GB1240285A - Purification of phosphoric acid - Google Patents

Abstract

1,240,285. Phosphoric acid. ISRAEL MINING INDUSTRIES - INSTITUTE FOR RESEARCH & DEVELOPMENT. 27 Sept., 1968 [27 Nov., 1967], No. 46064/68. Addition to 1,112,033. Heading C1A. A process for recovering phosphoric acid from technical grade phosphoric acid comprises treating technical grade phosphoric acid with a mixture of at least two extracting solvents of the kind defined in Specification 1,112,033, the temperature of the treatment being low enough for the formation of a clear homogeneous extract phase distinct from a residual aqueous phase, separating the extract phase from the aqueous phase, raising the temperature of the extract phase to that at which it separates into a lower layer containing phosphoric acid and an upper layer containing the solvents and separating the lower layer from the upper layer. The solvents are for example esters, ketones, glycol ethers and ethers, such as ethyl, butyl and amyl acetate, ethyl butyrate and cyclohexanone. Stratification is enhanced by the addition of a small amount of water or purified phosphoric acid. The yield is increased by incorporation of sulphuric acid in amount e.g. from 0À1 to 5% in the technical grade acid. The residual acid, after separation of the solvent extract may be acidified with sulphuric acid in amount 30 to 100% by weight of the phosphoric acid and subjected to a repeated extraction with one or mixture of extracting solvents and a mixture of purified phosphoric and sulphuric acids is recovered. Impurities in the original acid can be removed by addition of alumina, calcium compounds, active carbon silicon dioxide or active clay prior to the solvent extraction. Calcium hydroxide or phosphates and phosphate rock can be added to the feed phosphoric acid to neutralize free sulphuric acid present. In examples the solvents used are (1) ethyl ether and nbutyl ether; (2) n-butyl ether and dibutyl ether of ethylene glycol; (3) isopropyl ether and ethyl ether; (4) isopropyl ether and cyclohexanone; (5) ethyl ether and diethylene glycol mono nhexyl ether; (6) mixed diethylene glycol mono- and di-n-butyl ethers; (7) diethylene glycol dibutyl ether and diisobutyl ketone. In example (8) a residual fraction from the extraction of technical grade phosphoric acid with a mixture of n-butyl ether and ethyl ether in a process similar to example, is acidified with concentrated sulphuric acid and the mixture is extracted with a mixture of isopropyl ether and ethyl ether.