Current overview and future perspective in fungal biorecovery of metals from secondary sources

Driving sustainable circular economy in electronics: A comprehensive review on environmental life cycle assessment of e-waste recycling

E-waste, encompassing discarded materials from outdated electronic equipment, often ends up intermixed with municipal solid waste, leading to improper disposal through burial and incineration. This improper handling releases hazardous substances into water, soil, and air, posing significant risks to ecosystems and human health, ultimately entering the food chain and water supply. Formal e-waste recycling, guided by circular economy models and zero-discharge principles, offers potential solutions to this critical challenge. However, implementing a circular economy for e-waste management due to chemical and energy consumption may cause environmental impacts. Consequently, advanced sustainability assessment tools, such as Life Cycle Assessment (LCA), have been applied to investigate e-waste management strategies. While LCA is a standardized methodology, researchers have employed various routes for environmental assessment of different e-waste management methods. However, to the authors' knowledge, there lacks a comprehensive study focusing on LCA studies to discern the opportunities and limitations of this method in formal e-waste management strategies. Hence, this review aims to survey the existing literature on the LCA of e-waste management under a circular economy, shedding light on the current state of research, identifying research gaps, and proposing future research directions. It first explains various methods of managing e-waste in the circular economy. This review then evaluates and scrutinizes the LCA approach in implementing the circular bioeconomy for e-waste management. Finally, it proposes frameworks and procedures to enhance the applicability of the LCA method to future e-waste management research. The literature on the LCA of e-waste management reveals a wide variation in implementing LCA in formal e-waste management, resulting in diverse results and findings in this field. This paper underscores that LCA can pinpoint the environmental hotspots for various pathways of formal e-waste recycling, particularly focusing on metals. It can help address these concerns and achieve greater sustainability in e-waste recycling, especially in pyrometallurgical and hydrometallurgical pathways. The recovery of high-value metals is more environmentally justified compared to other metals. However, biometallurgical pathways remain limited in terms of environmental studies. Despite the potential for recycling e-waste into plastic or glass, there is a dearth of robust background in LCA studies within this sector. This review concludes that LCA can offer valuable insights for decision-making and policy processes on e-waste management, promoting environmentally sound e-waste recycling practices. However, the accuracy of LCA results in e-waste recycling, owing to data requirements, subjectivity, impact category weighting, and other factors, remains debatable, emphasizing the need for more uncertainty analysis in this field.

Biomining for sustainable recovery of rare earth elements from mining waste: A comprehensive review

Rare earth elements (REEs) are essential for advanced manufacturing (e.g., renewable energy, military equipment, electric vehicles); hence, the recovery of REEs from low-grade resources has become increasingly important to address their growing demand. Depending on specific mining sites, its geological conditions, and sociodemographic backgrounds, mining waste has been identified as a source of REEs in various concentrations and abundance. Yttrium, cerium, and neodymium are the most common REEs in mining waste streams (50 to 300 μg/L). Biomining has emerged as a viable option for REEs recovery due to its reduced environmental impact, along with reduced capital investment compared to traditional recovery methods. This paper aims to review (i) the characteristics of mining waste as a low-grade REEs resource, (ii) the key operating principles of biomining technologies for REEs recovery, (iii) the effects of operating conditions and matrix on REEs recovery, and (iv) the sustainability of REEs recovery through biomining technologies. Six types of biomining will be examined in this review: bioleaching, bioweathering, biosorption, bioaccumulation, bioprecipitation and bioflotation. Based on a SWOT analyses and techno-economic assessments (TEA), biomining technologies have been found to be effective and efficient in recovering REEs from low-grade sources. Through TEA, coal ash has been shown to return the highest profit amongst mining waste streams.

Fungal bioleaching of metals from WPCBs of mobile phones employing mixed Aspergillus spp.: Optimization and predictive modelling by RSM and AI models

In the present study, optimization and prediction models for fungal bioleaching for effective metal extraction from waste printed circuit boards (WPCBs) of mobile phones were developed employing central composite design (CCD) of response surface methodology (RSM), and two artificial intelligence (AI) models, i.e., artificial neural network (ANN) and, support vector machine (SVM), respectively. Two continuous process parameters, such as pH (4-9) and pulp density (1-10 g/L), and the bioleaching approaches, viz., one-step and two-step, were experimentally optimized for the extraction of targeted metals, i.e., Cu, Ni, and Zn from WPCBs by mixed cultures of Aspergillus niger and Aspergillus tubingensis. Datasets were then used for predictive modelling using AI tools. Results showed that the highest simultaneous bioleaching of Cu, Ni, and Zn, with an extraction efficacy of about 86%, 51%, and 100%, respectively, achieved at an optimal condition of pH 5.7 and pulp density of 3 g/L following the two-step bioleaching approach. Effective metal extraction in the two-step approach could be attributed to the abundant production of organic acids with a content of about 16.3 g/L, 8.4 g/L, and 0.5 g/L of citric acid, oxalic acid, and malic acid, respectively. Further, the predictive modelling revealed that the ANN model was found to predict the fungal bioleaching responses more accurately as compared to the SVM model with R2 values exceeding 0.96 for all targeted metals. This research demonstrates the applicability of the optimization and prediction models for efficient metal extraction from WPCBs using mixed Aspergillus spp. following the two-step approach.

