Selective Separation of Metallic Phases from Chalcopyrite

Owing to the environmental problems associated with copper extraction alternative
processes are sought. The carbothermic reduction of natural chalcopyrite concentrates,
from Ghatsila mines in Bihar, India, in the presence of lime, was studied across the
temperature range 850-1250°C. Studies have been completed previously in synthetic
chalcopyrite. This study stresses the need to investigate the reduction of natural
chalcopyrite.
The reduction of chalcopyrite proceeds in two steps, initially with the direct reduction
by carbon. This is followed by indirect reduction by the carbon monoxide evolved from
the first stage of reduction. Both stages of the reduction were investigated to determine
the reaction mechanism. Metallic copper and iron are produced from the reduction of
chalcopyrite. The oxysulphide phase, Cm, also produced from the reduction of
chalcopyrite, was not previously categorised. X-ray diffraction analysis and scanning
electron microscopy were utilised to evaluate the structure of Cm.
Silver is an important by-product of copper extraction therefore it was necessary to
study its path during the reduction of chalcopyrite. This was achieved by additions of
Ag and Ag2S prior to reduction. Silver will preferentially segregate out with the copper
phase hence providing a valuable metallic product from the reduction reaction. The
addition of Ag to the reduction mixtures facilitates metallic phase separation of copper
and iron.
Arsenic and antimony are deleterious elements present in naturally occurring
chalcopyrite. The addition of calcium sulphate and silica to chalcopyrite, heat treated
under partially reducing conditions, will produce a calcium silicate slag phase that will
entrain impurities such as arsenic and antimony, thus providing a method of control of
those elements. An initial investigation into the possible control and elimination of
impurities during extraction of copper has been conducted with favourable results.