Keisuke Fukushi | Search PubMed

PubMed2006

Anion adsorption on oxide surfaces: inclusion of the water dipole in modeling the electrostatics of ligand exchange.

Adsorption of aqueous anions, such as sulfate, arsenite, and oxalate, to oxide surfaces is important in the retardation of toxic species in the environment, but predicting the surface speciation as a function of environmental parameters is a major challenge. Recent laboratory spectroscopic studies defining surface speciation must be integrated with surface complexation models. However, the latter have neglected the electrostatic work of desorption of water dipoles in treating anion adsorption by ligand exchange. Taking this effect into account permits close quantitative description of anion adsorption and the prediction of anion surface speciation as a function of pH, ionic strength, and surface coverage in agreement with spectroscopic results.

Adsorption↗

PubMed2003

Solid-solution reactions in As(V) sorption by schwertmannite.

Sorption behavior of As(V) by synthesized schwertmannite was examined under pH 3.3 as a function of As(V) concentration in the initial solution and interpreted in term of solid-solution reactions. Results showed that schwertmannite released 0.62 mmol of SO4(2-) for every 1 mmol of H2AsO4- and 0.24 mmol of OH- that has been sorbed. As(V) replaced SO4 up to half of the total SO4 in schwertmannite. The quantitative relationship among the three chemical compositions indicated that As(V)-sorbed schwertmannite would behave as a solid solution between the As(V) free schwertmannite and schwertmannite containing the maximum level of As(V). The equilibrium constant for the anion exchange in the solid-solution reaction estimated from the reacted solution chemistry depicts the As(V) content found in precipitates formed in acid mine drainage and laboratory experiments. Although schwertmannite is metastable with respect to goethite, the transformation is significantly inhibited by sorption of As(V). The solid-solution reactions also explain the stabilization of schwertmannite by sorption of As(V).

Adsorption↗