Bioleaching of heavy metals from metal tailings utilizing bacteria and fungi: Mechanisms, strengthen measures, and development prospect

Recovering key metals from secondary sources is an indispensable strategy for preventing metal shortages and reducing the risk of toxic releases into the environment. Metal mineral resources continue to be depleted and the global supply chain will face metal scarcity. The use of microorganisms for metal transformation plays an important role in the bioremediation of secondary resources. It shows great potential for development due to its compatibility with the environment and possible cost effectiveness. The results of the study show that the influence of bioleaching processes and effects are mainly analyzed from microorganisms, mineral properties and leaching environmental conditions. In this review article, we elucidate light on the role and mechanisms of fungi and bacteria involved in extracting different metals from tailings, including acidolysis, complexolysis, redoxolysis, and bioaccumulation. Key process parameters that affect the efficiency based bioleaching are discussed, providing referenceable pathways to improve leaching efficiency. The investigation concludes that exploitation of the functional genetic role of microorganisms and their optimal growth conditions can achieve efficient leaching of metals. It was found that the improvement of microbial performance was achieved at the level of mutagenesis breeding, mixed culture microorganisms, and genetics. Moreover, control of leaching system parameters and removal of passivation films can be achieved by adding biochar and surfactants in the leaching system as an effective means to improve tailings leaching. Knowledge about cells with minerals and their detailed interactions at the molecular level is still relatively scarce and the field could be deepened and this area needs to be further explored in the future. The challenges and the key issues associated with the bioleaching technology development are elaborated as a green and effective bioremediation strategy for the environment and prospects for imminent are also highlighted.

Bio-based functionalized adsorptive polymers for sustainable water decontamination: A systematic review of challenges and real-world implementation

The overwhelming concerns of water pollution, industrial discharges and environmental deterioration by various organic and inorganic substances, including dyes, heavy metals, pesticides, pharmaceuticals, and detergents, intrinsically drive the search for urgent and efficacious decontamination techniques. This review illustrates the various approaches to remediation, their fundamentals, characteristics and demerits. In this manner, the advantageous implementation of nature-based adsorbents has been outlined and discussed. Different types of lignocellulosic compounds (cellulose, lignin, chitin, chitosan, starch) have been introduced, and the most used biopolymeric materials in bioremediation have been highlighted; their merits, synthesis methods, properties and performances in aqueous medium decontamination have been described. The literature assessment reveals the genuine interest and dependence of academic and industrial fields to valorize biopolymers in the adsorption of various hazardous substances. Yet, the full potential of this approach is still confined by certain constraints, such as the lack of reliable, substantial, and efficient extraction of biopolymers, as well as their modest and inconsistent physicochemical properties. The futuristic reliance on such biomaterials in all fields, rather than adsorption, is inherently reliable on in-depth investigations and understanding of their features and mechanisms, which can guarantee a real-world application and green technologies.

Perspective on the use of methanogens in lithium recovery from brines

Methanogenic archaea stand out as multipurpose biocatalysts for different applications in wide-ranging industrial sectors due to their crucial role in the methane (CH4) cycle and ubiquity in natural environments. The increasing demand for raw materials required by the manufacturing sector (i.e., metals-, concrete-, chemicals-, plastic- and lubricants-based industries) represents a milestone for the global economy and one of the main sources of CO2 emissions. Recovery of critical raw materials (CRMs) from byproducts generated along their supply chain, rather than massive mining operations for mineral extraction and metal smelting, represents a sustainable choice. Demand for lithium (Li), included among CRMs in 2023, grew by 17.1% in the last decades, mostly due to its application in rechargeable lithium-ion batteries. In addition to mineral deposits, the natural resources of Li comprise water, ranging from low Li concentrations (seawater and freshwater) to higher ones (salt lakes and artificial brines). Brines from water desalination can be high in Li content which can be recovered. However, biological brine treatment is not a popular methodology. The methanogenic community has already demonstrated its ability to recover several CRMs which are not essential to their metabolism. Here, we attempt to interconnect the well-established biomethanation process with Li recovery from brines, by analyzing the methanogenic species which may be suitable to grow in brine-like environments and the corresponding mechanism of recovery. Moreover, key factors which should be considered to establish the techno-economic feasibility of this process are here discussed.