Abstract:
This study explored, on a laboratory scale, how matte separates from the gangue in the black top of
a PGM smelter. Two PGM concentrates, one with high sulfide content (17.3 mass%, Platreef concentrate)
and the other with low sulfide content (1.3 mass%, UG-2 concentrate), were studied in the temperature
range of 800°C to 1480°C, which is the temperature gradient across the black top. The results showed that
effective matte separation occurs at temperatures when the matte is completely molten, and
a substantial amount of liquid silicate phase has formed. The main matte separation mechanism is the
coalescence of sulfide prills and their gravitational settling through the continuous path created by the
liquid silicate phase. Complete matte separation occurs at lower temperatures in Platreef concentrate
(1400°C in Platreef concentrate vs. 1480°C in UG-2 concentrate), due to the higher concentration of liquid
silicate phase of lower viscosity, as well as the higher amount of sulfide minerals in this concentrate. PGMs
already dissolve and collect in a nickel-iron-based alloy associated with the matte at temperatures as low
as 900°C.
