Authors: L. Malherbe, L. Nelson, L. Andrews, K. Hara, M. Legoabe, C. Sima
Pyrometallurgy 05, Cape Town, South Africa, March 2005
Abstract
The smelting efficiency of any furnace depends on the effective volume of the furnace and the mixing characteristics in the bath. Tracer experiments were conducted at the Mortimer Smelter to estimate the active bath volume. This is particularly important to establish in the case of smelting of UG2 platinum group metals (PGM) base metals sulphides concentrates, due to the formation of spinels that can accumulate at the matte-slag or refractory interfaces.
A simplified mixing model consisting of a single perfectly mixed tank with a small amount of plug flow and a region of dead water was used to describe the mixing in the furnace. It was demonstrated that the furnace has a significant dead water zone estimated to be over 60 %, probably due to spinel accumulation. Also, the remaining active slag bath in the furnace appears to be reasonably well mixed.
It appears that the sensitivity and resolution of the tracer test method and means of interpretation of mixing specifically adopted are insufficient to quantify the different furnace operation within the ranges of slag Cr and CaO contents investigated. Comments are made to rectify this in future tracer tests.
Despite this shortcoming, valuable insights are provided into the effects of smelting UG2 rich concentrates on the active furnace volume and extent of slag mixing on the rectangular 6-in-line furnace. This is interpreted to have progressively enforced migration in operation away from classical "immersed” electrode towards a more “shielded-arc” mode of operation, to secure smelting throughput on the Mortimer Smelter.
