Binding of inorganic phosphate to dissolved metal humates

A cobalt-wire electrode was used to determine the concentration of free phosphate (P) in solutions containing a series of metal humates (MHA). The results were used in Scatchard plots to determine the stability constants of the dissolved MHA-P complexes formed. The constants were found to be high, with log K values in the range 4.8-6.0. Solutions containing MHA-P complexes were found to be relatively inert to the addition of phosphate-precipitating cations, indicating that MHA has a solubilizing effect on P and may enhance its mobility in the environment.