clay and 2-4-6-trichlorophenol

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.

Topics: Adsorption; Aluminum Silicates; Aniline Compounds; Bentonite; Chlorophenols; Chromatography, High Pressure Liquid; Clay; Dose-Response Relationship, Drug; Geologic Sediments; Kaolin; Soil Pollutants; Solubility

Humic acids and clays are important soil components that influence the sorption and desorption of organic contaminants; however, it is unclear how humic acids influence the sorption of organic contaminants onto clays and their subsequent desorption. Sorption and desorption of 2,4,6-trichlorophenol (2,4,6-TCP) by and from humic acid-modified K(+)- and Ca(2+)-montmorillonite and -illite were compared with unmodified clays using batch equilibration methods. Commercial humic acid and the humic acid extracted from forest soil were employed in this experiment. The adsorbed amount of 2,4,6-TCP by commercial humic acid was almost twice as large as that adsorbed by the extracted soil humic acid. More 2,4,6-TCP was sorbed onto K(+)- and Ca(2+)-illite than onto K(+)- and Ca(2+)-montmorillonite. K(+) clays were more effective in adsorbing 2,4,6-TCP than Ca(2+) clays. Sorption of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-montmorillonite and -illite increased as compared with unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-illite increased remarkably as compared with the unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-montmorillonite increased slightly in contrast to unmodified montmorillonites. By comparing sorption and desorption results, we observed hysteresis for all sorbents including humic acids, clays, and humic acid-modified clays. Sorption nonlinearity and hysteresis were dependent on the structure of humic acids. Higher aromaticity of humic acids resulted in greater sorption nonlinearity and desorption hysteresis. In addition, sorption capacity (K(f)') was positively correlated with the humic acid content of the sorbents. These results show that modification of humic acids on clays can not only increase the adsorption ability of clays but also affect the sorption nonlinearity of 2,4,6-TCP, and the desorption hysteresis was probably due to the structural characteristics of humic acids.

Topics: Adsorption; Aluminum Silicates; Bentonite; Calcium; Carbon; Chlorophenols; Clay; Humic Substances; Minerals; Potassium; Soil Pollutants