K.Hill Manganese Project: A Detailed Look at the Recovery Methods Behind the HPMSM and HPMO Process

The K.Hill Manganese Project in Botswana, owned by Giyani Metals Corp., is designed to process 220 kt/a of run-of-mine ore through a flowsheet that combines crushing, grinding, reductive acid leaching, and purification steps to produce High Purity Manganese Sulphate Monohydrate and High Purity Manganese Oxide, along with a saleable ammonium sulphate by-product.

Critical Data

Overview

The K.Hill Manganese Project, located in Botswana and owned by Giyani Metals Corp., is planned as an open pit operation feeding a processing plant designed for 220 kt/a of dry run-of-mine ore. The plant targets two main products: High Purity Manganese Sulphate Monohydrate, commonly abbreviated as HPMSM, and High Purity Manganese Oxide, or HPMO. The process also generates ammonium sulphate as a saleable by-product. The mineralised resource consists of manganese and iron shales classified as soft ore, and it responds well to reductive acid leaching.

The flowsheet starts with crushing and milling to reach a target particle size. The milled ore then moves into an acid reductive leach at elevated temperature. The leach circuit discharges a solution containing manganese sulphate with impurities such as iron, aluminium, and base metals. A Fe/Al precipitation circuit removes iron and aluminium, followed by ion exchange to strip base metal impurities. The purified solution goes through a precipitation stage, and the filtered precipitate undergoes redissolution with acid. That manganese sulphate solution feeds the HPMSM crystallizer to produce the primary final product. An impurity purge stream from the crystallizer still carries a high manganese loading, so this manganese gets precipitated and converted to HPMO. The HPMO is filtered, dried, and bagged as a secondary product. The filtrate from the HPMO conversion step is mostly ammonium sulphate, which advances to water recovery for calcium removal, then concentrates by reverse osmosis. Crystallisation of that concentrated solution yields the saleable ammonium sulphate by-product.

One note from the feasibility study deserves attention. The neutralising reagent has not been finalised. The DFS process design, reagent operating cost, and the sulphate by-product revenue all assume ammonium hydroxide, the reagent tested during development. Sodium hydroxide remains under evaluation. The final selection could shift based on reagent operating cost and the type and value of the by-product.

Key Process Stages

The plant is organised into distinct areas, each handling a specific part of the flowsheet. Area 2100 covers primary and secondary crushing. A dump truck tips ROM ore into a stockpile, and a front-end loader transfers material to the ROM bin through a static grizzly screen. A hydraulic rock breaker handles oversized material on the grizzly. A vibrating grizzly feeder extracts material from the ROM bin and feeds the primary jaw crusher. Primary crusher discharge and grizzly undersize travel by conveyor to the secondary vibrating screen. That conveyor carries a weightometer for tonnage control, an XRF online analyser for manganese grade indication, and a belt magnet for tramp iron removal. Oversize from the secondary screen goes to the secondary crusher bin, with a tramp metal belt magnet protecting the secondary cone crusher. A belt feeder delivers crushed ore to the cone crusher, and the circuit runs in closed loop back to the screen. Screen undersize reaches a transfer tower where it either diverts to an emergency surface stockpile or moves to the ball mill feed bin. Mobile equipment reclaims ore from the emergency stockpile when needed. Dust suppression water is applied at both crushers and all transfer points.

Area 2200 is the grinding circuit. Its purpose is to reduce material to a size suitable for leaching and to get the slurry to the required density for extraction. A wet scrubber and a ball mill operate in closed circuit with a cyclone cluster. The ore first goes through the scrubber to remove fines and prevent overgrinding. Scrubber fines are pumped to the mill discharge sump, and oversize moves by conveyor to the ball mill. The scrubber can be bypassed by switching the direction of the reversible ball mill belt feeder. Mill discharge gets pumped to the cyclone cluster, where overflow feeds the mill thickener and underflow returns to the mill inlet. The cyclone underflow recycles to the ball mill for regrinding. Flocculant is added to the thickener feed tank. Thickener overflow feeds the process water tank in the milling area. Return water from the tailings dam solution pond also reports to this tank, with raw water available for top-up if needed. Lime can be added for pH control. Thickener underflow pumps to the reductive acid leaching section.

