Cation selectivity of a Ca2+ pre-exchanged clinoptilolite tuff

With the purpose to evaluate clinoptilolite for possible use in soil amendment strategies as a substitute of naturally occurring clay minerals, a marketed clinoptilolite-rich tuff coming from Anatolia, Turkey, was submitted, after exhaustive treatment with Ca2+ solutions, to exchange tests towards some nutrient or noxious cations. Accordingly, time-dependant and equilibrium data of exchange reactions of Pb2+, Cu2+, Zn2+, Na+, K+ and NH4+ for Ca2+ were collected and the corresponding thermodynamic and kinetic parameters were calculated following standard procedures. Results demonstrated an excellent to good propensity of Ca2+-clinoptilolite for K+, NH4+ and Pb2+ and a moderate affinity for the other three cations. The conclusion was that a Ca2+-rich clinoptilolite tuff can be considered as a good substitute for clay minerals to recover and/or rebuild degraded and depleted soils.