# Metal Recovery from Wastes: A Review of Recent Advances in the Use of Bioelectrochemical Systems
## 1 Introduction
The combination of electrochemical technology with bioprocesses stands up as an economical and sustainable alternative for metal recovery from wastes while simultaneously addressing environmental remediation. BESs combine a variety of microorganisms, such as fungi, bacteria, and archaea, with electrochemical processes to facilitate the solubilization and recovery of metals while minimizing energy consumption or enabling energy generation [2; 10; 25; 26; 27]. Table 1 compares the different technologies used for metal recovery, highlighting their efficiencies, advantages, disadvantages, and typical applications. As illustrated, BESs stand out for their potential to combine metal recovery with energy generation; however, their full-scale application remains limited due to slow kinetics and a low level of technological readiness. Over the last few decades, BESs have been increasingly studied as one of the key electrochemical technologies for metal recovery [28; 29; 30; 31; 32]. Extensive research efforts have introduced new materials, methods, operating conditions, and design improvements to enhance performance and expand their range of potential applications. Figure 1A presents the number of papers published related to \"Metal\", \"Recovery\", and \"Bioelectrochemical\" appearing in either abstract, title, or keywords categorized as Microbial Fuel cell (MFC) or Microbial Electrolysis Cell (MEC). As can be observed, there is a significant increase in the number of articles published on this topic, reflecting the growing interest of the scientific community and the versatility of this technology. Figure 1B displays the number of metal recovery studies reported in the literature during the last years when operating with MFC and MEC configurations. The data show a steady rise in publications in recent years, underscoring the increasing interest and relevance of metal recovery through BES systems [33]. \begin{table}
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**Technology** & **Process Description** & **Advantages** & **Disadvantages** \\ \hline Pyrometallurgy & High-temperature processes to extract and refine metals from ores or waste (e.g., smelting, roasting). & - Minimal pre-treatment required & - High energy consumption required & - Low selectivity - Loss of strategic metals - Emission of polluting gases \\ \hline \end{tabular}
\end{table} 
Table 1: Comparative analysis of metal recovery techniques. Figure 1: The number of papers published related to (**A**) “Metal”, “Recovery”, and “Bioelectrochemical systems” appearing in either abstract, title, or keywords; (**B**) the number of articles related to MFC and MEC metal recovery studies. Search results were obtained from the Scopus database. The search results from the Scopus database were analyzed using the free software VOSviewer(r), version 1.6.20, and the findings are presented in Figure 2, which provides a co-occurrence analysis of keywords associated with \"Metal\", \"Recovery\", and \"Bioelectrochemical\" from published research articles. This visualization highlights the most frequently used keywords as nodes, with the size of each node representing the frequency of the keyword's appearance in the dataset, while the connections between nodes indicate the strength of their co-occurrence. The analysis reveals distinct clusters that reflect major themes within the field, such as environmental applications like \"wastewater treatment,\" \"heavy metals\" and \"sewage\" (blue clusters); microbial and bioelectrochemical applications including \" microbial fuel cells\" and \"bio-electrochemical\" (green clusters); electrochemical processes and performance metrics such as \"electrodeposition\", \"energy utilisation\" and \"cathodes\". This network demonstrates the multidisciplinary nature of research in bioelectrochemical systems, showcasing the integration of biological, chemical, and engineering aspects while highlighting emerging trends in energy efficiency, sustainability, and hybrid technologies. About 200 papers were identified on this topic.