Document Type : Original Research Paper

Authors

• shima rahimi
• Mehdi Irannajad

Amir Kabir University of Technology, Hafez Ave., Tehran, Iran

Abstract

In this study, Red Mud (RM) as a byproduct in alumina production process from bauxite was used as an adsorbent for sulfate contaminant adsorption from acid mine drainage (AMD). AMD discharge led to the acidification of water which has detrimental effects on aquatic life and human health. Analytical methods, laboratory studies and molecular simulations were conducted to investigate sulfate adsorption on RM. Thermodynamic calculations were performed after optimizing of existing metal oxide in RM structure with the Material Studio software using the dmol3 and DFT method. The adsorption energy results by Adsorption locator module determined -819.09, -561.7, -268.8, -105.4, and -314.7 kcal/mol for Fe₂O₃, Al₂O₃, CaCO₃, TiO₂ and SiO₂, respectively. The most active compounds in RM structure (iron and aluminum oxides) account for 22.5% and 13.3% in the red mud structure, respectively. In addition, seawater washing was employed as RM modification methods, and it could decrease high rates of pH and improve the sorption capacity of raw RM. The effect of this modification was investigated by simulation of solvent in adsorption environment of sulfate on RM and the dielectric constant selection. For water as the primary solvent with a dielectric constant of 78.54, adsorption energy for RM was calculated to be -35.68 kcal/mol and it was increased to -56.69 kcal/mol for the seawater medium with a dielectric constant of 86. Therefore, RM can be considered as a potential sulfate adsorbent because of cost-effectiveness and alkaline pH that can lead to the neutralization of AMD.

Keywords

• Sulfate
• Adsorption
• Red Mud
• Seawater
• Molecular Simulation

Main Subjects

• Environmental Management