The paper presents the results of leaching tests carried out on compacted calcareous clay samples using water and zinc solutions as permeants. Sequential selective extraction was used to evaluate the contribution of the different soil constituents to zinc retention. The retention and swelling properties of the soil under the different conditions were related to its porosity by means of mercury intrusion tests. During the leaching tests, the swelling of the samples varies from 27% in the case of water to 16% and 21% in the case of zinc solutions with concentrations of 2.97 and 297 g/l, respectively. The quantity of zinc retained by the soil is derived from two methods: selective sequential extraction (SSE) and acid digestion. The results from SSE show that the total quantities of absorbed zinc are equal to 76.7 and 27.2 mg/g of soil for the samples saturated with zinc at the concentrations of 2.97 and 297 g/l, respectively. This method shows that carbonate plays a significant role in the retention process through two main mechanisms: (i) the formation of precipitates of zinc carbonates, oxides and hydroxides at the lowest zinc concentration and (ii) calcite dissolution at the highest zinc concentration. Acid digestion confirms the value of the total quantity of absorbed zinc, with a relative difference of 8% with SSE. Mercury intrusion porosimetry (MIP) shows that wetting the sample with water or zinc solutions results in different pore distributions. Compared to the initial state, the pore volume of the samples increases during hydration with water or with zinc solutions. In the initial state, the sample is characterised by pores located at 10 and 0.7 mu m. When the sample is saturated with water, the inter-aggregate pores increase to 30 mu m and the interparticular pores, to 1 mu m. When the sample is hydrated with the 2.97 g/l zinc solution, the increase of the pore size (to 20 mu m) only concerns the inter-aggregate pores but is slightly lower than in the case of water. When the sample is hydrated with the 297 g/l zinc solution, the interparticular pores disappear and only an inter-aggregate pore at 20 mu m is observed. The combination of the mercury intrusion and selective sequential extraction (SSE) results suggests that, for the sample saturated with the 2.97 g/l solution, the formation of precipitates leads to the obstruction of the pores, the reduction of the accessible porosity and a decrease in the swelling properties. On the other hand, carbonate dissolution leads to a widening of the pores and an increase in the accessible pore volume which is responsible for the increase in the swelling properties. (C) 2009 Elsevier B. V. All rights reserved.