Stoyan Gaydardzhiev’s research while affiliated with University of Liège and other places

Tantalum (Ta) and niobium (Nb) are two strategic metals which are extensively used in high-tech industries, such as microelectronics, defence, aerospace, manufacturing of high-strength low- alloy (HSLA) steel, etc. Current and future demand for these two metals will grow in parallel to high-tech equipment need expands. However, their extractive metallurgy remains a major challenge owing to economic and environmental constraints. Apart the well-known hydrofluoric acid media, alkaline media has attracted reasonable attention in processing of low-grade Ta-Nb bearing ores, but it is limited in terms of Ta and Nb purification. In our previous studies, we proposed a novel method for coltan ore processing based on alkaline roasting, water leaching, precipitation, and oxalic leaching of Ta and Nb, with the aim to deliver a suitable leachate for downstream treatment by solvent extraction. The current contribution reports results from the purification steps of Ta and Nb from an oxalic leachate containing about 11 g/L Nb and 2 g/L Ta. Solvent extraction was implemented using an Aliquat® 336 based extractant diluted in toluene and modified with 2% isodecanol. The used extractant is characterized by a higher flash point (132°C), compared to the conventional methyl isobuthyl ketone (14°C) which is very hazardous. The studied parameters have included Aliquat® 336 concentration, contact time, pH, extraction temperature and O/A volume ratio. At their optimum found values, over 98% of Ta and Nb were extracted and purified from impurities, and distribution coefficients of more than 300-Ta and 80-Nb were reached. Furthermore, selective stripping was carried out to separate the two metals enabling to produce high-grade oxides.

BACKGROUND A bioleaching process could offer the advantage of higher metal recovery in a sustainable manner even from lithium‐ion battery (LIB) samples with very low metal concentrations. In recent years, there has been a significant increase in the use of secondary resources such as LIBs for various purposes including transportation, large‐scale energy storage and use in portable devices. RESULTS The adaptation of a mixed culture of acidophilic microorganism (lab stock culture) to a representative LIB sample allowed the setting of 0.5% of the pulp density under lab scale conditions. The maximum metal dissolution by bioleaching in a 1‐L bioreactor for the as‐received and thermally treated samples was found to be Li (67% & 49%), cobalt (81% & 86%), nickel (99% & 87%) and manganese (86% & 75%). Likewise, on the 10‐L scale, the dissolutions observed were: Li (80% & 67%), Co (75%), Ni (91% & 88%) and Mn (63% & 75%) for the as‐received and heat‐treated samples, respectively. CONCLUSION Parameters such as particle size, leaching time, pH and iron ions (Fe²⁺) affect the efficiency of acidophilic bioleaching of Li, Co, Ni and Mn from spent LiBs. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Citation: Panda, S.; Akcil, A.; Gaydardzhiev, S.; van Hullebusch, E.D.; Gönen, M.; Dembele, S. Biotechnological Recycling and Recovery of Metals from Waste Printed Circuit Boards and Spent Li-Ion Batteries-Selected Results from the ERAMIN EU BaCLEM Project. Mater. Proc. 2024, 15, 76. Abstract: This project investigated metal recovery from waste printed circuit boards (WPCBs) and spent lithium-ion batteries (LiBs) using pure and mixed-culture acidophilic microorganisms. It was shown that the mixed culture could recover 80% of Li and 98% of Co from a representative LiB sample under shaken flask conditions while using a single acidophilic microorganism in a two-step bioleaching step, 82% of Cu and 100% of Ni could be recovered from PCBs. The removal of iron from the bioleaching solution reached 100% using NaOH.

This project investigated metal recovery from waste printed circuit boards (WPCBs) and spent lithium-ion batteries (LiBs) using pure and mixed-culture acidophilic microorganisms. It was shown that the mixed culture could recover 80% of Li and 98% of Co from a representative LiB sample under shaken flask conditions while using a single acidophilic microorganism in a two-step bioleaching step, 82% of Cu and 100% of Ni could be recovered from PCBs. The removal of iron from the bioleaching solution reached 100% using NaOH.

Among the different types of secondary post-consumption wastes, E-wastes or waste electrical and electronic equipment represent the fastest growing and most problematic waste stream with printed circuit boards (PCBs) constituting its major ingredient. Results from the extraction of Cu and Ni from PCBs using biogenic Fe2(SO4)3 obtained from the original isolate Acidithiobacillus ferrooxidans 61 (KM819692) are presented. At. ferrooxidans 61 was grown at a temperature of 30 °C in a modified 9 K medium supplemented with ferrous iron. Two-stage bioleaching was carried out at 600 rpm and 40 °C. Experiments were performed at 10% of pulp density (PD) with 48-h duration (each stage of 24 h), under pH 1 and 20 g/L Fe³⁺. Under these conditions, overall recovery of Cu and Ni of 95% and 87% respectively was achieved. The obtained results indicate that non-ferrous metals in PCBs may be efficiently leached within two-stage bioleaching coupling bio-oxidation to subsequent redoxolysis. Scanning electron microscope (SEM) images acquisition and elemental mapping were performed to assess the liberation degree of essential phases after size-reduction steps and their implication on bioleaching efficiency.

A strain of Leptospirillum sp. CC previously isolated from Akhtala polymetallic ore (Armenia) was studied. The main morphological and physiological characteristics of CC were revealed. The optimal growth temperature was 40 °C and optimal pH 1.5. A phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID OM272948) showed that isolate CC was clustered with L. ferriphilum and possessed 99.8% sequence similarity with the strain L. ferriphilum OL12-2 (KF356024). The molar fraction of DNA (G + C) of the isolate was 58.5%. Bioleaching experiment indicates that L. ferriphilum CC can oxidize Fe(II) efficiently, and after 17 days, 44.1% of copper and 91.4% of iron are extracted from chalcopyrite and pyrite, respectively. The efficiency of L. ferriphilum CC in pyrite oxidation increases 1.7 times when co-cultivated with At. ferrooxidans ZnC. However, the highest activity in pyrite oxidation shows the association of L.ferriphilum CC with heterotrophic Acidocella sp. RBA bacteria. It was shown that bioleaching of copper and iron from chalcopyrite by association of L. ferriphilum CC, At. ferrooxidans ZnC, and At. albertensis SO-2 in comparison with pure culture L. ferriphilum CC for 21 days increased about 1.2 and 1.4–1.6 times, respectively.