Non‐competitive and competitive adsorption of Zn(II), Cu(II), and Cd(II) by a granular Fe‐Mn binary oxide in aqueous solution

Abstract

AbstractThis work assessed the non‐competitive and competitive adsorption of Zn(II), Cu(II), and Cd(II) by a granular Fe‐Mn binary oxide (GFMO). Kinetic data for Zn(II), Cu(II), and Cd(II) adsorption followed with the pseudo‐second‐order model. Equilibrium data were well fitted using the Langmuir isotherm model both in single‐metal and in multi‐metal systems. The maximum adsorption capacities were determined to be 0.115, 0.124, and 0.055 mmol/g for Zn(II), Cu(II), and Cd(II) in the single‐metal solutions, respectively, while the maximum adsorption capacities were estimated to be 0.088, 0.112, and 0.041 mmol/g in multi‐metal systems. The adsorption of each metal ion was both nonspontaneous and endothermic demonstrated by thermodynamic assessments. The adsorption process was also greatly affected by pH, with the maximum adsorption at pH 6.0 for Cu(II) and 5.0 for Zn(II) and Cd(II). Metal ion adsorption was suppressed as coexisting metal ions competed for adsorption sites on the GFMO surface, suggesting an antagonistic effect. Adsorption data suggested that Cu(II) was preferentially adsorbed by GFMO in the multi‐component solutions. The adsorption of these metals by GFMO evidently proceeded on the basis of hydroxyl replacement, electrostatic attraction, and surface complexation.Novelty or SignificanceA granular Fe‐Mn binary oxide (GFMO) was synthesized in conjunction with polyvinyl alcohol to overcome the nano‐particles dispersion state of Fe‐Mn binary oxides. Because Zn(II), Cu(II), and Cd(II) with higher concentration and risk coexisted in road runoff, the performance of GFMO for Cd(II), Cu(II), and Zn(II) non‐competitive and competitive adsorption was investigated to identify their engineering application potential when GFMO applies as the filler in some green infrastructures, such as constructed wetlands, bioretentions, and rain gardens.