This report details the proposed processing methods for scheelite recovery at the Sangdong Project, based on Basic Engineering by Metso Outotec in February 2022 and supported by pilot plant testwork.
Report context
This technical report, dated February 2025, describes the recovery methods for the Sangdong Project. The current process flowsheet and plant design are based on comprehensive Basic Engineering conducted by Metso Outotec in February 2022. These designs show current production goals and operational efficiencies. Extensive testing, simulations, and industry best practices have informed these updated configurations.
Processing route
Process design
The optimised flowsheet for effectively recovering scheelite from Sangdong ore relies on structured flotation processes. The goal of this process is to produce a high-quality final concentrate containing approximately 65% WO₃. Pilot plant testing supports an overall average tungsten recovery rate of approximately 85%. The processing facility has been designed to operate at a nominal feed rate of 80 tph, with provisions allowing a design capacity extension up to 100 tph.
The processing plant was designed by Metso, along with AKTC technical personnel and external consultants. Process design criteria stemmed from Metso engineering data. The ‘One-Line’ parameters relate to the current mill construction and corresponding plant capacity of 1,920 tpd. The ‘Two-Line’ parameters relate to potential expansion in the future.
Overall process summary
The main process steps for treating the Sangdong ore are: primary, secondary and tertiary crushing and stockpiling; grinding; flotation divided into two sub-circuits (sulphide flotation and tungsten flotation); thickening; filtration and packaging section; a waste water treatment facility; and services section.
The processing sections include:
- Primary crushing and ore stockpiling, ensuring a steady feed to subsequent processes.
- Cone crushing for SAG oversize, for +25 mm material.
- Two-stage grinding utilising Semi-Autogenous (SAG) and Ball milling (SABC), ensuring precise particle size control.
- A comprehensive flotation section, divided into sulphide flotation for gangue mineral removal and scheelite flotation for tungsten recovery.
- Dedicated scheelite concentrate thickening and filtration facilities.
- Robust tailings thickening management.
- Advanced wastewater treatment facilities.
- Comprehensive reagent preparation, handling, and distribution systems.
- Fully integrated general plant services to support overall plant operations.
Crushing and stockpiling
Run-of-mine ore, initially delivered by 15 tonne trucks, will be either directly fed into the primary crushing system or placed onto a blending stockpile, aimed at a consistent feed quality. There is a second ROM stockpile area of 7,000 t capacity about 250 m north of the crushing area, as well as a reinforced stockpile area also having a capacity of 7,000 tonnes, which is next to the crusher feed and immediately next to the Monty B mine portal.
Ore from the mine will be dumped into a feed hopper. The ore will be extracted from the feed hopper by an apron feeder down to an inclined 600 mm square opening grizzly. A rock breaker will be used to bring the grizzly oversize down to 600 mm. The blended ore, nominally sized at -400 mm, will undergo primary crushing through a jaw crusher.
Scalping through precision vibrating screens will control the crushed size distribution. Crushed ore will be monitored and conveyed underneath magnets and metal detectors to remove metallic fragments. The crushing plant is designed to process ore at rates of up to 270 dmt/h, producing a product with a nominal p80 of 100 mm. Dust suppression and collection systems will be installed to minimise environmental impact and maintain occupational health standards. Ultimately, crushed ore will be transported via conveyor systems to a covered coarse ore stockpile with a capacity of 10,000 dmt, for sustained feed to downstream operations.
Grinding
Ore from the coarse stockpile will be reclaimed using variable-speed reclaim feeders and fed into the grinding circuit. There is a two-stage grinding configuration, consisting of Semi-Autogenous Grinding (SAG) mills and ball mills. SAG mill oversize material will be crushed in a cone (pebble) crusher and recirculated. Precision controls will include belt scales and automated water addition. The particle size target will be a P80 of 65 microns to meet the scheelite flotation criteria. Classification systems utilising cyclones and ultrafine screens are aimed at preventing overgrinding.
Flotation
Sulphide flotation circuit
The sulphide flotation circuit consists of a rougher flotation stage followed by two cleaner flotation stages, designed for removal of sulphide. Initially, ground pulp will be conditioned in a dedicated tank for about seven minutes, where Aero 3473 collector and MIBC frother will be introduced to enhance sulphide mineral attachment to bubbles. Subsequently, the pulp will be pumped to a bank of three 30 m³ flotation cells, configured sequentially to improve sulphide recovery. Rougher concentrate from these cells will then be pumped to the first cleaner flotation cells (four OK1.5 cells), where additional purification occurs. The concentrate from the first cleaner will then progress to the second cleaner flotation stage, utilising four smaller OK0.5 flotation cells. Cleaner concentrate, after this two-stage cleaning process, will be directed to the final tailings pump box. Inline samplers will allow continuous sampling for analytical quality control.
