First unit operation · Gravity plant
Grizzly feeder GF-3
The front end of our small-scale gold plant, designed to be built from Nigerian steel sections by a local welding workshop. It takes run-of-mine gravel by the barrow, washes it, rejects the stones, and meters an even feed into the 2 mm wash screen.
Prototype design, Rev A · not yet builtWhole unit. About 3 m high at the back edge of the deck, on a portable skid. About 1 tonne of mild steel.
Where it sits in the plant
Every tonne the plant treats passes over this unit first. It does three jobs: it holds a buffer of ore so the plant runs evenly between barrow loads, it washes clay off the gravel, and it removes stones that would tear the screen mesh.
In our plant design the feed end was an imported mini grizzly. GF-3 replaces it with a unit any local workshop can build, repair and copy.
- 300-GZ-01Grizzly feederWash, reject stones over 25 mm, meter the feed
- 300-SC-01Wash screenSplit at 2 mm; oversize over the sluice
- 300-CN-01Centrifugal concentratorHolds gold and heavy minerals
- 400-TB-01Shaking tableUpgrades the concentrate
- 400-FU-01Smelt with boraxGold doré, no mercury
How it works
Four steps, all by gravity and water. Pick a step to see the part on the model.
Design basis and sizing
Sized from the plant's own design basis: 2 t an hour of screened feed to the concentrator, with 30% of the run-of-mine rejected as oversize, on one 10-hour shift at 85% availability.
| Item | Value | How we got it |
|---|---|---|
| Run-of-mine feed | 2.86 → 3.0 t/h | 24.3 t a day over 8.5 working hours; designed for 3 t/h |
| Feed material | ≤ 300 mm lumps | Alluvial gravel and weathered ore, wet and clayey, free-digging |
| Bulk density | 1.6 t/m³ | Assumed for wet, loose gravel; to be measured on site |
| Grizzly deck | about 1.1 t/h per m² | A light load that leaves room for sticky ore |
| Bar gap | 25 mm | Keeps stones off the 2 mm screen mesh |
| Hopper | about 1.1 m³ | About 1.8 t, roughly 35 minutes of feed at 3 t/h |
| Water | about 3 m³/h | Spray bar about 2 m³/h and corner jets about 1 m³/h, drawn from the plant's recycled water and counted in its 7.1 m³/h slurry water |
| Power | none | Gravity feed; the gate is set by a hand wheel |
| Steel | about 1 t | Mild-steel plate and standard sections |
Design values for the prototype, Rev A. Throughput, blinding and water use are confirmed in the test plan below before the design is frozen.
Built locally
Everything on GF-3 is cut, drilled and welded from standard mild-steel sections sold in Nigerian steel markets. There are no machined parts, no motor and no imported wear parts, so a competent local welding workshop can build and repair it.
| Part | Made from |
|---|---|
| Hopper and side plates | Mild-steel plate |
| Grizzly bars | Flat bar, bolted in replaceable sets |
| Frame and skid | Steel angle and channel |
| Slide gate | Steel plate, threaded rod and a hand wheel |
| Spray bar and corner jets | Galvanised pipe and ball valves |
| Impact liner | Used conveyor belt |
- Easy to repairBars bolt in as replaceable sets, and worn bars are swapped with stock flat bar.
- Fits a containerThe deck and side plates unbolt, so the unit ships in a 20-foot container with the rest of the plant.
- Rubber where rock hitsUsed conveyor belt lines the face where stones land, so the hopper wall is not worn through.
- Safe by designThe 25 mm bars double as a fall guard. Nobody stands on the deck: oversize is raked from the bank, the gate wheel sits clear of the chute, and the gate is locked shut before anyone clears a hang-up.
Prototype test plan
The first unit is built in Osun State and tested on real run-of-mine ore before the design is frozen. Each test has a pass mark set from the design basis.
- Workshop checkPass: no leaks; the gate runs its full travel by hand.
Trial fit, weld inspection and a water test of the spray bar and jets. - Gate calibrationPass: a chart of tonnes an hour against gate opening, covering 1 to 4 t/h.
Weigh the feed delivered in timed runs at each gate opening. - Full-shift runPass: 3 t/h held through the shift with no blockage that stops the plant.
Feed run-of-mine ore at 3 t/h for a 10-hour shift, logging every hang-up and rake. - Water usePass: 3 m³/h or less in total.
Meter the spray bar and corner jets during the shift. - Wear checkPass: wear rate gives at least one season before the bars are turned.
Measure bar and liner wear after 100 operating hours.