PURPOSE: To recover In as a pure In concd. soln. from an In-contg. aqueous soln. of a specified pH value by extracting In ions in the aqueous soln. with a specified org. phase contg. mono- or di- and trialkylphosphoric acids followed by back extraction with an aqueous acidic soln. of sulfuric acid.

CONSTITUTION: An In-contg. aqueous soln. is adjusted to pH 0.25W4.5 and contacted to a soln. of an extracting co-reagent contg. mono- or dialkylphosphoric acid and trialkylphosphoric acid in a ratio of 1:(2W5) by vol. in a phase stabilizing water-immiscible org. solvent such as deodorized mineral spirit, whereby most of the In is extracted into the org. phase, yet Fe3+ is slightly extracted. This org. phase is then contacted to an aqueous acidic soln. of sulfuric acid contg. 100W500 g/l free sulfuric acid to back-extract the In into the soln., thus obtaining an In concd. soln.