Mining activities generate substantial amounts of gold mine tailings (GMT), often rich in rare earth elements (REEs) such as praseodymium (Pr), europium (Eu), and cerium (Ce). Despite their potential value, little information has existed on effectively extracting these elements from GMT. Recently, researchers have developed an innovative method involving bioleaching and oxalic acid pretreatment to facilitate this process, aimed at addressing both resource recovery and environmental concerns associated with tailings disposal.
The study, conducted by H. Fereydouni, T. Naseri, and S.M. Mousavi at Tarbiat Modares University, utilized Acidithiobacillus thiooxidans—a bacterium known for its ability to produce sulfuric acid through the oxidation of sulfur—to improve the extraction of REEs from mined materials. By applying 2 M oxalic acid pretreatment to GMT for six hours at 90 °C, researchers managed to selectively remove iron, significantly enhancing the bioavailability of the precious elements.
After the innovative pretreatment and subsequent bioleaching process, the recovery rates of Pr, Ce, and Eu increased by 24.4%, 14.4%, and 9.1%, respectively—a remarkable improvement due to the removal of iron, which had previously hindered extraction efforts. The successful recovery was attributed to the synergistic effects of combining biological and chemical processes, marking a substantial advancement over traditional mining techniques.
The backdrop of high environmental and economic costs of conventional mining methods, such as pyrometallurgy and hydrometallurgy, raises the stakes for alternative approaches to rare earth extraction. These traditional methods frequently lead to significant air, water, and soil pollution and are not viable for low-grade ores like those found in tailings. Hence, bioleaching emerges as a promising option due to its eco-friendliness, leveraging natural microbial processes for metal recovery.
Fereydouni and colleagues initially focused on the characteristics of GMT, provided by the Mouteh Gold Factory’s tailings dam, and measured its elemental composition, which revealed high concentrations of iron and certain REEs. By employing advanced analysis techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), the researchers traced structural changes indicating improvements from the bioleaching procedure.
What stands out is the clear relationship between the iron removal via oxalic acid treatment and the enhanced recovery of REEs during bioleaching. Researchers noted significant differences in metal recovery when comparing untreated and pretreated GMT: the efficiency of Pr, Ce, and Eu extraction markedly improved, validating the approach’s potential. The findings offer substantial evidence of how environmental concerns linked to mining can be alleviated by more sustainable resource recovery practices.
Using Acidithiobacillus thiooxidans effectively highlights the direct role of microorganisms as catalysts, accelerating the dissolution processes necessary for extracting valuable metals. The research advocates for broader implementation of bioleaching, especially as global demand for rare earth elements is projected to rise by over 40% by 2030, underscoring the urgency for innovative approaches.
This groundbreaking work not only contributes to the scientific discourse on sustainable mining practices but also opens new avenues for resource recovery from mining tailings. It positions bioleaching and pretreatment strategies as viable alternatives, possibly leading to reduced environmental impacts and increased recovery efficiency of precious elements. Future studies could benefit from applying these techniques across various mining contexts and refining them to maximize both economic and ecological sustainability.