Scheelite rougher circuit
The scheelite rougher flotation circuit will receive conditioned pulp following the sulphide flotation stage. The circuit consists of two sequential conditioning tanks, each designed to provide mixing and contact time of approximately 11 minutes. The first conditioning tank adjusts pulp pH and introduces critical flotation reagents such as sodium carbonate and sodium silicate, while the second tank dilutes pulp density to around 35% solids. Following conditioning, pulp will be transferred to a scheelite rougher flotation bank consisting of four 30 m³ flotation cells. Reagents, specifically TOFA as a primary collector, will be added to promote efficient scheelite mineral attachment. Rougher concentrate will proceed to the cleaner flotation circuit, while rougher tailings will be directed to scavenger flotation cells for further recovery.
Scheelite scavenger circuit
Tailings from the scheelite rougher flotation circuit will be pumped to the scavenger circuit, consisting of two separate banks of four 30 m³ flotation cells each. Before entering the scavenger flotation cells, the pulp will undergo additional conditioning where reagents, primarily TOFA, will be reintroduced to improve flotation effectiveness. The scavenger flotation stage is designed to capture scheelite particles that were not recovered in the initial rougher stage, to enhance overall tungsten recovery. Scavenger tailings, after passing through an inline sampler for continuous monitoring, will be considered final tailings and pumped to the tailings thickener for dewatering and disposal. The scavenger circuit is very important in minimising tungsten losses.
Scheelite cleaning circuit
The scheelite cleaning circuit provides a multi-stage flotation process for the final upgrading of scheelite concentrates derived from rougher and scavenger flotation stages. This circuit comprises four sequential cleaning stages. Cleaner stage 1 consists of three 5 m³ flotation cells, while cleaner stage 2 utilises two OK1.5 flotation cells. The final two cleaning stages (cleaner stages 3 and 4) will each utilise two OK0.5 flotation cells arranged sequentially. Throughout the cleaner stages, sodium silicate will be continually dosed as a depressant to prevent unwanted mineral flotation, to produce high purity scheelite concentrate. Temperature-controlled conditions (approximately 30–32.5 °C) will be maintained using a heated water system to assist flotation performance. Concentrate from the final cleaner stage, after upgrading, is directed towards concentrate thickening and filtration processes, in order to achieve the required market specifications of approximately 65% WO₃.
Final tails management
The final tailings from the concentrator plant, along with effluent from the paste plant, will be collected into a feedbox for a 20 m diameter High-Rate Thickener (HRT). The thickener feedwell will be equipped with auto-dilution capabilities to adjust feed slurry density from around 20% solids to an optimum 12%. Overflow from the thickener will be directed to an overflow tank and subsequently pumped to the water treatment plant. The thickener underflow, with approximately 50% solids, will be transferred to a buffer tank. A diaphragm pumping system, with an additional standby set, will move tailings to the paste plant. Coagulants and flocculants will be added into the thickener to enhance settling and clarity of the overflow. Spillage around the thickener area will be collected and pumped back to the thickener feedbox.
Fresh water quality
Fresh water will be provided to critical points within the flotation and reagent preparation areas of the plant. Heated fresh water from the water heating system will be provided for reagent mixing, related to flotation and thickener reagents. Unheated fresh water will be provided to the flotation section for analyser and multiplexer operation, for process monitoring. Service water will also be provided for hose-down and cleaning purposes within the flotation and dewatering sections. All water inputs, including fresh water, heated fresh water, and service water, will be centrally controlled and monitored via the plant Distributed Control System (DCS). The heated fresh water supply will support critical processes, maintaining optimal temperatures for flotation and reagent effectiveness.
Waste water treatment
Waste water from the plant will primarily consist of flotation chemical residues and tailings thickener overflow. This water will be directed to dedicated water treatment facilities designed within Almonty’s operational scope. Mechanical aeration processes in constructed lagoons will provide aeration to effectively reduce organic contaminants. The thickener overflow, containing residual reagents and suspended solids, will gravitate to an overflow tank and be subsequently pumped for further treatment.
Water quality will be managed to comply with environmental discharge standards. Although mechanical aeration will significantly reduce organic compounds, sodium ions introduced by flotation chemicals will remain relatively unchanged. Regular monitoring will be used to ensure the treated water quality meets environmental regulatory requirements before discharge.
