Kinetics of adsorption of benzoate and salicylate onto the natural hematite surfaces have been carried out at pH 5 and at a fixed ionic
strength (I=1
×10−4moldm−3). The state of equilibrium was attained at 144 and 70h for benzoate and salicylate, respectively. Adsorption
behaviour of benzoate and salicylate onto the natural hematite was studied over a wide range of pH at a fixed I=5
×10−4moldm−3 NaCl
and at different temperatures. The adsorption isotherms for both the adsorbates were Langmuir type up to pH 8. TheΓmax for benzoate is
≈2.7–13.7 times more than that of salicylate depending on the pH of the suspension. Unlike benzoate, salicylate is not only adsorbed at one
surfacesitebutalsocoversaroundthreeormoresurfacesitesofhematitesurface.Therateconstantforadsorption,K1 forsalicylateontothe
natural hematite is greater than that of benzoate and increases with the increase in temperature and
≈4 times greater at a fixed temperature.
Theactivationenergyfortheadsorptionofsalicylateontothenaturalhematiteis2.9timesmorethanthatofbenzoateonthesameadsorbent
resulting in lowerΓmax
