Study of the acid bake-leach process has shown potential advantages for the treatment of
enargite (Cu3AsS4) concentrates. Among the most important advantages of the
process is the transformation of enargite to water-soluble copper sulfate and highly
soluble arsenic trioxide (arsenolite). Because arsenic is retained in the condensed phase
during the baking, the vapor pressure of arsenic trioxide should be estimated at typical
baking temperatures (e.g. 473 K). To that end, the vapor pressure of As4O6 (g) was estimated under the
baking conditions based on published thermodynamic values. The vapor pressure of
arsenolite at 473 K was found to be approximately 9.03 × 10-4 atm. Based on the
linear regression analysis of the published vapor pressure values for arsenolite in the
temperature range 366−579 K,
the equation for the best fit line was found to be as follows, with a correlation
coefficient of 0.9973:
logPArsenolite
(atm) = (-5780.7)/(T (K))+9.16.
Available information on arsenic trioxide does not allow a definite conclusion regarding
the arsenolite/claudetite transformation temperature and their exact melting points.
However, the transition temperature has been reported to be in the wide range of
240−506 K in different
references. Furthermore, the thermodynamic information concerning arsenolite/claudetite is
sparse and at times not consistent. An effort has been made in this paper to compile the
most reliable thermodynamic information for arsenic trioxide (arsenolite and claudetite).