This report presents a preliminary economic assessment for the proposed hydrometallurgical processing of manganese carbonate material from the Plymouth deposit to produce electrolytic manganese metal.
Report context
The Preliminary Economic Assessment (PEA) on the Woodstock Manganese Property, New Brunswick, Canada, was prepared for Canadian Manganese Company Inc. The report is dated and contains the project identifier 1494720100-REP-R0001-04. The assessment evaluates a proposed processing route for the Plymouth deposit, which is a fine-grained manganese carbonate deposit. The processing methods and design criteria described are based on bench scale testwork completed to date, technical literature, and review of similar commercial operations.
Processing route
Process selection rationale
An initial review of processing options indicated that hydrometallurgical processing technologies are more amenable to fine-grained manganese carbonate deposits compared to high-temperature pyrometallurgical methods. The production of highly purified manganese sulphate solution using hydrometallurgical processing provides alternative production options for primary production of electrolytic manganese metal (EMM) with opportunities for co-production of alternative manganese products. By manganese industry standards, hydrometallurgical processing methods are recognized as commercially viable for low-grade manganese carbonate material (less than 25% manganese) with reduced environmental impact relative to pyrometallurgical methods.
The presence of manganese predominately as manganese (II) in rhodochrosite precludes the requirement for a reduction step to convert manganese (IV) to manganese (II) sulphate in solution. The hydrometallurgical process proposed for production of EMM from the Plymouth deposit is similar to that used by commercial plants in China for hydrometallurgical processing of manganese carbonate feedstocks. However, the proposed process incorporates improved measures for environmental sustainability and a novel arrangement of unit operations for iron precipitation to accommodate the high iron content of the Plymouth deposit.
Pre-concentration circuit
Pre-concentration of the Plymouth deposit using magnetic separation technology to upgrade the manganese content and selectively reject acid-consuming gangue minerals has been included as an integral part of the preliminary process block diagram. Grade and recovery assumptions used in process modelling and economic analysis for the magnetic separation pre-concentration circuit have been based upon the preliminary bench scale testing completed by Metso.
A conventional two-stage crushing plant is used to reduce the size of the run-of-mine mill feed to the required size for grinding. The primary jaw crusher will have a grizzly feeder to remove oversize material. After primary size reduction by the jaw crusher, the crushed material is conveyed to a screen where oversize material is fed to a secondary cone crusher for final crushing. Final crushed material is stored in a fine ore storage silo.
The grinding circuit utilizes a conventional two-stage, rod mill-ball mill configuration with the rod mill operating in open circuit and the ball mill operating in closed circuit. Size classification is by hydrocyclones. The target grind size of 80% passing 20 µm is based on achieving a similar particle size distribution in the feed to the pre-concentration circuit to that used in the preliminary magnetic separation testwork.
The ground material is fed as slurry through a dual-stage wet drum low-intensity magnetic separator (LIMS) to remove ferromagnetic iron prior to entering the high-gradient magnetic separation (HGMS) circuit. Based upon preliminary bench scale test results, a cleaning stage has been added to the conceptual design of the LIMS circuit to produce a saleable 62% iron, iron ore fines product. The LIMS tails feed the high gradient portion of the magnetic separation circuit, which consists of rougher and cleaner stages with the final concentrate subsequently being thickened and dewatered to 10% moisture for hydrometallurgical processing.
Hydrometallurgical processing
Dewatered HGMS cleaner concentrate is conveyed to the leach feed holding tank where it is mixed with acidic spent electrolyte solution from the electrowinning circuit. From the leach feed tank, the slurry overflows into cascading continuously stirred tank reactors (CSTRs) where sufficient quantities of makeup sulphuric acid are added to maintain the target leach pH set-point. Given the large quantity of sulphuric acid required, a sulphuric acid plant has been included for on-site acid production as an option to direct purchase.
The pregnant leach solution and leach residue overflow into a series of cascading CSTRs in which the primary iron precipitation reaction takes place. Pulverized limestone is added to partially neutralize the slurry and air is injected to facilitate conversion of ferrous iron to ferric. The leach-primary iron precipitation residue is filtered and washed by counter-current displacement washing. The filtrate is pumped to the secondary iron precipitation stage, where calcined lime is used to further neutralize the pregnant leach solution.
