Influence of humic acid on sorption of Co(II), Sr(II), and Se(IV) on goethite
This work examined the influence of a leonardite humic acid on the sorption of Co(II), Sr(II), and Se(IV) onto goethite as a function of pH. The sorption of humic acid and ions alone was first studied. The humic acid sorbs appreciably to the goethite surface according to a reversible process, with a maximum sorption of 19 mg of total organic carbon per g of goethite reached at lower pH values (» 5). Cobalt and selenium are significantly sorbed on goethite while strontium is only weakly sorbed. In the presence of humic acid, the cobalt sorption is enhanced in acidic media due to the humic acid sorption on goethite, which modified the surface properties by making it more negative. However, it decreases in alkaline media due to the complexation of Co(II) by soluble humic acid. The sorption of Sr(II) is significantly increased in the presence of humic acid even in alkaline media. The sorption of selenite ions (SeO3 2–) decreases in the presence of humic acid because a competition with humate ions occurs at the surface sites of the goethite. The results presented here constitute a good set of data for modelling the effect of humic acid on the sorption of ions on goethite.
Keyword: sorption, humic acid, goethite, cobalt, strontium, selenium
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