Comparison of chemical firmness of the titanium, tantalum and platinum in muriatic oxidizing environments in the autoclave

In modern hydrometallurgy, autoclave leaching processes are widely used, which is associated with a number of their advantages over processes occurring in open systems. In the Russian refining industry, the introduction of such technologies is difficult, and one of the reasons is the high requirements for the corrosion resistance of structural materials. In this work, the behavior of metal plates of tantalum, titanium and platinum in solutions of hydrochloric acid with additions of hydrogen peroxide under autoclave conditions was studied in the temperature range of 100-200°C. It has been shown that the specific dissolution rate of platinum under autoclave conditions is several orders of magnitude higher than the dissolution rates of titanium and tantalum under similar conditions. Thus, at a temperature of 130°C, a platinum plate dissolves completely within 2 hours, which corresponds to a specific dissolution rate of 1500·10-12 g m2/s; the dissolution rate of titanium and tantalum under the same conditions was 40·10-12 and less than 1·10-12 g·m2/s, respectively. The creation of oxidizing conditions promotes the passivation of tantalum and, to a large extent, titanium. Platinum, on the contrary, under oxidizing conditions intensively goes into solution. Taking into account the fact that in most cases PGM raw materials are dispersed powders with a high specific surface area, titanium equipment can be recommended for their processing. It has been established that titanium is quite stable in the presence of an oxidizing agent in solutions of 3 M hydrochloric acid up to a temperature of 160°C. Tantalum in hydrochloric acid oxidizing environments is stable up to a temperature of 200°C. The quantitative data obtained in the work can be used to develop technologies for processing raw materials containing platinum group metals and to create corresponding equipment.