Dye Adsorption on Expanding Three-Layer Clays

Many dyes that are used in the textile industry are toxic and tend to accumulate in living organisms directly or indirectly, causing various diseases and disorders. Clay minerals have recently been shown to be good candidates as dye adsorbents for wastewater treatment. This review discusses the use of both natural and modified three-layer clays such as bentonite, montmorillonite, and vermiculite to remove both cationic and anionic dyes. The most important parameters governing adsorption capacities are pH, ionic strength, and modification processes. Specific surface area is somewhat less important. Modification processes include thermal activation, acid activation, surfactant addition, and combinations of these, all of which increase adsorption capacities. Adjusting the pH changes both adsorbent surface properties and adsorbate dye ionization.