Graphite One Project — 2016 Technical Report (PEA)

This 2016 Preliminary Economic Assessment describes a vertically-integrated graphite project encompassing mining and mineral processing in Alaska with downstream purification and value-added manufacturing at a separate coastal plant.

Report context

The Graphite One Project was conceived as an American interstate, vertically-integrated manufacturing operation for high-grade coated spherical graphite. The November 28, 2016 technical report presents a Preliminary Economic Assessment (PEA) covering mining and mineral processing at the Graphite Creek property in Alaska and purification and value-added graphite processing at a proposed Product Manufacturing Plant at a developed brownfield site near a port. The report outlines a conceptual design whereby open pit mining would deliver 1,018,000 tpy of graphite mineralization to a Mineral Processing Plant for extraction and recovery of graphite into 60,000 tpy of concentrate grading 95% graphite (Cg). This concentrate would be transported to the port of Nome and shipped to a coastal location for further processing.

Processing route

Alaska Mineral Processing Plant

The Mineral Processing Plant was designed to receive run-of-mine material grading 7% Cg that has been crushed and beneficiated in close proximity to the mine. The processing sequence at the Mineral Processing Plant includes two stages of crushing, initial grinding followed by conventional cell rougher flotation and cleaner flotation, and multiple sequences of grinding or polishing with column flotation to progressively upgrade the concentrate to 95% Cg. The final concentrate is pressure filtered and pneumatically dried.

Crushing and grinding. Run-of-mine mineralized rock is delivered by truck to dump hoppers above grizzly feeders for removal of plus 500 mm material. Undersize is fed to a primary jaw crusher to reduce particle size from 400 mm to less than 100 mm. Vibrating screening ensures oversize is recirculated while undersize proceeds to secondary crushing where hammer mill crushers comminute material to 20 mm. Screening of hammer crusher discharge ensures oversize is recycled while undersize proceeds to storage bins as feed inventory to primary grinding. At full capacity, three crushing circuits operate in parallel. Crushed material is conveyed to the primary grinding circuit, which at full capacity consists of five rod mills operating in parallel. The rod mill is in closed circuit with cyclones where cyclone underflow is returned to the mill. Cyclone overflow at a particle size P80 of 150 mesh (100 microns) flows by gravity to the rougher flotation feed conditioning tank.

Rougher and cleaner flotation. Conditioned pulp is sent to a rougher cell bank consisting of four conventional impeller-agitated flotation cells, each of twelve cubic meter volume and arranged in series. Rougher flotation concentrate proceeds to a cleaner cell bank consisting of four conventional impeller-agitated flotation cells, each of five cubic meter volume and arranged in series. Graphite recovery of 95% was expected in an initial cleaner concentrate grading 45% C to 50% C in about 20% mass pull. This concentrate is directed to the column flotation circuit for further upgrading while tailings from both rougher and initial cleaner stages are pumped to tailings impoundment.

Column flotation. Upgrading of the initial cleaner concentrate is carried out in four stages of column flotation, each preceded by grinding or polishing of the feed pulp. Initial cleaner concentrate pulp is directed to the first regrind ball mill and then fed to the first flotation column. Successive column cleaner stages use different mills and grinding media: cleaner column two is preceded by attrition milling; cleaner columns three and four are preceded by friction milling with high density media. The progressive upgrading of the initial cleaner concentrate at 45% C during successive column cleaning is: 75% C in cleaner column one, 85% C in column cleaner two, 93% C in column cleaner three, and 95% C in the final column cleaner four at an overall recovery of 80%. Tailings from cleaner column one are pumped with rougher tails to impoundment, while underflow from cleaner columns two, three, and four is directed to dewatering cells ahead of scavenger flotation for additional graphite recovery.

Drying and packaging. Final concentrate overflow from cleaner column four is dewatered in plate and frame filter presses. Filter cake is conveyed to pneumatic dryers and then pneumatically conveyed to bulk bag fillers for packaging in one tonne super sacks.

Tailings and reagents. Tailings from rougher flotation, initial cleaner flotation, column one cleaner, and the scavenger circuit are pumped to a tailings pond for natural settling of rejected gangue. Process water is recycled from the tailings pond. Process reagents required are Flotanol and kerosene. It had not been determined if pH modifiers would be needed.

