X-ray Photoelectron Spectroscopic Studies of Cadmium and Selenite Adsorption on Aluminum Oxides

摘要

The sorption of cadmium(II) and selenite on two porous, high surface area aluminum oxides and a nonporous crystalline aluminum oxide (α-Al_2O_3, corundum) was studied by X-ray photoelectron spectros-copy (XPS). The porous adsorbents used (ALCOA types CP-5 and C-33) had different sizes and pore structure but otherwise had similar characteristics. CP-5 particles were smaller than C-33 and partly mi-croporous; C-33 particles were mesoporous and more crystalline than the CP-5 particles. The total aqueous concentrations of cadmium(II) and selenite were 1.0 x 10~(-4) and 1.0 x 10~(-3) M, respectively. Maximum surface coverages of the porous adsorbents, as estimated by XPS, were 0.8 and 0.5 monolayers for cadmium(II) and selenite, respectively. XPS estimates of cadmium and selenite surface coverages agreed well with the hypothesis that adsorbate intra-particle diffusion followed by sorption is the predominant mechanism of cadmium and selenite uptake by porous aluminas under these experimental conditions. XPS results of cadmium and selenite sorption on corundum agreed well with expected surface coverages, based on sorption isotherm data. These results have significant implications for the fate and transport of trace elements in the environment and the remediation of waste waters and contaminated groundwaters.