Four different Cu-rich polymetallic concentrates (additionally comprising Zn, Pb and impurity elements As, Sb) from various deposits in Sweden are examined, in particular for the sintering tendency during roasting in inert atmosphere. Experiments performed in a laboratory-scale roasting setup between 200 °C and 700 °C in intervals of 100 °C revealed that significant sintering initiates from 500 °C for all four concentrates. Two sintering mechanisms are determined from the examination of the sintered calcines: (1) solid-state assimilation of Cu-, Zn- and Fe-bearing main sulphide minerals to form a high-temperature solid solution, the iss phase belonging to the Cu-Fe-Zn-S system; (2) low-melting liquid phase formation due to partial melting of galena facilitated by the presence of impurity-bearing minerals, mainly the arsenopyrite and Sb sulphosalts such as tetrahedrite. Galena also forms a melt below 700 °C with the iss phase. Therefore, the presence of galena in polymetallic concentrates generally increases the susceptibility to early sintering. These experiments in inert atmosphere facilitate a fundamental study with practical relevance to the roasting in low oxidation potential environments, favourable for volatilization of impurity elements such as As and Sb.
Four different Cu-rich polymetallic concentrates are tested for volatilization of Sb and As during laboratory-scale roasting. The experiments are performed between 200 °C and 700 °C, at intervals of 100 °C and in an inert atmosphere. Sb volatilization is much less (maximum approximately 45 pct) than As volatilization (maximum approximately 95 pct) in these conditions at 700 °C. As volatilization is however limited from the concentrate having As mainly in a tetrahedrite solid solution ((Cu,Ag,Fe,Zn)12(Sb,As)4S13). Sb and As retained in the roasted calcine are found in the low-melting liquid phase, formed at approximately 500 °C. This melt phase gets enlarged and enriched in Sb with an increase in temperature. However, there is noticeable As volatilization from this melt phase with the temperature approaching 700 °C. Furthermore, there is an early and relatively high Sb volatilization from the concentrate having Sb substantially as gudmundite. Micron-scale elemental redistribution in gudmundite in the 350 °C roasted calcine confirms its transformation at this temperature. Other Sb minerals did not undergo any detectable transformation at this temperature, suggesting that the significant Sb volatilization starting between 300 °C and 400 °C was primarily from gudmundite. This benign attribute of gudmundite featured in this work in the context of roasting should also be relevant from the geometallurgical perspective during concentrate production, where concentrates bearing Sb are considered substandard for further Cu extraction irrespective of the Sb mineralogy.
A Cu-rich complex sulpfide concentrate (containing Sb as sulphosalts and gudmundite, and As as arsenopyrite) is roasted in Nitrogen atmosphere carrying traces of oxygen ($${\text{p}}^{{\text{O}}_{2}} \approx {10}^{-5.3}\text{ bar)}$$ p O 2 ≈ 10 - 5.3 bar) . In situ measurements through QMS indicated that the volatilized species are mainly elemental sulfur, S2(g), and gaseous sulfur oxides. Sb- and As-bearing volatilized species could not be detected, owing to their low concentrations in the gas phase. Characterization studies through XRD and SEM-EDS confirmed that the condensates collected at room temperature during the roasting experiments comprised of (1) cyclo-octa sulfur, S8(s) and polysulfur oxides, Sn−xOx(s); (2) amorphous trisulfides of Sb and As; (3) and cubic crystalline trioxides of Sb and As. The solid phases in the condensate were found to be fine-sized (sub-micronic) and widely intermixed. Consequently, quantification of the solid phases in the condensates through direct measurement techniques like QEMSCAN was not possible. A novel approach of partial quantification of solid phases in the condensate through a stochastic model-based calculation approach is also presented. The model results suggested the occurrence of vapor-phase complexation of sulfides of Sb and As in the gas phase. Additional attributes of the volatilized species could be determined through a thermodynamic equilibrium calculation showing that the formation of the complex oxides, As4−nSbnO6(g), would be negligible compared to that of the complex sulfides, As4−nSbnS6(g).
The iron and steel industry is one of the most important sectors worldwide, and it has a great impact on the global economy; however, this sector is still highly dependent on fossil carbon. To decrease this dependency, approaches to partially replace the injected pulverized coal with secondary, highly reactive, renewable (biomass) and H2‐rich materials are studied. The injection of such materials is expected to significantly decrease the emitted CO2 from blast furnaces. However, due to the different ash composition of these alternative materials (especially alkali and alkaline earth metals) compared to that of ordinary injected coal, these materials are expected to alter the raceway slag properties and affect the coke reactivity. Herein, the effect of the ash from different hydrogen‐rich carbonaceous materials on the raceway slag physicochemical properties as well as coke reactivity is reported. The melting characteristics of the ash briquettes in contact with the coke and wettability of the melted ash on the coke surface are determined visually using an optical heating microscope. The effect of the ash on the coke reactivity is studied by means of thermogravimetry under a continuous flow of CO2.
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