Pb, Cu and Cr interactions with soil: Sorption experiments and modelling

The objective of the study was to assess the extent of heavy metal contamination of a sandy soil submitted to long-term irrigation by effluent water. For this purpose, batch equilibrium technique on a sandy soil was adopted to investigate sorption of copper, chromium and lead at various pH and at ionic strength 0.01 M. Competitive sorption was evaluated as well for copper and chromium introduced at the same concentration. Batch experiments were carried out at 20 °C with the < 2 mm fraction of the soil, in suspension with 0.01 M NaNO3 and at pH ranging from 2.0 to 9.0. Metallic ions under their nitrate salt form were introduced at the concentration at 6.10−4 M. The PHREEQC 2.12 hydrogeochemical interactive code was used to model experimental sorption data on the basis of heavy metal complexation at the interface soil/solution metallic onto proton exchanging sites. The experiments were described by double layer model and the surface complexation constants considering one type of exchangeable sites were determined by this discrete site model.