Paste Backfill Plant

Putting tailings back underground

A paste plant turns tailings into a thick, non-settling paste and pumps it into the empty stopes left by mining. The fill gives ground support, so neighbouring ore can be mined safely and pillars can be recovered, and it reduces the tailings that must be stored on the surface.

1. Thicken: a high-rate thickener with flocculant produces a dense underflow and returns clear water to the plant.
2. Filter (where used): a vacuum disc filter removes more water; one plant reports a cake of about 78% solids.
3. Mix: a mixer blends the cake or thickened tailings with binder (usually Portland cement) and water to a controlled consistency.
4. Pump: a positive-displacement piston pump pushes the paste into the pipeline, because paste is too thick for ordinary centrifugal pumps.
5. Place: paste flows down a borehole and along the drifts to the stope, behind a bulkhead, where it cures.

Typical numbers and watch-points

• Binder additions are commonly about 3–11% by mass of solids, depending on the strength required (often 0.5–2 MPa or more).
• The delivery line must stay full: free-fall in a borehole lets coarse particles segregate.
• Common problems are borehole plugging, pump failure and cement setting inside pipes.

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