Effect of substrate amendment on alkaline minerals and aggregate stability in bauxite residue

Bauxite residue is an alkaline waste material in the process of alumina production due to its characteristics of higher salinity and alkalinity, which results in environmental issues and extremely restricts the sustainable development of alumina industries. In this work, we conduct a column experiment to study the effects of two amendments on aggregate stability and variations in alkaline minerals of bauxite residue. The two amendments are phosphogypsum (PG) and phosphogypsum and vermicompost (PVC). The dominant fraction in aggregate is 1-0.25 mm in diameter on the surface, which takes up 39.34%, 39.38%, and 44.51 % for CK, PG, and PVC, respectively. Additions of PG and PVC decreased pH, EC, ESP, exchangeable Na+ concentration and the percentage of alkaline minerals, and then increased exchangeable Ca2+ concentration in bauxite residue. There was significant positive correlation between pH and exchangeable Na+ concentration, the percentage of cancrinite, tricalcium aluminate and calcite; while negative correlation was found in pH value versus exchangeable Ca2+ concentration. Theses findings confirmed that additions of phosphogypsum and vermicompost have a stimulative effect on aggregate stability in bauxite residue. In particular, amendment neutralization (phosphogypsum + vermicompost) in column represents an advantage for large-scale simulation of vegetation rehabilitate in bauxite residue disposal areas.