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The rates of adsorption of a basic dye, Astrazone Blue, and an acidic dye, Telon Blue, on wood have been studied. The rate controlling step is mainly intraparticle diffusion, although a small resistance due to a boundary layer is experienced. The activation energies for the adsorption of Astrazone Blue and Telon Blue on wood are 16.8 kJ mol−1 and 9.6 kJ mol−1, respectively. The diffusion coefficients vary from 6×10−13 cm2 s−1 to 18×10−13 cm2 s−1 for Astrazone Blue at 18°C and from 3 × 10−13 cm2 s−1 to 8 × 10−13 cm2 s−1 for Telon Blue at 18°C. The variation in diffusivities is attributed to boundary layer effects.

SynopsisThe specific surface areas of various particle size ranges of wood and peat were determined. The methods employed are mercury porosimetry, nitrogen adsorption, and solution isotherms. The results indicate that dye solution isotherms offer an accurate means of surface area measurement, however, the values obtained are dependent on (a) the chemical nature of the solute and adsorbent and (b) the molecular dimensions of the solute. Nitrogen isotherms indicate specific surfaces of (21 X 103)-(27 X lo3) m2 kg-' for wood depending on the particle size, while an area of 26.5 X lo3 m2 kg-' was obtained for peat independent of particle size. Acid dye isotherms yield specific surfaces considerably lower than nitrogen isotherm values; for wood (7.3 X 103)-(9.6 X lo3) m2 kg-I and for peat, (5.2 X 103)-(11.8 X lo3) m2 kg-I. Basic dye studies, using wood, indicate surface areas similar in magnitude to those obtained from nitrogen isotherms. For peat, however, very large apparent surface areas are obtained (-100 X 103 m2 kg-') and are attributed to chemical interaction between dye molecules and adsorbent and stacking of dye molecules.

The ability of Sorbsil silica gel to remove dye from solution has been studied. The effects of contact time, initial dye concentration, and adsorption isotherms have been determined for different particle size ranges. The kinetics of the adsorption process have been studied and an overall diffusion coefficient has been evaluated. The dlffusivity for the adsorption of Astrazone Blue on silica has been determined to be 1.2 (±0.2) X 10~8 cm2 s~1.