The CESL Copper Process was developed for copper sulphide concentrates as a
hydrometallurgical alternative to smelting and refining. This process has been described
previously and consists of five main process steps, (Figure 1):
• Pressure oxidation of concentrate at ‘medium temperature’, i.e. above the
melting point of sulphur, but below phase transition point of sulphur
• Copper leaching of the solid oxidation product with raffinate at atmospheric
conditions to produce a PLS
• Solvent extraction of PLS to produce a high purity electrolyte and regenerate
raffinate
• Partial neutralization of raffinate to remove any excess sulphate
• Electrowinning to recover copper in commercial product form, (full cathodes).
The concentrate slurry and a recycled acidic chloride solution are pumped separately into
an autoclave operating at about 150ºC and 1,400 kPag total pressure. High purity oxygen
is added to achieve almost quantitative oxidation of the copper minerals within a retention
time of about 1 hour. Operating pH varies from about pH 1 to about pH 3, depending on
minerals in the feed concentrate and the other operating conditions.
Under these conditions, copper sulphide minerals are efficiently converted to an acidsoluble
sulphate salt, basic copper sulphate, which reports to the PO filter cake, or to the
PO product solution, depending on operating pH of the autoclave. Iron present in the
copper minerals is oxidized to hematite-type minerals, and sulphur is converted mostly to
elemental sulphur. Very little sulphur to sulphate oxidation occurs, and therefore acid
generation from sulphur oxidation is minimal.
The autoclave discharge slurry is thickened and filtered. Copper may be removed from the
autoclave leach liquor by solvent extraction if necessary, before it is recycled to become
feed to the autoclave.
The pressure oxidation filter cake is then leached at atmospheric pressure with recycled
raffinate at about pH 1 – 2, and the resultant residue separated from the solution by a CCD
circuit and final filtration. Wash liquor for the CCD is supplied internally from the process,
as a secondary raffinate. The copper-containing pregnant leach solution (PLS) is
processed in a conventional solvent extraction circuit, producing a raffinate which is
recycled back to leaching.
In the final process step, copper is recovered from the copper rich electrolyte solution
produced by the solvent extraction process by conventional electrowinning. The cathode
production meets LME Grade-A standards.
The waste streams from the plant include the final washed leach residue and the combined
gypsum product from neutralization. The leach residue contains the elemental sulphur,