Interaction of Hg(II) acid with kaolin-humic acid complexes

The adsorption and desorption of Hg(II) by humic acid (HA) previously adsorbed oil kaolin was studied. In the range of FIA concentration investigated (0.0-26.9 mg g(-1)), the Hg(II) adsorption capacity of kaolin at pH 4 is enhanced by the presence of FIA. For the complexes with the highest HA concentration and for low Hg(II) initial concentrations, adsorption was lower, i.e. as HA concentration on the complexes increases, Hg(II) equilibrium concentration also increases. This behaviour is due to the increasing presence of dissolved organic matter as the HA concentration oil the complexes increases. The dissolved organic matter is able to form a Soluble complex with Fig, thus decreasing adsorption. Hg(II) adsorption front a 2.5 x 10(-5) MHg(II) Solution was influenced by pH. For kaolin, a pH(max) (pH where maximum adsorption Occurs) of 4.5 was observed. At pH values >pH(max) retention decreased with increasing pH. This same behaviour Was observed for the kaolin-HA complex containing the lowest HA concentration (6.6 mg g-1). For the other kaolin-HA complexes there was little effect of pH on Hg(II) adsorption between pH 2.5 and pH 6.5. The presence of HA increased the adsorption of Hg(II) oil kaolin all along the pH range Studied. Desorption experiments showed that the amount of Hg(H) desorbed was quite low (<1%) for all the FIA and Hg(II) concentration range studied, except for the kaolin Lit acid pH (pH 2.5) where the Hg(II) released was >50% of Hg(II) previously adsorbed. The presence of HA dramatically reduced this percentage of desorption to values of <3%, indicating reduced risk of toxicity problems in surface and subsurface waters. The addition of Cu(II) did not favour any Hg(II) desorption, even though Cu exhibits a strong affinity for organic matter.