Abstract:
Sulphur driven off from the sulphides in the black top of PGM smelters has in past years caused failure
of copper coolers. When the magnesia-chromite bricks in the smelter were replaced with graphite blocks,
however, copper cooler corrosion drastically decreased and furnace campaign lives improved. This study
explores the role of the slag freeze lining in the permeation of sulphur to the copper cooler. This was done
by measuring the gas permeabilities of two freeze linings and comparing them against the permeabilities
of typical graphite and magnesia-chromite bricks that are used in PGM smelters; measuring the gas
permeabilities of the different layers (hot face, crystalline layers, and cold face) of a freeze lining; and
testing the permeation of liquid sulphur through freeze lining samples at 120 and 180°C. It was found
that the freeze lining samples had gas permeabilities of 1.5 and 0.8 cd at a differential pressure of 32
kPa, compared to the permeabilities of the magnesia-chromite (10.0 cd) and graphite bricks (4.85 cd).
The cold face layer of the freeze lining had the lowest permeability (1.8 cd), and the hot face layer the
highest (2.4 cd). At 120°C liquid sulphur permeated the freeze lining through cracks. The freeze lining
can therefore participate in preventing sulphur permeation towards the copper coolers, as long as its
cold face remains intact and crack free. An added benefit of using graphite blocks in the smelter is that it
establishes a glassy cold face layer in the freeze lining, which has a very low gas permeability.
