Heavy metal mobility assessment in sediments based on a kinetic approach of the EDTA extraction: search for optimal experimental conditions

The feasibility of kinetic extraction studies using EDTA as the complexing agent is evaluated for the extraction of Cd²⁺, Cu²⁺, Pb²⁺ and Fe³⁺ from contaminated sediments. In the first approach, the study was carried out in batch equilibrium conditions in order to determine optimal ranges for operational parameters, such as pH, concentration of EDTA and the ratio of mass of sediment to volume of EDTA, m/V. It has been concluded that the quantities of metal extracted by EDTA do not depend on the m/V ratio and that an EDTA concentration of 0.05 M ensures an excess of extractant. The kinetic studies were performed with the optimised experimental conditions. Two extraction protocols were used and compared in terms of experimental performance. The main difference between these two protocols is the use, in protocol I of a single sediment/EDTA mixture in which aliquots are collected at different times, whereas in protocol II several mixtures are stirred, each one for a different time. It has been shown that results of EDTA extractions can be influenced by the protocol used and we recommend protocol II for kinetic studies.