China
Africa
Explore chapters and articles related to this topic
Major Melt—Crucible Systems
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
Thorium melts at 1750°C, approximately 620°C above the melting point of uranium, and is the highest -melting component of the reaction mixture. Calcium fluoride melts at 1418°C. Sulphur is used as the booster with a large excess of calcium. The reaction between calcium and sulphur is highly exothermic, and the heat evolved is available for meeting the thermal requirements of the main reduction process. The bomb-type reactor is lined with graphite. The reactants are compacted together to form pellets and stacked inside the graphite liner. The reaction is initiated by means of an electrically heated molybdenum coil embedded in a trigger mixture of a few grams of calcium and sulphur. Well-formed thorium billets are obtained in over 90% yield. This was the UK process. Average impurity contents of billets produced were as follows: oxygen 0.26%, nitrogen 0.038%, carbon 0.24%, sulphur 1.0%, fluorine 0.33%, calcium 0.21%.
Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Fluorite (calcium fluoride) is a commercial mineral. Since it has commercial value it is also called ‘ore’. The ore is also known as fluorspar. It mostly occurs in igneous granite rock. The ore is used to make ornaments, ceramic, glass and optical lenses. Calcium fluoride plays a vital role in the chemical industry for the production of hydrofluoric acid (HF), which is used to make many chemical products.
The Rejection of Perfection
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
When there is a simple ratio between the different elements of a compound, and the atoms of the compound are present in the correct numbers for this ratio to hold true, that compound is said to be “stoichiometric.” For example, a perfect calcium fluoride crystal, which has a chemical formula of CaF2, will have two fluorine atoms for every atom of calcium throughout its structure.
Improved process to prepare high-purity anhydrous potassium fluoride from wet process phosphoric acid
Published in Chemical Engineering Communications, 2018
Bingwen Long, Zile Wang, Qi Zhang, Wenchang Ke, Yigang Ding
Potassium fluoride (KF) is an industrially important fluoride salt widely used in medicine, pesticides, and metal smelting with increasing demand in recent years (Kim et al., 2002). Traditionally, the fluorine in fluoride salts mainly originates from fluorite, a natural mineral mainly composed of calcium fluoride. With the rapid development of fluorine chemical industry during the last decades, there is a growing shortage of fluorite and the mining of fluorite has been stringently restricted by the main producer countries (Mondillo et al., 2016). On the other hand, there is always plenty of fluorine resource in accompany with phosphate rock and the content of fluorine in phosphate rock is generally about 2–4% by mass (Dorozhkin, 1996). During the industrial production of wet process phosphoric acid (WPA), 3–5% of the total fluorine in phosphate rock is volatilized in the form of silicon tetrafluoride and the rest 15–30% of total fluorine is precipitated out in phosphogypsum. The remaining fluorine then enters liquid phase together with phosphorus and many other elements, which, however, has negative effect on the downstream processing of WPA. (Mondillo et al., 2016; Kijkowska et al., 2002). Therefore, it is of great benefit to recover this portion of fluorine from WPA and use them as fluorine source to produce fluoride salts.
Fluoride and human health: Systematic appraisal of sources, exposures, metabolism, and toxicity
Published in Critical Reviews in Environmental Science and Technology, 2020
Humayun Kabir, Ashok Kumar Gupta, Subhasish Tripathy
Fluorine occurs naturally throughout the outer part of the Earth as the F− ion, and more than 200 minerals contain F−, predominantly as igneous or sedimentary (carbonate or phosphate) rock deposits (Lahermo et al., 1991; Sivasankar, Darchen, Omine, & Sakthivel, 2016; Weinstein & Davison, 2004). The F− content varies among minerals, from more than 70% in the rare mineral griceite (LiF) to less than 0.2% in many others. Calcium fluoride, commercially known as fluorspar, contains 49% F− and is mostly utilized industrially as a source of F− (Fuge, 1988; Jha, Mishra, Sharma, & Damodaran, 2011).