Kinetics and Controlling Factors of Phenanthrene Adsorption on Limestone

Abstract

Sorption kinetics and controlling factors of phenanthrene (PHE) adsorption on limestone were obtained by batch experiments. A pseudo-first-order equation fit well with the experimental data. Roles of carbonate and organic matter in the adsorption process of PHE were studied by using a sequential separation procedure. It was discovered that organic matter remarkably affected the behavior of PHE in the adsorption procedure, and carbonate slightly affected the adsorption process due to its influence on physical characteristics of limestone. Different pH conditions led to precipitation and dissolution of carbonate and dissociation of limestone hydroxyl groups, which affected adsorption capacity. In the presence of low ionic strength, calcium ions would occupy some adsorption sites, leading to a decrease in PHE adsorption. By contrast, standard free energy (DG 0 ) became more negative when the concentration of CaCl 2 increased from 0.005 to 0.1 M, which was consistent with the amount of adsorption increase. The influence of humic acids (HA) was also investigated. There was competitive adsorption between PHE and HA. The affinity of HA for limestone was stronger than that of PHE, which when adsorbed on limestone could be desorbed by HA added later. Finally, the coexistence of PHE and acenaphthylene indicated that there was a competitive adsorption between them, although it was easier for PHE to be adsorbed on limestone.