Preparation and Characterization of Red Mud-Based Geopolymer Composited with Rice Husk Ash for the Adsorption of Bromocresol Green in Aqueous Solution

Abstract

Geopolymer-based industrial waste as red mud (RM) was successfully obtained in the presence of different loadings of rice husk ash (RHA). During the preparation, the added amounts of RHA in the geopolymer composition were varied from 10 to 50 % when the mass ratio of binder solution (Na2SiO3) and activated alkali-metal solution (NaOH 7 M) were 2.5 and the curing condition was fixed at 333 K within 24 h. For characterization, the surface morphology was evaluated by scanning electron microscope (SEM) equipped with the energy-dispersive X-ray, which detected the distribution of elements before and after the geopolymerization. To indicate the formation of geopolymer, Fourier–transform infrared spectroscopy (FT-IR) was used. The effect of the loading amounts of RHA on the Brunauer–Emmett Teller (BET) surface area value and Barrett–Joyner–Halenda (BJH) pore size of the obtained geopolymers were determined using a nitrogen gas adsorption instrument. In the bromocresol-green (BG) adsorption performed at pH 2, the higher addition of RHA in the geopolymer composition enhanced the adsorption capacities within 180 minutes. In addition, the adsorption behavior of the mixed geopolymer to BG fits well the Langmuir model, indicating that the adsorption occurs on the homogeneous monolayer surface of geopolymer. From this study, the RHA could be a natural potential filler to improve the BG-uptake of RM-based geopolymer in wastewater treatment.