ADSORPTION OF CYANAZINE ON PEAT AND MONTMORILLONITE CLAY SURFACES

The adsorption of cyanazine by peat and montmorillonite is studied as a function of the crystal chemical characteristics of exchangeable cations and temperature. The adsorption kinetics of cyanazine on peat shows that the adsorption equilibrium is reached within 1 h. The values of the rate constants of the reaction seem to indicate that the adsorption rate of cyanazine by peat is mainly controlled by the diffusion process. The order of adsorption of cyanazine by peat is as follows: H+ -peat > Cu2+ -peat > Ca2+ -peat > Co2+ -peat > Mg2+ -peat > K+ -peat. The thermodynamic parameters seem to point to an adsorption mechanism by hydrogen bonds, although in the acidic and Cu2+ samples a protonation process and adsorption of the protonated species is also likely. The values of the adsorption rate constant of cyanazine by montmorillonite is ten times higher than that for peat. The adsorption of cyanazine by montmorillonite follows this order: Cu2+ -mont > Co2+ -mont > H+-mont; the adsorption of Cu2+-mont is five times greater than on the other samples. For the Cu2+ samples, the thermodynamic parameters seem to point to a mechanism of direct coordination cyanazine-Cu2+. The most probably mechanism for the adsorption of cyanazine by the Co2+ sample is by physical bonding. For the H+ sample there is a physical adsorption and an ionic one according to the following reaction: H+-mont + cyanazine --> mont - H+-cyanazine.