Kinetics and isotherms of dazomet adsorption on natural adsorbents

the adsorption of 3,5-dimethyltetrahydro-1,3,5-thiadiazine-2-thione (dazomet) on bentonite and clinoptilolite has been studied at four temperatures (288, 293, 298 and 303 k) and two different solutions (water and water-ethyl alcohol mixture, 50% v/v). the adsorption rates at low concentrations of dazomet were found to fit the first-order kinetic equation. for each system at constant concentration, the rate constants increased with increasing temperature in aqueous solution, but these constants decreased with increasing temperature for 50% (v/v) water-ethyl alcohol mixture solution. by using the arrhenius equation, the activation energies for each system were calculated. thermodynamic parameters were evaluated according to eyring's equation. the values of enthalpy of activation, dh*, are lower than tds*. the results indicated that the adsorption process was entropy-controlled for each system. adsorption isotherms were determined at 288 and 303 k. these isotherms were fitted to freundlich equation for aqueous solution at 15 °c, but adsorption from the two different solutions at 30 °c were modeled according to the langmuir and bet isotherms.