Reaction Investigation of Metal Salts with Tetrakis(hydroxymethyl)phosphonium Sulfate and Chloride

The interaction of tetrakis(hydroxymethyl)phosphonium sulfate (THPS) and chloride (THPC) with water-soluble and water-insoluble metal compounds was investigated. We evaluated solutions of the phosphonium salts for dissolution of metal sulfides, and complexation of the THP moiety with Fe2+, Fe3+, Cu2+, Zn2+, Hg2+, and Pb2+. Scanning ultraviolet/visible spectroscopy was deployed to monitor complex formation. Applying mole ratios of 1-9 THP:1M (n+) (Fe3+, Hg2+, and Pb2+) revealed the formation of several complexes. THP did not appear to complex with Fe2+ and Zn+2 although isobestic points were maintained in the UV spectra. The results of this investigation did not confirm prior studies that showed complexation of Fe2+ with THP in the presence of ammonium ion. Results suggest that THPS and THPC dissolved metal sulfide precipitates at mildly acidic conditions, and THP often formed stable complexes of variable stoichiometry with the metal cations.