Following two-stage iron precipitation, the advance electrolyte is further purified by sulphide precipitation using ammonium sulphide to remove residual heavy metals. The effluent is pumped through a pre-coated plate-and-frame filter to capture fine precipitate. The advance electrolyte is aged and re-filtered, then pumped through primary and polishing activated carbon columns to adsorb organics and residual reactive sulphide species.
Purified manganese sulphate advance electrolyte is fed to electrowinning cells for recovery of manganese as EMM. EMM sheets are harvested, washed, dried and crushed to produce a minimum 99.7% pure EMM flake product packaged in 1-t bulk bags.
Auxiliary systems
Auxiliary systems included in the conceptual process design comprise dust collection systems, reagent make-up systems, process area sumps, a CNG-fired boiler, an integrated limestone calcination and pulverizing facility, overhead cranes, wastewater treatment with tertiary ammonia removal, tailings treatment and pumping systems, compressed air systems, process water treatment, boiler feedwater treatment, cooling water systems, ammonia regeneration systems, and a sulphuric acid plant with auxiliary systems for sulphur handling and power generation.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| ROM Mill Feed Processing Rate | t/d | 1,513 and 3,026 | Based on annual processing plant availability of 95% |
| Manganese mineralogical composition | wt% of total Mn | 100.0% rhodochrosite | Based on XRD analysis of test program composite samples |
| Overall Recovery of Manganese | wt% | 77.1% | Based on results of bench scale test programs |
| EMM Product Grade | wt% Mn | 99.7% (minimum) | Based on commercial EMM product market specifications |
| Annual Plant Availability Factor | % | 95.0% | Overall processing plant availability over 365.25 days |
| Ball Mill Product P80 | µm | 20 | Based on matching P80 of Metso HGMS test program feed sample |
| Bond Ball Mill Grindability Index | kWh/t | 21.45 | Average of values reported for red and grey samples by Bond Work Index test |
| LIMS Magnetic Field Intensity | Gauss | 1,200 | Based on Metso test parameters |
| HGMS Magnetic Field Intensity | Gauss | 10,000 | Based on Metso test parameters |
| HGMS Circuit Mn Recovery (to magnetics) | wt% | 85.7% | Based on results of Metso single stage open circuit HGMS test, relative to ROM mill feed |
| Sulphuric Acid Leach Batch Residence Time | h | 8.0 | Based on bench scale hydrometallurgical test program parameters |
| Leach Operating Temperature | °C | 60.0 | Based on bench scale hydrometallurgical test program parameters |
| Primary Iron Precipitation Reaction pH | pH units | 4.0 to 4.5 | Based on bench scale hydrometallurgical test program parameters |
| Current Density | A/m² | 550 | Based on bench scale hydrometallurgical test program results |
| Current Efficiency | % | 65.0 | Based on typical values for commercial operations |
| Sulphuric Acid Plant Capacity | t H₂SO₄/day | 380.5 | Based on maximum demand for sulphuric acid over life of project |
Project website: https://canadianmanganese.com/woodstock-project/
Technical qualifications
The process design criteria used for conceptual design and estimation of process capital and operating costs are based on a review of similar commercial operations for production of EMM, technical literature, theoretical reaction stoichiometry, semi-detailed heat balance on hydrometallurgical unit operations, and bench scale test results where applicable. Hydrometallurgical process recoveries, operating parameters, and reagent consumption rates have been based on bench scale testing completed to date on representative samples from the Plymouth deposit wherever possible, and upon technical literature and review of similar commercial EMM production facilities in other cases. Reagent consumption rates for processing of HGMD concentrate have been adjusted from those obtained from bench scale testing using bulk composite samples based on reaction stoichiometry relative to rejection of acid-consuming gangue minerals in the magnetic separation circuit.
The selection of unit operations and process operating conditions is based upon commercially standard operating practices for similar plants and is supported by the results of bench scale metallurgical and hydrometallurgical test programs completed to date. Requirements for gaseous emission control systems have not been specifically defined as part of the current study.
*Source: Preliminary Economic Assessment on the Woodstock Manganese Property, New Brunswick, Canada, Canadian Manganese Company Inc., Report 1494720100-REP-R0001-04, Section 17.0 Recovery Methods and Section 17.1 Process Description and Section 17.2 Process Design Criteria.*
