The objective of this paper is to quantify the role of Natural Organic Matter in the retention processes of Ni on a natural sediment, sampled at two distinct depths. To assess the relevance of organic and mineral sites, adsorption experiments were carried out, on calcinated and non calcinated sediments, for the two depths investigated. The results have shown that the retention of Ni on the mineral surface sites could be described with one surface complex on a global mineral site. Due to the dual effect observed in the presence of organic matter, it was necessary to consider the formation of a ternary surface complex, and a Ni-organic matter complex in solution to account for the observed experimental results. Calculations have shown that mineral and organic functional groups were of same kind for the 2 depths and that the amount of organic matter was responsible for the enhancement of Ni adsorption at low pH values.
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