Electrochemical Equilibria of Copper in Aqueous Phosphoric Acid Solutions

The electrochemical behavior of copper in aqueous solutions containing phosphoric acid (orthophosphoric acid) and phosphate salts is important in a variety of industrial applications. This study presents aqueous solubility diagrams and potential-pH diagrams for a copper–phosphoric-acid–water system at a wide range of total dissolved copper, , and phosphoric acid activities, . and were used as the cupric-phosphate solid species in the constructions of the diagrams. The stability domains of these two solids were similar, but had a relatively narrower predominance region. The diagrams showed that a higher amount of is required to form the copper-phosphate solids when is increased. For the combinations of lower and higher values, phosphoric acid is expected to increase the solubility range of copper through the formation of aqueous copper-phosphate complexes. Increasing the temperature broadens the stability domain of . The aqueous solubility diagram constructed for copper electropolishing rules out the formation of any anodic solid films on the copper electrode during electropolishing in 85 wt % phosphoric acid. The predictions of the diagrams agree with the experimental data from the literature.