Kinetics of sorption-desorption

The fate of nutrients, pollutants and other solutes in natural waters is coupled to their distribution between solid, aqueous and gas phases. The processes of phase distribution are many, including penetration and absorption into one of the phases, or accumulation at the interface between them. The term sorption is defined here as the full range of processes whereby matter is partitioned between the gas, aqueous and solid phases. In geochemical systems, this includes adsorption of matter at the surfaces of solid particles (minerals and organic matter) or at the air-water interface, and absorption into the solids during surface precipitation or solid phase diffusion. The complexity of natural geomedia (Fig. 4.1) implies that both broad classes of sorption reaction may occur simultaneously. As discussed in this chapter, recent research into the kinetics and mechanisms of sorption for inorganic and organic species indicates that both processes are indeed important. The relative predominance of a given reaction and sorbate-sorbent structure is a function of time scale, system loading and geochemical conditions.