Adsorption and desorption characteristics of phenoxyacetic acids and chlorophenols in volcanic soil: Single component fixed bed studies

Widespread application of herbicides and pesticides in recent years resulte d in environmental contamination of soils and groundwaters. In this paper, we examine the adsorption and desorption characteristics of three phenoxyac etic acids and three chlorophenols in a volcanic soil using fixed bed soil columns. A theoretical model incorporating sorption, dispersion, film trans fer and surface diffusion in soils particles has been developed to predict the solute movement in fixed bed soil columns. The main feature of this mod el is that all the model parameters were obtained from independent experime nts or from literature correlations. Experiments were carried out to examin e the effect of concentration and flow rate on the breakthrough and elution of phenoxyacetic acids and chlorophenols from soil columns. The results in dicated that increasing the initial concentration and now rate resulted in a faster breakthrough and elution of solutes. The order of breakthrough and elution for phenoxyacetic acids was: 2,4-dichlorophenoxyacetic acid (2,4-D ) > 2-methyl, 4-chlorophenoxyacetic acid (MCPA) > 2,4,5-trichlorophenoxyace tic acid (2,4,5-T) and while for chlorophenols the order was: 2,4-dichlorop henol (2,4-DCP) >para-chloro-ortho-phenol (PCOC) > 2,4,5-trichlorophenol (2 ,4,5-TCP). The results have also shown that the equilibrium sorption played a dominant role in the breakthrough and elution of these chemicals from so il columns. The results of numerical calculations using the model are compa red with experimental results and in general, good agreement was obtained f or all chemicals considered.