Equipment and energy consumption
Major plant equipment includes primary crushers, grinding mills (SAG and Ball Mills), flotation cells (TankCells and OK cells), thickeners, filters, and comprehensive water and slurry handling systems. Total installed power within the plant is calculated as being approximately 4006 kW, showing enhancements in flotation cell sizing and energy-efficient equipment integration. Energy management strategies incorporate variable speed drives and high-efficiency motors, significantly improving the plant’s overall energy efficiency. Advanced automation and control systems will further support energy utilisation throughout plant operations.
A summary of all the major processing plant equipment, mostly sourced from Metso Outotec, is shown in Table 17-2 of the report.
Other services
Ancillary services will support continuous plant operation, including two large fresh water storage tanks (each 15 metres in diameter and 10 metres high), to provide reliable water supply. Dedicated compressor units supply air for plant operations, with a 150 HP unit designated for general use and a 50 HP compressor specifically for instrumentation air. A blower system rated at 210 HP will supply air to flotation cells. Additionally, the plant will include reagent and flocculant preparation facilities for precise reagent dosing. A dedicated steam boiler system equipped with a water treatment setup provides the heated water necessary for flotation conditioning and concentrate drying operation.
Manpower
The concentrator plant’s staffing strategy will involve approximately 36 personnel in total. Of these, 28 will be hourly operational employees responsible for routine plant operation, equipment monitoring, and basic maintenance duties. Additionally, the plant will employ eight salaried staff members, including supervisors, process engineers, and maintenance managers. The operational workforce will be supported by a structured training program aimed at maintaining safety, operational proficiency, and productivity.
Pilot plant
A pilot plant has been constructed on site, with a maximum processing capacity of 3 tonnes/hour. This has a jaw crusher, reducing rock size to below 100 mm, followed by a secondary crusher, a roll crusher, further reducing particle size to below 5 mm. A ball mill then grinds the material down to -200 mesh. As with the processing plant, there follows separate flotation equipment for removal of sulphide minerals and concentration of scheelite. This plant has already been used for metallurgical test work and will be available in the future for mill test work as required.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Nominal feed rate | tph | 80 | Design |
| Design capacity extension | tph | 100 | Design provision |
| One-Line plant capacity | tpd | 1,920 | Design (current mill construction) |
| Overall average tungsten recovery | % | 85 | Pilot plant testing |
| Final concentrate grade target | % WO₃ | 65 | Design target |
| Crushing plant throughput | dmt/h | 270 | Design |
| Crushing product size (p80) | mm | 100 | Design |
| Coarse ore stockpile capacity | dmt | 10,000 | Design |
| Grind size target (P80) | microns | 65 | Design |
| Sulphide rougher conditioning time | minutes | 7 | Design |
| Scheelite rougher conditioning time | minutes | 11 (each of 2 tanks) | Design |
| Scheelite rougher pulp density | % solids | 35 | Design |
| Cleaner flotation temperature | °C | 30–32.5 | Design |
| High-Rate Thickener diameter | m | 20 | Design |
| Thickener feed solids | % | 20 | Design |
| Thickener underflow solids | % | 50 | Design |
| Total installed power | kW | 4006 | Design calculation |
| Pilot plant capacity | t/h | 3 | Testwork |
| Total plant manpower | personnel | 36 | Design |
Project website: https://almonty.com/reopening-sangdong-how-a-korean-tungsten-mine-became-a-strategic-asset/
Project website: https://almonty.com/project/almonty-korea-tungsten/
Technical qualifications
The process flowsheet and plant design described in this report are based on comprehensive Basic Engineering conducted by Metso Outotec in February 2022, showing current production goals and operational efficiencies. The design criteria parameters are summarised in Table 17-1 of the report. The ‘One-Line’ parameters relate to the current mill construction and corresponding plant capacity of 1,920 tpd, while the ‘Two-Line’ parameters relate to potential future expansion.
The overall average tungsten recovery rate of approximately 85% is supported by pilot plant testing. The pilot plant, with a maximum processing capacity of 3 tonnes/hour, has been used for metallurgical test work and will be available for future mill test work.
No historical full-scale operating data from the Sangdong project were included in the supplied report sections. The supplied report sections do not contain economic parameters, feasibility classifications, mineral resource or reserve estimates, or current project status information beyond the February 2025 report date and the described plant construction photographs (Figure 17-3).
Source: *Technical Report on The Sangdong Project*, Almonty Industries Inc., February 2025, Sections 17.1–17.12.
