# Optimizing Boleaching for Printed Circuit Board Copper Recovery: An AI-Driven RGB-Based Approach
### The Bioleaching Plant  
Bioleaching leverages microorganisms to convert insoluble minerals into soluble forms through their metabolic processes, enabling the recovery of metals from low-grade ores where traditional mining and refining are not cost-effective [3; 4]. A major advantage of bioleaching is its ability to efficiently process both primary and secondary resources with far less environmental impact than methods like pyrometallurgy [5]. Unlike conventional chemical leaching, bioleaching minimizes ecological harm by employing naturally occurring microorganisms, avoiding the use of toxic agents such as cyanide or sulfuric acid [3; 4]. This makes the process safer and more sustainable. Economically, bioleaching provides a cost-effective solution, allowing the extraction of metals from low-grade ores that would otherwise be impractical. Additionally, bioleaching operates at ambient temperatures and pressures, reducing energy consumption compared to conventional chemical leaching, which typically requires high energy inputs due to extreme temperature and pressure conditions [6]. The BIOMETALLUM project operates a semi-industrial bioleaching plant at the EPSEM-UPC onsite facility dedicated to experimental research for enhancing and optimizing metal recovery, with a focus on copper (Cu (II)) and iron (Fe (III)) extraction from electronic waste like printed circuit boards (PCBs) from computers and mobile phones. Although the plant currently operates with an effective monitoring system, our research is advancing towards the integration of predictive, monitoring, and simulation technologies, including digital twins and machine learning models. These enhancements are expected to boost the precision and efficiency of metal recovery. These technologies could significantly reduce the environmental impact of the mining and chemical industries globally [7]. Figure 1 presents a graphical representation of the bioleaching plant, featuring a screen-shot taken from the Biometallum web-based digital twin, accessible via [8]. The plant is structured into three primary stations, each assigned to distinct operational tasks. Although the full industrial process is more intricate, a simplified overview of its operation is outlined below:  
B bioreactor: The bioreactor is a vital component of the bioleaching system, responsible for maintaining and regenerating the biological agents that drive the leaching process. It continuously monitors key parameters, including redox potential, pH, temperature, and dissolved oxygen, all of which are essential for optimizing microbial activity and ensuring efficient system performance. The bioreactor operates continuously, using an air injector to maintain oxygen levels and to ensure uniform mixing of the bioleaching solution. The temperature is regulated at 31 \({}^{\circ}\)C, which is optimal for microbial growth. pH is supervised within the narrow range of 1.6 to 1.8 using two pumps: PB1 for acid addition and PB2 for base addition. This regulation is crucial, as any deviation could deactivate the microbial agents, disrupting the leaching process. Real-time monitoring of dissolved oxygen and redox potential ensures continuous adjustment of operational parameters,while a maximum liquid level sensor prevents overflow. In the event of anomalies, such as an abnormal pH increase or redox potential drop, the system automatically adjusts reagent addition or mixing intensity to restore optimal conditions. Leaching Tanks: The leaching process transfers the biologically active solution from the bioreactor to the leaching tanks, where it interacts with the electronic waste material. Here, microbial agents facilitate the breakdown and dissolution of metal ions from the solid matrix. The tanks are equipped with sensors and actuators to maintain necessary environmental conditions. pH, temperature, and redox levels are monitored, while pumps and valves regulate the flow of leaching agents and removal of dissolved metals.