Biomimetic recovery of valuable metals from old flotation tailings in Majdanpek, Serbia, using Aspergillus niger for bioleaching and nanomaterial synthesis

The accumulation of old flotation tailings in Majdanpek, Serbia, presents significant environmental challenges and highlights the need for innovative, sustainable approaches to metal recovery. This study evaluates the bioleaching potential of the mould Aspergillus niger (A. niger) for extracting valuable metals from these tailings. Utilizing a batch system with A. niger cultivated in soybean broth we investigated its efficiency in leaching copper (Cu), zinc (Zn), manganese (Mn), aluminum (Al), and iron (Fe) under controlled conditions: initial pH 4, temperature 25 °C, and a solid-to-liquid (S/L) ratio of 1:20 (w/v). Over a 35-day period, approximately 45 % Cu, 40 % Zn, 35 % Mn, 5 % Fe, and 3 % Al were extracted from the tailings. Analytical techniques, including X-ray diffraction (XRD), optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), confirmed transformations in the mineral phases, with secondary minerals such as oxalates and oxides forming. Field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed the degradation of sulfides and carbonates, leading to the formation of oxides and crystallized oxalates on the mineral surfaces. Additionally, FESEM-EDS analysis of the bioleaching liquor identified nano-sized metal-based particles of Cu, Zn, Mn, Al, and Fe. The proposed bioleaching mechanism involves acidolysis, complexolysis, alkaline lysis, and biosorption. This study demonstrates that A. niger offers a viable green technology for both sustainable metal recovery and nanomaterial synthesis from mining tailings, presenting a novel biomimetic approach to utilizing unconventional raw materials.