Arsenic(V) adsorption onto alpha-Al2O3 between 25 and 70 degrees C

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 s trongly adsorbed at low pH and gets progressively released to the fluid wit h increasing pH above 7. At any pH, increasing temperature favors aqueous s pecies of As over surface species. Surface complexation constants were dete rmined at the experimental temperatures by fitting the adsorption data. Ads orption reactions were then converted to semi-isocolumbic reactions, i.e, r eactions with balanced like-charged aqueous species. Intrinsic adsorption c onstants 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 ther modynamic parameters of intrinsic surface complexation constants to be dete rmined. 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 le ss negatively charged species below a pH of 9 and more negatively charged s pecies above a pH of 10. Comparison with the stability of As surface comple xes with Fe suggests that surface complexes with Al are more stable. (C) 20 01 Elsevier Science Ltd. All rights reserved.