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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 (R2 : 0.997, 0.999, 1.000) than pseudo-first-order (R2 : 0.933, 0.900, 0.760). R2 is the determinable statistic coefficient that measures the goodness of fit. If the R2 value is closer to one, the fitting degree of the regression line is better. By the thermodynamic analyses, we obtained the ΔG°and ΔH°of samples at 298 °C, 303 °C, and 310 °C. The adsorption isotherms also better fitted a Langmuir model in which the process was nonspontaneous and exothermic. [ABSTRACT FROM AUTHOR]

The objective of the current effort was to determine the efficacy of Fe(II)-montmorillonite (Fe(II)-MMT) as an adjuvant for specific targeted adsorption of phosphate. Specifically, Fe(II)-MMT was studied to combat hyper-phosphatemia and anemia arising from chronic renal failure. The adsorption of phosphate over time, pH, and initial concentration was studied. The systems were characterized by X-ray diffraction (XRD), Raman, and zeta potential. The experimental results demonstrated the adsorption time was set to 140 min to achieve maximum adsorption efficiency. It was thus found that the maximum adsorption was at pH 3.0. In addition, it reached equilibrium when the initial phosphate concentration was at 60 mg/L while the maximum adsorption capacity was 5.75 mg of phosphate/g of Fe(II)-MMT. On the other hand, adsorption isotherms showed that the Langmuir model was better than the Freundlich model. This means that the adsorption of the phosphate on Fe(II)-montmorillonites was monolayer adsorption, and the phosphate was successfully adsorbed either onto the surface or intercalated within interlayer volume. Live experiments supported the ability of Fe (II)-MMT to control hyperphosphatemia and treat chronic renal failure. [ABSTRACT FROM AUTHOR]