Influence of natural regeneration on fractal features of residue microaggregates in bauxite residue disposal areas

Abstract

AbstractBauxite residue is often physically degraded, which limits vegetation establishment on the disposal areas. Microaggregate stability is an important physical property due to its significant effect on erosion and surface runoff; however, this is rarely reported for bauxite residue. Native plant encroachment on a bauxite residue disposal area in Central China has revealed that natural regeneration may ameliorate the residue and help to support plant growth. Residue samples from 5 different disposal ages were collected to determine microaggregate stability and to identify their fractal features. Following natural regeneration, the aggregate fraction 250–50 μm increased significantly from 27.4% to 40.3%, whilst the silt + clay size aggregate fraction decreased from 58.4% to 30.7%. With increasing disposal age, the residue clay dispersion ratio (CDR) ranged from 7.7% to 22.5%, whilst aggregated silt and clay ranged from 15.3% to 19.0%, indicating a stable microaggregate structure. The single‐fractal dimension (D) of the residues for different disposal ages varied from 2.2 to 2.4. The high pH and salinity of bauxite residue indicated a high value of single‐fractal dimension. The multifractal parameters of residue microaggregates, including capacity dimension (D0), information dimension (D1), and information dimension/capacity dimension (D1/D0), decreased, which resulted in homogeneity following natural regeneration. Correlation analysis revealed that both single‐fractal and multifractal dimensions had significant correlations with residue microaggregate stability. Our results suggested that natural regeneration may improve microaggregate stability of bauxite residue, and fractal parameters of residue microaggregates may be used to describe residue microaggregate stability and the physical condition of bauxite residue.