Adsorption of Phosphate and Arsenate on New Al₁₃-Oxalate Precipitate: Spectroscopic and Macroscopic Competitive Adsorption Investigations

Abstract

Coprecipitates of aluminum-organics play important roles in the transport of phosphate and arsenate in soil environment. A new polynuclear aluminum organomineral precipitate (Al₁₃-Oxalate precipitate) was prepared to investigate the adsorption behavior of phosphate and arsenate on a noncrystalline aluminum precipitate. Important thermodynamic parameters of adsorption reactions were evaluated using macroscopic adsorption data and the macroscopic competitive adsorption of two oxyanions also was investigated. The result shows that the adsorption reactions basically are a diffusion process, and that phosphate has a stronger chemical interaction with substrate than arsenate. FTIR spectroscopic studies have provided evidence for the formation of two different types of phosphate complexes in substrate, protonated bidentate and deprotonated bidentate complexes at pH 4 and pH ≥6, respectively. The XPS studies indicate that the precipitate substrate can acts as Lewis acid when adsorbing two oxyanions, and that more electron transfer relative to O in the substrate occurs during adsorption of phosphate compared to that of arsenate, meanwhile surface carboxylic carbon (COO−) is involved in the complexation reaction.