A method of selectively extracting trivalent ions of Fe and Al from process acid solution containing said trivalent ions and also containing at least one divalent ion selected from the group consisting of Ni, Co, Fe, Cu, Mn and Mg which comprises,
- uniformly mixing said solution with a feed liquid organic extractant comprising an organophosphorus compound and a sulfonic acid dissolved in a water-immiscible organic solvent,
- said organophosphorus compound being selected from the group consisting of ##STR5## where R is a long chain hydrocarbon selected from the group consisting of n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, 2-ethyl-4-methylpentyl, 2-propyl-4-methylpentyl, octyl-2, diisobutylmethyl, 8-phenylpropyl, phenyl-2-ethylhexyl, n-decyl, n-octyl, 2,6,8 trimethylnonyl-4 and 3,9-diethyltridecanol-6,
- said sulfonic acid having the general formula ##STR6## where R is an alkylaromatic hydrocarbon substituent and the mole weight of the sulfonic acid is at least 300
- the molar ratio of said sulfonic acid to said organophosphorus compound being 1:4 to 10:1, continuing said mixing for a time sufficient to effect solvent extraction of at least said trivalent iron in an iron extraction stage and provide a first raffinate impoverished in at least said iron and containing at least one of said divalent ions and a first loaded extractant containing at least said trivalent iron,
- separating said first loaded extractant from said raffinate,
- scrubbing said loaded extractant with a first mineral acid scrubbing solution of concentration ranging from about 0.5 N to 5 N to effect extraction of aluminum and divalent ions from said extractant while leaving iron in said first extractant,
- separating the first loaded extractant from said first scrubbing solution,
- stripping the iron from said scrubbing first extractant by mixing said extractant with a mineral acid of concentration ranging from about 4 N to 12 N and produce an acid solution containing said trivalent iron and regenerate said organic extractant,
- recycling said regenerated organic extractant for further extraction of said trivalent iron from process solutions,
- merging said first scrubbing solution with the feed extraction in the iron extraction stage and provide said first raffinate for the subsequent recovery of aluminum therefrom,
- mixing said merged solutions with a second liquid organic extractant of the aforementioned composition for a time sufficient to effect solvent extraction of at least said trivalent aluminum and form a second loaded organic extractant and a second raffinate substantially impoverished in iron and aluminum,
- separating said second raffinate from said second loaded extractant,
- scrubbing said second loaded extractant with a second mineral acid scrubbing solution of concentration ranging from about 0.5 N to 5 N to effect extraction of divalent ions from said second extractant while leaving aluminum therein,
- separating said scrubbing solution from said second extractant,
- and then stripping aluminum from said second extractant by contacting it with a mineral acid of concentration higher than said scrubbing solution and ranging from about 4 N to 12 N, thereby regenerating said second organic extractant and produce an aqueous solution containing aluminum,
- separating said regenerated second extractant from said aluminum-containing solution and recycling said regenerated second extraction for treatment of said first raffinate solution.