Gold miners are racing to recycle water. The tailings thickener is doing the heavy lifting.

Gold‑carbon‑in‑pulp (CIP) is a hydrometallurgical flow sheet—crushing, grinding, leaching, adsorption, elution, detox—run as a fine ore slurry with cyanide. The water load is huge. Across water‑stressed regions, the industry target is to recirculate >80–90% of process water in closed circuits (www.flsmidth.com).

One study put a CIP gold mine’s blue water footprint at ~452 m³ per kg Au, with ~260 m³/kg lost via the tailings pond (www.mdpi.com) (www.mdpi.com). Indonesian rules (UU No.17/2019) explicitly push raw water conservation (merdekacoppergold.com), and operators like PT Merdeka Copper Gold reclaim detoxified cyanide water for reuse once it meets standards (merdekacoppergold.com).

In 2022, Merdeka’s Tujuh Bukit mine recycled ~702 ML (≈7%) of its total water usage from detoxification back to processing (merdekacoppergold.com). The bigger opportunity: capture far more water before it ever hits a dam.

Upgrading a tailings thickener—essentially a large gravity settling tank—raised one gold mine’s underflow from ~35% to 50% solids (w/w), cutting water to tailings by ~46% and enabling ≈80% of process water to be recycled (www.flsmidth.com) (www.flsmidth.com).

Water footprint and context

CIP (carbon‑in‑pulp) uses activated carbon in slurry to adsorb dissolved gold; the slurry water is the lifeblood. A recent footprint analysis quantified the burden: ~452 m³/kg Au blue water footprint with ~260 m³/kg lost in the tailings pond (www.mdpi.com) (www.mdpi.com).

Regulatory direction mirrors the economics: Indonesia’s UU No.17/2019 mandates conservation; Merdeka cites closed‑loop circuits and reuse of detoxified water that meets standards (merdekacoppergold.com) (merdekacoppergold.com).

Tailings thickening as primary lever

Tailings storage facilities hemorrhage water—evaporation and seepage can leave recovery at <50% in arid climates (www.911metallurgist.com). Thickening tails at the plant flips the equation: underflow carries concentrated solids; overflow returns as clarified process water to grinding and leaching.

Modern high‑rate/high‑density and deep‑cone designs, with better feedwells and dilution control, aim for faster settling and higher underflow density. Well‑run CIP thickeners routinely deliver very clear overflow—a few hundred mg/L of suspended solids—and recycle water immediately to the mill.

Underflow density and cyanide retention

Underflow density is the key metric: higher % solids means less water lost. The FLSmidth case saw ~35% → 50% solids, a ~46% cut in water sent to tails and ≈80% recycled water overall (www.flsmidth.com).

Immediate thickening also curbs cyanide degradation. With <3 h retention in a high‑rate thickener, cyanide losses by volatilization/oxidation are “negligible,” unlike long‑detention dams (www.911metallurgist.com). Some operations explicitly target cyanide recovery: at the Cosmo Howley gold mine, tails were maintained at ~800 ppm CN to extract it back into the plant (www.911metallurgist.com).

Chemical flocculation and clarity

Flocculants are high‑molecular‑weight polymers—often polyacrylamide (PAM) or polyacrylate (PAA)—that bind fine particles; coagulants like polyaluminium chloride (PAC) neutralize surface charge to kick‑start aggregation. In practice, the flocculant program, dosed consistently with an accurate dosing pump, determines settling velocity and overflow turbidity.

Bench tests at an Indonesian gold tailings facility (Cibaliung) found that at pH ≈8, adding ~10 mL PAC and 20.5 mL flocculant at 100 ppm concentration (per 1 L slurry) achieved TSS ≈368 ppm in the supernatant (text-id.123dok.com). Lower pH or dosage left dozens to hundreds of ppm more solids suspended.

In an iron‑ore thickener trial, stepping pH from 8.1 to 11.2 and floc feed from 8 to 13 g/t increased underflow density and overflow clarity (www.researchgate.net). Field takeaway: each 1 g/t can move the needle; similar trends are expected in gold tails.

