Solvent extraction of Al(III) from sulfate solutions using bis (2,4,4-trimethylpentyl) phosphinic acid - mechanism and complexation

Extraction of Al(III) from aqueous sulfuric acid solutions into organic Cyanex 272(R)-carbon tetrachloride systems was investigated from a multi-component mixture containing aluminum, cobalt and nickel. AI(III) extraction efficiency was quantitative with 1.0 M Cyanex 272(R) in two stages at an aqueous:organic (A:O) phase ratio of 1:1 and an equilibrium pH of 3.2. The stripping of Al(III) from the loaded organic (LO) with different acids indicated sulfuric acid to be the best stripping agent. More than 99% stripping of Al(III) from the LO was achieved using 2 M H2SO4 at an A:O phase ratio of 1:1 in a single stage. The stoichiometry of the extracted species of Al(III) was determined by the slope analysis method. The extraction reaction proceeded via the cation exchange mechanism and the extracted species was assumed to be AlA(3)center dot 3HA, where HA refers to the dimeric and A the anionic form of the extractant, Cyanex 272(R). The extraction of Al(III) was studied in the presence of various ions to ascertain the tolerance limit of individual ions.