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.