Stabilization Pb, Zn, and Cd-Contaminated Soil By Means of Natural Zeolite

This article aims to investigate the stabilization of Pb, Zn, and Cd contained in contaminated soil from a former mining site in Montevecchio, Sardinia, using clinoptilolite-rich tuff from Pentalofos, Evros. The study included (1) batch experiments and their environmental characterization and (2) column experiments. The first tests involved 1-month pot experiments with varying soil-zeolite mixtures, and their evaluation was carried out by standard USEPA leaching tests (TCLP, EPT test, SPLP). Moderate solubility reductions were recorded according to the TCLP (Pb: 38%, Zn: 33%, and Cd: 32%) due to the introduction of competing Na ions in the solution, while the EPT test showed more significant variations (Pb: 55%, Zn: 74%, and Cd: 46%). A major decrease is achieved in both cases by 10% w/w zeolite addition. The study was complemented by column experiments involving soil-zeolite mixtures eluted by CH3COOH solutions (0.003N and 0.05N). The solubility of Pb was reduced by 50 to 60% compared with the control column, thus indicating the considerable selectivity of clinoptilolite for Pb. In addition, Na and Ca measurements in the leachates confirmed that the immobilization of Pb was mainly attributed to ion exchange reactions.