| 摘要 |
Fluoride-containing relatively dilute (i.e. not more than 30% by weight BO5 phosphoric acid is defluorinated by mixing it with an amount of volatile mineral acid such that the weight ratio of said mineral acid (calculated as equivalent HCl) to phosphoric acid (calculated as P2O5) in the mixture is at least 0,1, preferably between 0,3 and 0,8, heating the mixture to a temperature sufficient to vaporize the volatile fluoride constituents thereof, e.g. from 100 DEG to 500 DEG F., and recovering the defluorinated phosphate acid product. Reactive silica may be added in addition to mineral acid, the amount of silica added being sufficient to convert to fluosilicic acid all of the fluorides not already present in the form of fluosilicic acid. Specified mineral acids are hydrochloric acid, nitric acid, and perchloric acid. The heating may be continued until the acid mixture contains less than one part by weight of fluorine per 100 parts by weight of phosphorus, and concentrated phosphoric acid containing at least 40% by weight P2O5 may be produced. The process is particularly suited to the defluorination of phosphoric acid produced by the acidulation of phosphate rock, and in this case reactive silica may be added to the phosphoric acid during the production process. In an example the temperature to which the mixture is heated is 280 DEG F.
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