Temperature effects on arsenate adsorption onto goethite and its preliminary application to arsenate removal from simulative geothermal water

Abstract

Laboratory batch experiments were conducted in order to assess the impacts of temperature on the performance of goethite in removing arsenate from water. All batch experiments were conducted at four temperatures (30, 50, 70 and 90 °C) and pH 4.6. The results showed that both the arsenic uptake rate and capacity were significantly enhanced with increasing temperature from 30 to 90 °C. The adsorption kinetics followed a pseudo-second-order model with coefficients of determination (R²) all above 0.999. The process followed the Langmuir model, and several thermodynamic parameters were calculated. Arsenate adsorption was facilitated more under simulative geothermal water conditions than in RO (reverse osmosis) water. The crystalline structure of goethite was not changed after adsorption at various temperatures. XPS results showed a decrease in the content of iron hydroxyl groups, which demonstrated that arsenate adsorption onto goethite may be realised through the replacement of the iron hydroxyl group to form inner-sphere bidentate/monodentate complexes at pH 4.6.