Intensification of Opening a Thrust Alloy Based on Platinum and Rhodium

Abstract

Alloys based on platinum group metals have high chemical resistance, which causes a number of difficulties when dissolving them. Currently, among hydrometallurgical methods, dissolution in aqua regia is one of the most effective methods for opening corrosion-resistant alloys. The main disadvantage of this method is the release of toxic gases such as nitrosyl chloride and nitrogen oxides. To reduce the volume of released gases without reducing the oxidation-reduction potential (ORP) of the system, a method for dissolving a Pt–Rh alloy in HCl–HNO₃ with dosed addition of HNO₃ at a given value of the redox potential of the system is proposed in this study. The system potential chosen on the basis of the potentials of the HNO₃–HCl–Pt and HNO₃–HCl–Rh systems is 0.85 and 0.9 V. The influence of dispersion and defectiveness of the Pt–Rh alloy on its dissolution indices is also investigated. As a result, it is shown that the dissolution of the Pt–Rh alloy with a rhodium content of 15% in HCl–HNO₃ at a constant ORP value of 0.9 V compared to the use of classical mixture (HCl : HNO₃ = 1 : 3 (vol)) decreases the nitric acid consumption by 40%, reduces the process time, and increases the recovery factor as for platinum, and for rhodium, and also reduces the volume of released nitrogen oxides by half (theoretical calculation). It is established that the process of mechanical activation of the alloy reduces the dissolution time and leads to almost quantitative dissolution of the sample.