Coordination of Cd ions in the internal pore system of zeolite-X: A combined EXAFS and isotopic exchange study |
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| Authors: | IAM Ahmed SD Young NMJ Crout |
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| Institution: | a School of Biosciences, Division of Agriculture & Environmental Sciences, University of Nottingham, Nottingham NG7 2RD, UK
b Diamond Light Source Ltd., Diamond House, Chilton, Didcot, Oxfordshire OX11 0DE, UK |
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| 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. |
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