Influence of pH on cadmium sorption onto humic acids
2004
Madaras, M.,Soil Science and Conservation Research Institute, Bratislava (Slovak Republic) | Barancikova, G.,Soil Science and Conservation Research Institute, Bratislava (Slovak Republic) | Makovnikova, J.,Soil Science and Conservation Research Institute, Bratislava (Slovak Republic)
Humic acids (HAs) are considered as predominant metal binders in soil due to their excellent sorption properties, which are dependent on their chemical structure and composition. Aim of this paper is to clarify the nature of cadmium (Cd)-HA interactions on the basis of sorption experiment in which effect of pH on Cd sorption onto HAs was studied, using HAs of different origin and composition. HAs were isolated from soils Chernozem and Cambisol and lignite. Among investigated HAs, significant differences in Cd sorption were observed. The lowest sorption was observed for Cambisol HA within all pH values of original Cd solution (pH 3, 4 and 5). Maximum sorption was measured for Chernozem HA at pH 4 and 5, at pH 3 for lignite HA. Value of Langmuir sorption maximum for all HAs was in evident linear relationship with increasing pH. Based on the result it is hypothesized that the dominant role in Cd sorption in an acid environment is played by carboxyls. In addition to their amount per unit HA weight, their structural arrangement is probably important as well, causing different sorption behaviour of HAs with similar carboxyl content.
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