This paper describes cation exchange technology for removal of contaminants from ammoniacal ammonium molybdate solutions using macroreticular resin having iminodiacetate chelating-type functional groups. Copper is effectively scavenged in the pH range 7 - 8, zinc at pH 8 - 9, and magnesium pH 9 - 10. 2N HCl strips the resin. Water washing, followed by regeneration with 2 N aqueous ammonia, removes chloride and returns the resin to its initial capacity.