Partitioning of heavy metals on soil samples from column tests

In this study, column tests were used to determine the retention capability of three types of estuarine alluvia collected adjacent to landfill sites i n South Wales. Selective sequential extraction (SSE) was used to study the retention mechanisms of heavy metals in the soil columns obtained from leac hing experiments. Acid digestion was later used to check the validity of th e SSE results. Breakthrough curves show good retention of heavy metal ions (Pb, Cu, and Zn) by all soils, where almost 99% of heavy metals were retain ed with the C-e/C-o values in the order of 10(-3). The retention strength o f these soils was observed to be constant up to five pore volumes (PV). Thi s corresponds with the pH of the effluents and pore water of soil slices, w hich also show good buffering capacity against very acidic leachate up to 5 PV. The heavy metal extraction profiles from SSE show very similar trends w ith the retention profiles from the leaching experiments, where heavy metal s were retained mainly at the top parr where the leachate entered the colum n. SSE indicates qualitatively that heavy metals precipitated with carbonat es and amorphous materials (oxides/hydroxides) are higher than heavy metal retention via exchangeable mechanisms. The mass balance calculation gives r ange of deviation of 1-16% of the total soil extraction. The distribution o f the heavy metals with various soil constituents are ranked in the followi ng order: Carbonates > Amorphous oxides hydroxides > Organic matter > Excha ngeable phases. (C) 2001 Elsevier Science B.V. All rights reserved.