What is fluoride?
What is fluoride?
The chemical element fluorine forms fluorides when it is combined with other chemical elements. Fluorine is found principally in a mineral called fluorspar which is also sometimes known as fluorite. It is a naturally occurring mineral which may contain up to 45% calcium fluoride (CaF2). In its natural state it occurs with other minerals such as barytes, galena, pyrites and other sulphides. In its pure form it is colourless and transparent or translucent, with a glossy lustre. Impurities in the mineral can give it a wide variety of colours, and some types exhibit fluorescence. It is in fact one of the most colourful minerals in the world, appearing in a variety of shades from yellow and green through rose, red, pink and reddish orange to blue and black.
The main deposits of fluorspar are now to be found in China, Mexico, Mongolia, South Africa and Namibia. Europe still has a small number of viable fluorspar mines, although the total has declined gradually over the years. It is a truly international business with world-wide consumption estimated at around 4.5 million tonnes per year.
Production of hydrofluoric acid (HF)
The main grades of fluorspar available are:
The most popular is the acid grade, used as raw material to produce hydrofluoric acid, with a worldwide production capacity of more than three million metric tonnes.
After the ore is dug from mines or from open quarries, the impurities are removed to leave a fluorspar which contains minimum 97% calcium fluoride. Most of the co-products are also separated and collected, and serve a variety of industrial purposes. The acid grade fluorspar is then transported to the hydrofluoric acid plants by ship, road, rail or barge. Here it is reacted with sulphuric acid to form hydrogen fluoride gas. This is either collected and stored for use as a liquefied gas, or it can be diluted with water to make aqueous solutions of hydrofluoric acid.