Effect of Red Mud and Rice Husk Ash-Based Geopolymer Composites on the Adsorption of Methylene Blue Dye in Aqueous Solution for Wastewater Treatment

In this study, geopolymer originating from locally industrial byproducts as red mud (RM) was successfully prepared in the presence of different loadings of rice husk ash (RHA) used for the adsorption of methylene blue (MB) in wastewater. During geopolymerization, various mixing amounts between RM and RHA were conducted when the weight ratio of binder solution/activated alkali-metal solution (Na2SiO3/ NaOH 7 M) was 2.5 and the curing temperature was set at 60 °C for 24 h. As a result, the surface area value of the prepared geopolymer composited with RHA at 0 and 60% was increased from 19.2 to 29.5 m2/g, while the BJH pore size of the prepared geopolymer was reduced to 6.68 and 5.76 nm, respectively. In the dye removal test, higher additions of RHA in the RM-geopolymer maintained better retention of the MB ion due to the increase in the adsorption binding site. The maximum uptake amount of dyes performed at pH 8 was changed from 6.59 to 10.74 mg/g, while RHA was from 0 to 60% after 180 min of immersion in MB solution. The adsorption isotherms well obeyed the Langmuir model, as the relative coefficient R2 was 0.999. Based on these, the initial agricultural waste as RHA and industrial byproducts as RM were valued as functional materials used for dye treatment in wastewater.