Effect of phosphate on Cd(Ⅱ)adsorption on the surface of lepidocrocite
The adsorption of toxic metals by iron oxides is widespread in natural environments.It is well known that oxyanions can alter the adsorption behavior of trace metals through cooperative adsorption or competitive effects.However,the specific co-adsorption mechanisms are not yet fully understood.In this study,the adsorption behavior of cadmium(Cd(Ⅱ))on synthetic lepidocrocite(Lep)in the presence of phosphate was investigated using macroscopic adsorption experiments,in-situ attenuated total reflectance Fourier-transform infrared spectroscopy(ATR-FTIR),and X-ray photoelectron spectroscopy(XPS).The isothermal adsorption experiment results showed that in the absence of phosphate,the adsorption capacity of Lep for Cd(Ⅱ)was 1.91 mg·g-1 with an initial Cd(Ⅱ)concentration of 1 mmol·L-1.When the molar ratios of phosphate to Cd(Ⅱ)were 1∶1 and 2∶1,the adsorption capacity of Lep for Cd(Ⅱ)increased by 3.67 times and 16.62 times,respectively,compared to the absence of phosphate;however,when the molar ratio of phosphate to Cd(Ⅱ)was 5∶1,the adsorption capacity of Lep for Cd(Ⅱ)only increased by 12.93 times.Adsorption edge results demonstrated that pH had little effect on the phosphate-mediated adsorption behavior of Lep for Cd(Ⅱ),likely due to the strong coordination ability of phosphate.XPS and ATR-FTIR analyses indicated that Cd(Ⅱ)can complex with phosphate on the surface of Lep to form ternary complexes(Cd(Ⅱ)-phosphate-Lep),with phosphate primarily binding to the Lep surface through inner-sphere complexation.Moreover,2D-COS analysis revealed the formation of multiple configurations of phosphate-Cd(Ⅱ)-Lep ternary complexes on the Lep surface,including bidentate binuclear and monodentate binuclear complexes.These complex configurations are typical models of synergistic adsorption of phosphates and Cd(Ⅱ)on the Lep surface through the formation of ternary complexes.
NETL
NSTL
万方数据
