The use of organoclays as adsorbents in the remediation of polluted water has been the subject of many recent studies. In the present work, a Tunisian smectite modified with two cationic surfactants was used as an adsorbent to examine the adsorption kinetics, isotherms and thermodynamic parameters of fluoride ions from aqueous solution. Various pH values, initial concentrations and temperatures have been tested. Two simplified kinetic models, first-order and pseudo-second-order, were used to predict the adsorption rate constants. It was found that the adsorption kinetics of fluoride onto modified smectites at different operating conditions can best be described by the pseudo-second-order model. Adsorption isotherms and equilibrium adsorption capacities were determined by the fitting of the experimental data to well known isotherm models including those of Langmuir and Freundlich. The results showed that the Langmuir model appears to fit the adsorption better than the Freundlich adsorption model for the adsorption of fluoride ions onto modified smectites. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy. Results of this study demonstrated the effectiveness and feasibility of organoclays for the removal of fluoride ions from aqueous solution.

RPA 201772 is a preemergence herbicide that undergoes rapid conversion to a diketonitrile metabolite (DKN) in soil. The half-life of RPA 201772 is very short, but the half-life of DKN is much longer; hence, DKN remains for an extended time in soil. Sorption studies were conducted with five soils varying in physical and chemical properties using the batch equilibration technique. Analysis of 14C-ring–labeled DKN was performed using liquid scintillation counting, and sorption data were fitted to the Freundlich model. Isotherms of DKN were nonlinear in all the soils as depicted by the Freundlich exponent (n < 1.0), indicating differential distribution of site energies for sorption. Multiple regression of the sorption constants against selected soil properties indicated that soil organic matter content was the best single determining factor of DKN sorption (r 2 = 0.961) followed by soil pH (r 2 = 0.947). The Freundlich sorption coefficient (KF) decreased in the following order Chelsea, MI > Amherst, MA > Moorhead, MN > East Monroe, CO > South Deerfield, MA. The organic matter content of the soils decreased in the same order. Clay content had a minimal effect on the sorption of DKN, whereas the sorption of DKN increased with an increase in organic matter content and a decrease in soil pH. There was an increase in the sorption of DKN with an increase in Ca2+ concentration of the soil solution, whereas the net sorption constant (Kd) was correlated to the organic matter content of the soils. The site energy distribution of DKN sorption was governed mainly by the organic matter content of the soils.