Ultrafiltration technique in conjunction with competing ligand exchange method for Ni-humics speciation in aquatic environment

The combination of ultrafiltration technique with competing ligand exchange method provides a better understanding of interactions between Ni and different molecular weight fractions of humic acid (HA) at varying pH in aquatic environment. This study suggests that the concentration of aggregated HA (HA with higher molecular weight) becomes high at acidic condition (lower pH) and the molecular weight of HA gradually decreases with the increasing pH. The disaggregation property of HA which involves the release of monomers from the surface of the aggregates produces HAs of different intermediate molecular weights with different Ni complexing capacity. It is observed that Ni prefers to form strong complexes with HAs of lower molecular weight at higher pH and weak complexes with HA of higher molecular weight. (C) 2012 Elsevier B.V. All rights reserved.