A group of biological approaches has been critically reviewed for the selective recovery of lithium (Li), cobalt (Co), and rare-earth elements from high-salinity industrial and mining wastewaters. Researchers explored the potential of microalgal and cyanobacterial systems, highlighting biological mechanisms, regulatory frameworks, and integrated co-design strategies for sustainable critical metal recovery. Their findings were published in the journal Environments.
Study: Microalgal Systems for Selective Recovery of Lithium, Cobalt and Rare Earth Elements from Waste Streams: A Critical Review. Image Credit: ULTRA31/Shutterstock.com
Critical Metals Recovery Context
The growing demand for critical minerals such as Li, Co, and rare earth elements (REEs) is driven primarily by the rapid expansion of battery technologies, electrification, and renewable energy deployments.
These minerals are essential components for batteries, permanent magnets, and advanced electronics needed in low-carbon energy systems. However, conventional mining faces environmental, geopolitical, and supply risks, amplified by the concentration of key mineral reserves in limited global regions, such as Li in Chile and Co in the Democratic Republic of Congo.
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Mining and industrial operations also generate saline and acidic wastewater rich in these elements, which represent untapped secondary resources. Recovery of critical metals from such complex waste streams is hindered by high ionic strength and the presence of competing ions.
Consequently, researchers are exploring biological methods, particularly microalgal systems, that leverage biosorption, bioaccumulation, and extracellular polymeric substances (EPS) for metal recovery in harsh environments typical of mining effluents.
Microalgal Recovery Case Studies
This review highlights several studies examining microalgae and cyanobacteria as biological agents for selective metal recovery from mining and industrial wastewaters. Halotolerant taxa such as Nannochloropsis oceanica, acidophilic species like Galdieria sulphuraria, and cyanobacteria such as Synechococcus elongatus have shown promise in metal binding within hypersaline and acidic conditions often found in mining effluents.
Microalgae remove metals primarily through biosorption, where negatively charged functional groups (carboxyls, phosphates, hydroxyls, and aminos) on their cell surfaces and EPS bind metal ions. For example, Nannochloropsis spp. thrives in saline mine waters, secreting EPS that increase metal-binding capacity.
Galdieria sulphuraria tolerates extreme acidity (pH <3) and elevated metal loads characteristic of acid mine drainage (AMD) and geothermal fluids, accumulating metals intracellularly alongside EPS-mediated binding. Synechococcus spp. combines rapid growth with surface chemistry conducive to efficient biosorption and subsequent bioaccumulation.
Laboratory studies using synthetic solutions have demonstrated efficient removal of Co and REEs, with removal efficiencies up to 90% under controlled conditions. Some real wastewater trials with Galdieria species in acidic AMD have confirmed metal recovery, albeit with performance reductions likely due to competing ions and complex wastewater chemistry.
The review also acknowledges emerging strategies such as modular multi-strain systems combining complementary binding traits, hybrid bio-physicochemical processes integrating algae with membrane filtration or solvent extraction, and valorization of metal-laden biomass into high-value products.
Co-Design and Recovery Challenges
The biosorption process exploits the presence of functional groups and EPS that sequester metal ions extracellularly, while bioaccumulation and biomineralization processes mediate intracellular uptake and potential precipitate formation.
Salinity and metal stress can induce EPS overproduction, potentially enhancing binding capacity. These biological traits open pathways for process designs that co-optimize strain physiology, wastewater chemistry, and downstream methods.
However, the review highlights several limitations. Low affinity for Li and interference from dominant ions like Na+ and Mg2+ in brines markedly reduce binding efficiency. This presents a major bottleneck for Li recovery from mining brines, which typically have high Mg/Li ratios. Additionally, scaling laboratory successes to pilot or industrial scales is hindered by challenges in biomass harvesting, regeneration, and metal desorption.
From an engineering perspective, capital and operational costs are largely driven by photobioreactor infrastructure and energy-intensive mixing and harvesting operations. While chemical inputs are reduced compared to hydrometallurgical methods, longer treatment times and larger land footprints are required. Economic viability could improve by valorizing residual biomass for biofertilizers, pigments, or bioenergy feedstocks, consistent with circular economy models.
Policy frameworks in the EU, US, and UK are increasingly supportive of sustainable circular recovery of critical raw materials from secondary sources such as mine waters, establishing ambitious targets and regulatory drivers.
Nevertheless, microalgal recovery technologies are at low technology readiness levels (TRL 2-4), with few pilot-scale demonstrations in mining contexts. Regulatory barriers around genetically modified organisms and biosafety concerns also complicate strain engineering efforts aimed at improving metal selectivity and tolerance.
Future Prospects of Microalgal Recovery
The urgent need to secure critical minerals for low-carbon technologies amidst geopolitical and environmental constraints places secondary resource recovery from mining wastewaters in the spotlight. Microalgal and cyanobacterial systems offer a compelling biological approach for recovering Co, REEs and, to a lesser extent, Li from saline and acidic mining effluents.
Despite encouraging laboratory-scale results, significant hurdles remain in enhancing Li selectivity, overcoming ion competition, and scaling cultivation and recovery processes. Integrating strain-level biotechnology advances with system-level engineering and process co-design will be key to realizing the potential of biological recovery methods.
With cross-disciplinary innovation and strategic collaboration, microalgal systems can contribute to transforming mining wastewaters from environmental liabilities into valuable, sustainable sources of critical minerals.
Journal Reference
Silkina A., Gayo-Peláez J.I., et al. (2026). Microalgal Systems for Selective Recovery of Lithium, Cobalt and Rare Earth Elements from Waste Streams: A Critical Review. Environments 13(7). https://www.mdpi.com/2076-3298/13/7/363.