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The number of metal-containing waste streams resulting from electronic end-of life products, metallurgical by-products, and mine tailings to name but a few, is increasing worldwide. In recent decades, the potential to exploit these waste streams as valuable secondary resources to meet the high demand of critical and economically important raw materials has become more prominent. In this review, fundamental principles of bio-based metal recovery technologies are discussed focusing on microbial metabolism-dependent and metabolism-independent mechanisms as sustainable alternatives to conventional chemical metal recovery methods. In contrast to previous reviews which have partially addressed this topic, a special focus will be given on how fundamental principles of bio-based recovery technologies can influence the selectivity and specificity of metal recovery. While conventional methods for metal recovery show benefits in terms of economic affordability, bio-based recovery technologies offer advantages in terms of efficiency and environmentally friendliness. Modifications and adaptations in the processes of biosorption, bioaccumulation and bioelectrochemical systems are highlighted, further emphasizing the application of metal-binding peptides and siderophores to increase selectivity in the recovery of metals. Single metal solutions or mixtures with a low complexity have been the focus of previous studies and reviews, but this does not reflect the nature of complex industrial effluents. Therefore, key challenges that arise when dealing with complex polymetallic solutions are addressed and the focus is set on optimizing bio-based technologies to recover metals efficiently and selectively from bio-leachates or liquid waste streams.

The demand for lithium-ion batteries (LIBs) has dramatically increased in recent years due to their application in various electronic devices and electric vehicles (EVs). Great amount of LIB waste is generated, most of which ends up in landfills. LIB wastes contain substantial amounts of critical metals (such as Li, Co, Ni, Mn, and Cu) and can therefore serve as valuable secondary sources of these metals. Metal recovery from the black mass (shredded spent LIBs) can be achieved via bioleaching, a microbiology-based technology that is considered to be environmentally friendly, due to its lower costs and energy consumption compared to conventional pyrometallurgy or hydrometallurgy. However, the growth and metabolism of bioleaching microorganisms can be inhibited by dissolved metals. In this study, the indigenous acidophilic chemolithotrophs in a sediment from a highly acidic and metal-contaminated mine pit lake were enriched in a selective medium containing iron, sulfur, or both electron donors. The enriched culture with the highest growth and oxidation rate and the lowest microbial diversity (dominated by Acidithiobacillus and Alicyclobacillus spp. utilizing both electron donors) was then gradually adapted to increasing concentrations of Li+, Co2+, Ni2+, Mn2+, and Cu2+. Finally, up to 100% recovery rates of Li, Co, Ni, Mn, and Al were achieved via two-step bioleaching using the adapted culture, resulting in more effective metal extraction compared to bioleaching with a non-adapted culture and abiotic control.

In recent decades, a shift has been seen in the use of light-emitting diodes over incandescent lights and compact fluorescent lamps (CFL), which eventually led to an increase in wastes of electrical equipment (WEE), especially fluorescent lamps (FLs) and CFL light bulbs. These widely used CFL lights, and their wastes are good sources of rare earth elements (REEs), which are desirable in almost every modern technology. Increased demand for REEs and their irregular supply have exerted pressure on us to seek alternative sources that may fulfill this demand in an eco-friendly manner. Bio-removal of wastes containing REEs, and their recycling may be a solution to this problem and could balance environmental and economic benefits. To address this problem, the current study focuses on the use of the extremophilic red alga, Galdieria sulphuraria, for bioaccumulation/removal of REEs from hazardous industrial wastes of CFL bulbs and the physiological response of a synchronized culture of G. sulphuraria. A CFL acid extract significantly affected growth, photosynthetic pigments, quantum yield, and cell cycle progression of this alga. A synchronous culture was able to efficiently accumulate REEs from a CFL acid extract and efficiency was increased by including two phytohormones, i.e., 6-Benzylaminopurine (BAP - Cytokinin family) and 1-Naphthaleneacetic acid (NAA - Auxin family).

Modern society is heavily dependent on critical raw materials, such as rare earth elements (REEs), for use in electronic devices. The increasing demand for these materials has led to the need for environmentally friendly methods of processing non-recycled materials from e-waste and wastewater, as well as waste streams from cleaning and manufacturing facilities. Modern society’s dependence on such materials is growing by the day, and with it, the need for environmentally friendly processing of non-recycled materials from e-waste and wastewater in the form of “end-of-life” products, as well as waste streams from cleaning and manufacturing facilities, also increases. As these are problematic indications for modern isolation methods in the industry, these sources may be more suitable for new techniques as they have low concentration and high throughput for bioaccumulation. Chemical methods using nanomaterials are already being tested for their possibilities but still depend on acids and harsh chemicals. Microorganisms, on the other hand, can adsorb/absorb REEs in a more ecological way. Previous studies could already show that it is possible to accumulate REEs in the precipitates of bacterial cultures spiked with REEs to a value of over 50%. However, the question arose whether rare earths were spun into the pellets by centrifugation, adsorbed, or really incorporated in the cells. Therefore, we established a new easy-to-use experimental design in which the microorganisms were spiked with an REE standard and washed to minimize the falsification of measurements by peripheral binding of ions before being analyzed for REE contents by ICP-OES. The bioaccumulation of rare earths in microorganisms was monitored, yielding an uptake rate of up to 53.12% of the overall present ionic REE concentration. In this manuscript, we present the different concentration measurements that were taken during the process, before and after washing of the cells, to create a full picture of the localization, binding, incorporation, and occurrence of the ions of interest. The setup also showed a correlation between the introduction method of rare earths and the uptake of certain elements that might be correlated with the differentiation between light and heavy rare earth elements, while Y and Sc often seem to represent outliers.