A research team reveals that native halophytic plants—species adapted to saline and alkaline environments—can biologically initiate the transformation of toxic bauxite residue (BR), also known as red mud, into early-stage soil.
By stimulating mineral weathering and contributing in situ organic carbon through root activity, these plants provide a sustainable solution for rehabilitating alumina waste deposits without large external organic inputs.
Bauxite residue, the byproduct of aluminum production, represents one of the most pressing global environmental challenges, with billions of tons stored in vast tailing dams. Its extreme alkalinity and salinity inhibit vegetation and hinder natural soil formation. Conventional rehabilitation relies on costly amendments, such as gypsum and imported organic matter, to neutralize alkalinity and restore ecological function. Given these constraints, scientists have turned to eco-engineering—using plants and microbes to accelerate early soil formation by promoting mineral weathering, organic matter accumulation, and organo-mineral interactions. However, whether halophytes can serve as biological drivers for initiating soil formation under field conditions remained unclear. Based on their natural resilience and ability to exude organic acids, halophytic plants may provide an in situ pathway for the gradual neutralization and stabilization of BR.
A study (DOI:10.48130/een-0025-0006) published in Energy & Environment Nexus on 24 September 2025 by Longbin Huang’s team, The University of Queensland, could substantially reduce the need for costly organic or chemical amendments, offering a low-input rehabilitation strategy for vast BR disposal sites worldwide.
To examine the rhizosphere-driven transformation of BR by halophytic plants, researchers employed a suite of advanced spectroscopic and analytical techniques, including quantitative X-ray diffraction (qXRD), synchrotron-based X-ray absorption fine structure spectroscopy (XAFS), and Fourier-transform infrared spectroscopy (ATR-FTIR), alongside measurements of pH, electrical conductivity (EC), and total organic carbon. The field experiment assessed mineralogical, chemical, and organic changes in BR after nearly three years of plant root colonization. The results showed that the establishment of halophytic plants markedly reduced alkalinity, with pH values decreasing from >9.5 to 8.5–9.0 and EC falling below 3.0 mS·cm⁻¹, meeting previously defined rehabilitation criteria. According to qXRD, plant colonization reduced sodalite-like minerals from 10–14% to <10% and hematite from 25–30% to <20%, while increasing amorphous mineral phases to about 60%. Synchrotron XRD confirmed weakened sodalite peaks, indicating mineral weathering induced by root activity. Further, Fe K-edge XAFS revealed the formation of amorphous Fe–Si short-range ordered minerals, while Al and Si K-edge NEXAFS detected amorphous Al(oxy)hydroxides and SiO₄⁻ structures, with Atriplex aminocola promoting silicic acid generation. ATR-FTIR spectra showed diminished Si–O–Si and Fe–O vibrations, suggesting reduced Si/Al polymerization and Fe (oxy)hydroxide transformation. Chemical analyses revealed higher total carbon and nitrogen concentrations in rhizosphere BR, accompanied by distinct organic functional groups such as aliphatic, phenolic, and carboxylic compounds. Synchrotron C K-edge NEXAFS identified carboxyl carbon as the dominant form (>60%), with scanning transmission X-ray microscopy (STXM) confirming tight associations between organic carbon, nitrogen, and minerals. Together, these findings demonstrate that halophyte root activities induce substantial mineral weathering, amorphous mineral formation, and organic carbon enrichment, collectively initiating early-stage soil formation in alkaline BR under field conditions.
The findings provide the first field-based evidence that native halophytic plants can biologically drive the early stages of soil formation in alkaline, organic-deficient bauxite residue. By naturally lowering pH and enhancing organo-mineral interactions, these pioneer species create more hospitable conditions for subsequent vegetation and ecosystem development. This plant-based eco-engineering approach Moreover, the generation of Fe–Si–Al-rich amorphous minerals and stable organo-mineral complexes lays the foundation for long-term soil stability, carbon sequestration, and biodiversity restoration.
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References
DOI
10.48130/een-0025-0006
Original Source URL
https://doi.org/10.48130/een-0025-0006
Funding Information
This work is financially supported by the Australian Research Council Projects (LP190100975 and DP240102434), Rio Tinto (Aluminum) Ltd, and Queensland Alumina Ltd (QAL).
About Energy & Environment Nexus
Energy & Environment Nexus is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.