This profile summarises the proposed mineral processing route for Stage 2 of the Kipoi Copper Project, based on a November 2011 NI 43-101 Preliminary Economic Assessment. The Stage 2 design comprised a combined tank leach and heap leach circuit feeding a solvent extraction and electrowinning (SX/EW) plant to produce LME Grade A copper cathode.
Report context
The November 2011 technical report was prepared for Tiger Resources Limited by Cube Consulting Pty Ltd, with contributions from CSA Global Pty Ltd and Mworx Pty Ltd. The document presents a Preliminary Economic Assessment (PEA) for Stage 2 processing of the Kipoi Copper Project in the Democratic Republic of Congo. At the time of reporting, Stage 1,a heavy media separation (HMS) plant treating 900,000 tpa of high-grade oxide and transition ore to produce +25% copper concentrate,was already in operation. The Stage 2 SX/EW plant was planned to supersede Stage 1, with commissioning targeted for mid-2014, initially processing HMS plant residues containing approximately 4.8 Mt at 3% Cu.
Processing route
Feed preparation and classification
The Stage 2 plant design called for single-stage crushing followed by classification. The crushed ore was split by size: fine ore was directed to a tank leach system, while coarse ore was sent to a heap leach. A heap leach operation was initially required to process fines and floats from the existing HMS plant, operating for approximately one year in conjunction with the first SX/EW train.
Leaching circuits
The tank leach system comprised sulphuric acid leaching of fine ore in agitated leach tanks. Metallurgical testwork on Kipoi Central ores demonstrated that the copper mineralisation was predominantly acid-soluble minerals, primarily malachite, with over 95% acid-soluble copper content. Sequential copper assays from Amdel (2008) confirmed the ore contained very little cyanide-soluble copper (indicating absence of secondary sulphides like chalcocite) and minimal residual copper (indicating low primary sulphide content such as chalcopyrite). Low sulphur assays supported these findings.
Tank agitation leach testwork (summarised in the report) showed fast leach kinetics, with the majority of leaching complete within four hours. Key observations included:
- Total copper extraction from acid-soluble copper averaged 96.5% across tested samples
- Gangue acid consumption was low, averaging 7.7 kg/t, attributed to low carbonate levels and the presence of dolomite rather than calcite
- Little difference in leach kinetics or gangue acid consumption was observed with finer grinding, suggesting coarser grinds were viable
- Leach solution assays showed low levels of common acid-consuming ions: Mg < 50 ppm, Ca < 50 ppm, Fe < 200 ppm, Mn < 150 ppm, Al < 150 ppm
The coarse ore fraction was directed to a heap leach using sulphuric acid. The report noted that only one qualitative column permeability test had been conducted (by Ammtec in 2007), and that ore sample failed both the slump test and drainage test used to assess heap leach suitability. However, the report cautioned that the test procedure and sample representativeness were unknown, and the results did not preclude heap leaching as a viable option,for instance, the sample may have contained a large portion of fines or lacked agglomeration.
Counter current decantation and clarification
Pregnant leach solution (PLS) from both leach circuits was processed through counter current decantation (CCD) and clarification stages. The CCD system was designed with a wash ratio of 2.0 m³/t.
Solvent extraction
The solvent extraction circuit was split into two separate processing trains: one for tank leach PLS and one for heap leach PLS. This configuration allowed for staged construction. The SX/EW circuit was planned to be built in two 25,000 tpa copper stages. Design PLS copper concentrations were 4.7 g/L for the heap leach stream and 4.0 g/L for the tank leach stream. Design PLS flow rates were 770 m³/h for heap leach and 450 m³/h for tank leach.
Electrowinning
The electrowinning circuit was designed to produce LME Grade A quality copper cathode at the mine site. Design copper production rate was 121 t/d cathode.
Tailings and water management
Tailings were not neutralised; the entire process circuit was designed to remain acidic. The tailings dam was specified with HDPE lining. In situ leaching of secondary copper oxides in the tailings dam was considered negligible. The mass balance was developed with a requirement to ensure no net gain or loss of water and acid.
