“…Several hydrometallurgical processes have been worked out on different scales to recover metals from spent Ni-MH batteries. Sulfuric and hydrochloric acids have been widely used as leachants (Fernandes et al, 2013;Santos et al, 2014;Turek, 2018;Korkmaz et al, 2018;Oliveira et al, 2017), in the concentration range from 1 to 12 mol L -1 , at a temperature range from 25 to 95°C, over a long period of time (> 80 min) (Turek, 2018). The addition of a reductant like hydrogen peroxide improves leaching of many metals as it converts sparingly soluble forms in higher oxidation states (e.g., Co 3+ , Ni 3+ , Mn 4+ ) to lower valence ions (e.g., Co 2+ , Ni 2+ , Mn 2+ ) which are leachable and stable in acidic solution (Vieceli et al, 2018;Santos et al, 2014).…”