¦IVKOVI et al.
Conclusions
Results of thermal analysis of oxidation process for
natural copper sulfides chalcocite and covellite are
presented in this paper. Based on the results of
DTA-TG-DTG, RDA and chemical analysis, mecha-
nisms of oxidation processes were defined and con-
firmed by thermodynamic analysis. Kinetic parame-
ters and activation energies of investigated processes
were determined using Sharp’s method of reduced
halftime of reaction.
Values of activation energies indicate that for
both investigated samples oxidation process begin in
kinetic, which means that temperature has overall in-
fluence on oxidation rate, and moves to diffusion area
with change of a reaction mechanism.
References
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Fig. 9 Arrhenius diagrams for process of oxidation of:
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chalcocite, 77 kJ mol –1
¾¾¾¾¾¾® ¾¾¾¾¾¾®
covellite, 33 kJ mol –1
while in second period, this sequence is given as:
9 J. G. Dunn and C. Muzenda, J. Therm. Anal. Cal.,
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covellite, 29 kJ mol –1 chalcocite, 19 kJ mol –1
¾¾¾¾¾¾® ¾¾¾¾¾¾®
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Such values obtained for activation energies point
out to the fact that for both investigated samples begin-
ning of oxidation processes are going on in a kinetic
area. It should be mentioned that higher values for Ea
obtained for chalcocite show dominant influence of
temperature on oxidation rate, while for covellite pro-
cess is near to the transition area.
After change of a reaction mechanism, at a near
40–50%, influence of diffusion is stronger, which
leads to decrease of Ea values to diffusion area.
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Table 3 Summarized results of kinetic investigations of Cu2S
and CuS oxidation processes
Activation energy/kJ mol–1
Mineral
Received: January 6, 2004
until fraction
after the fraction
In revised form: October 25, 2004
chalcocite
covellite
77
33
19
29
720
J. Therm. Anal. Cal., 79, 2005