15
Fluorine [F, 9]
15.1 INTRODUCTION
Fluorine (F) is an element of the halogen group 17 in the periodic table of elements.
Its total content in the upper crust of Earth is estimated at up to 625 mg/kg. In igneous rocks its concentrations vary between 300 and 1200 mg/kg, being the highest in
mafic rocks. It is likely to accumulate in argillaceous sediments and in black shales
(500–800 mg/kg). Its lowest contents are in calcareous rocks (50–350 mg/kg). Hard
coal contains F usually up to 100  mg/kg, but higher contents, up to 200  mg/kg,
especially in bituminous coals, are noticed. High levels of F (as fluorapatite and fluorspar) are associated with various phosphate deposits. Fluorine is a common constituent of magmatic and volcanic exhalations, and may also occur in some rocks
as gaseous nebulae.
Fluorine, occurring mainly at −1 oxidation state, is a yellow gas, very toxic, and
reactive with both organic and inorganic substances. Metallic fluorides are highly
toxic, whereas organic fluorides are almost harmless. Its most common mineral,
fluorite (also called fluoride or fluorspar), CaF 2 is often associated with sellaite,
MgF 2 , and is widely distributed in both lithosphere and hydrosphere. Other common
minerals are cryolite, Na 3 (AlF 6 ); fluorapatite, Ca 5 (PO 4 ) 3 F; and topaz, Al 2 F 2 SiO 4 , a
popular gemstone, and depending on the addition of some metals may be of various
colors.
World mine F production (excluding the United States) as fluorspar (rounded)
in 2010 was 5400 kt, of which the People’s Republic of China produced 3000 kt;
Mexico produced 1000 kt; and Mongolia produced 450 kt (USGS 2011). Also, F gas
is produced at about 2.4 kt/yr in some countries.
A high proportion of F goes to the aluminum industry and to steel industries,
mainly as hydrogen fluoride (HF) and hydrofluoric acid. It is also greatly used in
glass, ceramic, and plastic production. Most feldspar consumed by the glass industry
is for the manufacture of container glass. Because of environmental initiatives, fiberglass consumption for thermal insulation is forecast to expand steadily. Domestic
feldspar consumption has been shifting from ceramics toward glass markets. Another
growing segment in the glass industry is solar glass. As a highly oxidizing element,
F is broadly used in various chemical processes. Fluorine is a common compound of
freon gases and chlofluorocarbons used for the refrigeration.
HF is a colorless gas and is the main source of F for industrial processes. It is
lighter than air and easily dissolves in water. It is produced from the mineral fluorite
and also obtained as a by-product of the P-fertilizer production. Common range of
F in P fertilizers is 8,500–38,000 mg/kg.
Fluorine has been added, for a long period, to municipal drinking water (at
the level up to 1.9  mg/L) for the prevention of tooth decay. It is still added to
toothpastes.
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