The use of coal spoils as feed materials for alumina recovery by acid-leaching routes. 4. The extraction of iron from aluminiferous solutions with amines, in particular alamine 336

Abstract

The removal of iron from acidic leach solutions is a necessary step in the process flowsheet for the production of alumina from colliery spoil materials. After considering a number of extractants, Alamine 336, a tertiary amine, was found to be the most satisfactory reagent for the extraction, requiring one to three theoretical stages. The amount of metal extracted was found to be independent of the initial metal concentration in the aqueous solution but very dependent on the initial acid concentration. The equilibrium diagrams suggested the formation of an extracted species with 1.3 moles of Alamine 336 per mole of iron(III). The extraction data are explained in terms of the formation of both polymeric and polynuclear iron species. The work was extended to investigate the treatment of chloride/fluoride solutions, obtained by the leaching of uncalcined colliery tailings with hydrochloric acid containing small amounts of fluoride ions. In this case, it was necessary to convert ferrous iron to the ferric state before extraction. The results obtained indicated that the presence of fluoride ions did not significantly affect the efficiency of the iron extraction.