Desert Lion Energy Inc. — 2018 Technical Report

This report details the proposed two-part recovery process, comprising a concentrator near the Rubicon and Helikon mines and a chemical plant near Walvis Bay, for producing lithium carbonate from lepidolite ore.

Report context

Dated Friday, November 23, 2018, this NI 43-101 technical report for Desert Lion Energy Inc. describes the recovery methods proposed for processing lithium-bearing ore from the Rubicon and Helikon deposits. The process design is split into a concentrator, to be located close to the mines, and a chemical plant, to be located near Walvis Bay and its port. The report presents two production scenarios under consideration by DLI.

Processing route

Overview and production scenarios

The recovery process is divided into two parts: the concentrator and the chemical plant, to be installed in two different locations. The concentrator will be located close to the Rubicon and Helikon mines, and the chemical plant near Walvis Bay and its port. Two production scenarios are being considered by DLI.

The first production scenario is to size both the concentrator and chemical plant to allow the production of 20,000 tpa of battery grade lithium carbonate (Li₂CO₃). It is estimated that 2,350,000 tpa of material will feed the concentrator, and 226,000 tpa (dry basis) of lepidolite concentrate from the concentrator will be trucked to the chemical plant in Walvis Bay for conversion to lithium carbonate.

The second production scenario is a concentrator to treat approximately 910,000 tpa (dry basis) of material. This concentrator is to produce a lepidolite concentrate, a petalite concentrate and a tantalum by-product. The lithium concentrates will not be converted to lithium carbonate in a DLI chemical plant. This production scenario is treated as a cost alternative.

Concentrator plant design basis

To develop the concentrator flowsheet, a literature review on lepidolite, petalite, and tantalum mineral recovery was first conducted to identify the most promising processing routes. The concentrator flowsheet was then developed based on information gathered from the literature review, SGS test results, Hatch in-house experience from other lithium and tantalum projects, and mass and energy balance simulation. As such, the plant flowsheet and equipment sizing remains preliminary.

DLI is considering two possible production scenarios for the concentrator. The concentrator case presented in this section refers to the Phase 2 concentrator, which includes two development phases: the Phase 1B concentrator, which will have a small capacity to process approximately 480,000 tpa of run of mine (ROM) ore and will produce only lepidolite concentrate (designed by a third party and not discussed in this report), and the Phase 2 concentrator to provide an additional capacity of 1,870,000 tpa ROM ore (combined throughput of 2,350,000 tpa ROM ore), which along with the Phase 1B concentrator will be able to satisfy the feed for the 20,000 tpa lithium carbonate chemical plant.

Crushing, coarse grinding and ore sorting

Run of Mine (ROM) ore is reclaimed from a stockpile by a front-end loader and fed to the primary crusher through a grizzly screen to reduce the 80% passing size from 300 mm to 101 mm. The primary crusher product is passed through the ore sorting double deck feed screen, where the oversize material is separated and sent to the ore sorter. Undersize product (<20 mm) from the bottom deck and oversize product from the top deck (>120 mm) bypass the ore sorter as it is outside of the size range required for effective ore sorter performance.

The ore sorter is a vendor package which is currently in operation on site for processing historical waste dumps to produce a 1.7–2.0% Li₂O lepidolite concentrate for sale to a Chinese off-take partner. Results to date have shown that the equipment can upgrade the Li₂O content in the ore by rejecting mining dilution material as well as some dilution material from within the lepidolite zone that has been liberated by the primary crusher. The reject stream is stored on a stockpile, and the product stream is sent to the secondary crusher, where the 80% passing size is reduced to 29 mm.

The secondary crusher product is combined with the ore sorting feed screen undersize and is conveyed to a storage stockpile from where it is reclaimed to feed the HPGR. Due to the geometry of the grinding rolls, it is necessary to reduce the top size in the feed to ensure it is within the nipping radius of the HPGR machine, so a closed milling circuit for the secondary crusher is included in the design.

The HPGR coarse grinding is also a closed circuit, aimed at producing a product size distribution of 80% passing at 768 μm, which is suitable for the recovery of tantalum via gravity separation. The undersize of the HPGR screen is deslimed before being sent to tantalum recovery, with the cyclone overflow sent to the lepidolite flotation desliming cyclone.

