Partial Roasting of High-Arsenic Copper Concentrates
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NTRODUCTION
SINCE high-arsenic copper concentrates with > 0.3 wt pct arsenic cannot be processed by conventional smelting-converting processes, they require a prior arsenic removal step to reduce its content to manageable levels. Partial roasting, particularly in fluidized bed reactors, has been used industrially to remove arsenic, since enargite and arsenopyrite, as well as other sulfides generally found in copper concentrates, such as pyrite and covellite, decompose readily above 770 K (500 C), releasing, in addition to gaseous arsenic trisulfide, gaseous sulfur, which by oxidizing to SO2 generates most of the heat required by the process. Desarsenifying roasting (or partial roasting) has being applied industrially at a large scale since 2015 at the Ministro Hales Division of CODELCO in Chile and also has been practiced by others like the Boliden Company in Sweden at its Ronnskar plant for several decades to process dirty copper concentrates.
IGOR WILKOMIRSKY is with the Department of Metallurgical Engineering and Unidad de Desarrollo Tecnol o´gico UDT, University of Concepcio´n, E. Larenas 285, 4070371 Concepcio´n, Chile. Contact email: [email protected] ROBERTO PARRA, FERNANDO PARADA, and EDUARDO BALLADARES are with the Department of Metallurgical Engineering, University of Concepcio´n, E. Larenas 285, 4070371 Concepcio´n, Chile. JORGE ETCHEVERRY and RODRIGO DI´AZ are with the DMH Division of CODELCO, Calama Road, Km. 5, 8340424 Calama, Chile. Manuscript submitted April 2, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
There is not much information in the literature about industrial or pilot plant results of desarsenifying roasting of high-arsenic copper concentrates, with most of the published information being laboratory results. Chakraborti and Lynch[1] analyzed the Fe-As-S-O quaternary system between 873 K and 1023 K (600 C and 750 C) thermodynamically, concluding that under reducing conditions the species present in the gas phase are As4(g) and As4S4(g), while under oxidizing conditions the species present is As4O6(g). Lynch[2] extended the analysis further to the physico-chemistry of arsenic, presenting the most complete revision of the thermodynamic data on arsenic compounds at that time. Nakasawa et al.[3] simulate the behavior of arsenic during the roasting of high-arsenic copper concentrates by means of the free energy minimization method, assuming that the calcine behaves like a pseudo-solid solution and the arsenic compounds are solutes in it, far from their equilibrium conditions. The model shows that the temperature, time, initial arsenic content and oxidation of the labile sulfur are the most influential parameters in arsenic removal. Imris and Klenovcanova’s[4] study at the laboratory level investigated the removal of arsenic, antimony and mercury from polymetallic copper concentrates. At 1073 K (800 C) under neutral atmosphere, from 96 to 99 pct of the arsenic and similar values for mercury can be removed in < 15 minutes, while antimony removal was much lower with 95 pct between 773 K and 97
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