• Journal of the Mineralogical Society of Korea
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• v.21 no.2
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• pp.117-127
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• 2008

The characteristics of phosphate adsorption-desorption on kaolinite was studied by batch adsorption experiments and detailed adsorbed state of phosphate on kaolinite surface was investigated using ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) spectroscopy. The phosphorous contents were measured using UV-VIS-IR spectrophotometer with 820 nm wavelength. The adsorbed P was generally increased with increasing pH value in the range of pH 4 to pH 9, however it is not distinct. Moreover the adsorbed P was significantly changed with different initial phosphate concentration. The adsorption isotherms were well fitted with the Langmuir equation, Temkin equation, and Freundlich equation in descending order. The maximum Langmuir adsorption capacity of kaolinite KGa-2 is 232.5 ($204.1{\sim}256.5$) mg/kg and has very higher value than that of kaolinite KGa-1b. Most of adsorbed phosphate on kaolinite were not easily desorbed to aqueous solution, but might fixed on kaolinite surface. However it needs further research about the exact desorption experiment. It was impossible to recognize phosphorous adsorption bands on kaolinite in ATR-FTIR spectrum from kaolinite bands themselves, because the absorption peaks of phosphorous have very similar positions with those of kaolinite, and the intensities of the former were very weak in comparison with those of the latter.

• Journal of the Mineralogical Society of Korea
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• v.17 no.1
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• pp.1-9
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• 2004

Copper(II) sorbed on kaolinite (KGa-lb) was studied using electron paramagnetic resonance (EPR) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The sorbed copper(II) had an isotropic EPR signal with $g_{iso}\;=\;2.19$ at room temperature. At 77 K, the isotropic signal converted to an axially symmetric anisotropic signal with $g_{\$\mid$}\;=\;2.40,\;g_{\bot}\;=\;2.08,\;and\;A_{\$\mid$}\;=\;131\;G$. These EPR results suggest that the sorbed copper(II) forms an outer-sphere surface complex with a tetragonally distorted $CuO_{6}$ octahedral structure on the kaolinite. In the sorption measurement, the amount of sorbed copper increased with increasing pH of the solution. However, the intensity of the isotropic EPR line was not directly proportional to the amount of sorbed copper. This discrepancy was resolved by assuming the formation of a surface precipitate at higher pH that is invisible by EPR. The EXAFS data confirmed the existence of the surface precipitate. The best fit for the EXAFS of the sorbed copper showed that each copper on the kaolinite had 6.8 copper neighbors located $3.08\;{\AA}$ from it, in addition to the first shell oxygen neighbors, including 4 equatorial O at $1.96\;{\AA}$ and 2 axial O at $2.31\;{\AA}$. This work shows that the local environment of the copper sorbed on the kaolinite changes as a function of pH and surface loading, and that the EPR and EXAFS are useful in studying such changes.