Efficient Removal of Crystal Violet Using Fly Ash Steel Slag Based Geopolymer

Abstract

The low adsorption capacity and structural limitations of conventional geopolymers hinder their application in wastewater treatment. This study addresses these challenges by developing a carbonated fly ash-steel slag-based geopolymer (GP) for efficient Crystal Violet (CV) dye removal. Carbonated GP (GP-C) was synthesized via alkali activation and CO₂ curing, achieving a 91.66% removal efficiency and 6.11 mg/g adsorption capacity (vs. 76.04% and 5.07 mg/g for non- carbonated GP). BET analysis confirmed that carbonation increased the specific surface area from 13.14 m²/g to 56.70 m²/g by refining mesopores from 15–40 nm to 5–15 nm, enhancing adsorption efficiency. while FTIR/XPS identified key mechanisms: (1) hydrogen bonding between CV and hydroxyl groups (Si-OH) and (2) electrostatic attraction between CV⁺ and aluminosilicate gels ([AlO⁴]^4-/[SiO⁴]^4-). The adsorption adhered to the Freundlich isotherm (heterogeneous surface) and pseudo-second-order kinetics. GP-C also exhibited broad pH adaptability (optimal at pH 9) and rapid equilibrium (90 min). This work highlights the dual role of carbonation in enhancing porosity and surface reactivity, offering a sustainable strategy to repurpose industrial waste (steel slag/fly ash) for dye pollution remediation.

Keywords: geopolymer; carbonation; adsorption; crystal violet; fly ash; steel slag; industrial solid waste

DOI: 10.7176/JEES/15-2-06

Publication date: April 30th 2025