Extraction of silver from spent silver oxide–zinc button cells by using Acidithiobacillus ferrooxidans culture supernatant

The silver extraction from spent silver oxide–zinc button cell battery was investigated by using Acidithiobacillus ferrooxidans (A. ferrooxidans) culture supernatant. Parameters such as duration of leaching, volume of culture supernatant, pH, initial shaking speed, and temperature were optimized for the silver extraction. About 98% silver was dissolved in 1 h, at an initial pH of 2.5, 30 °C temperature, 150 rpm shaking speed and by using 50 mL culture supernatant. The use of only culture supernatant for silver extraction indicated that an indirect non-contact leaching was the predominant mechanism for metal solubilization. There was no need for bacteria themselves to be present for the silver extraction. Hence the role of A. ferrooxidans was most likely to regenerate Fe3+ as an oxidant. The reported method could be considered the first step to recycle spent silver oxide–zinc button cell batteries to overcome pollution problems.

► The biologically produced ferric ions take part in silver dissolution.
► There is no need for bacteria themselves to be present for the silver extraction.
► A cleaner metal recovery process can be developed.