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Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures
RAFAEL PADILLA, ALVARO ARACENA, and MARIA C. RUIZ
Roasting of enargite (Cu3AsS4) in the temperature range of 648 K to 898 K (375 C to 625 C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:First stage: 4Cu3AsS4 s
+ 13O2 g
= As4O6 g
+ 6Cu2S s
+ 10SO2 g
Second stage: 6Cu2S s
+ 9O2 g
= 6Cu2O s
+ 6SO2 g
Third stage: 6Cu2O s
+ 3O2 g
= 12CuO s
The three reactions occurred sequentially, each with constant rate, and they were affected significantly by temperature and partial pressure of oxygen. The kinetics of the first stage were analyzed by using the model X = k1t. The first stage reaction was on the order of 0.9 with respect to oxygen partial pressure and the activation energy was 44 kJ/mol for the temperature range of 648 K to 898 K (375 C to 625 C).
DOI: 10.1007/s11663-012-9675-x The Minerals, Metals & Materials Society and ASM International 2012
I. INTRODUCTION
ROASTING is a pyrometallurgical process used in the metallurgical industry to transform sulde minerals into oxides, sulfates, or other compounds more amenable for subsequent treatment toward the production of metals. In the case of copper concentrates, roasting is commonly used for the elimination of toxic arsenic and other deleterious elements through the gas phase, mainly because copper concentrates containing high amounts of arsenic are not apt for conventional smelting-converting technology because of the high risk of ambient contamination with arsenic compounds and the risk of producing nal copper with unacceptable high levels of arsenic.
Arsenic in copper concentrates is present primarily as the enargite mineral (Cu3AsS4), and when these copper concentrates contain appreciable amounts of enargite, they must be pretreated to eliminate the arsenic before smelting. Roasting is the preferred pretreatment process,[13] where most of the deleterious arsenic is eliminated through the gas phase inasmuch as arsenic compounds (including oxides and suldes) have high vapor pressures at relatively low temperatures. Thus, the volatilization of arsenic at roasting...