Abstract
Pressure acid leaching (PAL) of lateritic nickel ores requires the use of extremely severe processing conditions (250 °C, > 4000 kPa, 98 % H2SO4). In addition to the severe corrosive nature of the acid solution, up to 30% of abrasive solids are present in the slurry. PyroGenesis Inc. has applied its expertise in materials science and thermal spray technologies into developing and commercially applying coatings for the protection of ball valve components used in PAL autoclaves. Vacuum plasma spray (VPS) and atmospheric plasma spray (APS) processes are used to apply coatings of metals and ceramics for corrosion and wear resistance, respectively. A comparative study on the microstructure and mechanical properties of different coatings, applied with the two processes, will be presented. Although APS coatings provide enhanced abrasive resistance, VPS coatings have shown the potential for superior properties. The extreme temperatures and pressures associated with the actual PAL conditions are too severe to simulate in laboratory conditions, hence, corrosion testing was not possible. Microstructural analysis, microhardness, adhesion, and abrasion testing were determined for each coating/processing combination.
