Technology evolution in the Southern African Ni-Cu-Platinum Group Metals (PGM) smelting industry

The Southern African Ni-Cu-PGM smelting industry has evolved significantly from 1937 to date. As demand for platinum group metals has increased, smelting technology development has been closely linked to the need to process more concentrate, but also to changes in the chemistry and mineralogy of concentrates from the various platinum group metals-containing reef types. Early technologies relied on blast furnaces and Great Falls converters, but from the late 1960s, electric furnaces and Peirce Smith converters were commissioned. In the early 1990s, the introduction of water-cooled copper plate coolers into the slag zones of the primary furnaces enabled greater power intensity and throughput, with further intensification from the early 2000s requiring the use of deep-cooled copper coolers. Converting technology was also modernised to include a top submerged lance converter in one instance. Approaches to converter slag cleaning have evolved from recycling slag to the primary furnaces, to milling and flotation or electric furnace slag cleaning as the Cr2O3 content in slags has increased. The shift in the 1990s from Merensky ore derived concentrates to those from UG2 ores impacted the process design for the primary furnaces, with UG2 concentrates having lower matte falls and higher Cr2O3 levels. Conversely, concentrates derived from Platreef and Great Dyke ores, with high matte falls and lower Cr2O3 levels, have introduced other challenges. Furnace designs and operating philosophies have been improved to better handle these ranges of concentrates, the resulting slags and superheated mattes, the containment of which is non-trivial. The smelting of non-roasted concentrates in the primary furnaces gave rise to rapid corrosion of the copper coolers, and triggered development of corrosion mitigation strategies. Advances in SO2 emissions control have transitioned from single contact sulphuric acid plants in the 1970s, to the adoption of double contact acid plants, tailgas, and dual-alkali scrubbing in the early 2000s. Low SO2 strength off-gas streams from primary furnaces are abated in some cases, with technologies such as the Sulphacid process introduced from the early 2000s and the Wet-gas Sulphuric Acid process from the early 2020s. With advances in process intensification, increases in operating temperatures and throughputs, and use of water cooling, consequences of furnace failures have become more severe. Water leaks into the molten material environment, primary furnace containment, and slag granulation have been particularly challenging. Technologies, operating, and maintenance philosophies have been developed for prevention and mitigation of failures, and the adoption of process safety management approaches has yielded systematic benefits. With the outlook in demand for PGMs changing as a function of automotive requirements, smelting technology will continue to evolve for further enhancement of safety and environmental protection, reduced costs, and greater efficiencies.