Extraction kinetics of copper,zinc, iron,and manganese from contaminated sediment using Disodium Ethylenediaminetetraacetate

One technique for cleansing heavy metal contaminated soils is to wash the excavated soil with an extraction solution of a chelating agent. The rate of extraction is an important parameter when considering the length of time needed for soil clean-up and the amount and concentration of wash solution required. The extraction kinetics of copper, zinc, iron and manganese from a contaminated sediment of the Clark Fork River in western Montana, U.S.A., with Disodiun Ethylenediaminetetraacetate (Na₂EDTA) as the extraction agent, were investigated. The results showed the extraction process consisted of rapid extraction in the first minutes followed by much slower extraction for the remainder of the experiment. The rate of extraction, particularly in the rapid phase, demonstrated clear pH dependence: the lower the pH, the faster the extraction rate. In the EDTA concentration range of 0.01 M to 0.05 M, the effect of the EDTA concentration on the extraction rate was not important compared with that of the solution pH. Extraction kinetics for different size particles were similar, although in the first few minutes, EDTA extracted more metals from clay and silt than sand. The two reaction, diffusion, and two-constant kinetic models were compared to experimental results. The two reaction model did not fit any of the data well, and only iron extraction could be described with a simple diffusion model. In general the extraction rates can be well described by the two-constant model, C=A t ^B, up to 600 minutes and under different conditions such as solution pH, EDTA concentration, and different sediment particle size.