Laboratory experiments on diffusion and sorption of heavy metals in a marine clay

Sorption capacity and diffusion of the marine clay of Taranto industrial area (Southern Italy) with respect to heavy metals at low concentration levels were measured by means of Batch-Equilibrium and Column tests. Single-species and multiple-species solutions of Cd\(^{2+}\), Cr\(^{3+}\) and Cu\(^{2+}\) were utilized. These solutions contained only these heavy metals as cations. Furthermore, the clay was not previously subjected to pre-treatment. The note describes the experimental results, that do not conform with the literature, as the measured clay sorption capacity for multiple-species solutions larger than for the single-species solutions, in spite of the competition among metals. A tentative explanation of this unexpected response is given in the conclusions.