Continuous-flow system for reduction of metal readsorption during sequential extraction of soil

Abstract

A continuous-flow sequential extraction system developed in our laboratory for metal fractionation in solid materials has shown many advantages over the batch system such as speed of extraction, simple procedure, less risk of contamination and less dependency on extraction conditions. This report emphasizes the reduction of readsorption problem achieved from this system. Five metals (Pb, Cu, Zn, Ni and Cd) were studied because of their significance as environmental contaminants. A method of standard addition into extractants was used to evaluate readsorption phenomena in a three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR). The continuous-flow system showed less degree of readsorption compared with the batch system. The extent of readsorption was found to be dependent on elements, properties of soil especially organic matter content, extracting flow rate and metal concentration level. Metal readsorption from acid soluble fraction to oxidizable fraction was greater for soil of high organic matter than soil of low organic matter content. Lower extracting flow rate and lower concentration of metals in sample showed lower degree of readsorption. The behavior of metal readsorption during extraction was observed as two patterns. In pattern one, readsorption was observed at the earlier step and the adsorbed metal was leached in the following step. In pattern two, readsorption and desorption were observed in the same extraction step.