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Time-dependent sorption of Cd2+ on CaX zeolite : experimental observations and model predictions.

Research output: Contribution to journalJournal article

Published

Journal publication date1/10/2006
JournalGeochimica et Cosmochimica Acta
Journal number19
Volume70
Number of pages12
Pages4850-4861
Original languageEnglish

Abstract

The effect of prolonged contact time (up to 130 days) on the immobilization of Cd by sorption to calcium exchanged zeolite-X (CaX), under environmentally relevant conditions, was studied using both isotopic exchange and extended X-ray absorption fine structure spectroscopy (EXAFS). Sorption and isotopic exchange measurements revealed time-dependent Cd sorption and indicated the movement of Cd2+ ions into less accessible sites due to ageing. EXAFS suggested progressive fixation of Cd in the double six-ring (D6R) unit of the CaX structure. Proportional allocation of the apparent Cd–Si bond distance to two ‘end-members’, across all contact times, indicated that the bond distance for labile Cd was 3.41 Å and for non-labile (or fixed) Cd was 3.47 Å.