Sorptive Removal of Color Dye Safranin O by Fibrous Clay Minerals and Zeolites

Abstract

The increased use of color dyes in industry imposes a great threat to the environment. As such, developing cost-effective techniques for dye removal from wastewater attracted great attention. Earth materials, particularly those with large specific surface area (SSA) and high cation exchange capacity (CEC), were evaluated for their potential use for wastewater treatment. In this study, palygorskite, sepiolite, and clinoptilolite were evaluated for their removal of cationic dyes using safranin O (SO+) as a model compound. The CEC values of the materials played a key role in SO+ removal while other physicochemical conditions, such as temperature, equilibrium solution pH, and ionic strength, had less influence on SO+ removal. Sorbed SO+ cations were limited to the external surfaces of the minerals, as their channel sizes are less than the size of SO+ cation. Molecular dynamic simulations showed dense monolayer SO+ uptake on palygorskite due to its relatively large CEC value. In contrast, loosely packed monomer SO+ uptake was adopted on sepiolite for its large SSA and low CEC. Dense multilayers or admicelles of SO+ formed on zeolite surfaces. As such, for the best SO removal, palygorskite is better than sepiolite, though both are fibrous clay minerals.