The present invention resides in part in a process for removing a multivalent metal ion contaminant such as can be found in an acidic waste water. The waste water may also contain one or more extraneous metals such as copper. This process aspect then more particularly involves the steps of (1) simultaneously reducing said multivalent contaminant to a lower valence state and said extraneous metal to a metal state, while at the same time inhibiting reoxidation of the multivalent contaminant to a higher valence state; and (2) removing the multivalent contaminant which has been inhibited from reoxidation.