Intensity Factor in Liquid/Solid Ion Adsorption Systems

Experiments of Zn2+ and Cd2+ adsorption on vermiculite in aqueous solutions were carried out in ion concentration range 25～500 mg/L and adsorbent concentration range 10～150 g/L at a constant temperature of 25 ℃.Results obtained from the tests indicate that the equilibrium adsorption density q_e(the ratio of adsorption quantity to adsorbent quantity) was uniquely determined by the difference between C_0/W_0(the ratio of initial ion concentration C_0 to adsorbent concentration W_0) and C_e/W_0(the ratio of the equilibrium ion concentration in liquid phase C_e to W_0),independent of ion and adsorbent concentration and process history.Repeated tests have confirmed that given C_0/W_0,q_ecorresponded to a unique C_e/W_0.The argument presented here is that the intensity factor in a liquid/solid ion adsorption system is not the volume-based ion concentration but rather the ratio of ion quantity to adsorbent quantity as it is the relative level of ion quantity to adsorbent quantity that determines both the direction and rate of the ion adsorption.Ion adsorption arrives at equilibrium only when the difference in sum of ion and adsorbent chemical potentials between liquid and solid phases is zero.