Investigating the effects of bauxite residue amelioration on the soil structure and roots growth with the use of μCT-scanning

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The amelioration of Bauxite residue (BR) followed by the establishment of vegetation, which is important for the ecosystem restoration of mines, was investigated. Seeds of ryegrass (Lolium perenne) were planted on cylinders filled with five different combinations of bauxite residue from Bacarena (Brazil), and amendments. The combinations used were: (i) 90% of BR mixed with 10% gypsum, (ii) 90% of BR mixed with 5% of organic food waste and 5% of gypsum, (iii) 85% of BR mixed with 5% of organic food waste and 10% of gypsum, (iv) 90% of BR with 5% of açai waste (Euterpe oleracea) and 5% of gypsum and (v) 85% of BR mixed with 5% of açai waste and 10% of gypsum. The five cylinders were scanned using a micro-CT before and after grass seeds were planted and scanned before the seeds were planted and after ca. 2 weeks. The Root Volume Density (RVD), Root Depth (RD), Root Area Ratio (RAR), were systematically determined from the CT-scans using image analysis techniques. Additionally, the changes in soil porosity and the development of root features over time were investigated. By only visually observing the grass growth, it was concluded that the best amelioration used was the gypsum at 10%, as it allowed a good shoot development rather quickly. This was confirmed by quantitative image-based results, indicating that this amelioration allowed the grass to thrive and to develop a deeper and stabilizing root system. Even though less vegetation growth was observed for the mixture of 10% gypsum and 5% açai, this mixture allowed the roots to grow deeper. This preliminary study highlights the importance of using gypsum and açai waste for vegetation growth and provides valuable insights about the best mixture (from the ones considered in this study) to be possibly used in the amelioration and revegetation of mine bauxite residual soil. Note that a comprehensive and long-term field study will be needed to corroborate the findings of this research.

9th International Congress on Environmental Geotechnics (ICEG2023)

Resource Mining and Extraction