This report describes the processing route designed to treat Run of Mine ore at between 360ktpa and 430ktpa to produce approximately 15.5ktpa of tin concentrate.
Report context
The 2020 technical report presents a process plant design for treating Run of Mine (RoM) ore from a mining operation. The concentrator has been designed to treat between 360ktpa and 430ktpa of RoM ore, generating approximately 15.5ktpa of tin concentrate. Changes to the Life of Mine (LoM) plan have resulted in the planned ore feed increasing to about 384ktpa. The plant will run at a reduced throughput during the 2020 year of the forecast LoM before reaching the new LoM steady state forecast of 384ktpa.
Processing route
Crushing and ore preparation
Ore is delivered to the RoM pad and either tipped directly into the RoM feed bin or onto a RoM stockpile. Material is withdrawn from the bin by apron feeder and passes through a primary jaw crusher, which reduces material from nominally -450mm to -150mm. The jaw crusher product is conveyed to the secondary crusher sizing screen, with oversize feeding the secondary crusher feed bin and undersize feeding the tertiary crusher screen. The tertiary crusher screen is also fed by products from the secondary and tertiary crushers in a closed-circuit arrangement. Screen oversize from the tertiary crusher screen is conveyed to the tertiary crusher bin, while undersize is conveyed to the plant feed stockpile. Under nominal conditions all screening is conducted dry, with provision for intermittent wet screening on the tertiary crusher screen.
Material is withdrawn from the bottom of the secondary and tertiary crusher bins by vibrating feeder and directed through secondary and tertiary cone crushers respectively. The secondary crusher produces a product of nominally -32mm, while the tertiary crusher produces a product of nominally -8mm. Both products are collected on a common conveyor and conveyed back to the tertiary crusher screen.
The crushing and screening circuit operates on 5,200 hours annually with a design throughput of 100 t/hr. The 1,900t plant feed stockpile serves as a buffer between the crushing circuit and the remainder of the plant, which operates on 7,000 hours annually.
Coarse jigging circuit
The -8mm material is reclaimed from the plant feed stockpile via front-end-loader (FEL), a small plant feed bin, and a belt feeder at nominally 52 t/hr, then conveyed to the rougher jig. The jig effects a density separation: less dense reject material gravitates to the tailings dewatering screen, while more dense concentrate material gravitates to the cleaner jig. The cleaner jig also effects a gravity separation, with tailings pumped back to the rougher jig and concentrate gravitated to the concentrate dewatering screen.
Both jig concentrate and tailings are dewatered on a screen with a cut size of 1mm. The combined -1mm slurry is pumped to the low grade gravity concentration circuit. The -8mm+1mm jig tailings, at nominally 37 t/hr, are conveyed to a tailings stockpile for reload by FEL onto trucks for disposal at the tailings storage facility. The -8mm+1mm jig concentrate is conveyed to the high grade mill feed bin.
High grade gravity circuit
Jig concentrate is withdrawn from the bottom of the high grade mill feed bin at a controlled rate, nominally 4 t/hr, by weigh feeder and fed into the primary peripheral discharge ball mill. The mill circuit includes a sizing screen and produces a product with a p80 of 425µm, which is pumped to the high grade gravity concentration circuit.
The high grade circuit is arranged so that a rougher spiral produces concentrate and tailings. The concentrate feeds a shaking table, while tailings feed a scavenger spiral. The rougher shaking table concentrate (HG gravity concentrate) is pumped directly to the product magnetic separator feed tank due to its low contaminants and high tin values. The shaking table tails are combined with the rougher spiral tailings and pumped to the scavenger spiral.
The scavenger spiral produces concentrate, which is gravitated to another set of shaking tables, and tail (HG gravity tails), which is directed to the low grade regrind circuit. The shaking table concentrate (HG gravity middlings) is gravitated to the high grade regrind mill, and tailings are recycled to the scavenger spiral feed.
Low grade gravity circuit
The -1mm stream from the jig product and discard dewatering screens, nominally 13 t/hr, is pumped to a rougher spiral, which produces concentrate gravitated to a bank of shaking tables and tailings pumped to a scavenger spiral. The scavenger spiral produces tailings (LG gravity tails) pumped to the tailings thickener and concentrate gravitated to the same shaking table bank.
The low grade shaking tables produce concentrate (LG gravity concentrate) reporting to the high grade regrind circuit and tails (LG gravity middlings) reporting to the low grade regrind mill.
Low grade regrind gravity circuit
The high grade gravity tails together with the low grade gravity middlings report to a regrind ball mill and screen, producing a product with a p80 of 106µm. This stream reports to a bank of shaking tables, which produce concentrate (LG regrind concentrate) reporting to the sulphide flotation feed, and tailings (LG regrind tailings) pumped to the tailings thickener.
