Bio-dissolution of spent nickel-cadmium batteries using Thiobacillus ferrooxidans.

In this study, the production of sulphuric acid in bioreactors with Thiobacillus ferrooxidans attached on elemental sulphur was investigated. These bioreactors reached a maximum H+ productivity of 80 mmol kg-1 d-1 of support. This medium was used for the indirect dissolution of spent nickel-cadmium batteries recovering after 93 days 100% of cadmium, 96.5% of nickel and 95.0% of iron. Moreover, recoveries higher than 90.0% were reached when anodic and cathodic materials were directly added to Thiobacillus ferrooxidans cultures with sulphur as the sole energy source. The results presented show an economic and effective method which could be considered the first step to recycle spent and and discarded batteries preventing one of the many problems of environmental pollution.