Influence of exogenous organic matter and P synergies on the geochemical behavior of vanadium in the rehabilitation of bauxite residues

Bauxite residues (BR) from the Bayer process to produce alumina are highly alkaline and saline, containing high-level toxic elements (such as vanadium (V)), which are soluble in water under the alkaline pH condition. Ecological engineering of the BR can significantly improve physicochemical, mineralogical, and biological conditions, leading to the productive growth of pioneer plants. However, it remains unknown the fate of vanadium in response to the eco-engineering-driven changes of mineralogy, geochemistry, and organic matter decomposition.

The primary distribution of V in the BR-technosols will be characterized in sequential extraction and fractionation. The results of sequential extraction over show that the main vanadium pools in BR-technosols are in the iron oxide and organic matter phases, which provoked an investigation into the controlling mechanisms and specific sorbents, through microstructural and spectroscopic analysis combined with multivariate analysis. The alkaline environment was found to be the main controlling factor leading to elevated bioavailable vanadium in the bauxite residue. Within the iron oxide phase, amorphous iron oxides are expected to play an important role in sorption and therefore the conversion of crystalline iron-bearing minerals to the amorphous phase during weathering will be a direction of concern during long-term rehabilitation. Organic matter under natural soil conditions is an important vanadium sorbent, and additional additions of organic matter did not observe a significant improvement in this study sample, but when combined with P additions, a significant reduction in pH occurred, as did water-soluble vanadium. More investigation needs to be stimulated in terms of the role of P in promoting the addition of organic matter.

The expected results will aid the risk assessment of the eco-engineered BR-technosols and necessary intervention to mitigate the identified risks of V pollution in seepage and surface runoff in the future.