Extended validation of an expression to predict ORP and iron chemistry: Application to complex solutions generated during the acidic leaching or bioleaching of printed circuit boards

The expression developed in our previous work to predict the redox potential of the quaternary H2SO4-Fe2(SO4)3-FeSO4-H2O system can still be used to predict the redox potential of the Fe3 +/Fe2 + couple in more complex acidic iron sulfate solutions generated during the acidic leaching and bioleaching of Printed Circuit Boards (PCBs). This expression can also be employed to determine the ferrous and ferric concentrations based on measured redox potential, temperature and total iron by AAS, especially in ferric or ferrous-dominant solutions. This equation therefore provides an alternative to the traditional colorimetric or volumetric methods for ferric and ferrous determination. The applicability of this equation in acidic iron sulfate solutions containing cupric ions was also supported by the experimental results in the literature. It is also shown that the measured redox potential is highly useful to estimate and understand the iron chemistry of industrial leaching processes.