Kationos felületaktív anyag (hexadecilpiridinium-klorid monohidrát) adszorpciója talajokon | Adsorption of cationic surfactant (hexadecylpyridinium chloride monohydrate) on soil

Studies were made on the adsorption of a cationic surfactant, hexadecylpyridinium-chloride (CPC), on various soils, sediments and minerals. Very few data are available in the literature on the CPC adsorption on real soil. The aim was to determine which soil characteristics have the greatest influence on surfactant adsorption. The mineral composition of the samples was measured by X-ray diffractometry, which revealed six groups based on the dominant mineral: 1: Smectite soils (soils with low- charged montmorillonite); 2. Vermiculite soils; 3. Illite soils also containing smectite; 4. Soils containing chlorite/vermiculite; 5. Illite- and chlorite-containing soils; 6. Soils with high quartz content. The samples were treated with surfactant in the course of static equilibrium experiments. The quantity of surfactant adsorbed by the samples was plotted as a function of the concentration of the CPC solution, after which Langmuir isotherms were fitted to the measurement points. The specific quantity of surfactant required to make the adsorbents hydrophobic was determined based on the adsorption isotherms, assuming that a monomolecular surfactant layer was formed on the surface of the soil particles. The fitted curves were of the saturation type, the first section of which was characteristic of high affinity (H-type) isotherms. Later, logarithmic plotting was employed, and the analysis of the surfactant adsorption values thus obtained showed that the surfactant quantities needed to form a monomolecular layer differed significantly for the individ-ual samples. The specific CPC quantity was highest for the smectite samples, which have high clay content, and lowest for the quartz sand. Pearson’s correlation coefficients were calculated to determine which characteristics of the samples were correlated with the specific CPC quantities. Strong stochastic relationships were detected with the cation exchange capacity (CEC) and with the adsorbed water vapour (hy ₁), which can also be considered as monomolecular. A weaker but significant correlation was found with the soil pH(H ₂O). After backward elimination, the regression equations found to describe CPC adsorption involved the clay content, BET specific surface area, humus content, carbonate content and pH(H ₂O).