Removal of Sparingly Soluble Organic Chemicals from Aqueous Solutions with Surfactant-Coated Ferrihydrite

A surfactant, sodium dodecyl sulfate (SDS), was adsorbed onto ferrihydrite at low pH and desorbed at high pH. Adsorption isotherms of SDS on ferrihydrite yielded an S-shaped curve typical for surfactant adsorption on mineral surfaces. This behavior is due to the surfactant forming aggregate structures on the solid surface. SDS adsorption and desorption experiments revealed that both processes were fast, with equilibrium being reached within 1 h. Toluene, p-xylene, and trichloroethylene sorption experiments demonstrated that the SDS-coated ferrihydrite was able to remove these sparingly soluble organic chemicals (SSOCs) from solution. The amount of SSOC sorbed was directly related to the amount of SDS coating the ferrihydrite. The SSOC with the lowest solubility (p-xylene) had higher removals than the high-solubility SSOC (TCE).