Effect of linear-dodecylbenzenesulfonate and humic acid on the adsorption of tricresyl phosphate isomers onto clay minerals

The adsorption of three tricresyl phosphate (TCP) isomers, o-, m-, and p-TC P, onto kaolin, alumina, and montmorillonite without coating or coated with linear-dodecylbenzene-sulfonate (DBS) or humic acid was studied. The amoun t of TCP isomers adsorbed per unit mass of mineral followed the order alumi na < kaolin < montmorillonite, but that per unit surface area of mineral wa s in the order kaolin < montmorillonite < alumina. The amount of TCP adsorb ed was almost constant between pH 4 and 9. Higher adsorption per unit surfa ce area on alumina might be due to the strong interaction between Al and ph osphate oxygen (P=0) of TCP. Adsorption of TCP isomers on kaolin and alumin a followed the order o-TCP < m-TCP < p-TCP, depending on their steric hindr ance. Adsorption of TCP isomers on kaolin and alumina was enhanced with an increase in DBS adsorbed. This might be due to the hydrophobic interaction of TCP isomers with DBS adsorbed on minerals. Similarly, the adsorption of TCP isomers was accelerated in the presence of humic acid. However, adsorpt ive capacity of TCP isomers on minerals coated with humic acid was smaller than that with DBS. This is possibly due to the difference in hydrophobicit y between humic acid and DBS adsorbed. It was confirmed that the carbon-nor malized adsorption coefficient (K-oca) decreased with increasing carbon mas s fraction of DBS and humic acid adsorbed on minerals.