Caesium is a precious and rare alkaline metal with physical and chemical properties similar to those of rubidium and potassium. It is a silvery white, soft, ductile metal, it has a hardness of 0.2 Mohs. At slightly above room temperature, caesium exists in the liquid state. It has the lowest boiling point and melting point, highest vapor pressure, highest density, and lowest ionisation potential. Moreover, the metal ignites spontaneously in the presence of air and reacts explosively in water.
Pollucite, mainly found in association with lithium-rich, lepidolite-bearing or petalite bearing zoned granite pegmatites, is the principal caesium ore mineral. Caesium has been sourced from Tanco mine in Canada and Bikita mine in Zimbabwe, and lepidolite deposits in China. The Sinclair deposit in Australia was discovered in 2016 with mining completed over a four-month period in late 2018.
Today, caesium oxide, metal, and derived fine chemical salts products are widely used in the modern economy including:
- National defence (such as night vision imaging)
- Aerospace (such as ion propulsion engines)
- Communications (such as 5G, cloud communication)
- New energy industry (such as magnetic fluid power generation materials)
- Biochemical and pharmaceuticals (such as sleeping pills, tranquilizers and drugs for epilepsy)
- Special glass, and catalysts (such as caesium vanadium catalyst).
Its main commercial use is in the manufacturing of caesium formate, a heavy liquid (1.8 to 2.4 g/cm3) used in high-pressure, high temperature well drilling for oil and gas exploration and production.
Occurrence and Production
Caesium occurs in the hard rock alumino-silicate mineral pollucite (Cs2Al2Si4O12), seawater, brines (salt lakes), and underground hot springs. The stoichiometric content of Cs in pollucite is 42.6%, but samples of ore typically contain 18 – 26 % caesium oxide. Its appearance is very similar to that of quartz and thus it can easily be overlooked.
In terms of global resources, according to the United States Geological Survey (“USGS”), an approximate amount of caesium can be estimated from the contained Cs value found within Li-Cs-Rb mineral pegmatites which is estimated to around 180,000 tonnes (Cs oxide equivalent), of which the caesium-bearing resources are mainly distributed in Canada, Zimbabwe, and Namibia. Of which, Canada is host to 80,000 tonnes, accounting for the 44% share of global caesium mineral reserves, followed by Zimbabwe with 60,000 tonnes accounting for 33% share and Namibia with 30,000 tonnes accounting for 16%.
In terms of global caesium production, over the past few decades, nearly all of the world’s supply has been from the Tanco Mine in Canada, Bikita Mine in Zimbabwe, Karibib Desert, Nambia, and Sinclair Mine in Australia. In China, caesium resources mainly come from Yichun 414 Ta-Nb-Li Mine and lepidolite deposits which are mined for their lithium. During 2021, no primary mining was reported globally but it was produced as a by-product of mining in China. Existing stockpiles at former mines continue feeding downstream refineries, though reports indicate stockpiles will be depleted within a few years.
The caesium industry chain consists primarily of upstream mining and downstream processing where caesium is extracted from mine sources such as pollucite or lepidolite and upgraded from caesium oxide into caesium fine chemical salt products which are sold and marketed to customers.
The main caesium-based chemical salt products include Cs carbonate, Cs hydroxide, Cs sulfate and high value-added caesium fine chemical salt products include Cs iodide, Cs fluoride, Cs bromide, Cs chloride and Cs nitrate.
Caesium metal and caesium salts are marketed in metal-based purities from 99% for technical grades to 99.999% for high-purity compounds. For some applications, a crude form with 85% purity can also be produced. The salts are available in solid form or directly supplied as solutions in water.
Caesium formate brine is an aqueous solution of Cs formate used primarily by the oil and gas industry as a drilling fluid, drill tip lubricant, and a foundation stabiliser due to its high density, environmental friendliness, and stability under high temperature and pressure environments.
Today, Sinomine Resource Group Co., Ltd, a large-scale new energy mining and development company focused on the mining, beneficiation, and chemical salt businesses of lithium, caesium, and rubidium with mining exploration services and construction as ancillary business units is the world leader in Cs production.
In July 2019, Sinomine paid a total consideration of US$135 million to acquire a 100% interest in Cabot Corporation’s Specialty Fluids division (“Cabot SF”), a vertically integrated producer of Cs and fine chemical salts making Sinomine the most complete manufacturer in the global Cs industry, with a fully-established vertically integrated business chain forming the ability to mine, process, produce fine chemical products and provide technical services for Cs. In addition, the Company has established a provincial-level Rb-Cs materials and engineering research center in Jiangxi Province and has obtained a number of patents covering Cs fine chemicals.
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