Design considerations. The report states that mineral processing testwork indicated that the apparent coarse fraction of graphite was either low or sufficiently fragile to disintegrate or dissociate under mechanical stress. The design uses five parallel circuits of smaller-scaled equipment rather than one or two larger-scale equivalents in a single series for mineral beneficiation, intended to allow better flexibility on production and improve graphite recovery. The plant is designed to run on a year-round (12 month) schedule, with road clearance during winter months to ensure year-round access.

Product Manufacturing Plant

The Product Manufacturing Plant would receive 60,000 tpy of concentrate grading 95% Cg from the Graphite Creek Mineral Processing Plant. All received concentrate is thermally purified. State-of-the-art electric-powered thermal purification was selected over acid chemical purification. The plant would produce 41,850 tpy of high-grade coated spherical graphite for lithium-ion battery applications and 13,500 tpy of refined, sub-20 micron graphite powder for various end-uses.

Raw material handling. Graphite concentrate packaged in one-tonne super sacks and stacked in 20-foot shipping containers are deposited at the unloading station. Super sacks are removed by forklift and loaded onto bulk bag discharging systems. Graphite is conveyed to four storage silos each of 125 m³ capacity.

Graphite purification. Thermal purification of static samples at high temperature under a halogen atmosphere successfully achieved and surpassed target graphite purity of 99.95% C while also lowering problematic metallic impurities to below threshold limits. For high volume production, purification furnaces are designed as high throughput, low residence time units operating under dynamic fluidizing conditions with an inert atmosphere at high temperature. Fine material is pelletized in drum pelletizers, fed into a furnace feed hopper, and top-fed to multi-story cylindrical furnaces where graphite pellets descend and circulate through a heat affected zone before settling in a chilled zone at the furnace bottom. The furnace operates as a fluidized bed with bottom-feeding of inert gas. Heat is created by an electrical arc between the graphite electrode and graphite lined walls, maintaining temperatures of 2,500 to 3,000 °C. At full scale production, eleven purification furnaces are planned with ten units nominally operating at one tonne graphite per hour and one unit on standby, treating concentrate at a daily rate of 238 tpd.

Graphite spheronization and coating. Exploratory product development tests indicated that purification and mechano-chemical processing of the entire size distribution of a non-classified graphite concentrate resulted in recovery of spherical graphite of which nearly 75% was suitable for EV lithium-ion batteries. This was achieved without prior jet milling, using the entire size distribution of the graphite feed, and required half the residence time with one third of the energy input compared to conventional Chinese flake graphite. Other size fractions suitable for non-EV lithium-ion batteries end-use increase combined recovery to 91%. Spheronizing and coating is carried out on a batch basis. Purified graphite powder is spheronized and classified into various size fractions. Spherical graphite size fractions suitable for lithium-ion batteries are combined with coating precursor and recycled to the spheronizing mill. The green surface coated graphite product is collected and heat treated at about 1000°C in kiln type furnaces. At full scale production, eleven spheronizing-coating systems and four carbonization furnaces would be in operation.

Key reported parameters

Technical qualifications

The report is a Preliminary Economic Assessment and as such the processing information presented is conceptual in nature. The mineral processing recovery of 80% is assumed under optimized conditions. Testwork indicated that the apparent coarse fraction of graphite was either low or sufficiently fragile to disintegrate or dissociate under mechanical stress, as stated in the report. Exploratory product development testwork demonstrated results for spheronization, but the report notes that pilot scale equipment from vendors will be necessary to define the yield and number of circuits required for the Graphite Creek concentrates. The 91% spheronization recovery for all lithium-ion battery applications was described as an acceptable assumption at the conceptual level. It had not been determined if pH modifiers would be needed for flotation conditioning or tailings slurry. Detailed study of the tailings was to be investigated in the future. Future investigations on optimizing the spheronization process and customizing the surface coating process may alter the final number of installed units.

Source: Graphite One Resources Inc., PEA on the Graphite One Project, November 28, 2016, Section 17 Recovery Methods.