The adsorption of As(V) onto alpha -Al2O3 was investigated at 25, 50 and
70 degreesC using batch adsorption experiments. Results indicate that As
is strongly adsorbed at low pH and gets progressively released to the
fluid with increasing pH above 7. At any pH, increasing temperature
favors aqueous species of As over surface species. Surface complexation
constants were determined at the experimental temperatures by fitting
the adsorption data. Adsorption reactions were then converted to
semi-isocolumbic reactions, i.e, reactions with balanced like-charged
aqueous species. Intrinsic adsorption constants of semi-isocolumbic
reactions change linearly when plotted against inverse temperature,
suggesting that the heat capacity of these reactions remains constant
over the temperature range considered. This permitted thermodynamic
parameters of intrinsic surface complexation constants to be determined.
Changes in surface complexation constants result in a change in the
surface speciation with increasing temperature. This change is similar
to the one observed for aqueous species, i.e. increasing temperature
favors less negatively charged species below a pH of 9 and more
negatively charged species above a pH of 10. Comparison with the
stability of As surface complexes with Fe suggests that surface
complexes with Al are more stable. (C) 2001 Elsevier Science Ltd. All
rights reserved.