This report details the optimised processing flowsheet for the Kitumba Copper Project, designed to achieve over 90% copper recovery through a combined flotation, pressure oxidation, and atmospheric leaching route.
Report context
The Kitumba Copper Project technical report, dated 25 September 2014, presents the recovery methods and process design for an Optimised Pre-Feasibility Study (OPFS). The report was prepared to NI 43-101 standards and describes a processing facility designed to treat 3 Mtpa of ore. The flowsheet development work, including batch testwork and process engineering, was conducted between November 2013 and February 2014.
Processing route
Flowsheet development history
An earlier flowsheet utilising flotation and atmospheric leaching, as adopted for the initial prefeasibility study, achieved only 76% copper recovery. The primary objective in developing the optimised flowsheet was to increase copper recovery while containing capital and operating costs. The revised flowsheet, while more complex than its predecessor, achieves greater than 90% copper recovery at a significantly lower unit operating cost of production.
The individual unit processes selected for the optimized flowsheet are well understood and have been based on successful operating practices at a number of commercial copper processing operations worldwide.
Comminution and flotation
The processing facility comprises a comminution circuit followed by flotation to produce a sulphide-rich concentrate. The flotation tail is combined with the pressure oxidation (POX) leach discharge slurry for subsequent atmospheric leaching.
Pressure oxidation
The flotation concentrate is leached in a POX autoclave. Sulphuric acid and ferric species generated in the POX circuit are used to facilitate copper dissolution, while steam generated from the oxidation of sulphur heats the incoming atmospheric leach feed slurry to enhance leach kinetics.
Atmospheric leaching
The flotation tail combined with the POX leach discharge slurry is processed in a series of atmospheric leach tanks to solubilise residual copper.
Solid-liquid separation and counter-current washing
The discharge slurry from the atmospheric leaching circuit is washed in a series of six counter-current decantation (CCD) thickeners to separate the copper-rich pregnant leach solution (PLS) from the barren leach solids. The washed barren solids are neutralised and discarded to a tailings storage facility.
Solvent extraction and electrowinning
The PLS is fed to a solvent extraction circuit. Loaded strip solution is fed to a copper electrowinning tankhouse for generation of copper cathode product. Residual soluble copper is precipitated from a bleed stream of solvent extraction raffinate solution and recycled, while the barren liquor provides the wash solution for the CCDs.
Testwork and design criteria
A series of batch flotation, leaching, settling, and neutralisation tests was carried out between November 2013 and February 2014. Results from these tests were used to generate process design criteria, which in turn were used to develop mass and energy balances for the revised flowsheet. These outputs were used to size mechanical equipment and estimate reagent and utility requirements.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Ore feed rate | 3 Mtpa | Design |
| Nominal copper cathode production | 60,000 tpa | Design |
| Peak copper cathode production | 70,000 tpa | Design, achievable by increasing plating current density |
| Plating current density (design) | 310 A/m² | Design |
| Plating current density (peak) | 357 A/m² | Maximum |
| Copper recovery (initial prefeasibility flowsheet) | 76% | Historical design |
| Copper recovery (optimised flowsheet) | >90% | Design |
| CCD thickeners | 6 | Design |
| Testwork period | November 2013 – February 2014 | Batch flotation, leaching, settling, neutralisation tests |
Project website: https://ca.finance.yahoo.com/news/intrepid-mines-limited-kitumba-technical-120000723.html
Technical qualifications
The report notes that while the initial batch tests provided substantial insight into the behaviour of the leaching processes, a pilot campaign is planned to provide a full set of criteria for the Definitive Feasibility Study (DFS). Consequently, a number of assumptions remain in the process design criteria for this optimised pre-feasibility study. The design presented is considered to provide a reasonable basis on which to assess the project.
Source: Kitumba Copper Project, NI 43-101 Technical Report, 25 September 2014, Section 17.0 Recovery Methods, Section 17.1 Process Flowsheet Development.
