Development and Characterization of Porous Geopolymer Pellets for Dye Adsorption

Apart from being a water-intensive process, the textile industry also poses problems in wastewater generation. The dyeing section alone contributes to about 15-20% of total waste water that is generated in an average sized textile mill. Various techniques for dye removal have been employed and some of these are physical separation method, biological treatment, and chemical method. However, these techniques suffer from flaws one way or another and are still not widely used in the industry for reasons like economical, disposal or availability of raw material. This project aims to develop a novel method of converting raw fly ash to porous geopolymer pellets for the purpose of dye wastewater treatment by adsorption. The porous geopolymer pellets were prepared from mixing raw fly ash and 10M of NaOH as alkali activator. Various amounts of sodium silicate were added as desired in order to vary the Si/Al ratio. It has been found that parameters such as curing temperature of the pellets, Si/Al ratio and pH of the dye solutions greatly affect the dye adsorption capacity of the samples. The geopolymer pellets that were cured at 70°C with 1.8 Si/Al ratio and pellets that were cured at 60°C with Si/Al ratio of 2.0/1 show the most promising adsorption capacity without compromising the mechanical properties of the sample. Also, at lower pH, the adsorption of all samples have decreased which is due to the presence of H+ ions in the dye which gets selectively adsorbed by the geopolymer pellets. After analyzing the plot of kinetic models and adsorption isotherms, pseudo-second order and two-site Langmuir isotherm models were identified as the best-fit curves for the acquired experimental data. The results imply that the geopolymer pellets have a high potential to be packed in a column which can provide an alternative means of treating dye wastewater in an industrial scale.