Bioleaching as a tool for waste valorization and metal extraction

Bauxite is the primary ore for aluminum production, while red mud is a highly alkaline and toxic waste by-product of alumina extraction via the Bayer process. This process generates significant environmental challenges due to the large quantities of waste produced and the hazards associated with its disposal. Despite containing valuable elements like iron, aluminum, and titanium, conventional red mud disposal methods, such as landfilling, present ecological risks. Bioleaching, which employs microorganisms to extract metals from ores and waste, presents a sustainable alternative. This study explored the bioleaching potential of Acidithiobacillus ferrooxidans (strain B2 from lake Robule, Bor, Serbia) for processing bauxite (particle size >125 μm) and red mud. A 28-day leaching experiment was conducted using a neutralized 9K medium, with final pH values of 3 for red mud and 1 for bauxite. Results confirmed the microorganisms effectiveness in metal recovery, as determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis. Both abiotic and biotic leaching of bauxite recovered certain amounts of cerium, copper, neodymium, zinc, and yttrium, along with smaller quantities of lanthanum, praseodymium, samarium, thorium, erbium, and ytterbium. For red mud, abiotic leaching showed no change after 28 days, whereas biotic leaching recovered notable amounts of yttrium (from 282 to 10958 μg/L), cerium (from 126 to 7781 μg/L), neodymium (from 212 to 7176 μg/L), and other elements. Biotic leaching consistently yielded higher recovery rates compared to abiotic methods, highlighting the potential of Acidithiobacillus ferrooxidans as an effective agent for metal recovery from industrial waste.