Improvement of aggregate-associated organic carbon and its stability in bauxite residue by substrate amendment addition

Bauxite residue has extreme alkalinity, poor aggregate stability, and low organic carbon content, which limits plant growth on large expanses of bauxite residue disposal areas. Soil formation of bauxite residue is one of the effective approaches to transform bauxite residue into a soil-like medium for revegetation. In order to improve aggregate stability and organic carbon content in the short term, addition of substrate amendments is crucial to accelerate soil formation of bauxite residue. Nevertheless, the effect of different amendments on the stability, organic and humic substances distribution in bauxite residue aggregate is unclear. Therefore, a column experiment was used to investigate the distribution and stability of aggregate, and aggregate-associated carbon by adding phosphogypsum and vermicompost (PVC), and biosolids and microorganism (BSM). The average particle sizes of CK (control check), PVC, and BSM treatments were observed to be similar to 114, similar to 157, and similar to 188 nm, respectively. Compared with CK treatment, the contents of organic carbon, humic acid, and fulvic acid following PVC treatment increased by 1.65, 1.59, and 1.57 times, respectively, and the increased contents of organic carbon, humic acid, and fulvic acid following BSM treatment reached 2.90, 2.69, and 2.60 times, respectively. Results demonstrated that amendment additions enhanced aggregate stability and carbon sequestration, but the effects of BSM treatment were better than those of PVC treatment. The findings offer an evidence that BSM treatment is a feasible approach to accelerate soil formation of bauxite residue, which shows promising applications to reclaim bauxite residue disposal areas.