Equilibration Time in Adsorption Studies When faced with the question of how long the solution and solid should be left in contact for adsorption equilibrium to be established, a vague estimate of 1-3 hr may be suggested, and when poor results are obtained it is not unknown for the blame to be attached to "insufficient time allowed for equilibration." A convenient instrumental method for obtaining an experimentally hased answer, for the adsorption of an acid onto a solid, involves following the pH change of the acid solution with time. Typical results, shown in the figure, indieate that equilibrium time may be short in same eases, but in excess of 1hr in others. This method, which avoids lengthy sampling and titration techniques, could be applied t o many other simple systems of different adsorbent and adsorbate, using other instrumental techniques (conductance, ion selective eketrodes, etch
J. A. Wood
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Department of Chemical Sciences T h e Polytechnic Queensgate, Huddersfield HDL 3DH, England
Volume 56, Number 4, April 1979 / 277
