Gold and copper mills are closing the water loop. The tailings thickener makes it work.
Modern grinding circuits now recycle 80–90% of their water, with tailings thickeners and polymer programs doing the heavy lifting. The payoff: dramatic cuts in freshwater intake, clearer overflow, and real OPEX savings.
Across the world’s big concentrators, the new default is simple: close the water loop. Thickening and recycling circuits routinely return roughly 80–90% of process water to the mill, and industry sources note that a well‑designed thickener “can recycle up to 90% of the original feedwater” (AT Minerals).
In practice, major concentrators routinely recycle ≥80–90% of their water. Case studies show operations cutting freshwater intake by ~60–70% through water‑balance optimization and high‑rate thickening (WesTech) (Mineral Processing). By maximizing cyclone overflow and tailings thickener overflow return, mills can sharply reduce fresh water use (often by half or more) while maintaining throughput. Closed‑circuit design (minimizing uncontrolled losses and using return dams/ponds) is standard, and many grinding circuits essentially operate on recycled water, with fresh water added only to offset evaporation or losses.
The economics are compelling too. One plant saved 23% of total water and about $576,000 annually by improving flocculation and thickener performance (Bohrium).
High‑rate thickening and water recovery
Thickeners sit at the center of the loop. By compressing tailings slurry, a thickener produces a clear overflow and a high‑density underflow; overflow is typically reused in the plant and, in well‑run circuits, is often below 100 ppm (parts per million) suspended solids. The dense underflow is sent to disposal or further processing. Modern deep‑cone or paste thickeners reach underflow densities “up to and exceeding 70 wt% (weight percent) solids” (FLSmidth), while many operations see ~30–60% (by mass) as common practice, liberating most of the water.
Industry literature confirms that thickening can recover 80–95% of slurry water; one case achieved ~96–98% total water recovery by combining primary and paste thickeners (WesTech). Mines like Chile’s Los Pelambres recycle over 80% of plant water (Mineral Processing), and South Africa’s Khumani mine reported over 90% water recovery after installing high‑rate and paste thickeners (Mineral Processing). Surveys corroborate these figures, with many operations recycling ~85–90% of feedwater (Mineral Processing).
The operational levers are direct. Every 10% gain in thickener recovery translates into reduced fresh‑water demand and smaller tailings ponds. Well‑run thickeners also lower the footprint of tailings dams and simplify tailings management by producing denser tailings (gravity or paste) and clearer overflow.
Chemical flocculants and overflow clarity
Chemical flocculants (typically high‑molecular‑weight polyacrylamides) bridge fine particles, forming rapidly settling flocs that accelerate settling and improve clarity. Optimizing flocculation—polymer type, dose, and addition method—can markedly enhance thickener performance; suppliers of flocculants provide the polymers used in these programs. In one study, raising slurry pH and increasing flocculant dosage from ~8 to 13 g/t (grams per tonne of solids) significantly increased underflow density and overflow clarity (Bohrium), cutting overall plant water use by 23% (≈$576k savings; same source).
In general, flocculants enable higher solids—often +5–20 wt% in underflow—and much clearer overflow, with turbidity (clarity metric) drops of 75% or more. Bench tests on fine tailings show optimal polymer doses in the range 10–50 g/t can reduce overflow turbidity to single‑digit NTU (Nephelometric Turbidity Units). A coal‑tailings study achieved an overflow turbidity of only 7.4 NTU at ~32 g/t polymer (SciELO) versus ~30 NTU without flocculant. An iron‑ore thickener achieved overflow solids of ~0.008% (77 mg/L) with optimized flocculation (MDPI). In practice, achieving below 50–100 NTU overflow turbidity is a common target for recycling water back into grinding.
Execution details matter: adequate flocculant dosing stabilizes thickeners and reduces upsets from floc shear, while overdosing yields diminishing returns—operators balance polymer cost against water savings. Accurate chemical metering, for example via a dosing pump, supports consistent addition method and performance.
Data‑driven thickener control and regulation
Modern circuits often recycle 80–90+% of mill water (AT Minerals) (Mineral Processing). Effective flocculation can cut overflow solids to a few ppm and boost underflow solids above 50–70% (FLSmidth) (SciELO), and these measures have enabled >60% reductions in fresh‑water intake at some mines (Mineral Processing). Data‑driven optimization of the thickener/flocculant system—from feed concentration and rake speed to polymer type/dose—is therefore a high‑priority strategy for any large‑scale gold or copper mill seeking sustainable, cost‑effective water management.
Regulatory pressure reinforces the trend. Indonesia’s environmental rules now mandate treatment of mining effluent, effectively forcing on‑site reuse (JDIH Kemenko).
(Additional source links referenced in this article: WesTech; Mineral Processing; Bohrium; Mineral Processing; Mineral Processing; Mineral Processing; Mineral Processing.)