Adsorption of dyes using different types of clay: a review

Increasing amount of dyes in the ecosystemparticularly in wastewater has propelled the search for moreefficient low-cost adsorbents. The effective use of thesorption properties (high surface area and surface chemistry,lack of toxicity and potential for ion exchange) of differentclays as adsorbents for the removal of different type of dyes(basic, acidic, reactive) from water and wastewater aspotential alternatives to activated carbons has recentlyreceived widespread attention because of the environmen-tal-friendly nature of clay materials. Insights into the effi-ciencies of raw and modified/activated clay adsorbents andways of improving their efficiencies to obtain better resultsare discussed. Acid-modified clay resulted in higher rate ofdye adsorption and an increased surface area and porosity(49.05 mm2and 53.4 %). Base-modified clay has loweradsorption capacities, while ZnCl2-modified clay had theleast rate of adsorption with a surface area of 44.3 mm2andporosity of 43.4 %. This review also explores the grey areasof the adsorption properties of the raw clays and theimproved performance of activated/modified clay materialswith particular reference to the effects of pH, temperature,initial dye concentration and adsorbent dosage on theadsorption capacities of the clays. Various challengesencountered in using clay materials are highlighted and anumber of future prospects for the adsorbents are propose