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Electrokinetic and FT-IR study of the influence of polyacrylic acids and fulvic acids on SiO_2, Al(OH)_3 and Al_2O_3 which are used as models for clay mineral surfaces

The influence of fulvic acid (FA) and poly(acryl acid) (PAA) on the electrokinetic potentials of model oxides, SiO_2, Al(OH)_3 and Al_2O_3 in 1x10-3 mol dm-3 NaCl solutions at constant pH of 6.5 was investigated. Amorphous SiO_2 shows no influence of FA. Al(OH)_3 shows a significant increase of the negative electrokinetic potential with increasing concentration of FA. For Al_2O_3 the reversal of charge occurs at approx. 4 mg dm-3 of FA in a steeply rising potential with a slope of cca. 60 mV/log c, towards high negative values. FT-IR spectrum of adsorbed fulvic acid on Al_2O_3 is characterized with a new band at 1385 cm-1 comparing to the FT-IR spectrum of pure aluminum oxide. After adsorption of polyacrylic acids, new bands at 1560 and 1323 cm-1 appeared in the FT-IR spectrum of Al_2O_3.

clay mineral surfaces; electrokinetic measurements; adsorbed organic material; FT-IR

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