Selective removal of metals from aqueous solutions with dithiophosphinic acids

A process for the extraction of metals selected from the group consisting of zinc (II), silver (I), cadmium (II), mercury (II), nickel (II), cobalt (II) and copper (II) from an aqueous solution containing, in addition to said metals, metals selected from the group consisting of calcium (II) and magnesium (II) comprising contacting said solution having a pH within the range of about 0.2 to about 3.0 with an extraction solvent at about 0.degree. to about 80.degree. C. and thereafter separating the aqueous phase from the extraction solvent phase containing the extracted metals, wherein said extraction solvent comprises:

• (a) from about 2 to about 99 parts by volume of an organic-soluble dithiophosphinic acid or the ammonium, alkali or alkaline earth metal salt thereof represented by the formula:
• ##STR5## wherein R.sup.1 and R.sup.2 are the same or different and are selected from the group consisting of substituted or unsubstituted alkyl, cycloalkyl, alkoxyalkyl, alkylcycloalkyl, aryl, alkylaryl, aralkyl and cycloalkylaryl radicals having from about 2 to about 24 carbon atoms and X is either hydrogen or an ammonium, alkali or alkaline earth metal salt forming radical;
• (b) from about 98 to 1 parts by volume of a water immiscible organic diluent;
• and
• (c) from 0 to about 15 parts by volume of a phase modifier.