Area 2300 is the extraction circuit. Manganese in higher oxides such as cryptomelane, hollandite, and bixbyite occurs as Mn(III) or Mn(IV), and these forms must be reduced to Mn²⁺ to become soluble sulphate. The reduction happens in a sulphuric acid medium. Mill thickener underflow goes to the agitated leach feed tank, where process condensate dilutes the feed to correct density. A de-sanding pump serves the feed tank. Slurry advances through four agitated leach tanks in series, with acid added to each tank to dissolve the manganese minerals. Overflow between tanks moves the slurry down the train, and a de-sanding pump on each tank continuously pushes settling solids to the next tank. Each tank can be bypassed so the circuit keeps running if one tank goes offline. The last leach tank discharges into a sump, and pumps send the slurry to iron and aluminium precipitation.

Area 2350 removes iron and aluminium. A recirculating slurry stream of Fe/Al precipitate is recovered from the thickener underflow into a conditioning tank, then pumped to the leached slurry neutralisation tank for pH adjustment and precipitate seeding. This high-density sludge process creates larger particles that filter more easily. The neutralisation tank overflows to four precipitation tanks in series. Limestone and hydrated lime are added to the precipitate tanks. Slurry from the final precipitation tank goes to the Fe/Al thickener feed tank, which also receives coagulant, flocculant, Fe/Al filtrate, and polishing filter backwash from the ion exchange circuit. The thickener underflow pumps to the Fe/Al filter press feed tank. A constant bleed stream of underflow feeds the HDS process. Thickener overflow reports to the overflow tank. Filter presses arranged in parallel handle the slurry, and each press discharges onto its own cake belt feeder. A common transfer conveyor feeds the Fe/Al repulp tank. The filter cake gets repulped with process condensate and pumped to tailings handling. Filtrate collects in the filtrate sump and returns to the thickener overflow tank. Solution from that tank passes through polishing filters to reach very low total suspended solids, then discharges into the filtrate tank before pumping to the PLS storage tank, which provides surge capacity for the ion exchange circuit.

Area 2360 is the base metal ion exchange section. The feed is filtrate from the Fe/Al polishing filters. The system uses a microporous, weak basic resin to adsorb base metal ions from the aqueous phase. The tank farm holds five tanks: resin holding, wash water, eluant, eluate, and conditioning. Fresh resin prepares in the holding tank for transfer to any of the three IX columns. Wash water is prepared with reverse osmosis water as make-up, and it serves as pre-elution wash, post-elution wash, and backwash. Concentrated sulphuric acid mixes with post-elution wash water in the eluant tank to reach the required strength. Adsorbed base metal ions strip from the resin by the eluant, and that solution goes to the eluate tank for elimination from the process via the by-product. In the conditioning tank, neutralising reagent dilutes with RO water and circulates through the eluted column to activate the resin for reuse. Off-gas from the conditioning tank goes to a scrubber. Each of the three columns operates with stay-in-place resin in a lead-lag-elution sequence. The lead column captures the bulk of target metals, the lag column polishes to maximise removal of base metals and iron, and the third column sits offline or in elution or conditioning. Resin arrives in bulk bags and transfers by hoist to the holding tank, with RO water easing the transfer and limiting breakage. When filling an empty column, the column first fills to 30 percent with water to protect the resin.

Area 2400 covers manganese precipitation and HPMO conversion. The purified PLS from the IX circuit gets neutralised to raise pH and precipitate manganese while impurities stay in solution. The filtered cake redissolves, and the manganese sulphate solution crystallises as HPMSM crystals. An unfiltered solution from the HPMSM crystallizer purges, and a second phase of manganese precipitation recovers that manganese, converting it to HPMO precipitate.

Area 2450 is the HPMSM crystallisation plant. It consists of a pre-concentrator stage and two-stage crystallisation. The MnSO₄ solution feeds the pre-concentrator, where boiling brings the solution near its saturation point without precipitating manganese sulphate. A trash filter removes solids or dirt from the discharge stream before crystallisation. The clean saturated solution feeds the crystallisation stage, where water boils off to form manganese sulphate monohydrate crystals. Vapour from the crystallizer compresses into super-heated liquid used to heat other processes. The crystallizer includes a fines destruction step to build larger particle size and minimise fine crystals in the product. Part of the mother liquor purges to a manganese recovery step to prevent impurity build-up. Centrifuges separate the crystals, and washing with RO water or clean saturated liquor removes trapped impurities. The washed crystals advance to drying.

