Estudio físico-químico de los materiales refractarios usados en hornos pirometalúrgicos de la industria del cobre

Abstract

This research work entitled “Physical-chemical study of the refractory materials used for the lining of the furnaces in the pyrometallurgical copper-making process”, carried out along four years, is the result of collaboration between Atlantic Copper (an affiliate of Freeport McMoran) and the University of Huelva. The main aim of this research is the study of the refractory wear (magnesia-chromite type) used for the lining of the pyrometallurgical furnaces in the copper making industry from polymetallic sulfide ores. The work is divided into five research lines. The first of them is focused on the study of the starting materials used in the magnesia-chromite refractory making, as well as the as-delivered refractory (before being used in the furnaces). This study the starting point for better understanding of the refractory wear shown in the rest research lines of this work. Subsequently, three research lines are carried out to study the chemical degradation mechanisms of the refractory in different furnaces used in the copper making industry: Peirce-Smith Converter, Submerged Arc Furnace and Anode Furnace. The results of the microstructural analyses of the refractory samples collected from the different areas of these furnaces after their working campaign, show the differences in the degradation process. These analytical results are supported by thermochemical calculations of the interaction between the molten phases present in these furnaces and the refractory, under standard process conditions, as well as under non-standard conditions (to obtain results under different scenarios). Since the wetting and infiltration of the refractory by the molten phases are the initial stages for the refractory degradation, the last research line of this work was focused on the study of these phenomena: different refractory substrates (and raw materials) and several molten phases present in the pyrometallurgical process were used. Additionally, a novel dynamic test was developed to evaluate the refractory wear as a consequence of the interaction with the fayalitic slags by submerging refractory probes in a launder with slag from a Submerged Arc Furnace. The degradation of the intergranular phases of the refractory (microstructure) by infiltration of the molten phases through the open porosity, leads to the dissolution of them. It involves the degradation of the refractory due to the weakening of the microstructure. Moreover, the dissolution of these intergranular phases promotes the greater contact between the phase that has infiltrated and the refractory grains. The last causes the greater or lesser chemical attack to these refractory grains (greater attack for the case of fayalitic slags). The degradation of the magnesia phase of the refractory is a consequence of dissolution in the fayalitic slag, leading the formation of olivine solid solution with high Mg#. This high-magnesium olivine tends to solidify rapidly due to its higher solidus due to its magnesium content. As observed in the micrographs of the post-mortem analyses and in the results of the thermochemical calculations, it occurs quite fast.