Abstract: Ammonium sulfate-bisulfate solution contaminated with metal and other ash producing contaminants is treated by adjusting the pH of the solution to the range that produces a precipitate of the contaminant by the addition of ammonia or ammonium hydroxide; cooled to at least the temperature at which a precipitate is produced; removing the precipitate from the solution; the pH of the solution from which the precipitate has been removed is adjusted to the range at which precipitation is substantially completed by the addition of sulfuric acid; and the SO.sub.4.sup.= ion concentration and the NH.sub.4.sup.+ ion concentration of the solution are adjusted to the range of the solution before initial circulation to produce a solution in which the metal concentration has been sufficiently reduced to permit recycle for use in reclaiming used motor oils.