Songwe Hill Rare Earth Recovery: Flotation & Hydrometallurgy

Source: Mkango Resources Ltd (2026)
Website: https://mkango.ca/projects/songwe/

Critical Data

Overview

Mkango Resources Limited operates the Songwe Hill Rare Earth Element (REE) Project located in the south-eastern region of Malawi. The project, detailed in the NI 43-101 Updated Technical Report dated 29 April 2026 (effective 30 June 2025), targets production of a high-grade, cerium-depleted mixed rare earth carbonate (MREC) product. The significance of Songwe Hill lies in its ability to process a 1.5% TREO head grade ore using a two-circuit plant: a concentrator (crushing, grinding, flotation) and a hydrometallurgical refinery. The concentrator produces a 15% TREO flotation concentrate at 74.1% recovery, which is then treated in the hydrometallurgical plant via gangue leach, caustic conversion, cerium oxidation, and rare earth leach to produce 10,826 t/a of MREC solids containing 5,954 t/a of TREO. The process design is based on extensive test work, emphasizing fine grinding to a P80 of 16.7 μm, high-intensity conditioning, elevated temperature, and a tailored reagent suite to effectively float rare earth oxides from carbonaceous gangue. This integrated approach positions Songwe Hill as a strategically important rare earth project, with continuous 24/7 operation and robust metallurgical accounting via on-stream analysers and sampling systems.

Key Process Stages

• Stage 1: Crushing and Ball Milling – Run-of-mine ore is crushed through a primary jaw crusher, secondary and tertiary cone crushers with screens, then fed to a ball mill operating in closed circuit with hydrocyclones. The mill reduces ore to a target P80 for fine grinding; steel media addition is controlled via mill power draw. The circuit provides 8 hours of surge capacity in the mill feed bin, allowing for the 65% crushing plant availability.
• Stage 2: Ultra-Fine Grinding – Ball mill cyclone overflow gravitates to regrind mills (stirred media mills using ceramic media) in closed circuit with another cyclone cluster. Four duty mills operate in parallel with one standby to achieve the flotation feed particle size of P80 16.7 μm. Cyclone overflow passes through a trash screen to remove wood chips before entering flotation.
• Stage 3: Multi-Stage Flotation – The flotation circuit includes sulphide pre-float rougher and cleaner cells (collector & frother) to remove sulphides, followed by TREO rougher (4 cells), scavenger (2 cells), cleaner (4 cells), and cleaner scavenger (3 cells) flotation. Key to REO flotation is elevated temperature achieved by steam sparging in conditioning tanks, together with reagents M4P, M7, caustic soda, collector, and frother. Blower air is supplied via a low-pressure air reticulation system. All streams are monitored by an on-line stream analyser for process control.
• Stage 4: Concentrate Dewatering and Filtration – Cleaner flotation concentrate is thickened in a concentrate thickener with flocculant addition, then filtered by two duty filter presses operating in parallel staggered cycles. Filter cake is discharged onto conveyors for transport to the hydrometallurgical plant or to an emergency stockpile. Filtrate is returned to the thickener; final concentrate mass pull is 7.4% of feed.
• Stage 5: Hydrometallurgical Processing – The flotation concentrate undergoes gangue leach with dilute acid to dissolve acid-consuming minerals, with liquor purified to regenerate HCl and produce gypsum for sale. Residue then undergoes caustic conversion (concentrated NaOH at high temperature) to convert insoluble REE minerals to soluble hydroxides, followed by cerium oxidation (air sparging) to render cerium insoluble. A severe rare earth leach with HCl extracts REEs, and after purification (heavy metals/radionuclides removal), the liquor is precipitated as a mixed rare earth carbonate product. Tailings are neutralised and sent to the TSF.

Additional Interesting Data and Summary

The Songwe Hill processing facility is designed for a ROM feed rate of 1,000,000 t/a with a head grade of 1.5% TREO, yielding a flotation concentrate at 15% TREO grade and 74.1% recovery. The concentrator operates at 92% availability (flotation and hydrometallurgical plants) while crushing has 65% availability. The hydrometallurgical plant receives 10.8 t/h of concentrate to produce 10,826 t/a of dry mixed rare earth carbonate solids containing 5,954 t/a of contained TREO. Environmentally, the project includes a tailings storage facility (TSF) for combined flotation and hydrometallurgical tails, with gypsum generated from the gangue leach filtered, dried, and sold to the cement and allied industries, reducing waste. The caustic conversion step includes evaporation and causticisation to regenerate sodium hydroxide for reuse, improving sustainability. Economic impact is significant as the project targets a high-value MREC product with cerium depletion, aligning with market demand for magnet and battery rare earth elements. The process design has been maintained from the earlier PFS, with updated CAPEX and OPEX to 2025 pricing, reflecting the project’s readiness for detailed feasibility. Future outlook includes potential optimisation of the flotation reagent suite and continued test work to enhance recovery and grade. This facility is a pivotal step for Malawi’s mining sector, providing a domestic rare earth supply chain with minimal environmental footprint through acid regeneration and gypsum valorisation. The use of on-line stream analysers and rigorous metallurgical accounting ensures consistent product quality and operational efficiency.

Key Processes: Flotation, Gravity Separation, Ball Mill, Crushing

Target Commodities: Zinc, Uranium