Tantalum recovery

Following the coarse grinding and desliming, the material is fed to the gravity recovery circuit composed of rougher, cleaner and rougher scavenger spirals. The concentrate from the cleaner is sent to shaking tables for further tantalum upgrading. Two stages of shaking tables are included in the design to produce a concentrate containing 25% w/w Ta₂O₅ in tantalite. The concentrate product from the shaking tables is then dewatered via thickening and filtering to reduce the residual moisture to 10% w/w, and the dewatered product is packed in 100 L drums for sale.

Fine grinding and lepidolite flotation

The tailings from the spiral circuit are subjected to fine grinding before flotation using a traditional horizontal overflow ball mill to reduce the feed to 80% passing 212 μm.

Prior to lepidolite flotation pre-conditioning, the ball mill cyclone overflow passes through the desliming cyclones where fine material (<20 μm) is removed and sent to the tailings. The lepidolite pre-conditioning consists of the addition of process water for solids density control (30% w/w), Calgon to act as a quartz depressant, and a Complex Flotation Reagent to act as both a frother and collector. This flotation reagent was specifically developed for lepidolite flotation by a Chinese company, and testwork later performed by Nagrom has also shown this is a functionable reagent for lepidolite recovery.

The conditioned stream is pumped to rougher flotation, where the preliminary lepidolite concentrate is sent to further pre-condition and the tailings are pumped to petalite flotation. The preliminary lepidolite concentrate is then upgraded further in two stages of cleaners before dewatering. The middlings from the first cleaner are further processed in a cleaner scavenger to recover lepidolite. The lepidolite concentrate (approximately 4% w/w Li₂O) is dewatered by thickening and filtering to reduce the residual moisture to less than 10% w/w, stored in a stockpile, then reclaimed and trucked to the chemical plant for further processing.

Petalite flotation

The lepidolite flotation tailings are dewatered in cyclones before being sent to pre-conditioning for subsequent petalite recovery. The petalite pre-conditioning consists of the addition of hydrochloric acid to regulate the pH at 2.5, process water for solids density control (30% w/w), MIBC to act as a frother, amines to act as a collector (as per literature recommendations and use in industry), sodium chloride to act as a depressant for the gangue material, and hydrofluoric acid to act as a depressant for the gangue material. The report notes that potassium chloride may be more effective than sodium chloride but is more expensive, and that the benefits of hydrofluoric acid should be investigated during testwork as it would be advantageous to remove this reagent based on probable improvements to the materials of construction and to workplace health and safety.

The conditioned slurry is sent to rougher scavenger cells. The petalite concentrate generated is then further refined through a 4-stage cleaning circuit, and the tailings is sent to the neutralisation tank. The tailings, which is acidic due to the conditioning reagents, is neutralized with calcium hydroxide before the tailings thickener such that the process water recycled to the ball mill is not corrosive and the underflow sent to the tailings storage facility is not acidic. The petalite concentrate (approximately 4.1% w/w Li₂O) is dewatered by thickening and filtering to reduce the residual moisture to 10% w/w, stored in a stockpile, then reclaimed and trucked to port for sale.

Chemical plant design basis

To develop the chemical plant flowsheet, a literature review on lithium extraction from lepidolite minerals was first conducted to identify the most promising processing routes. Based on the review, the sulfation roast-leach scouting testwork was conducted. The plant flowsheet was then developed based on information gathered from the literature review, SGS test results, roast-leach scouting test results, Hatch in-house experience from other lithium projects, and mass and energy balance simulation. As such, the plant flowsheet and equipment sizing remains preliminary.

In the chemical plant, 226,000 t/y (dry basis) of lepidolite concentrate are processed to produce approximately 20,000 t/y of lithium carbonate and an anhydrous sodium sulfate by-product.

Sulfation roast

The pelletized mixture (lepidolite concentrate combined with sodium sulfate, potassium sulfate and calcium oxide) is transferred into the sulfation kilns, two direct-fired rotary kilns in series using coal as fuel. The lepidolite first reports to the pre-heating kiln, where the mixture is dried and heated to approximately 750°C. The mixture then passes through to the holding kiln, where it is held at a temperature of approximately 875°C for one hour. The sulfated lepidolite is transferred to the roast product cooler and cooled to under 100°C with cooling water sprayed onto the shell of the rotary cooler. The cooled solids are then transferred to the roast product storage bin.

