Phosphoric acid solvent extraction, zinc

The extractant agent is di-2-ethylhexyl phosphoric acid. The extraction grade depends on the pH of the operation, in a range between 1.5 and 5. In the lower range, the solvent extraction capacity is relatively low, compared to that obtained at pH = 5. However, it is not possible to operate at high pH s because of the presence of iron and other cations in the zinc-rich solution which precipitate as hydroxides, causing troubles in the phase distribution. 

A mixture of 2.65 g. of freshly distilled 2,3-O-isopropylidene-D-glycerose, 1.5 ml. of ethyl acetoacetate, 0.7 g. of zinc chloride, 20 ml. of N sulfuric acid, and 20 ml. of 96% ethyl alcohol is kept at room temperature for twenty-four hours. After addition of 3 g. of crystalline sodium acetate and keeping for a further 48 hours at room temperature, the mixture is heated for 15 minutes at 90°. It is then repeatedly extracted with ether, and the united extracts are successively washed with water, an aqueous solution of sodium bisulfite, and a small quantity of aqueous sodium hydroxide solution. The ether layer is dried with anhydrous sodium sulfate and the solvent is evaporated, yielding an oil which is saponified with aqueous sodium hydroxide solution (4 ml. of 10%) by heating on a steam bath for one hour. The aqueous solution is extracted with ether, acidified (to Congo Red) with phosphoric acid, and then repeatedly extracted with ether the united extracts are dried with anhydrous sodium sulfate and the solvent is evaporated, giving a residue which crystallizes from water yield, 0.2 g. of the product (X) m. p., 153-155°. 

Zincex [Zinc extraction] A process for extracting zinc from pyrite cinder leachate, using organic solvents. The chloride leachate is first extracted with a secondary amine, and then with di(2-ethylhexyl)phosphoric acid to remove iron Developed by Tecnicas Reunidas, first commercialized in 1976, and now used in Spain and Portugal. 

Kunzmann, M. and Kolarik, Z., Extraction of zinc(It) with di(2-ethylhexyl)phosphoric acid from perchlorate and sulfate media. Solvent Extract. Ion Exchange, 10 (1), 35-49, 1992. 

Ajawin,L.A., Perez de Ortiz,S.E. and H.Sawis-towslci. "Kinetics of extraction of zinc by di (2-ethyl-hexyl) phosphoric acid in N-heptane". (Proceedings of Int. Solvent Extraction Conf., ISEC 80, Belgium, 1980). 

Kunzmann, M.W., Kolarik, Z. Extraction of mono and polynuclear complexes of zinc(n) with di(2-ethylhexyl) phosphoric acid. In Solvent Extraction 1990, Sekine, T., Ed., Part(A). Elsevier, New York, 1990, pp. 207-211. 

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