An evaluation of the adsorption dynamics of phosphate ions onto Fe(II)-montmorillonites

摘要

Fe(II)-montmorillonites (Fe(II)-MMTs) were prepared by mixing solutions of Fe(II) and montmorillonite at pH 3.5. Two different Fe(II)-MMTs were prepared and the ferrous iron contents were 40 mg/L and 80 mg/L. All samples were characterized by XRD, FT-IR, TGA, DSC, and nitrogen adsorption. By nitrogen adsorption, the pore size can be obtained in the pore diameter curve with average pore widths of 6.67 nm, 9.96 nm, and 17.07 nm, respectively. The removal rate of phosphate increased rapidly during the first 40 min, in which Fe(II)-MMT (1) and Fe(II)-MMT (2) were stronger adsorption systems than MMT. The maximum adsorption was 48.38 mg/g at pH 2.0. The kinetics of phosphate adsorption were better described using pseudo-second-order models (R$^{2}$: 0.997, 0.999, 1.000) than pseudo-first-order (R$^{2}$: 0.933, 0.900, 0.760). R$^{2}$ is the determinable statistic coefficient that measures the goodness of fit. If the R$^{2}$ value is closer to one, the fitting degree of the regression line is better. By the thermodynamic analyses, we obtained the $Delta $G$^{circ}$ and $Delta $H$^{circ}$ of samples at 298 $^{circ}$C, 303 $^{circ}$C, and 310 $^{circ}$C. The adsorption isotherms also better fitted a Langmuir model in which the process was nonspontaneous and exothermic.