Lithium in the lepidolite is converted to leachable lithium sulfate with a conversion efficiency of approximately 93%. A portion of the aluminium, manganese, caesium, rubidium and potassium present in the ore are also converted to leachable metal sulfates. During the sulfation roast, some fluorine is liberated from lepidolite. Most of the fluorine in the concentrate reacts with the calcium oxide and is fixed as insoluble calcium fluoride. Approximately 10% of the fluorine reports to the kiln off-gas as hydrofluoric acid, while 3% forms a soluble fluoride salt.

Water leach and impurity removal

Sulphated lepidolite from the sulphation kilns is combined with leach feed liquor in the leach slurry feed tank which discharges directly into three agitated leach tanks operating in series. The leach liquor is recycled from various areas of the process, and make up water is also added to avoid the leach solution exceeding 90% of sulfate saturation. In the leach tanks, the lithium sulfate, potassium sulfate and sodium sulfate dissolve into aqueous forms. Some metal sulfate impurities of aluminium, manganese, caesium and rubidium, as well as some fluoride, also leach into solution.

The leach slurry is pumped to a leach slurry storage tank before being filtered on the primary filtration belt filter. During filtration, the solids undergo three stages of countercurrent washing to achieve a high recovery of the lithium sulfate. The wash filtrate is recycled back to leaching, and the silicate residue is conveyed to the residue stockpile for transport out of the site by trucks.

Belt filter filtrate is collected and discharged into the liming tank where the pH of the filtrate is increased by the addition of calcium hydroxide, facilitating the removal of aluminium, manganese and fluoride. The resulting slurry is then pumped to the calcium removal tank, where calcium is removed by adding sodium carbonate to precipitate calcium as calcium carbonate. The aluminium, manganese, calcium and fluoride solids are removed in the polishing filter. The filtrate is pumped to the leach filtrate storage tank.

Lithium carbonate production

Mixed sulfate salt centrate from the PLS storage tank is pumped to the crude lithium carbonate crystallisers. Crude lithium carbonate is produced by reacting the liquor with sodium carbonate solution added to the first of three reactor tanks, operating at 75-95°C where lithium carbonate has reduced solubility. The precipitated lithium carbonate slurry is dewatered through a thickener and centrifuge.

Crude lithium carbonate is mixed with pure lithium carbonate mother liquor to create a slurry discharged into the digester tanks, where crude lithium carbonate solids are converted to aqueous lithium bicarbonate by the addition of carbon dioxide and recycle liquor at approximately 35°C.

The lithium bicarbonate solution from the digester tanks is pumped to the ion exchange (IX) system to purify it. Residual contaminants (including iron, calcium, magnesium and aluminium) are removed from solution to achieve the target product purity. The liquor first passes through a cartridge filter to remove trace solids. Three IX columns are used in a lead/lag/regeneration configuration.

Purified lithium bicarbonate liquor from the ion exchange system is discharged into the purification crystalliser tanks. Steam is sparged into the crystallisers to provide heat, which results in lithium bicarbonate decomposition and crystallization of purified lithium carbonate. Carbon dioxide is evolved and is recycled to digestion. The precipitated lithium bicarbonate slurry is dewatered in the purification thickener and pure lithium carbonate centrifuge. Dewatered pure lithium carbonate is dried in the LPG fired pure lithium carbonate dryer. The dried solids are indirectly cooled with cooling water then pneumatically conveyed to a pure lithium carbonate storage bin. From there, the lithium carbonate is pneumatically conveyed to the pure lithium carbonate micronizer, which uses a jet mill to produce a product with a 50% passing size of 5 μm. The micronized product is bagged in plastic-lined 1 tonne bags.

Key reported parameters

Technical qualifications

The concentrator flowsheet and equipment sizing remains preliminary, developed based on information gathered from a literature review, SGS test results, Hatch in-house experience from other lithium and tantalum projects, and mass and energy balance simulation. Similarly, the chemical plant flowsheet and equipment sizing remains preliminary, developed based on information gathered from a literature review, SGS test results, roast-leach scouting test results, Hatch in-house experience from other lithium projects, and mass and energy balance simulation. The chemical plant roast-leach recoveries are assumed based on scouting testwork results.

The Phase 1B concentrator, which will have a small capacity to process approximately 480,000 tpa of ROM ore and produce only lepidolite concentrate, will be designed by a third party and its process is not discussed in this report.

Source: Desert Lion Energy Inc. NI 43-101 Technical Report, Friday, November 23, 2018, Section 17 Recovery Methods.