High grade regrind circuit
Feed to the high grade regrind circuit consists of high grade gravity middlings and low grade gravity concentrate. The mill circuit includes a ball mill with a screen and produces a product with a p80 of 106µm. The ground stream is combined with the low grade regrind concentrate and pumped to sulphide flotation.
Sulphide flotation, magnetic separation and filtration
Product from the high grade regrind mill together with the low grade regrind concentrate reports, via a two-hour buffer tank, to a bank of conventional sulphide rougher flotation cells. Sulphide minerals, which are contaminants in the final concentrate, are floated off with the froth, while non-floated material is combined with the high grade gravity concentrate and pumped to the product magnetic separator.
The magnetic separator removes any free iron minerals present, along with iron added during grinding stages. Magnetic separator tails are combined with the flotation froth and pumped to the tailings thickener, while magnetic separator concentrate reports to the product filter via a two-hour buffer tank. The single concentrate stream is dewatered with a vacuum belt filter before being bagged and set aside for storage.
Tailings, thickening and pumping
Various tailings streams produced throughout the process are thickened and water recovered. Streams are pumped and gravitated to a thickener feed box. After flocculant addition, slurry is gravitated to the thickener. Thickener underflow is controlled by pumps, which pump tailings to the tailings disposal section. Thickener overflow gravitates to the process water tank. Thickener underflow is collected in a surge tank, from where it is pumped to the tailings storage facility using either of two sets of parallel pumps. Two tailings lines to the tailings storage facility are provided.
Services
Water services: In early stages, raw water is pumped from a river to the raw water tank. Later, excess water produced by the mine is gravitated to the raw water tank instead. Water is filtered and pumped to the plant area to serve as level make-up water in the process water tank, gland service water for the tailings pumps, and make-up water for reagents. Thickener overflow water gravitates to the process water tank for distribution to required process areas.
Compressed air services: An operational and standby air compressor is used with associated filters, dryers and receiver to provide instrument and plant air.
Reagents
Flocculant: The required quantity is emptied into a hopper, fed by screw feeder to a wetting head, then to a mixing/activation tank. After suitable hydration time, typically two hours, flocculant is transferred to a dosing tank and pumped to the thickener.
Frother: Frother from isotainers is pumped directly to required addition points.
Sulphide collector: Xanthate pellets are weighed in the store and added by hand to the storage tank and diluted. Xanthate is then pumped to the sulphide flotation circuit.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant throughput (design range) | 360–430 ktpa RoM ore | Design |
| Planned ore feed (LoM change) | ~384 ktpa | Design (revised LoM) |
| Tin concentrate production | ~15.5 ktpa | Design |
| Crushing circuit utilisation | 50% | Design (due to remote location) |
| Rest of plant utilisation | 85% | Design (due to remote location) |
| Crushing circuit annual hours | 5,200 hrs/yr | Design |
| Crushing circuit throughput | 100 t/hr | Design |
| Plant feed stockpile capacity | 1,900 t | Design |
| Plant annual hours | 7,000 hrs/yr | Design |
| Plant feed rate (from stockpile) | 52 t/hr (nominal) | Design |
| Final crusher product | -8 mm | Design |
| Jig tailings (coarse) flow | 37 t/hr (nominal) | Design |
| High grade mill feed | 4 t/hr (nominal) | Design |
| High grade mill product p80 | 425 µm | Design |
| Regrind mill product p80 | 106 µm | Design |
| Final concentrate grade (testwork target) | >60% tin | Testwork indication |
| Overall recovery (testwork) | At least 80% | Testwork indication |
| Concentrate grade (LoM planning) | ~62% tin | Business planning |
| Process recovery (LoM planning) | ~72% | Business planning |
| Filter cake moisture | 10–15% | Design |
| Sulphide flotation rougher cells | 6 cells | Design |
| Tin flotation circuit | 6 flotation cells as rougher bank | Design |
Project website: https://www.alphaminresources.com/2016/08/31/bisie-tin-project-congo/
Technical qualifications
The process design incorporates lower than normal availabilities due to the remote location of the plant. The crusher plant has been designed to run at 50% utilisation and the remainder of the plant at 85%.
The test work, conducted at Mintek, indicated that a tin concentrate with a grade greater than 60% tin can be achieved with an overall recovery of at least 80%. However, owing to potential plant performance uncertainties, a process recovery of approximately 72% with a grade of approximately 62% tin concentrate has been specified for the Life of Mine business planning.
The complete process design criteria are recorded in document DRA-C0216-PROC-DC-028.
—
*Source: Tin Project , 2020 Technical Report, Section 17 Recovery Methods*
