Effect of Humic Acid on the Sorption of Sr(II) on Kaolinite

Abstract

The distribution coefficient of Sr(II) ions for kaolinite was measured as a function of pH from 4.0 to 11.0, and humic acid (HA) concentrations from 0 to 400 ppm, at an ionic strength 0.1 M (NaClO4) at 298 K with N2 bubbling. The sorption of Sr(II) ions in the absence of HA increased with pH up to approximately pH 7. There was a plateau between pH 7 to 9, after which the sorption increased with increasing pH. The sorption was not affected by the presence of HA at concentrations up to several tens of ppm. At higher HA concentrations, the presence of HA did not affect the sorption at pH values up to 5, and above pH 5 the sorption reduced by introducing HA. Estimated values of the distribution coefficient in the presence of HA based on a linear additive model did not agree with the experimental data well.