INFLUENCE OF HUMIC-ACID ON WATER-ADSORPTION CHARACTERISTICS OF KAOLINAND QUARTZ

Water vapor adsorption isotherms were measured for samples of kaolin a nd quartz amended with different amounts of humic acid extracted from a Cambic Arenosol under forest. Applying the approximation of the adso rption isotherms with the BET equation the monolayer capacities (surfa ce areas) for the studied systems were calculated. for kaolin systems the surface area decreased sharply at low humic acid additions and thi s slowly increased with the further rise of the humic acid content, wh ereas for the quart the increase of surface area was only noted for hi gh humic acid contents. Using an exponential isotherm equation with a local BET model, thee absorption energy distribution functions were ca lculated for kaolin systems. The shape of the adsorption energy distri butions shown that the increase in humic content changed the character of the surface from more hydrophilic to more hydrophobic. For interme diate humic acid contents, the energy distribution function had two ma xima - more polar and less polar. At high humic acid contents the ener gy distribution function tended to the estimated value for pure humic acid, indicating high surface-coverage with organic material. As measu red by the mercury intrusion porosimetry, for the kaolin samples the a mount of the largest pores decreases and the amount of the smallest po res increases with the accumulation of humic acid. For the quartz syst ems only very high doses of humic acid are reflected in changes of por e size distribution.