Hydrodynamic cavitation in mineral processing

What cavitation does in a mineral pulp

In the studies, a cavitating device did three jobs: it made very small bubbles inside the pulp, it acted mechanically on particle surfaces, and it intensified contact between gas, liquid and solids in leaching. The Venturi tube is the device most used in flotation Zhou et al., 2018. How cavitation forms is covered in What hydrodynamic cavitation is.

Bubble size is the reason. Flotation recovers particles efficiently only in a window of roughly 10–100 µm. Fine particles are lost mainly because they rarely collide with a bubble, coarse particles mainly because they detach, and a review of bubble size in flotation found smaller bubbles the most effective way to address both Tao, 2005.

A 2026 critical review of cavitation in metal recovery judged it most credible as "a targeted module applied to a verified process limitation." It cautioned that a result cannot be credited to cavitation from the device's name alone, because pumping, mixing, heating, gas injection and chemical additives can act at the same time Albanese, 2026.

Cavitation-made bubbles in fine-particle flotation

Cavitation bubbles formed preferentially on hydrophobic particles. In microflotation of scheelite finer than 10 µm, hydrophobized particles acted as nuclei for cavitation, while hydrophilic particles had little effect. Bubbles then formed directly on the mineral surface, because the work of adhesion between solid and water is lower than the cohesion of water Zhou et al., 2018.

Where cavitation happened mattered. Cavitating the whole pulp improved scheelite recovery more than cavitating only the reagent solution. Bubbles attached to the particles lowered their surface charge, so they repelled each other less and aggregated more Zhou et al., 2018. How attached nanobubbles speed up bubble–particle attachment, and the gains reported by mineral, are covered in Nanobubble-enhanced flotation.

Picobubble and column flotation

Coal researchers call the sub-micron bubbles made by cavitation "picobubbles." In a laboratory column 2 inches across, picobubbles generated on the hydrodynamic cavitation principle were mostly smaller than 1 µm and attached preferentially to hydrophobic surfaces. With a West Virginia coal, they raised fine-coal recovery by 10–30%, depending on feed rate and collector dosage, and acted as a secondary collector that cut collector dosage by one-third to one-half Tao et al., 2006.

In a 5 cm column, picobubbles raised combustible recovery by up to 10% for a highly floatable coal and by up to 40% for a poorly floatable one Tao et al., 2008. Another design combined a cavitation Venturi tube with a static mixer in a column 5.08 cm across and 162 cm tall. From a feed at 29.6% ash, it recovered 85–90% of the combustible material at 10–11% ash, with much less frother and collector than conventional column flotation Peng & Yu, 2015. All three are laboratory columns about 5 cm in diameter.

Conditioning or separation: where to cavitate

In 1 L laboratory flotation of coal, slurry was pumped through a Venturi tube at different stages Han et al., 2020:

• Both stages. Cavitation during conditioning and separation raised combustible recovery by about 6%; either stage alone gave about 3%. The flotation rate constant rose from 1.65 to 2.21.
• Time. Cavitation shortened conditioning, but longer cavitation did not keep improving results.
• Breakage. After 6 min, the +0.25 mm fraction fell from 24.99% to 20.65% of the sample; the authors reported that cavitation liberated coarse coal from gangue.
• A trade-off. Cavitation during separation alone lowered the hydrophobicity of the concentrate.

The critical review adds that excessive shear can break aggregates or destabilize froth, so there is an operating window rather than a gain that grows with intensity Albanese, 2026.

Surface cleaning: clay slimes and coatings

Clay slimes can coat coal and depress its flotation. In a laboratory study, nanobubble water was made with a micro-nanobubble nozzle working on the hydrodynamic cavitation principle, at 0.2 MPa and 18 L/min. With 25% kaolinite in the feed, combustible recovery fell from 73.68% to 60.07% in deionized water, a drop of 13.61 points, but from 79.51% to 70.91% in nanobubble water, a drop of 8.60 points Li et al., 2020.

The authors linked the smaller loss to kaolinite platelets aggregating with one another, which left fewer free particles to coat the coal. The same group had earlier found that nanobubbles increased kaolinite entrainment into the froth, so clay behavior needs watching in both directions Li et al., 2020.

A 2025 laboratory study examined the removal of clay coatings from coal surfaces by cavitation-generated nanobubbles Qiao et al., 2025. This lesson does not report its results, because they could not be checked against an accessible abstract.

Leaching: early and indirect evidence

Evidence for cavitation in leaching is thin, and in each case cavitation acted together with other effects.

• Gold. The Jetleach reactor impacts two pulp streams against each other. On a flotation concentrate from an operating South African gold-tailings plant, it raised gold recovery by almost 10% while cutting cyanide use by almost 8% and oxygen use by 50%. The authors "surmised" that micro-cavitation improved mass transfer Mbayo et al., 2022. The critical review reported gains of about 8–15 percentage points across Jetleach studies, but found no non-cavitating impinging-jet control, so the gain cannot be credited to cavity collapse alone Albanese, 2026.
• Tungsten. In a 220 mL laboratory reactor, cavitation started at an orifice and the bubbles were collapsed by ultrasound. Leaching scheelite in 10 mol/L sodium hydroxide at 40–80 °C, the hybrid reached 71.5% recovery of tungsten oxide (WO₃), against 36.7% without ultrasound, with 130 kWh of acoustic energy per kilogram of concentrate Johansson et al., 2021. The hydrodynamic contribution in that reactor cannot be isolated Albanese, 2026.
• Uranium. The review reported that cavitation-assisted nitric acid leaching of a slag raised recovery from about 72–78% to 84–87%. The gain was larger for coarse or poorly liberated material and shrank after fine grinding Albanese, 2026.

Heaps are a harder fit, because the ore cannot pass through the cavitation zone Albanese, 2026. Dissolved oxygen in bioleaching and ozone bubbles in oxidative leaching are covered in Leaching and tailings.