Proton Charge and Adsorption of Humic Acid and Phosphate on Goethite.

Little information is available about the changes of the proton charge of goethite in the presence of phosphate (P) and humic acid (HA). The objectives of this study were to systematically measure the proton charge of the ternary mixture and adsorption of HA and P on goethite. The potentiometric titration method was used to measure proton charges in single, binary, and ternary mixtures of goethite HA, and P as a function of pH and ionic strengths. Results showed that proton charge in the ternary mixture became more negative with increasing pH and the loadings of HA and P. The point of zero charge (PZC) decreased linearly with the initial concentrations of HA and P. At low to intermediate pH, little variation was observed in adsorption of P on goethite in the presence of HA. A small reduction in the adsorption of P in the presence of HA was observed when compared with the control (without HA loading) at high pH. fri 2008, Weng al. developed a model describing the electrostatic interaction between HA and Pat the 1-plane of the compact part of the electrical double layer (EDL). In this study, Weng et al's model was used to interpret the effect of adsorbed HA on the adsorption of P on goethite as well as the nonsignificant interaction of PZC between HA and P. [ABSTRACT FROM AUTHOR]