Abstract
The extraction rate of aluminum from sulfuric acid solution with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester was studied. The two phases in a conical flask were mixed by shaking at 298 K. The initial aluminum concentration in aqueous solution was chosen to be 2 mol/m3, so as to minimize the variation of pH during the extraction reaction. The extractant concentration was changed from 0.1 to 1.5 kmol/m3, and pH was varied from 1.0 to 3.0.The extraction rate was found to be of the first order with respect to the aluminum concentration in the aqueous phase. A different dependence of the extraction rate on pH and the extractant concentration was observed in the following regions: (1) When pH is below 2 or when the extractant concentration is lower than 0.2 kmol/m3, the extraction rate is of the −1 order of hydrogen ion concentration in the aqueous phase and is of the 0.5 order of the extractant concentration. (2) When pH is above 2 and the extractant concentration is higher than 0.2 kmol/m3, the extraction rate is of the 1.5 order of the extractant concentration, and as the extractant concentration increases, the dependence on the hydrogen ion concentration in the aqueous phase varies from −1.5 to −2.5 order.Detailed consideration of the experimental results and numerical analysis with computor elucidate that there are three paths in the extraction mechanism of this system. The first pass is expected to be a series of reaction from Al3+ ion and is shown as follows:(This article is not displayable. Please see full text pdf.) The second one is a path from AlOH2+, as is shown with the following reactions:(This article is not displayable. Please see full text pdf.) The third path is expected to be the following reaction:(This article is not displayable. Please see full text pdf.) The rate constants calculated for Al3+ and AlOH2+ are in good agreement with those obtained in hydrochloric acid solution.
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