Adsorption of Acid Dyes on Anionic Clays

The presence of colour in many industrial effluent streams especially from the
textile industry is aesthetically undesirable. Traditionally both biological and chemical
methods have been employed for dye removal from waste streams, but these techniques
have not been successful due to its highly structured polymers which are very difficult to
decompose. Many physical and chemical treatment methods including coagulation,
precipitation, filtration, membrane separation and oxidation have been used for the
treatment of dye-containing effluents. Over the last few decades, sorption (as adsorption,
biosorption and ion exchange) has gained importance as an effective purification and
separation technique used in wastewater treatment. Activated carbon has been the most
widely used adsorbent because of its high capacity for the adsorption of organic species.
However due to the difficulty, high cost and expensive regenerationof the activated
carbon, clays are being considered as alternative low cost adsorbents. A potential
candidate is the hydrotalcite, a type of layered double hydroxide (LDH), occurs as natural
clay like mineral and can be readily synthesized by co-precipitation method.