A Mineralogical Investigation of Sintering in Cu-Rich Polymetallic Concentrates During Roasting in Inert Atmosphere

Abstract

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.

A Mineralogical Investigation on Volatilization of Impurity Elements from Cu-Rich Polymetallic Concentrates During Roasting in Inert Atmosphere

“…Usage of the size fraction < 38 lm in this experiment however did not affect the study in any way since this experiment was performed at 350°C, at which particle size alterations do not take place because of any physicochemical mineralogical interaction. [6] The chemical compositions of the initial concentrates and the roasted calcines were provided by ALS Global AB, Lulea˚. The method included melting with LiBO 2 , digestion in HNO 3 /HCl/HF and measurement using ICP-SFMS in accordance with SS EN ISO 17294-2: 2016 [51] and EPA method 200.8: 1994.…”

“…Experiments on laboratory-scale roasting were performed in a vertical tube furnace setup. These experiments were referred to as the isothermal roasting experiments in Prasad et al [6] In the beginning of each experiment, the concentrate sample was positioned in a cold zone while the furnace was heating up to the experimental temperature. Once, the desired furnace temperature was achieved, the sample was lifted into the hot zone.…”

“…However, these individual metal-rich concentrates are still polymetallic, containing low proportions of the other metals, and therefore still considered complex for further extraction. For instance, the Cu-rich concentrates studied by Prasad et al [6] were essentially polymetallic, containing approximately 5 to 10 wt pct Zn, 5 to 15 wt pct Pb, Ag>250 ppm, As>0.2 wt pct and Sb > 1.3 wt pct.…”

“…[44][45][46] However, in a complex polymetallic concentrate, the behavior of As and Sb minerals may change due to interaction with the other minerals. For instance, Prasad et al [6] presented an investigation on early sintering susceptibility during roasting due to mineralogical interactions among numerous major and minor minerals existing in Cu-rich polymetallic concentrates. It would be important to investigate the effect of these mineralogical interactions in complex concentrates during roasting on the extents of As and Sb volatilization.…”

“…A detailed study of such transformations tracking the deportment of As and Sb in the mineral phases with an increase in temperature is missing, which is the focus of this work. This article discusses the extent of As and Sb removal in the laboratory-scale roasting experiments presented in Prasad et al, [6] where the complex concentrates experienced sintering during roasting in inert atmosphere. These experiments were performed in inert atmosphere to facilitate a fundamental study on the mineral assemblies in low oxidation potential roasting environments, which are considered favorable for the impurity volatilization.…”