Sorption and hydrolysis of carbaryl in clay-water suspensions

We studied the influence of clay preparation methods on sorption and hydrolysis of carbaryl by reference clay K-SWy-2.Three different ways of preparation were used: (1) unfractionated (whole clay), (2) fractionated by low speed centrifugation (clay-cent), and (3) fractionated by sedimentation (clay-sed). All clay preparations were K+ saturated. Each preparation manifested mineral fractions with significantly different abilities to hydrolyze carbaryl to 1-naphthol, decreasing in the order: whole clay >> clay-sed. > clay-cent. The extent of 1-naphthol disappearance from solution followed the order: whole clay >>> clay-sed. > clay-cent. X-ray diffraction of the heavy fraction revealed peaks corresponding to calcite and dolomite. Aqueous slurries of whole clay and claysed. were alkaline, whereas the pH of slurried clay-cent. was neutral. Dissolution of carbonates with sodium acetate buffer eliminated hydrolytic activity associated with SWy-2. We recommend for particle size separation the low speed centrifugation procedure followed by treatment with acetate buffer. Sorption of 1-naphthol, by reference clay K-SWy-2, at high and low pH, was studied. We used: (1) whole clay, (2) carbonate-free clay, and (3) carbonate-free clay amended with calcite. For whole clay and carbonate-free clay amended with calcite, ∼80% and 90% of the initial concentration of 1-naphthol disappeared from solution within 24 h, corresponding to 2.0 and 2.3 mglg of clay, respectively. In carbonate-free clay, ∼35% of the initial concentration of 1-naphthol was sorbed by the clay within 24 hours. Negligibly amounts (>1%) of 1-naphthol could be recovered from clay after methanol extractions. It is apparent that 1-naphthol is rendered unextractable by K-SWy-2. The FTIR spectra show that structural OH stretching and deformation bands are perturbed. The OH deformation bands show that only the OH deformation band associated with Fe3+ is reduced for the whole clay, but not for the carbonate-free clay. Oxidative products of 1-naphthol may be produced and caused the change and darkening of color in presence of clay and carbonates.