An investigation into the reliability of some locally manufactured crucibles and possible remedies.

Abstract

Crucibles are important units in pyrometallurgical operations as they serve as containers within which high temperature reactions are conducted. For a given operation, good crucibles should be chemically inert, withstand high temperatures, thermal shock and prevent seepage of molten charge. In addition they should be robust enough to withstand the stresses involved in shipping and handling. Formerly, most of the crucibles utilized in the Ghanaian mining industry were imported but in recent times, some local crucible manufacturers have emerged. There are some challenges with the use of these locally manufactured crucibles as the failure rate is high, especially when used in fire assaying and in smelting of gold concentrates. In this study, the integrity of crucibles manufactured by two major local entrepreneurs, “A” and “B” was investigated. X-ray fluorescence spectroscopy indicated that the major minerals in the crucibles were Al2O3 and SiO2 with crucible “A” having 20% and 42% respectively and 32% Loss On Ignition (LOI) while that in crucible “B” were 34% and 42.9% respectively with 17.5% LOI . Crucible “A” had feed particle size with 80% passing 78 μm while that of “B” was 54 μm. It was realised that failure was mainly due to the presence of coarse particles that reduce packing density and volatile material that escape on heating to create weak zones and channels that allow seepage of molten material. The combined effects of finer particle size, higher Al2O3 content and lower LOI gave crucible “B” superior performance over “A”. This paper critically investigated the credibility of local crucibles and presents recommendations. The investigations included an audit of the processes involved, pre-smelting heating analysis, particle size analysis, volatile/combustible matter content analysis all in the vein of testing the crucible‟s chemical inertness, physical and mechanical strength etc. Crucible preheating increased the success rate of the crucibles by about 20%. A good grind was necessary for good moulding of the crucible consequently strengthening it. Minimal combustible and volatile matter was advantageous.