Dewatering & Tailings

After concentration, water must be removed from concentrate and tailings. Learn pulp density calculations, thickeners and their sizing, filters, water recovery, tailings storage facilities, and alternatives such as thickened, paste and filtered (dry-stack) tailings.

A concentrator uses 0.5–1 m³ of water per tonne of ore. Recovering water from tailings is vital in arid regions, and safe storage of tailings — billions of tonnes of fine waste — is one of mining's biggest responsibilities.

An analogy

Dewatering is like draining pasta: the water goes back to the pot (process water), and the solids are kept as compact as possible.

Thickeners and filters

Thickeners are large tanks where flocculated solids settle; clear overflow water returns to the plant. High-rate and paste thickeners reach 55–70 % solids. Pressure and vacuum filters dewater concentrates to ≈ 8–10 % moisture for shipping.

Tailings storage facilities (TSFs)

Conventional slurry tailings are pumped to dams built by upstream, centreline or downstream raising. Upstream dams are cheapest but most vulnerable (Brumadinho 2019, Mariana 2015). The Global Industry Standard on Tailings Management (GISTM) now requires rigorous design and oversight.

Alternatives

Thickened tailings (≈ 55–65 %), paste (≈ 70 %+, no water release), filtered dry-stack tailings (≈ 80–85 %) — more water recovered and safer landforms, but higher operating cost.

Water balance

Site water balances track rainfall, evaporation, seepage, entrainment in tailings pores and reclaim. Minimising water locked in tailings is key in desert mines (Chile, Australia).

Formulas

• Water with solids: Water = Solids × (100 − C_w)/C_w
• Pulp density: 1/ρ_p = C_w/ρ_s + (1 − C_w)/ρ_w
• Thickener area: A = UA × solids (t/d), D = √(4A/π)
• Tailings volume: V = tonnes / ρ_d

Worked example: Water recovery by thickening

Given: 1000 t/h tailings solids at 30 % solids; Thickened to 60 %

Find: Water recovered.

• Water in feed = 1000 × 70/30 = 2333 t/h
• Water in underflow = 1000 × 40/60 = 667 t/h
• Recovered = 1667 t/h

Answer: ≈ 1670 m³/h returned to the plant

Worked example: Pulp density

Given: 30 % solids, ρ_s 2.7

Find: ρ_p.

• 1/ρ = 0.3/2.7 + 0.7 = 0.811

Answer: 1.23 t/m³

Common mistakes

• Wrong: Choosing upstream dams in seismic, wet regions. — Right: Use downstream/centreline or filtered tailings.
• Wrong: Ignoring water locked in tailings. — Right: Include entrainment in the water balance.

Applications

• Water-scarce mines: High-rate thickening and dry stacking.
• Concentrate shipping: Filters meet transportable moisture limits.
• Tailings safety: GISTM compliance and monitoring.

Key takeaways

• Water = solids × (100 − C_w)/C_w.
• Thicken and filter to recover water.
• TSF design and GISTM matter.
• Dry stacking and paste reduce risk.

Going further

• Rheology: Yield stress limits paste pumping.
• Liquefaction analysis: Static/seismic liquefaction of tailings.
• Co-disposal: Mixing tailings with waste rock.