Ashram Project – Preliminary Economic Assessment

This PEA describes a proposed 4,000 tpd flotation mill and sulphuric acid cracking plant for the Ashram rare earth project, with no historical milling background.

Report context

The report, dated as part of the Preliminary Economic Assessment for Commerce Resources Corp. – Ashram Project, was prepared by SGS Geostat. Since Ashram is a new project, there is no historical milling background. The assessment presents a proposed mill design and processing route based on testwork and assumptions, with operating cost estimates considered to have an accuracy range of +/-30%.

Processing route

Historical background

Since Ashram is a new project, there is no historical milling background.

Proposed mill design and assumptions

A 4,000 tpd mill is proposed in this study. The mill process will be conventional with operation relying on operators’ experience and skill supported by electronic monitoring and instrumentation. Mill design criteria follow those used in several mines in Canada where, apart from the run of mine grizzly, hopper, jaw crusher and water tanks, the entire mill services and operations are under the same roof.

The preliminary assessment is based on assumptions including: a good mill design will have a good overall TREO grade and recovery; Commerce will buy new milling equipment unless in extremely good working condition; the mine will be able to feed the mill at a rate of 4,000 tpd, 7 days per week; no major setbacks will be encountered with environmental agencies, trade unions and/or indigenous people; 3-phase diesel power generators delivering about 10MW will be available on site; approximately 5 hectares of a more or less flat site will have to be prepared for the mill and its ancillary infrastructure; it will be possible to dispose of tailings without jeopardizing the surrounding environment; the mineral concentrate grade will be a minimum of 10% TREO with recovery in the 70% range; the ore liberation size is typically less than 30 µm, down to <5 µm; and no provision was made for the recovery of other minerals (fluorite, apatite).

Crushing

Run of mine ore is delivered from the mine by haul trucks. Whenever possible the ore will be dumped directly in the jaw crusher feed hopper. Because mining and crushing operations will not always be on the same time schedule, it is assumed that 25% of the time the haul trucks will proceed to the run of mine stockpile and the rest of the time they will dump directly onto the grizzly above the crusher feed hopper. The run of mine stockpile area is sized to hold approximately 30,000 tonnes of ore. Secondary handling will be by a Caterpillar 938 front end loader.

A grizzly having 15” x 20” openings scalps the oversize rock. Oversize will be broken in place with a pneumatic rock breaker. Grizzly undersize falls into a 100 tonne capacity hopper which feeds a 17’ x 5’ apron feeder discharging on an incline fix bar scalper. Bar scalper oversize falls by gravity into a 48” x 60” jaw crusher while undersize, crushed ore and fines from the apron feeder report to a 60” wide sacrificial belt conveyor, then to a 36” wide belt conveyor which discharges on a buffer stockpile. The stockpile, which is above ground, has a live load of 4,000 tonnes and feeds through longitudinal slots two apron feeders located in an 8’ x 8’ underground concrete tunnel.

Grinding and classification

Apron feeders discharging on a second 36” belt conveyor feed a 10’ x 20’, 1200 kW SAG mill. The SAG mill discharges on a set of three 60” x 120”, 16 mesh Derrick screens. Derrick screen oversize is conveyed back to the SAG mill feed via three 24” belt conveyors in series while undersize is pumped to a set of two 20” cyclones. Cyclones underflow flow by gravity to a 4-way splitter box feeding four 13.5’ x 13’, 900 kW ball mills in parallel. Cyclone overflow reports to the first conditioner of the flotation circuit. The SAG and ball mills are sized for an ore having an average Work Index of 14.0 kW-h/t.

Flotation

The larger conditioner, with dimensions 3 m diameter x 4 m height, overflows to a second 2.5 m diameter x 3 m height conditioner that reports to a bank of Denver DR type 300 x 4 cells rougher. Rougher tailings are pumped to a third 2 m diameter x 2 m height conditioner, overflowing in a primary Denver DR type 100 x 6 cells scavenger. Tailings from the primary scavenger are pumped to a fourth 2 m diameter x 2 m height conditioner which overflows into a second Denver DR type 100 x 6 cells scavenger. Tailings from the second scavenger are pumped to a fifth 2 m diameter x 2 m height conditioner overflowing into a third Denver DR type 100 x 6 cells. Tailings from this bank of cells are the final tailings, which after sampling are pumped to the tailings pond.

Rougher concentrate is pumped to a bank of Denver DR type 24 x 4 cells primary cleaner. Concentrate from this cleaner is the final concentrate and is pumped to the mill thickener. Conditioner and flotation cells are roughly sized from Hazen’s metallurgical tests.

Thickening and filtration

Concentrate from the primary cleaner is pumped to a high capacity thickener. Thickener underflow is pumped via a diaphragm pump to a stock tank having a 2-hour retention time. From the stock tank, the thickener underflow concentrate is pumped via a second diaphragm pump to a Larox type pressure filter. From the pressure filter the concentrate at approximately 8% moisture is conveyed to the concentrate shed or to the acid cracking plant. No tests were done to size the filter and the thickener.

Thermal cracking

Since thermal cracking of the mill concentrate to produce high grade TREO product is ongoing, it is not possible to give an exact description of the process. For the economic evaluation of the PEA, a sulphuric acid cracking technique, resulting in the production of a rare earth carbonate (REC) product, is selected.

The major components of the acid cracking section include roasting, leaching, calcium and fluorine removal, thorium and iron precipitation and removal, REE carbonate precipitation, centrifuging and drying of the REE carbonate. The chemical upgrading begins with the mill flotation concentrate being soaked in concentrated sulphuric acid (98% pure). The acidified concentrate is roasted at a temperature of ±250°C in a rotary kiln to decompose the rare earth minerals (monazite, bastnäsite, and xenotime) as well as the gangue. The roasted concentrate is water leached, thickened and filtered. Rare earths and other elements are in solution, with calcium being removed as gypsum (CaSO₄) to the residue. Hydrogen fluoride (HF) created is scrubbed and disposed of. The solid residue (gypsum) is disposed to the mill tailings pond while the rare earth element enriched solution undergoes clarification. Leached radioactive elements (thorium only as uranium is not present) and other impurities are selectively removed via pH control and neutralization with caustic soda, precipitated, and allowed to report to the mill tailings. When impurities are removed, the REE enriched solution is precipitated with sodium carbonate into an REE carbonate form, then filtered, dried and bagged ready for dispatch. For the purposes of the PEA, the cracking process will end at the production of a REC product.

Key reported parameters

Technical qualifications

The mill operating costs presented in this section are strictly for the mineral processing for the production of a 10% TREO mineral concentrate. The mill operation costs are considered to have an accuracy range of +/-30%. Conditioner and flotation cells are roughly sized from Hazen’s metallurgical tests. No tests were done to size the filter and the thickener. Because thermal cracking of the mill concentrate to produce high grade TREO product is ongoing, it is not possible to give an exact description of the process. For the cracking plant, OPEX and CAPEX were estimated from available studies realized for ore deposits similar to Ashram.

Source: Commerce Resources Corp. – Ashram Project – Preliminary Economic Assessment, SGS Geostat, Section 17 Recovery Methods.