The Physical Chemistry of Copper Smelting Slags and Copper Losses at the Paipote Smelter Part 2-Characterisation of industrial slags

The results of an investigation on copper losses in industrial slag from the Teniente converter (TC) and from the electrical slag cleaning furnace (EF) at the Paipote smelter in Chile are presented. Slag samples from each furnace were characterised using chemical and mineralogical techniques. The distribution of the various phases, including entrained matte, was quantified by semi-automatic image analysis. The level of soluble copper was measured by EPMA on samples cooled at a fast cooling rate. The phases found in the slag samples after such cooling are in agreement with thermodynamic calculations of the solidification process. Two types of magnetite crystals were observed in the TC slag samples: magnetite formed during slag solidification (type II) and magnetite which was present as a solid in the melt (type I). The portion of magnetite (type I) was found negligible in the EF slag samples. Sulphide phases were identified in the slag samples as solidified entrained matte, and sulphides present via ex-solution from the liquid slag during solidification. In the case of the TC, the present study has shown that with similar to 4.6 wt-%Cu in slag, about 87% was present as entrained matte. For the electrical furnace, the amount of entrained matte represents some 25% of the copper when the average copper level in EF slag samples was similar to 0.74 wt-%Cu.