Adsorption Properties And Mechanisms Of Cu(Ⅱ) Soil Humin

In this paper,we study the structural characteristics and the copper ion adsorption behaviors of humus substances in several typical zonal soils of China by means of the elemental analysis,solid-state carbon-13 cross-polarization magic-angle-spinningnuclearmagneticresonance,pyrolysis-gas chromatography/mass spectrometry（Py-GC/MS）conventional,beamline-based FTIR,Synchrotron-based FTIR scanning electron microscopy/energy dispersive X-ray spectroscopy（SEM-EDS）,X-ray photoelectron spectroscopy（XPS）and batch equilibrium experiment.The results are as follows:1.In brown soil and lateritic red soil,HU has higher aliphaticity,stronger stability and lower polarity compared with HA,but the proportion of methoxy carbon,carbonyl carbon,lignin and phenolic compounds is lower in the molecule.The adsorption amounts of Cu（Ⅱ）on humin increased with increasing contact time,Cu（Ⅱ）concentrations,and reaction temperatures.The adsorption kinetics could be best described by pseudo-second order equation with equilibrium achieved at approximately 120 min,and the adsorption isotherms were well fitted by Freundlich and Langmuir equations.Based on the activation parameters calculated from temperature dependent adsorption kinetics,the adsorption reaction required energy and was an endothermic process and associated mechanism.The thermodynamic parameters from temperature dependent adsorption isotherms further indicated that the adsorption was a spontaneous,endothermic,and randomness increases process.In both humin and humic acid,octahedral Cu（Ⅱ）binding site was tetragonally distorted.Cu（Ⅱ）was coordinated by 4 O/N atoms at a bond distance of 1.91-1.97?in the first coordination shell（Cu-O）and by 2 C atoms at a bond distance of 2.80-2.83?in the second coordination shell（Cu-C）.This provide evidence that Cu（Ⅱ）is preferentially adsorbed to the organic functional groups of humin surface by forming inner-sphere complexes.2.Compared with HA,FA exhibited higher aliphaticity and oxidizability,but lower aromaticity in dark brown soil.The adsorption capacity of Cu（Ⅱ）on the dark brown soil HA and FA was expressed as:FA>HA.The adsorption amounts of Cu（Ⅱ）on HA/FA increased with increasing pH（2⁸）.When the solution pH was 8,the adsorption rate closed to 100%.With an increase of ionic strength（0¹.0 mol/L）,the adsorption amounts of Cu（Ⅱ）on HA/FA reduced,whose trend is particularly evident in the range of 0⁰.2 mol/L.The amount of Cu（Ⅱ）adsorbed increased with an increase of contact time,and the adsorption kinetics followed the pseudo-second-order equation.the adsorbate concentrations（0⁶00 mg/L）were positively correlated whith the adsorption amounts of Cu（Ⅱ）,the adsorption isotherms were better fitted by Langmuir equation than Freundlich and Temkin equations.Based on the thermodynamic parameters from temperature dependent adsorption isotherms,the adsorption was a spontaneous,exothermic,and randomness increases process.3.the amounts of Cu（Ⅱ）adsorbed on humin increased with increasing solution pH（2–8）,initial Cu（Ⅱ）concentrations(0–100 mg L^–1),contact time（5–1440 min）and reaction temperatures（298–318 K）,whereas the amounts decreased with increasing ionic strengths(0.01–1 mol L^–1).Adsorption kinetics followed pseudo-second-order equation with equilibrium achieved at approximately 120 min,and adsorption isotherms were well fitted by Langmuir equation.The activation parameters calculated from temperature-dependent adsorption kinetics indicated that the adsorption reaction required energy and was an endothermic process and associated mechanism.The thermodynamic parameters obtained from temperature-dependent adsorption isotherms demonstrated that the adsorption was a spontaneous,endothermic,and randomness increases process.Synchrotron X-ray absorption spectroscopy revealed that,independent of the adsorption conditions,Cu（Ⅱ）was coordinated by 4oxygen/nitrogen atoms at bond distance of 1.92-1.96?in the first coordination shell and by 2 carbon atoms at bond distance of 2.79-2.84?in the second coordination shell,confirming that Cu（Ⅱ）was preferentially adsorbed onto the organic functional groups of humin surface via inner-sphere complexation.