Reagents
Reagents specified in the design included:
- Sulphuric acid for leaching
- Flocculant for thickener solids-liquid separation
- Lime slurry for emergency neutralisation only
- Diluent and extractant for solvent extraction (diluent make-up 0.14 g/t ore; extractant make-up 3.1 g/t Cu)
- Guar as smoothing agent for electrowinning and clarification
- Cobalt sulphate to prevent lead anode spalling in electrowinning
- Diesel for oil heater burners
Testwork limitations
The metallurgical testwork had significant limitations. The initial Ammtec program (2007) was described as a "sighter" program using samples from trenches and small-scale open cut workings at the northern end of the Kipoi Central orebody, which were potentially non-representative. The second phase (Amdel, 2008) used diamond drill core samples representing four main lithologies from oxide and transition zones. However, all tank leach testwork was conducted on relatively high-grade samples, and no testwork had been undertaken targeting cobalt content. The report noted that residue copper content in coarser grinds may be related to slow-leaching copper oxide minerals such as chrysocolla. The manganese levels in the ore were described as significant, requiring monitoring in leaching and potentially a wash stage in solvent extraction, though no wash step was included at the scoping study level.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant feed rate | 4.5 Mtpa | Design (mass balance) |
| ROM feed rate | 541 t/h dry solids | Design (mass balance) |
| Average ore feed grade | 1.13% Cu | Design assumption |
| Annual copper cathode production | 50,000 t | Design target |
| Copper cathode production rate | 121 t/d | Design (mass balance) |
| Overall copper recovery | 82.5% | Design calculation |
| Acid-soluble copper in plant feed | 93.2% of total Cu | Design basis |
| Tank leach extraction of acid-soluble Cu | 96.4% | Design basis |
| Heap leach extraction of total Cu | 80% | Design basis |
| Soluble copper losses | 0.50% | Design assumption |
| Tank leach acid consumption (testwork average) | 7.7 kg/t | Measured (testwork) |
| Tank leach total Cu extraction (testwork average) | 95.7% | Measured (testwork) |
| Tank leach acid-soluble Cu extraction (testwork average) | 96.5% | Measured (testwork) |
| Tank leach residue total Cu (testwork average) | 0.20% | Measured (testwork) |
| Acid-soluble copper content of ore (testwork average) | 95.7% of total Cu | Measured (testwork) |
| Loss in mass over leach | 7.1% | Design (mass balance) |
| CCD wash ratio | 2.0 m³/t | Design |
| Heap leach PLS flow rate | 770 m³/h | Design (mass balance) |
| Tank leach PLS flow rate | 450 m³/h | Design (mass balance) |
| Heap leach PLS copper concentration | 4.7 g/L | Design (mass balance) |
| Tank leach PLS copper concentration | 4.0 g/L | Design (mass balance) |
| Electrolyte flow rate | 401 m³/h | Design (mass balance) |
| Diluent make-up | 0.14 g/t ore | Design (mass balance) |
| Extractant make-up | 3.1 g/t Cu | Design (mass balance) |
| Miscellaneous acid losses | 2.3 kg/t ore | Design (mass balance) |
| SX/EW stage capacity | 25,000 tpa Cu each | Design concept |
| Stage 1 HMS concentrate grade | +25% Cu | Design specification |
Project website: https://miningdataonline.com/property/1612/Kipoi-Operation.aspx
Technical qualifications
This profile is a historical snapshot based solely on the November 2011 NI 43-101 technical report. The Stage 2 processing route described was a PEA-level design, not a feasibility study. All references to planned commissioning (mid-2014), staged construction, and production targets are proposed timelines and design assumptions from the report, not confirmed events. The heap leach testwork was limited to a single inconclusive column permeability test. Tank leach testwork was conducted on high-grade samples only, and no cobalt recovery testwork was performed. The Stage 1 HMS plant was reported as operational at the time of writing. No information on subsequent project status, current ownership, or resource/reserve updates is contained in or implied by this profile.
Source: "Independent Technical Report (NI 43-101) Kipoi Copper Project Stage 2 Preliminary Economic Assessment Democratic Republic of Congo," prepared for Tiger Resources Limited by Cube Consulting Pty Ltd, November 2011. Sections 13.0 (Mineral Processing and Metallurgical Testing) and 17.0 (Recovery Methods).
