Batch and fixed bed adsorption of methylene blue onto foamed metakaolin-based geopolymer: A preliminary investigation

Synthetic dyes, represent a serious hazard for the aquatic environments and groundwater system. The removal of dyes by the adsorption process avoids the production of sludge and secondary toxic compounds and offers high efficiency and very short operational times. In the present work, cationic Methylene Blue (MB) dye was used as a model pollutant to investigate the adsorption properties of a foamed geopolymer. The adsorbent has an apparent density of 0,75 g/cm3. It is characterized by a complex system of spherical and interconnected macro-pores with a mesopore volume of 0.143 cm³ /g that favors the mass transport and a pHpzc equal to 8.2. Batch and fixed granular bed column tests were carried out. The maximum MB uptake, in batch experiments, was 40.0 mg/g. Removal efficiency was around 95% up to a MB concentration of 25 mg/L. The pseudo second order kinetic model and Langmuir isotherm model better describe MB adsorption onto geopolymer. Fixed granular bed column tests were carried out by varying the initial dye concentration at a constant flow rate and bed height. Results are better fitted by Yoon and Nelson model. The obtained results demonstrate that foamed geopolymers are good candidates for the removing MB from aqueous solutions.