Attapulgite as Potential Adsorbent for Dissolved Organic Carbon from Oily Produced water

Abstract

The adsorption capacity of attapulgite, a natural clay, for the removal of dissolved organic carbon (DOC) from oily water was investigated in a batch system. The aim of this study was to understand the mechanism associated with the removal of DOC by attapulgite. The effectiveness of attapulgite to adsorb DOC was investigated as a function of equilibrium time, initial DOC concentration, solution pH, temperature, and attapulgite concentration. Two particle sizes of attapulgite were used, granular (1 mm) and powder (0.25 mm). In most cases the equilibrium data fit best with the Langmuir isotherm. The maximum monolayer coverage was found to be 31 mg/g for granular and 65 mg/g for powder attapulgite. The separation factor, RL, from the Langmuir isotherm and, n, the constant from the Freundlich isotherm indicated favorable adsorption. Changes in the pH of the oily water had no significant influence on the adsorption capacity. The adsorption follows the pseudo-second order model. The governing transport mechanisms in the sorption process appear to be both external mass transfer and intra-particle diffusion. The adsorption process was found exothermic in nature. The Langmuir isotherm model equation was adopted to design a single-stage batch absorber for DOC adsorption onto attapulgite. The study demonstrated that attapulgite can be utilized as a potential alternative low-cost adsorbent for the removal of DOC from oily water.