Grinding aids and rheology modifiers are letting sticky nickel ores run at higher % solids — and that is translating into lower kWh per ton, less water, and finer product, according to lab, pilot, and simulation data.
Industry: Nickel_Mining | Process: Ore_Crushing_&_Grinding
Comminution — the industry term for crushing and grinding — is the hungriest unit operation in mineral processing, often 40–50% of a mine’s energy use (mining.com; ceecthefuture.org). A Metso‑sponsored industry summary pegs comminution at ~53% of mine energy and ~10% of production cost (mining.com), underscoring why even small efficiency gains matter.
Nickel plants — especially Ni‑laterites rich in clays — face another drag: high slurry viscosity. Serpentinite‑type nickel ores often must be ground at less than 10% solids because higher densities dramatically raise viscosity, a practice that drives water use and trommel‑power penalties (patents.justia.com).
A growing body of evidence says a small dose of chemistry can flip that script. Grinding aids (low‑dosage dispersants/surfactants added in the mill) and rheology modifiers (polymers, surfactants, or dispersants added to the slurry) adsorb on fine particles, reduce inter‑particle attraction (“halo”), prevent clay‑fine gelation, and lower the apparent viscosity or yield stress (the minimum stress needed to make a slurry flow). With viscosity down, plants can push to higher solids content — more rock per unit energy.
Slurry rheology and particle dispersion
Bench and mill tests have long shown that a more dispersed, lower‑viscosity slurry grinds faster. The classic metallurgist Klimpel (1978–82) noted that as solids content (“particle packing” by mass) increases, the grinding rate increases — provided the slurry viscosity does not become too high (911metallurgist.com). In practice, an additive shifts the viscosity curve so mills can run thicker pulps before hitting the rheology wall.
Laboratory work confirms that surfactant or polymer dispersants prevent fine‑particle flocculation, trim yield stress, and cut the energy needed to flow or grind the slurry (911metallurgist.com; mdpi.com). Plants typically source these as dispersants under programs that, in cooling‑water parlance, would sit alongside dispersant chemicals designed to prevent particle agglomeration and reduce fouling.
Evidence from labs, mills, and simulations
One tin‑polymetallic test is illustrative: adding a 0.2–0.4% polyacrylamide (PAM) grinding aid at 65% solids shifted the product distribution by several percent — one chemistry increased the 0.2–0.038 mm fraction by ~5% and cut the coarse (>0.2 mm) fraction by 4–9% — with no change in mill power or filling (mdpi.com; mdpi.com). The mechanism: chemistry‑mediated rheology control, not more horsepower.
Lower viscosity lets coarse mills run at higher % solids (less water), often producing a coarser cyclone feed that boosts throughput and lowers specific energy. Models show grinding performance improving into the mid‑70% solids; one iron‑ore mill simulation found optimal specific energy at 76–80% solids (42–48% by volume) (mdpi.com). Each percent increase in solids lets the mill process more rock at the same power. Conversely, reducing solids (more water) raises kWh/t sharply at fixed mill power (mdpi.com). In practical terms, raising a mill from, say, 60% to 70% solids often translates to 5–10% lower kWh/t output.
Industry and academic reports echo the theme: additives in mills “promote grinding efficiency” and “decrease water consumption” by “optimizing material mobility” (mdpi.com). In cement, triethanolamine‑based aids routinely reduce specific energy by several percent; in minerals, 10–15% energy savings is often cited for effective aid programs (researchgate.net). Coarse‑ore case studies (e.g. of iron ore pellets) and grinding simulations indicate similar gains apply in mining. For nickel plants specifically, additives that cut viscosity enable raising solids well above typical 50–60% levels. In some lab studies, rheological additives have cut slurry yield stress by tens of percent, letting solids climb by 5–10 points. Even a +5% solids increase can deliver roughly a 5% drop in mill power/ton (when mill draw stays constant). Qualitatively, this aligns with industry reports: because comminution can be ~10% of production cost (mining.com), even a few‑percent grind‑efficiency gain saves large energy bills.
Suppliers position these chemistries as part of mining reagent portfolios; grinding‑aid candidates often sit alongside chemicals for mining applications that target throughput and water reduction.
Plant trial protocol for metallurgists
Baseline characterization: run the mill under normal conditions for 24–48 hours and record ore feed rate, grind size (P80, the size at which 80% of product passes), mill power draw (kW), circulating load, current slurry % solids by mass, and viscosity/yield‑stress. Measure slurry rheology on‑site with a field viscometer or lab rheometer on grab samples at a defined shear rate — often ~100 s⁻¹ — and fit to a Bingham or Casson model (rheological models that relate shear stress to shear rate) to establish a baseline flow curve.
Laboratory screening (optional but recommended): in parallel, run “spin tests” or small ball‑mill trials per Klimpel (911metallurgist.com) to screen candidate additives and dosages. Dose each candidate into a slurry at target solids and measure viscosity/yield‑stress; identify dosages that deliver, say, 20–50% reduction in yield‑stress or viscosity, or a clear downward curve. Then use a bench‑scale mill to confirm faster grind (e.g., more fines in a fixed time) without over‑flocculation.
Stepwise dosing and controls in the mill
Inject the chosen additive into the grinding circuit — commonly ahead of the ball‑mill feed or directly into the mill slurry — starting at a low dose and stepping up gradually. Isolate variables: hold ore feed rate and liner/ball charge constant, and run long enough at each step (several hours to a day) to reach steady‑state. Continuously log the same metrics as baseline: mill motor amps/power, pulp density, cyclone feed size, energy per ton, and chemical consumption (kg/t ore). Plants typically meter these reagents with an accurate dosing pump to maintain steady dose control.
Rheology checks and solids increase
Periodically sample the slurry and measure rheology live during the trial. Verify that increasing dose shifts the viscosity curve downward (lower flow resistance). Use that headroom to raise the feed‑solids set‑point by adding more ore or trimming water until reaching a constraint (constant pressure/power) or loss of efficiency. Compare the maximum stable % solids versus baseline.
Performance comparison and control lines
Quantify changes: compute specific energy (kWh/t) before/after and track product size distribution, including P80 and oversize. A worthwhile result might be a 5–10% drop in kWh/t or an equivalent throughput increase at constant power. Where possible, run a “wash vs no‑additive” split test by alternately applying the additive and then stopping it, or use a parallel identical line as a control, to control for ore variability.
Downstream impacts and compliance
Document side‑effects beyond energy and grind. Check that the additive does not upset downstream flotation or thickening; monitor float recovery or froth rheology, since some additives can carry over. Verify environmental compliance, handle per MSDS, and confirm plant wastewater remains within permit. Many operators fold reagent stewardship into broader chemical programs already covering mining, water, and wastewater.
Economics and decision criteria
From trial data, compute average energy savings, solids increases, or throughput gains with standard statistics. For example, if baseline mill draw was 100 kWh/t and it dropped to 90 kWh/t after additive (at the same solids), that is a 10% energy saving. Similarly, if the mill can run 5% higher in solids while meeting size control, record the denser slurry and estimate volumetric throughput gain. A successful trial justifies full‑scale adoption when it shows measurable gains (e.g., X% lower kWh/t or Y% higher throughput) at acceptable reagent cost and no downstream penalty.
Bottom line and sources
Chemical grinding aids and rheology modifiers disperse fines and lower pulp viscosity, allowing mills to run higher slurry densities and do more grinding per unit energy. Studies consistently show such additives can cut water use and energy demand — often single‑digit percentage improvements — while improving product size distribution (mdpi.com; mdpi.com). In nickel comminution, where sticky clays force very dilute grinding, these additives may enable raising solids by 10–30 points. The reading list spans Zeng et al. (2023) on slurry rheology in grinding (mdpi.com), Faria et al. (2019) on mill energy (mdpi.com), Klimpel’s classic work on chemical grinding aids (911metallurgist.com), and industry energy surveys (mining.com; ceecthefuture.org), plus a patent on Ni‑serpentinite slurry behavior (patents.justia.com). All citations are given inline for the data points above.
