Methods for producing antimony

Antimony smelting methods are divided into pyrometallurgy and hydrometallurgy, with pyrometallurgy still being the main method. Pyrometallurgical antimony smelting mainly uses the volatilization roasting-reduction smelting method or volatilization smelting-reduction smelting methods, that is, antimony trioxide is first produced by volatilization roasting (smelting), and then the antimony trioxide undergoes reduction smelting and refining to produce metallic antimony. In addition, for high-grade stibnite or concentrates, the precipitation smelting method can be used to directly produce metallic antimony. According to the nature of the solvent used, hydrometallurgical antimony smelting can be divided into two methods: alkaline leaching-sodium thioantimonite solution electrolysis; and acid leaching-antimony trichloride solution electrolysis. The former method uses sulfide as a leaching agent and is an antimony smelting process that gradually emerged in the 20th century.

Volatilization roasting-reduction smelting of stibnite ore and concentrates, precipitation smelting of stibnite concentrates, and alkaline leaching-leachate electrolysis are the main antimony smelting methods currently used in industrial production. In addition, antimony smelters can also use rich ores as raw materials to produce crude antimony (antimony trisulfide) using the liquation method. The main difference between antimony production methods and other non-ferrous metal production methods is that the raw materials used are not standardized, and the production method should be determined according to the grade, form, and product requirements of the raw materials.

More than 95% of antimony smelters in China use pyrometallurgical antimony smelting technology, that is, stibnite ore or concentrate is first volatilized and roasted (smelted) to produce antimony trioxide, and then the antimony trioxide is reduced and smelted and refined to produce metallic antimony.

The volatilization roasting process of stibnite ore and concentrates has been widely used in industrial production. The basic principle of volatilization roasting is based on the fact that stibnite is oxidized to volatile antimony trioxide when heated under insufficient air. The antimony trioxide enters the dust collection system with the furnace gas and condenses into white powdery crystals, achieving the separation of antimony from gangue.

The oldest volatilization roasting equipment is some vertical shaft furnaces, also known as shaft furnaces, which process lumpy antimony ore containing about 15% or less antimony. A Chinese-style vertical shaft furnace similar to the Herreshoff furnace is commonly used in China. In addition, volatilization smelting equipment that has been researched or put into production and use for many years includes rotary kilns, fluidized bed furnaces, sintering machines, tunnel kilns, suspension furnaces, blast furnaces, and cyclone furnaces.

The vertical shaft furnace, a volatilization roasting equipment, has been widely used for a long time and has a long history. It has gradually been eliminated. It originated in France, and China has used this type of equipment for a long time to process cheap and low-quality hand-picked ore. It has low fuel consumption and can produce high-quality antimony trioxide.

The rotary kiln is also an earlier antimony volatilization roasting equipment used. The former Yugoslavia has long used it and has rich experience. Later, Italy developed a new method of flash roasting in a rotary kiln, directly processing powdered flotation stibnite concentrate. This method is unique, the equipment process is simple, no flux needs to be added, the energy consumption is low, the antimony content in the kiln slag is low, and the direct recovery rate is as high as 96%. This type of furnace has the characteristics of a sulfur-state fluidized bed furnace, with fast reaction speed, large processing capacity, high volatilization rate, and good quality of antimony oxide powder produced.

Fluidized bed roasting is mainly used to process stibnite ore. The Beijing Nonferrous Metals Research Institute and the Xikuangshan Mining Bureau have conducted experimental research on fluidized bed roasting of flotation stibnite concentrate and low-grade antimony oxide materials. The former Soviet Union has tested fluidized bed roasting and sintering roasting for low-grade antimony ore (antimony matte, oxide ore, tailings, leaching residue) with less than 5% antimony, with antimony volatilization rates of 80% and 90%~97%, respectively. The former Soviet Union has used it for roasting low-grade ores, and a certain factory in China has used it to process brittle antimony lead ore concentrate.

Tunnel kiln volatilization roasting of antimony concentrate is a research achievement in China. This process can process both stibnite concentrate and a mixture of stibnite and antimony oxide concentrate. The antimony volatilization rate is high, and the quality of the antimony oxide powder produced is good.

Xikuangshan in China once used existing condensation dust removal equipment to conduct suspension roasting tests of flotation antimony concentrate. Japan uses suspension roasting to process antimony concentrate containing precious metals, with an antimony volatilization rate of 87%~90%, and the roasted sand is further processed to recover precious metals.

Antimony trioxide production can also be achieved by volatilization smelting. This method maximizes the volatilization of antimony in the form of antimony trioxide under high temperature, strong oxidizing atmosphere, and molten material, thus overcoming the difficulties caused by material sintering during volatilization roasting. Volatilization smelting has developed from ordinary blast furnace smelting and is suitable for processing high-grade concentrates, sulfur-oxygen mixed ores, and various metallurgical intermediate products. Mexico once used a hot top blast furnace smelting method to process oxide ores, volatilizing 80% of the antimony into antimony trioxide and reducing 20% of the antimony into crude antimony. China has made creative developments in blast furnace antimony smelting. In addition to the hot top, low material column, thin material layer, large air volume, and full volatilization process are also used, which can process high-grade stibnite concentrate. The former Soviet Union and Czechoslovakia, and the Vento smelter in Bolivia have all carried out cyclone furnace volatilization smelting operations. In addition, Japan has conducted converter smelting tests, and the United States has also made some progress in the research on antimony enrichment smelting, improving smelting efficiency.

Stibnite concentrate can also be dead-roasted below the melting point of stibnite and under sufficient air to oxidize it into non-volatile antimony tetroxide, and then reduction smelting is performed to produce metallic antimony. Arsenic, mercury, and other easily volatile components can also be separated from antimony during the roasting process. This method is mainly used to process high-grade stibnite concentrates. Because the gangue and impurity content in the concentrate is low, the difficulty of subsequent reduction production is not great. The Stibnite antimony smelter in the United States uses a multiple-hearth furnace to roast antimony concentrate containing 18% arsenic, with 75% of the antimony remaining in the roasted sand in the form of Sb ₂0₄ Chile uses rich concentrate containing 60%~65% antimony and niter in a multiple-hearth furnace for dead roasting, with only 16% of the antimony entering the gas phase. When processing mercury antimony ore, because mercury is easily volatile, the former Soviet Union and Czechoslovakia have adopted methods to control the atmosphere and temperature of roasting, so that antimony mainly remains in the roasted sand in the form of Sb ₂0₄ and then undergoes reduction treatment.

Because antimony trioxide is easily volatile, the above volatilization process can also be used to treat antimony oxide concentrates or sulfur-oxygen mixed concentrates mainly composed of valentinite and stibnite.