Area 2480 is by-product crystallisation. Brine from manganese recovery pumps to the by-product brine tank, which provides surge capacity. Two parallel falling film evaporators using mechanical vapour recompression pre-concentrate the dilute feed liquor. Multi-stage designs handle the high boiling point elevation, optimising surface area and allowing a single stage of MVR compression. Feed liquor preheats in counter-current exchange with hot process condensate to maximise energy recovery. A small make-up steam flow balances the energy equation. The crystallizer is a draft tube baffle type designed to grow large crystals, with a fines destruction heater. A bottom entry agitator provides high recirculation rates through the draft tube to manage supersaturation and ensure good mixing and boiling patterns. An annular baffle extracts fine crystals, which get destroyed in the fines-destruction heater. Two-stage MVR fans compress vapours to the heater shell for energy input. Process vapour condenses and discharges to the condensate tank, and non-condensable gases vent. Wet by-product crystals move to product handling for drying and bagging.

Area 2500 handles products. Three drying and packaging units serve HPMSM, HPMO, and the by-product. For HPMSM, wet crystals feed from a belt feeder to the wet crystals bin, then a vane feeder moves them to the rotary dryer. Medium-pressure steam and hot air from the air pre-heater evaporate entrained water. Dry product discharges onto a conveyor. Dryer vent flows to a cyclone to recover entrained particles, and cyclone overflow goes to a baghouse for fine particle recovery. Cyclone underflow joins the dry product on the discharge conveyor. Everything transfers to the HPMSM product silo, which provides buffer capacity. The dried crystals bag in 1-tonne bulk bags through a filling plant that includes filling, weighing, sampling, bag sealing, tagging, and palletising. Forklifts collect palletised bags and transfer them to the HPMSM product store for shipping. The HPMO handling plant mirrors the HPMSM plant, with the filter cake fed to a wet precipitate bin, dried in a rotary dryer, and bagged in 1-tonne bulk bags stored separately in the HPMO product store. The by-product plant also follows the same pattern, with wet crystals fed to a bin, dried, and bagged in 1-tonne bulk bags stored in the by-product store.

Area 2800 covers reagents. Bulk bags deliver reagents to site, where hoists lift them and bins store the contents. Dust collectors above the bins handle dust from emptying. Screw feeders deliver reagent to the mixing tank, which receives process condensate for dilution, and the solutions transfer to dosing tanks. Flocculant arrives in bulk bags or 25 kg bags and feeds through a hopper to a hydration tank. Hydrated flocculant transfers to a mixing and dosing tank, with process condensate making up a dilute solution. Flocculant doses to the thickener feed tanks and dilutes tenfold through in-line mixers at point of use. Spillage pumps to tailings handling. Coagulant arrives as a liquid, mixes with process condensate, and doses to the Fe/Al precipitate thickener feed tank with the same tenfold dilution. Bulk sulphur arrives by road and transfers to a stockpile. A front-end loader moves sulphur to a feed conveyor, and hydrated lime blends in before the sulphur melter. The sulphuric acid plant produces strong acid and liquid SO₂ from molten sulphur. The plant recovers energy as high-pressure superheated steam for power generation. A VPSA oxygen plant supplies high purity oxygen for the acid plant. H₂SO₄ from the plant or bulk tanker stores in the acid storage tank and pumps out for distribution.

Area 2700 covers water services. Raw water comes from the Water Utilities Company through an expanded network of wells at the Dilokwane well field, pipelines, and a new dedicated reservoir. Untreated raw water feeds the fire water tank, which overflows to the raw water tank that also receives process condensate. Raw water pumps to dust suppression and to RO Plant 2. That treatment plant has three stages: ultrafiltration, reverse osmosis, and ion exchange. RO permeate stores in the RO water storage tank, which also receives water from the manganese water recovery unit, RO Plant 1. RO water serves as reagent make-up, dust suppression feed in the comminution circuit, gland seal water, and flushing and hosing water. Brine flows to a storage tank and pumps to the evaporation pond or the brine tank feeding the by-product crystallizer and ammonia off-gas scrubber. Potable water comes from the ultrafiltration stage into a storage tank, then pumps into the safety shower ring main and take-off points for drinking water and ablution. The process water tank near the milling circuit receives mill thickener overflow, tailings return dam solution, and storm water pond water. Process condensate supplements during start-up. Hot condensate from crystallizer circuits and excess steam condensate from the boiler system collects in a hot process condensate tank, then pumps through a heat exchanger heating the acid leach feed to recover excess heat. Acidified process water prevents manganese precipitation in the Fe/Al filter wash stages. Dust suppression water uses grey water from ablution facilities, raw water, and storm water, stored in a haul road dust suppression tank and pumped to an elevated bowser fill tank. Tailings from various plant sources feed the tailings repulping tank, with process condensate for make-up and dilution, then pump to the tailings storage facility. Gland seal water fills from process condensate and pumps to all users.