At PT Nusa Halmahera (gold‑Merrill Crowe), a proprietary polymer “Powerfloc” at 45 g/t and 10–15% feed solids delivered the highest settling flux (~1.1–1.2 ton/m²·h), with clear supernatant. Lower doses (15–30 g/t) or silica‑heavy 40% solids feeds slowed settling and raised turbidity (eprints.upnyk.ac.id). The Malaysian study concluded that modest increases in polymer dose (to 45 g/t) were needed to hit ~50% underflow solids and target clarity at those conditions (eprints.upnyk.ac.id).

Hardware and mixing matter too. An FLSmidth upgrade with improved dilution and feedwell design cut polymer consumption by ~40% per tonne of tailings and dropped overflow particulates, enabling 35% less scale inhibitor downstream (www.flsmidth.com) (www.flsmidth.com). Plants often tie such programs to flocculant and PAC coagulant packages and, where scaling risk persists, optimize scale inhibitor dosing alongside thickener improvements.

Return water quality targets

Overflow clarity is not a nicety; it dictates where and how much recycle water can flow. With optimized chemistry, clarified overflow can land in the 100–500 mg/L TSS range (the Cibaliung bench optimum was ≈368 ppm) (text-id.123dok.com). Cleaner water lets operators run recycle rates of 80–90% without upsetting leach kinetics or grinding performance.

In the FLSmidth customer case, a cleaner thickener overflow supported ≈80% recycled water and “minimum” fresh make‑up (www.flsmidth.com).

Local practice and compliance

In Indonesia, closed‑loop water management is now standard practice. Tujuh Bukit supplies from on‑site reservoirs and boreholes and recycles detoxified process water back into grinding and leaching (merdekacoppergold.com). Operators often pump reclaimed thickener overflow to grinding cyclones or leach feed, and regulators require water balance justifications. Guidance (e.g., PCN 2023) encourages thickeners and dry stacking to shrink the dam water inventory.

Measured gains and payback

Upgrading thickening systems commonly delivers 10–20 percentage point increases in underflow solids (e.g., 35% → 50%) and trims raw water draw accordingly (www.flsmidth.com). Plants report 75–90% process water recycled once thickeners are optimized (www.flsmidth.com), versus 30–50% from conventional dams (www.911metallurgist.com).

Case data include a ~46% reduction in water to tails, hundreds of cubic meters per hour less process‑water loss post‑retrofit, and a ~40% reduction in polymer per tonne with improved feedwell/dilution (www.flsmidth.com). Thickening also prevents up to ~90% of cyanide loss that would occur in ponds (www.911metallurgist.com).

Economically, thickener upgrades typically pay back in <1–2 years via water/chemical savings and productivity gains; one source cites payback reduced to 11 months with modern feedwell design (www.911metallurgist.com) (www.flsmidth.com).

Bottom line for CIP circuits

Maximizing tailings thickener performance—hydraulics, underflow density, feedwell mixing—and tuning flocculant/coagulant chemistry are proven levers for water conservation in CIP. The documented outcomes: >80% recycle water, 30–50% reductions in water sent to tails, clarified overflow at a few hundred mg/L TSS, and tangible cuts in polymer and downstream chemicals (www.flsmidth.com) (text-id.123dok.com).

In Indonesia’s framework (UU 17/2019 and related KPIs), these measures align with national sustainability goals and corporate commitments (merdekacoppergold.com) (merdekacoppergold.com).

Sources: Recent peer‑reviewed studies and industry reports on mining water reuse, thickener performance and flocculation (e.g. Arjmand et al. 2019 (www.researchgate.net), Hamraoui et al. 2024 (www.mdpi.com) (www.mdpi.com), FLSmidth data 2023 (www.flsmidth.com) (www.flsmidth.com)), plus Indonesian mining water management documents (merdekacoppergold.com) (text-id.123dok.com), provide the above figures and trends. All data cited are from these sources.