Abstract
A study was made on the rate and the equilibrium of aluminum extraction from hydrochloric acid solution with di-2-ethylhexyl phosphoric acid (DEHPA) in paraffine diluent.From the equilibrium study, it was concluded that AlR3·HR was the extracted species in the organic phase.In the kinetic study, the influence of pH of the aqueous phase and the extractant concentration in the organic phase on the extraction rate was investigated. The experimental data were well explained by assuming that the extraction reaction proceeded along two parallel paths described below.The first path was shown by the following reactions with Al3+ ion;(This article is not displayable. Please see full text pdf.) \ oindentEither equation (\ efe3) or (\ efe4) was assumed to be the rate determing step.The second path was shown by the following reactions with AlOH2+ ion;(This article is not displayable. Please see full text pdf.) \ oindentThe equation (\ efe5) was posturated to be the rate determing step.The kinetic parameters calculated in this study were compared with those obtained in previous studies on 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (DEHEHP).In the first reaction path, where the reaction rate was assumed to be propotional to 1.5 or 2 powers of the extractant concentration in the organic phase, the value of the kinetic constant kf1 calculated in this study was about 50 times as large as those obtained in the systems with DEHEHP in hydrochloric, nitric and sulfuric acid solutions.In the second path from AlOH2+ ion, where the reaction rate was assmed to be independent of the extractant or its concentration in the organic phase, the calculated value for the kinetic constant kf2 agreed very well with those obtained in the systems with DEHEHP.
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