Area 2900 covers utilities. A steam boiler produces medium-pressure steam for acid plant start-up. The acid plant's waste heat boiler generates high-pressure superheated steam in excess of plant heating needs, so it directs to a steam turbine for electricity generation. Medium-pressure steam extracts from a turbine port, passes through a desuperheater, and supplies plant heating requirements. The turbine exhaust condenses in an air-cooled condenser, and condensate returns to the steam condensate tank. Steam condensate from users returns to the same tank, pumps to the acid plant deaerator, and serves as boiler feed water. RO water tops up steam condensate as needed. Cooling water comes from forced ventilation, closed circuit cooling towers, pumped from the return sump to users including HPMSM crystallisation, by-product crystallisation, the sulphuric acid plant, redissolution tanks, and process condensate heat exchangers. RO water makes up evaporation and blowdown losses. Plant and instrument air produces as dry instrument air through dryers and filters, distributed through receivers and utility stations.

Area 4000 is the tailings storage facility. Tailings slurry flows to the TSF, and tailings solution pumps or siphons from the dam to the return dam solution settlement pond. From there it pumps to the process water tank at the comminution circuit.

Additional Interesting Data and Summary

The design accommodates feed grade variability. The plant capacity sits at 220 kt/a, but the feed rate can vary by plus or minus 10 percent of design, providing operating flexibility when feed grade changes. The crushing circuit is scheduled for 365 operational days per year, with availability and utilisation both at 80 percent. The milling and hydromet circuit also runs 365 days, with availability at 94.25 percent and utilisation at 93.9 percent.

Product output depends heavily on feed grade. At the design basis of 16.08 percent Mn, HPMSM production is 82,922 t/a. At 16.84 percent Mn in years one through six, that number rises to 87,600 t/a. At 11.88 percent Mn in years six through eight, production drops to 61,908 t/a. At 9.90 percent Mn in years eight through twenty-five, HPMSM output is 51,588 t/a. HPMO follows a similar pattern: 5,433 t/a at design grade, 5,736 t/a at the highest grade, 4,056 t/a in the middle period, and 3,384 t/a in the later years. The by-product ranges more widely, from 56,640 t/a at design grade up to 100,332 t/a at the highest feed grade, then 70,908 t/a and 59,076 t/a as grade declines.

Reagent selection remains an open item. The DFS uses ammonium hydroxide for the neutralising reagent, and the by-product revenue assumes that reagent. Sodium hydroxide is still under evaluation, and the final choice may change based on operating cost and by-product value.

Major equipment shows a standard hydrometallurgical train. A Metso Nordberg C80 jaw crusher handles primary crushing, and a Metso HP100 cone crusher does secondary duty. The ball mill includes all ancillaries, and a thickener serves the milling circuit. Leach tanks are cylindrical flat bottom agitated vessels. Filter presses are plate and frame type with power packs. Ion exchange columns are SS316L with SS316L header laterals distributors. Redissolution filters are Scheibler type.

The demonstration plant work informed the flowsheet development, covering mineralogy, comminution, solid-liquid separation, leach development, solution purification, HPMO development, crystallisation, and manganese hydroxide process development. The reference process flow diagrams cover every area from primary crushing through tailings storage.

Key Processes

• Primary jaw crushing followed by secondary cone crushing with interstage screening, including an emergency surface stockpile for feed flexibility
• Wet scrubbing and ball mill grinding in closed circuit with a cyclone cluster, with thickener producing feed slurry for leaching
• Reductive acid leaching in four agitated tanks in series using sulphuric acid to dissolve manganese minerals
• Iron and aluminium removal through high-density sludge precipitation with limestone and hydrated lime, followed by thickening and filter pressing
• Base metal removal by ion exchange using a microporous weak basic resin in a three-column lead-lag-elution configuration
• Manganese precipitation, filtration, and redissolution to produce a purified manganese sulphate solution
• HPMSM crystallisation with pre-concentration, fines destruction, and centrifuge separation
• HPMO conversion from the crystallizer purge stream
• By-product ammonium sulphate crystallisation using falling film evaporators with mechanical vapour recompression
• Rotary drying and 1-tonne bulk bag packaging for HPMSM, HPMO, and by-product
• On-site sulphuric acid production from molten sulphur with energy recovery through a steam turbine
• Water treatment including ultrafiltration, reverse osmosis, and ion exchange, with potable water, process water, and dust suppression systems

Source: K.Hill Manganese Project NI 43-101 Technical Report Feasibility Study, July 10, 2026. Project website: K.Hill Manganese Project