Insights into the impact of amendment effect on aggregate stability and organic carbon sequestration in bauxite residues

Abstract

Bauxite residue is a large-scale solid waste that is difficult to dispose of owing due to its poor physical properties, weak aggregate stability, and low organic carbon content. Ecological engineering is a unique strategy to realize soil formation and reclamation of bauxite residue. In this study, the effects of incorporating ferric sulfate (FS) and corn straw (CS) on aggregate variation, carbon sequestration, and ryegrass growth in bauxite residue were systematically investigated. The results showed that FS and CS treatments easily facilitated the transformation of bauxite residue aggregates from microaggregates to macroaggregates and raised the MWD value and average particle size of bauxite residue aggregates. Compared with the control group (CK), the average particle sizes of bauxite residue aggregates increased from ∼102 nm to ∼167 nm upon FS treatment and to ∼250 nm upon CS treatment. Upon FS and CS treatments, the aggregate-associated organic carbon content increased in the 2–1 mm and 1–0.25 mm bauxite residue aggregates and decreased in the 0.25–0.05 mm and <0.05 mm bauxite residue aggregates. Compared with CK, following FS and CS treatments, C content increased by 3.0 and 5.5 times and O content increased by 1.6 and 2.1 times, respectively. In addition, FS and CS treatments improved the organic functional group content and ryegrass growth. Among the different treatments, the CS treatment exhibited superior performance in reclamation of bauxite residue, which can be attributed to that CS treatment easily forms more stable aggregates for carbon sequestration and the introduction of corn straw into bauxite residue provides organic matter for microorganism proliferation and nutrients for ryegrass growth. These findings suggest that CS treatment is a facile approach to improve aggregate stability, organic carbon sequestration, and ryegrass growth in bauxite residue, showing potential for the reclamation of bauxite residue.