A. Langella et al., NH4+, Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ in a sedimentary clinoptilolite, North Sardinia, Italy, MICROP M M, 37(3), 2000, pp. 337-343
Recent findings of clinoptilolite-bearing volcanoclastic deposits in northe
rn Sardinia promoted a study aimed at evaluating the cation exchange proper
ties of this zeolite in view of a possible future utilization of the parent
rock. Isotherms of NH4+, Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ at 25
degrees C and 0.1 total normality were obtained and the related thermodynam
ic quantities K-a and Delta G(0) computed. The maximal exchange level was i
n any case less than 100% for each cation investigated. Good selectivities
were recorded for NH4+ and Pb2+, whereas clinoptilolite proved to be unsele
ctive for Cu2+, Zn2+ and Cd2+ The cation selectivity sequence NH4+ > Pb2+>
Na+> Cd2+ >Cu2+ congruent to Zn2+ was obtained.
The results are discussed in the light of literature data, and contrasting
performances of various clinoptilolites were ascribed to different cationic
compositions of the minerals, due to different minerogenetic conditions, w
hich were proved to affect both cation exchange capacity and selectivity. T
his led to the conclusion that any practical utilization of a clinoptilolit
e-rich rock as cation exchanger should be preceded by basic studies on repr
esentative samples from the deposit under examination. (C) 2000 Elsevier Sc
ience B.V. All rights reserved.