Comparative study on the adsorption kinetics and equilibrium of common water contaminants onto bentonite

Abstract

The adsorption of phenol (Ph), bisphenol A (BPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and ibuprofen (IBU) from aqueous solutions on two raw bentonites was investigated. The adsorption was strongly pH-dependent—the removal of all the adsorbates decreased significantly with an increase in the initial pH of the solution. The kinetics was fitted with the pseudo-first-order, pseu-do-second-order, Elovich, and intra-particle diffusion models and the adsorption kinetics was better represented by the pseudo-second-order equation. The adsorption rate increased in the order: Ph < 2,4-D < BPA < IBU on both the adsorbents. The equilibrium adsorption data were modeled with Langmuir, Freundlich, and Langmuir-Freundlich equations and results showed that it was better described by the Langmuir-Freundlich equation. Adsorption of the selected contaminants on both the adsorbents increased in the order Ph < 2,4-D < BPA < IBU, which correlates well with the respective decrease in solubility of the adsorbates. Adsorption of the Ph, BPA, 2,4-D, and IBU on the bentonites is more or less comparable with other low-cost sorbents.