Leaching of metals from waste button cell batteries was explored in this study. Aspergillus niger spent medium was used for metal leaching to avoid toxicity of metals toward microbial cells. Process parameters including time, temperature, shaking speed, and volume of the spent medium were optimized. We obtained 100% leaching of zinc and silver in six hours at 60 °C and 100 rpm using 15 mL spent medium. The use of spent medium supported the indirect leaching process. The organic acid produced by fungi acts as a lixiviant, aiding the metal leaching in this process.

Background The replacement of lead (Pb)-bearing solders by several Pb-free solders is a subject of intense research in these days due to the toxic effects of Pb on the environment. However, the Pb-free solders contain metals such as silver (Ag), copper (Cu), and zinc (Zn). The increasing use of these Pb-free solders again increases the risk of release of Ag, Cu, and Zn metals into the environment. The Pb-free solders can, therefore, be used as a secondary source for the metals which will not only help in environmental protection but also for the resource recovery. Results This study reports a process to leach metals from hazardous soldering materials by acetic acid. Acetic acid was found more effective for metal recovery from the tin–copper (Sn–Cu) solder than tin–copper–silver (Sn–Cu–Ag) solder. Various process parameters were optimized for recovery of metals from Sn–Cu solder. It required 30 h for 100% recovery of Cu and Sn, respectively. The metal recovery increased gradually with an increase in acid concentration approaching complete recovery at an acid concentration of 80%. Effect of shaking speed and temperature on the recovery of metals from Sn–Cu solder was studied. The metal recovery decreased with an increase in solder weight. Conclusion The present study reveals an effective process to recycle the Pb-free solders. The low concentration of acetic acid was also found significant for metal leaching from solder. The research provides basic knowledge for recovery of metals from Pb-free solders.

Although many available metal recycling methods are simple and fast, they are also expensive and cause environmental pollution. Biohydrometallurgical processing of metals offers an alternative to overcome these issues, as the use of biological means not only helps to conserve dwindling ore resources but also fulfills the need for the unambiguous need to extract metals in nonpolluting, low-energy, and low-cost way. This book covers biohydrometallurgy and its application in the recovery of metals from secondary sources like wastes. It aims to provide readers with a comprehensive overview of different wastes for metal recovery and biological treatment methods that are both environmentally friendly and economically viable.