Characterization of the clomazone sorption process in four agricultural soils using different kinetic models.

Kinetic studies are important for understanding the parameters and processes involved in the sorption of pesticides to soil. Considering the agricultural and environmental relevance of clomazone, its sorption kinetics was studied in four agricultural soils (Regosol, Planosol, Chernozem and Vertisol) at two concentrations (0.5 and 15 mg L-1). Different kinetic models were applied to the experimental data. The pseudo-second-order model described the data much better than the hyperbolic and pseudo-first-order models, and the kinetic rate constants indicated concentration-dependent clomazone sorption kinetics. The application of the two-site nonequilibrium model (TSNE) revealed a more time-dependent sorption of the lower clomazone concentration than that of the higher clomazone concentration, and the greatest concentration impact occurred in Regosol. Elovich and intraparticle diffusion models predicted more intensive sorption during the slower second phase and that sorption kinetics is governed more by mass transfer across the boundary layer than by a intraparticle diffusion process at higher clomazone concentration. Intraparticle diffusion is the rate-controlling process in Regosol at lower concentration, while this process and the boundary layer control the sorption kinetics in other soils. Significant correlations between some kinetic parameters and soil properties indicate an impact of the soil texture on the clomazone sorption mechanism, which must be considered in assessing the clomazone leaching behavior.

Examination of the influence of phenyltrimethylammonium chloride (PTMA) concentration on acetochlor adsorption by modified montmorillonite.

The results presented in this paper show an impact of the concentration of the aromatic organic cation on the adsorption of acetochlor on the surface of the organic-modified montmorillonite. Natural montmorillonite from Bogovina (Boljevac municipality, Serbia) was used for organic modification in this experiment. Cation exchange capacity of this montmorillonite (86 mmol 100 g-1 of clay) was determined using the methylene blue method. In pretreatment, montmorillonite was modified with NaCl. For the purpose of organic modification, three different concentrations of phenyltrimethylammonium chloride (PTMA) have been selected, based on calculated CEC value: 43 mmol 100 g-1 of clay (0.5 CEC), 86 mmol 100 g-1 of clay (1 CEC) and 129 mmol 100 g-1 of clay (1.5 CEC). The changes in the properties of the inorganic and organic modified montmorillonite were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and batch equilibrium method. Freundlich coefficients show higher uptake of the herbicide by montmorillonite modified with PTMA, compared to inorganic-modified montmorillonite. The results also indicate the influence of the organic cation concentration on the adsorption of the selected herbicide.

Influence of the organic complex concentration on adsorption of herbicide in organic modified montmorillonite.

This study was undertaken to determine the impact of the organic complex concentration on the adsorption of herbicide (acetochlor) at the surface of the organic modified montmorillonite. In this work, natural montmorillonite from Bogovina (Boljevac municipality, Serbia) was used for organic modification. Cation-exchange capacity of this montmorillonite was determined using a methylene blue method (86 mmol/100 g of clay). Montmorillonite has been modified first with NaCl and then with hexadecyltrimethylammonium bromide (HDTMA-bromide) organic complex. Saturation of cation exchange capacity (CEC) was 50%, 100%, and 150%. Changes in the properties of the inorganic and organic montmorillonite have been examined using the X-ray diffraction, Fourier transform infrared spectroscopy, and batch equilibrium method. Montmorillonite modified with HDTMA-bromide demonstrated higher uptake of the herbicide, compared to the inorganic montmorillonite. Comparing the values Freundlich coefficients in batch equilibrium method, it can be seen that the adsorption of acetochlor decreased in the series: 0.5 CEC HM > 1 CEC HM > 1.5 CEC HM > NaM.

Near-infrared spectroscopy study for determination of adsorbed acetochlor in the organic and inorganic bentonites.

NIR spectroscopy is used to determine acetochlor herbicide adsorption on Na-montmorillonite (NaP) and organically modified montmorillonite (NaOM). Both montmorillonites NIR spectra shows bands at 7061 and 6791 cm(-1). Organo-montmorillonite is characterised by two emphasized bands at 5871 and 5667 cm(-1) that are attributed to the fundamental overtones of the mid-IR bands at 2916 and 2850 cm(-1). Bands at 6017 and 6013 cm(-1) are attributed to acetochlor adsorbed to organo-montmorillonite and Na-montmorillonite, which is confirmed by X-ray powder diffraction (XRPD). Greater quantity of acetochlor is adsorbed to organo-clays compared to non-modified montmorillonite. Acetochlor poses high risk to environmental contamination. Organo-clays are the most useful for removing acetochlor from water and soil.

Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia).

Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H(2)SO(4) acid caused an exchange of Al(3+), Fe(3+) and Mg(2+) with H(+) ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC) and significant increase of specific surface area from 6 to 387 m(2) g(-1) (bentonite from Petrovac) and from 11 to 306 m(2) g(-1) (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites.