The quiet efficiency play in copper and gold: chemical aids that let mills run denser, cheaper

In mineral processing, the biggest energy lever often hides in plain sight: the pulp itself. Grinding circuits alone can use 40–60% of a plant’s electricity (www.mdpi.com), and comminution (crushing plus grinding) accounts for roughly 4% of global electrical energy (pmc.ncbi.nlm.nih.gov).

That’s why operators are zeroing in on slurry rheology—how pulp flows under stress. Lower its apparent viscosity (flow resistance) and yield stress (stress needed to start flow), and mills can carry more solids with less drag, cutting specific energy and increasing fines production. Reviews tie pulp rheology directly to mill power draw and breakage rates (www.researchgate.net; www.mdpi.com), and show that high yield stress means more power is needed and fewer fines are produced (www.mdpi.com; www.mdpi.com).

The pitch from chemical suppliers is straightforward: add small doses of dispersants and deflocculants to neutralize surface charges, stop fines from clumping, and let the mill run a denser, freer‑flowing pulp. As one review puts it, such agents “promote grinding efficiency, decrease water consumption, optimize material mobility, and narrow the product size distribution” (www.mdpi.com).

Grinding aids: mechanism and dosage

Chemical grinding aids (GAs) are specialty reagents added at typically ≤0.25% of ore mass to improve grindability and reduce energy use (pmc.ncbi.nlm.nih.gov). Common examples include organic molecules such as alcohols, glycols, and amines (e.g., triethanolamine or propylene glycol) or polymeric dispersants (pmc.ncbi.nlm.nih.gov; www.nbmcw.com).

These molecules adsorb at newly created mineral surfaces, neutralizing surface charges and imparting steric/electrostatic repulsion to prevent agglomeration on grinding media and mill liners (www.nbmcw.com; www.mdpi.com). In practice, GAs are reported to “promote grinding efficiency, decrease water consumption, optimize material mobility, and narrow the product size distribution” (www.mdpi.com; www.mdpi.com).

Case data underscore the point. In laboratory tests on a magnetite ore, a polysaccharide‑based GA at 0.1 wt% cut energy use and delivered a finer grind: the work index dropped ~31% (from 18.0 to 12.4 kWh/t, where kWh/t is kilowatt‑hours per tonne), with a narrower P80 (the 80% passing size) and higher surface area (pmc.ncbi.nlm.nih.gov). Reviews conclude grinding aids can reduce mill energy by 10–30% or more under the right conditions (pmc.ncbi.nlm.nih.gov; www.mdpi.com).

Even as interest rises, adoption in mining has lagged the cement sector. Challenges include reagent cost, limited knowledge of ore‑specific effects, and concerns about downstream impacts; one review notes the “high cost of GAs” and potential contamination of products affecting flotation or leaching, plus the risk that high‑charge amines (e.g., TEPA) can generate ammonia/nitrate on wear (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov). These are specialty chemicals; in mining, they sit within the broader portfolio of chemicals for mining applications.

Rheology modifiers and high‑solids operation

Beyond GAs, rheology modifiers (dispersants and deflocculants) target viscosity and yield stress directly. These include inorganic salts or pH adjusters, polymeric dispersants, surfactants, or even nanoparticles (www.mdpi.com; www.mdpi.com). In clay‑rich or ultrafine slurries (common with gold and copper), platey minerals like kaolinite and montmorillonite form gel‑like networks that spike viscosity; rheology modifiers break up these networks via electrostatic/steric effects, allowing flow at much higher solids (www.mdpi.com; www.mdpi.com).

The behavioral shift matters: a slurry can move from Bingham‑like (with a notable yield stress) to pseudo‑plastic (shear‑thinning) with the right dispersant dose. Raising solid fraction generally helps grinding—up to a point. Past about 70–75% solids by weight, viscosity climbs exponentially; one study noted proportional increases with solids and “sharply” higher viscosity beyond 75% (www.mdpi.com). A grinding model found that lowering a mill’s solids from an inefficient 83% to ~76–80% actually increased throughput by ~10% (www.mdpi.com).

In practice, a well‑dispersed slurry may allow a mill to operate a few percentage points higher solids (e.g., from 70% to 75%), reducing water load and energy per tonne. Lower viscosity also reduces power draw for slurry pumps and decreases liner wear. Reviews emphasize that in stirred mills, higher yield stress means energy consumption rises, breakage rates decrease, and fine production declines (www.mdpi.com).

Flotation and circuit‑wide effects

The viscosity story continues into flotation. Analyses show a 5% increase in apparent viscosity doubles viscous dissipation (more energy lost from particles) and cuts efficient particle–bubble collision probability by ~12% (www.mdpi.com). Small changes can have big money implications: a separate plant trial at Ernest Henry using high‑chrome media (not a chemical additive) delivered a 2% increase in Cu recovery on a copper‑gold ore—≈US$18.7 million per year at then‑current prices (www.ceecthefuture.org).

The broader context is unforgiving. With ore grades declining, plants process more ultrafines and clays—making rheology increasingly critical (www.mdpi.com). Regulatory shifts—such as Indonesia’s new mining law requiring more domestic processing (www.reuters.com)—only raise the stakes. Reviews in Minerals call slurry rheology a “primary parameter” for optimizing mill power draw and fine production (www.mdpi.com).

Plant trial protocol (metallurgy guide)

Baseline characterization: establish current performance without additive. Document ore feed (grade, mineralogy), mill throughput, power draw (kW), pulp density (% solids), product PSD (P80), circulating load, and slurry rheology (viscosity/yield stress) under stable conditions (consistent feed, liner wear state). Collect several shifts of data for variability.

Laboratory screening: run batch/continuous tests with the ore and candidate additive. Measure Bond Work Index with and without reagent; use lab or stirred mills to assess energy versus grind fineness. Rheology tests (viscometer/rheometer) should show how the additive shifts viscosity or yield stress curves. Use this to select doses (e.g., 0.02–0.10% by weight) that deliver clear viscosity reductions or grind improvements.

Trial design: plan alternating blocks—Additive ON vs OFF—to average out drift. For example, run the mill at 100% solids and fixed feed rate first without additive for X hours, then introduce the additive at a target dosage (e.g., 200–300 g/t). Allow time to reach steady state (typically several hours), then record data for another X hours. Repeat the cycle; paper‑blinding can reduce operator bias.

Data collection: continuously log mill feed and product tonnage, motor power, slurry pump pressure/flow, and cyclone pressure. Sample pulp periodically for % solids and rheology. After each segment, analyze PSD (P80 and coarse tail) and metallurgical performance downstream (flotation or leach). Note operational issues (foaming, scaling, froth changes).

Analysis: compare average ON vs OFF results. Primary KPIs are specific energy (kWh/t), throughput (t/h at the same mill load), and grind size. The magnetite example showed −5.6 kWh/t (31%) energy use at 0.1 wt% additive (18.0 to 12.4 kWh/t), with a narrower size distribution (pmc.ncbi.nlm.nih.gov). Apply statistical tests (e.g., t‑tests) to ensure differences exceed normal variability.

Scaling solids: if viscosity drops, step up mill solids to find a new optimum. Even a 3–5% increase (e.g., from 70% to 73%) can deliver water and energy savings. Monitor mill filling and transport line pressures to maintain circulation.

Safety and compliance: ensure the additive meets environmental and safety rules. In Indonesia, for example, any new chemical must meet Ministry of Environment discharge limits; review how the additive degrades or accumulates. If necessary, install monitoring (e.g., COD/TDS in tailings). Consider dose control hardware—sites commonly meter reagents using a dedicated dosing pump—and check material compatibility.

Reporting and economics: quantify net benefits. Calculate annual energy savings (kWh/t saved × annual throughput) and any increase in metal production, then convert to dollar value. The Ernest Henry media trial’s 2% Cu recovery gain equated to ≈US$18.7 million per year (www.ceecthefuture.org). Account for additive cost (grams per tonne) and any water savings from higher density.

Key references: Minerals reviews emphasize that “adjusting the rheological behavior of the pulp shows high application value in grinding energy saving” (www.mdpi.com), and that GAs improve flowability and fine generation (www.mdpi.com; www.mdpi.com). Plant trials should aim to confirm these under site conditions.

Measured outcomes and the bottom line

Across studies, rheology control and grinding aids deliver measurable effects: energy down 10–30%, narrower product size distributions, and higher throughput when solids are optimized (pmc.ncbi.nlm.nih.gov; www.mdpi.com). The magnetite case’s 31% drop in work index at 0.1 wt% additive is a stark example (pmc.ncbi.nlm.nih.gov). Modeling shows that dialing solids from 83% to ~76–80% can lift capacity ~10% (www.mdpi.com). In flotation, a 5% viscosity rise can halve collision efficiency’s odds by ~12% through viscous dissipation (www.mdpi.com).

Conclusion and sources

In gold and copper grinding circuits, chemical aids and rheology modifiers offer a data‑backed route to efficiency. By lowering slurry viscosity or yield stress, these additives enable higher solids, higher throughput, and lower kWh/t—backed by empirical reports such as a 31% energy cut at 0.1 wt% additive (18.0 to 12.4 kWh/t) (pmc.ncbi.nlm.nih.gov). A well‑designed plant trial—with controlled conditions, careful logging, and baseline comparison—can quantify site‑specific benefits. When successful, the gains in energy cost, mill throughput, and metal recovery can each justify the reagent expense.

Sources: peer‑reviewed articles and industry reports, including Minerals reviews and Scientific Reports (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov; www.mdpi.com). The Ernest Henry protocol highlights the value of rigorous trials (www.ceecthefuture.org). Indonesian mining news (Reuters) signals the trend toward enhanced processing and regulation (www.reuters.com).