Obtenção do sulfato de alumínio a partir da bauxita e a eliminação de ferro (processo ácido).

Abstract

The objective of this work is to evaluate the performance of an acid process to obtain aluminum sulfate by the reaction of bauxite with sulfuric acid, with further steps of purifications, to obtain it with minimum impurity of iron. The process involves the following three steps: leaching of the bauxite ore with sulfuric acid, separation of the aluminum sulfate from iron sulfate by crystallization with ethanol, and the final purification of the aluminum sulfate by liquid-liquid extraction using an organophosphoric acid (di-2-ethylhexyl phosphoric acid). During the leaching step, the bauxite was treated directly with sulfuric acid giving the aluminum sulfate as principal product; and iron and aluminum contents were determined by classical methods of analysis. To determine the best conditions in this step, the variables studied were: concentration of the acid, quantity of the acid and leaching time. In the second step, the crude aluminum sulfate obtained in the previous step was treated with ethanol, and due to solubility relations the aluminum sulfate precipitated purer leaving major part of the iron in the solution, thus obtaining the aluminum sulfate with minimum iron content. The following parameters were studied for maximum removal of the iron present: concentration of the ethanol, temperature of the aluminum sulfate solution and the cooling velocity. Finally, as the last step the liquid-liquid extraction technique was used with a view to eliminate the rest of the iron present in the aluminum sulfate obtained after the alcoholic treatment. To evaluate the performance of the extraction process the aqueous solutions of the crystallized aluminum sulfate were treated with the solution of di-2-ethylhexyl phosphoric acid (HDEHP) diluted in toluene. The influence of the variation of concentration of HDEHP and of concentration of iron (III), and number of pratical stages were studied by means of distribution coefficient, maintaining a constant initial pH and the volume ratio of the phases.