Metallurgy
Hydrogen Peroxide and Caro’s acid
Hydrogen Peroxide is a very attractive reagent to use in metallurgy as its decomposition products are only water and oxygen. A limitation on its efficient use in some applications is a tendency to decompose in the presence of transition metal ions at elevated temperatures. This can be overcome by conversion to Caro’s acid (H2SO5—a stronger oxidant than H2O2) by the following easily performed reaction which is usually carried out at the user’s site:
Extraction of uranium
Uranium is most frequently leached from its ores using a mixture of sulphuric acid and oxidant to convert insoluble uranium (IV) to soluble uranium (VI). Of the commercially available oxidants suitable for this purpose, Caro’s acid combines environmental acceptability with ease of use and ease of control. Caro’s acid acts by oxidising iron ( II ) to iron ( III ) which oxidises uranium.
Oxidation of Mo, V, Cr, Fe, Se, As ions
Many metal ions are oxidised to higher valency states by Hydrogen Peroxide and Caro’s acid over a wide range of pH, in reactions which are generally more rapid and stoichiometric than possible with other commonly used oxidants. Selective oxidation of one metal in a mixture of metal ions can often be achieved by control of pH and oxidation potential.
Reduction of Co and Mn from higher valency states
In the presence of some transition metal ions in higher valency states, Hydrogen Peroxide behaves as a reducing agent in acidic solutions. This is a very simple way of dissolving insoluble oxides such as cobalt (III) and manganese (IV).
Precipitation of uranium peroxide
Hydrogen Peroxide reacts with solutions of uranium(VI) in mildly acidic solutions to form insoluble uranium peroxide. As very few other metals form insoluble peroxides under acid conditions, it provides a widely used method for the selective precipitation and purification of uranium.