Evaluating aggregate stability, surface properties and disintegration behaviour of bauxite residue induced by Ca/Na

Abstract

Bauxite residue, a typical industrial solid waste which contains a large amount of Na+, is usually physically degraded. Understandings of aggregate formation, which is a critical process in soil development, are essential to facilitate ecological rehabilitation on the disposal areas. However, few studies have investigated the aggregation behaviour and mechanisms of key salt ions (Ca2+ and Na+) in residue aggregates. Therefore, an integrated method of Le Bissonnais' method, the combined determination method and laser diffraction measurements was applied to evaluate aggregate stability, surface properties and disintegration behaviour of bauxite residue following Ca/Na additions. With increasing Ca2+ addition, mean weight diameter increased, indicating improved resistance to dispersion. Ca2+ had a positive effect on flocculation of silt‐size microaggregates, while disintegration was induced following Na+ addition. Repeated laser diffraction analysis of residue samples circulating in 50 mmol L−1 electrolyte solution (Ca2+/Na+) provided a detailed view of the changes in particle size distribution as aggregates fragmented. The visualized three‐dimensional surface map revealed that Na+ promoted the disintegration of >250 μm aggregates into finer dispersed particles, while Ca2+ protected the microaggregates from fragmenting into smaller particles. Variation in electrochemical properties of aggregate surfaces affected the micro‐morphology significantly. The findings provide a new approach to specify pedogenic aggregate behavior of bauxite residue, while revealing the effects of Ca2+/Na+ on aggregate stability, surface electrochemical properties and its micromorphology. The results will provide a detailed understanding of aggregate behavior during soil formation process in bauxite residue.

The aggregation effect of organic matter on bauxite residue particles and its improvement mechanism

“…In addition, companied with the transform of the aggregates' morphology from the loose microstructure (CK) to a soil-like structure appearance (HS3) (Figure 7C), there was a markable increase for the distribution of Ca, Fe and Al elements on the aggregate surface (Figures 7A,B). It showed that Ca 2+ had a good affinity with the soil colloidal surface, which could reduce the dispersion of clays, and promote the flocculation and stability of aggregates (Harris and Rengasamy, 2004;Xue et al, 2021). So that, beside of the directive cohesion between aggregates, Increasing the level of Fe/Al oxides and Ca 2+ also is principal way for organic amendment to promote the aggregation of fine bauxite residue particles.…”