BKM Copper Project — 2023 Technical Report

This technical report summarizes the proposed copper recovery process for the BKM Copper Project, based on a 2023 preliminary economic assessment.

Report context

This report, dated 2023, describes the proposed processing approach for the BKM Copper Project, a preliminary economic assessment. The report is independent and technical in nature. The processing route described is a conventional heap leach, solvent extraction, and electrowinning (SX-EW) flowsheet.

Processing route

The proposed process is described in the report. The major steps are:

Crushing

Ore will be hauled from the pit to a dump hopper. There is little allowance for blending on the run-of-mine (ROM) stockpile due to limited space. The crushing plant will operate 24 hours per day.

• Primary crushing: The ROM ore will be reduced.
• Screening: The primary crushed ore is conveyed to double deck screens. Material smaller than the required product size is removed.
• Secondary and tertiary crushing: Oversize from the top deck is sent to the secondary crusher, and oversize from the bottom deck to the tertiary crushers. The crushed material is recycled to the screen feed.
• Product size: The target product size is a P80 of between 19 mm and 8 mm.

Agglomeration and Stacking

• Agglomeration: Crushed ore is fed to an agglomerator. Sulphuric acid and raffinate are added under ratio control to bind fines to coarser particles and provide an intimate mix of acid and ore.
• Stacking: The agglomerated ore is stacked on the leach pad using a mobile stacker fed by trucks. The design stacking height is a nominal 6 meters, with a range of 2 to 8 meters.

Heap Leaching

The process is designed as a single-stage leach in a “valley fill” style, dictated by the steep topography.

• Irrigation: Leach solution is applied with dripper irrigation systems during the wet season and wobbler (sprinkler) systems in the dry season. Drippers can be covered with an HDPE “raincoat” to divert rainwater.
• Collection: Pregnant leach solution (PLS) drains to a collection pond and is pumped to the Solvent Extraction (SX) plant.
• Raffinate: Copper-depleted raffinate is recycled to the heap for irrigation.
• Water Management: The water balance is a key issue. The report notes a lack of data on rainfall design events, evaporation rates, and catchment yields, which will be addressed in the next phase of study. Excess water will be managed through neutralization, evaporation with water cannons, and storm water ponds.

Solvent Extraction

The SX plant is designed to selectively transfer copper from the PLS to an electrolyte.

• Process configuration: The plant consists of a single train of extraction and stripping mixer-settlers. The design allows for up to 92% copper removal.
• Extraction: The process uses two series extraction stages (E1 & E2) and one parallel extraction stage (E3p).
• Stripping: Loaded organic is contacted with lean electrolyte to produce a rich advance electrolyte (AE) containing 50 g/L Cu.
• Entrainment control: A multimedia filter is used to remove entrained organic and contaminants from the AE before it goes to electrowinning.
• Crud management: The report anticipates crud formation due to silica in the PLS. Measures to manage crud include an integrated removal system, safe access to settlers, a tri-canter centrifuge, and regular clay treatment.

Electrowinning

• Electrolyte Heating: The advance electrolyte is heated from the SX operating temperature (about 30°C) to the EW temperature (about 45°C) using heat recovery from the spent electrolyte.
• Electrolyte Control: Cobalt sulphate is added to the electrolyte to protect the anodes. Polyacrylamide is added as a growth modifier to improve cathode quality.
• Deposition: The EW cells contain 48 stainless steel cathodes and 49 lead anodes. Copper is deposited on the cathodes. The typical growth cycle is 6 to 8 days.
• Stripping: Cathodes are washed and stripped in a semi-automatic machine, and the final copper product is bundled, weighed, marked, and strapped for shipment.
• Iron Bleed: A small stream is bled from the circuit to control iron and other impurity build-up.

Neutralization

This plant is used to reduce the acid concentration and precipitate metals from water before discharge.

• Process: Limestone is crushed, ground to a slurry, and mixed with sediment in a sludge reactor. The conditioned sludge is added to the neutralization reactor.
• Sludge Recycle: The sludge recycle helps minimize reagent consumption and scale. The process yields a sludge with a lower neutralizing capacity than a conventional process.
• Dewatering: The sludge is filtered; the excess solution is returned to the process, and the filter cake is used as fill or disposed of with mine waste.

Key reported parameters

Technical qualifications

The report includes several statements that limit the technical confidence and define the level of study:

• The report is a Preliminary Economic Assessment (PEA).
• The site water balance has not been developed due to a lack of data on rainfall design events and return intervals, evaporation rates, and catchment yields. These will be addressed in the next phase of the study.
• A more detailed control philosophy will be included in a subsequent feasibility level study.
• The report notes that predicting the quantities of crud likely to be generated in a new SX circuit is difficult.
• The process site was selected based on specific criteria, including haul distance, topography, and water management. Two alternative sites to the east of the proposed pits were considered but rejected due to longer hauls, the need for a bridge over a significant stream, catchment issues, and space constraints.

Source: PT Kalimantan Surya Kencana – BKM Copper Project, 43-101 Independent Technical Report Preliminary Economic Assessment – V6-1, 2023.