Material properties and environmental implications of red mud solidified with blast-furnace slag, silica fume, and sodium hydroxide

Abstract

Red mud, an alkaline waste from bauxite refining, takes up land and poses environmental risks from its storage. This study examines red mud treatment, assessing blast furnace slag (GGBS), silica fume (SF), and sodium hydroxide (SH) for solidification. Tests show a mix of 79% red mud, 15% GGBS, 3% SF, and 3% SH yields a 28-day compressive strength of 13.12 MPa, suitable for industrial materials. Solidified red mud’s resistivity rises and permeability drops over time, enhancing impermeability and compactness. Durability tests through seven wet-dry and freeze–thaw cycles show solidified red mud’s excellent durability, with mass loss below 2% and compressive strength over 9.67 MPa. Scanning Electron Microscopy and Energy Dispersive Spectroscopy show solidified red mud is filled with Calcium-Alumino-Silicate-Hydrate gel and ettringite crystals, reducing porosity and improving particle bonding. X-ray diffraction and Mercury Intrusion Porosimetry tests confirm their even distribution within the mud. Environmental analysis shows solidified red mud reduces heavy-metal leaching and stabilizes radioactive nuclides. Life-cycle assessment indicates it cuts carbon footprint by about 45.23% compared to traditional cement, highlighting sustainability and economic advantages. In summary, the study validates that GGBS, SF, and SH enhance red mud’s environmental performance, offering new paths for sustainable industrial waste utilization.

Graphical abstract