Industrial Sources of Fluoride Pollution

Fluoride emissions into the atmosphere are derived mainly from modern-day anthropogenic sources, particularly industrial sources. They include steel industry, phosphate fertilizer industry, aluminum industry, ceramics 

Fluorides emitted into the atmosphere from different sources include both gaseous and particulate forms. Historically, most of the F pollution problems occurred as a result of emissions from anthropogenic sources. Such emissions occasionally resulted in the presence of harmful levels of F compounds in the environment as well as in body tissues. The forms of F emitted from these sources include hydrogen fluoride, cryolite, fluorspar, and silicon tetrafluo-ride (SiF4). The anthropogenic sources also contribute F to surface waters. 

Some heavy discharges of F into the atmosphere and waters have occurred in connection with the manufacture of elemental phosphorus, phosphate fertilizer, and aluminum. In the manufacture of elemental phosphorus, ground phosphate rock, whose main component is Ca10F2(PO4)6, is mixed with silica and coke and then heated in a carbon-lined furnace with carbon electrodes. Equation (8.1) shows the chemical reaction involved in this process  

2Ca10F2(PO4)6 + 18Si02 + 30C - 18 CaO. Si02. l/9CaF2 + 30CO + 3P41 

Aluminum, on the other hand, is produced by dissolving alumina (A1203) in molten cryolite followed by electrolytical reduction. The net chemical change is shown in Equation (8.2)  

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