeration, aeration mechanical stirring, etc.
In ancient China, the natural hydrophobicity of the mineral surface was used to purify mineral drugs such as cinnabar and talc, so that the mineral powder floated on the water surface and separated from the sinking gangue. When washing gold in the placer, feathers were dipped in oil to catch the oil-loving and hydrophobic gold and silver fine particles, which was called goose feather scraping gold, and it is still used today. The Ming Dynasty's "Heavenly Creations" records that when gold and silver workshops recycled gold and silver powders from discarded utensils and dust, "a few drops of clear oil were dropped and gathered at the bottom." This is a method of sorting using differences in surface properties. There is also evidence of the use of oil and asphalt to collect minerals in ancient Greece and Europe.
In the 18th century, people knew that gases adhered to solid particles and rose to the surface of the water; in the 19th century, people used bubbles produced by gasification (boiling slurry) or acid addition and reaction with carbonate minerals to float graphite. In the late 19th century, due to the increasing demand for metals, the resources of coarse-grained lead, zinc, and copper sulfide ores that could be processed by gravity separation gradually decreased. In Australia, the United States and some European countries, flotation was used to select fine-grained ores to provide concentrates for smelting. Thin film flotation and full oil flotation were used in the early stage. The former is to sprinkle the ore powder on the flowing water surface in the flotation machine, and the hydrophobic minerals float on the surface and are recovered; the latter is to mix a certain amount of mineral oil into the ore pulp, to capture the hydrophobic and oleophilic ore particles and float them to the surface of the ore pulp for recovery.
By the beginning of the 20th century, the foam flotation method was used to select the ore particles according to their different affinity for bubbles in the water. In 1922. cyanide was used to inhibit sphalerite and pyrite, and the preferential flotation process was developed. In 1925. synthetic flotation agents represented by xanthate were used, and the dosage of agents was reduced from 1-10% of the ore amount in full oil flotation to a few ten-thousandths of the ore amount, which made flotation a major development and widely used in industrial production.
At the same time, the research on flotation theory also developed rapidly, such as Gordon's "Flotation" in the United States in 1932. Rebentier's "Physical Chemistry of Flotation Process" in the Soviet Union in 1933. and Wacker's "Principles of Flotation" in Australia in 1938. Before 1949. there were only a few flotation plants in China. After 1949. hundreds of modern flotation plants for processing various ores were built. Achievements have been made in the fields of separation and flotation of polymetallic ores, comprehensive utilization of complex ores, flotation of iron ore, and flotation of non-metallic ores and coal.
The theoretical basis of various flotation processes is roughly the same, that is, the ore particles can aggregate at the liquid-gas or water-oil interface due to the hydrophobic properties of their own surfaces or the hydrophobic (air-loving or oil-loving) properties obtained after the action of flotation agents.
The most widely used method at present is froth flotation. The ore is crushed and ground to dissociate various minerals into monomer particles, and the particle size is made to meet the requirements of the flotation process. Various flotation agents are added to the ore pulp after grinding and stirred and blended to act on the mineral particles to expand the floatability differences between different mineral particles. The adjusted ore pulp is sent to the flotation tank and stirred and aerated. The mineral particles in the slurry contact and collide with the bubbles. The mineral particles with good floatability selectively adhere to the bubbles and are carried up to form a mineralized foam layer composed of gas-liquid-solid three phases. They are mechanically scraped or overflow from the surface of the slurry, and then dehydrated and dried into concentrate products. Mineral particles such as gangue that cannot float are discharged from the bottom of the flotation tank as tailings products with the slurry. Sometimes, useless mineral particles are floated out and useful mineral particles are left in the slurry, which is called reverse flotation, such as floating quartz from iron ore.
From its early use in ancient gold washing to today’s advanced froth flotation systems, flotation technology has revolutionized mineral processing. By selectively separating minerals through surface chemistry, it enables efficient extraction of metals and non-metals, supporting industries worldwide. Continued advancements in reagents and equipment ensure flotation remains a cornerstone of modern mining and resource recovery.
