CHAPTER 8

Applicability of Activated Carbon

8.1 Liquid-Phase Adsorptions

Applications of activated carbons (AC) in liquid-phase adsorptions are extensive, the num-ber running into thousands. This Chapter makes no attempt to summarize such involve-ments, but concerns itself with explanations of mechanisms of adsorption of inorganic and organic species from the aqueous phase. In this way, an understanding of the factors which control extents of adsorption is made available and can be extended to other systems. This Chapter also highlights applications of major industrial importance.

8.1.1 Introduction

AC is dominantly used for purposes of adsorption, a task for which it is well designed. Essentially, adsorption is restricted to working in one of two phases, from the gas/vapor phase (usually air) or from the Hquid phase (usually water). Fortunately, there is only one gas/vapor phase, but for liquids, two distinct phases need to be considered, namely adsorp-tion from aqueous systems and adsorption from non-aqueous systems.

From the point of view of research investment, studies into the properties of AC have massively been concerned with one-component systems (gas and liquid phases). To go to two-component, gas-phase systems requires a significant upgrading of experimental complexity requiring analysis of the gas phase as well as pressure changes. To go to three-component systems, as may be found in industrial environments, indeed, will be a chal-lenging experiment.

Adsorption from solution, in comparison, is relatively simple to do experimentally, as no volume changes are involved and modern analytical techniques can be easily adapted to measure concentration changes in solutions as complex as you wish. But, do not be deceived by this apparent simplicity. Competitive adsorption may occur between the solv-ent and the solute. Adsorption from solution may be further complicated because the solute may change chemically, or its concentration may change in the solution. Thus, con-centration of an acidic molecule is a function of the pH of the solution and it is to be noted that both the non-dissociated molecule and an associated ion may be adsorbed.

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