G. E. Kim, Perpetual Technologies, Inc., Ile des Soeurs, QC, Canada
High pressure acid leaching (HPAL) of low grade ore utilizes very severe processing conditions to hydrometallurgically recover metals such as nickel, cobalt, and gold. The severe conditions include high temperatures, high corrosivity, and high pressures. In addition, the presence of solids in the slurry make the environment highly abrasive and erosive. Ball valves play a critical role in containing and directing the flow of very hot acidic slurry within the autoclaves. Without a protective coating, even solid titanium valves have been reported to last less than a month time in actual service. Since May of 2000, Perpetual Technologies, in partnership with F.W. Gartner Thermal Spraying Co. and Mogas Industries has carried out failure analyses of past coatings, developed a nanostructured titanium dioxide coating, carried out lab tests, and applied the novel coating onto actual ball valve components used in HPAL service. In 2001, Mogas Industries qualified and applied a nanostructured titanium oxide (n-TiO2) coating for gold and nickel/cobalt HPAL services. The n-TiO2 coating provided dramatically superior protection against abrasive and erosive wear, fared very well against high-pressure autoclave corrosion testing, and has performed well in HPAL service.
Summary: High pressure acid leach (HPAL) is a very aggressive environment with respect to wear and corrosion. A novel nanostructured thermal sprayed titanium oxide coating has been successfully developed and applied onto ball valves used in HPAL service.
