Determination of Ni ( II ) Uptake Mechanisms on Mordenite Surfaces : 1 A Combined Macroscopic and Microscopic Approach

The uptake mechanisms of Ni(II) on mordenite were investigated by 13 macroscopic experiments and extended X-ray absorption fine structure (EXAFS) 14 spectroscopy. The results demonstrated that Ni(II) could be retained via different 15 mechanisms, depending on pH, ionic strength, temperature etc. At low pH, the uptake 16 of Ni(II) is primarily dominated by cation exchange and/or outer-sphere surface 17 complexation. The interatomic distances of Ni-O (~2.05 Å) and the coordination 18 number (~6.0) are similar to those of Ni(II)(aq) reference sample, suggesting that 19 Ni(II) is present in an [Ni(H2O)6] 2+ octahedral environment at low pH. With 20 increasing pH, the uptake of Ni(II) on mordenite tends to form inner-sphere surface 21 complexes and precipitation/co-precipitation at high pH. The uptake of Ni(II) on 22 *Revised Manuscript in 2p 300 66 09 09 , v er si on 1 18 J an 2 01 2 Author manuscript, published in "Geochimica et Cosmochimica Acta 75 (2011) 6520-6534" DOI : 10.1016/j.gca.2011.08.024