Emulsified Oil in Battery Material Product Liquids: How CDOF Breaks the Film and Holds 3mg/L

Two kinds of oil, two very different problems

Product liquids in battery-material production, nickel sulfate solution, ammonium sulfide solution, sodium sulfate solution, are judged on purity, and oil is the variable that most often spoils it. The oil phase turns up in two forms, and they behave nothing alike. Dispersed oil floats as comparatively large droplets, typically above 10um in diameter, and separates under gravity without much argument. Emulsified oil is the difficult one: droplets far smaller, each wrapped in an interfacial film built from surface-active species. That film stops droplets from coalescing and keeps the whole system stable, which is why conventional physical interception, coalescing filter cartridges included, has essentially no leverage on it.

The traditional combination, coalescing deoiling followed by activated carbon filtration, has sat at 60%~80% efficiency for years. The reason is structural rather than operational. Coalescing media cannot break the film, adsorption and filtration are limited by throughput, and the effluent figure wanders as a result. Cartridges need replacing often, and that replacement cycle is what quietly pushes O&M cost up year after year.

None of this is a criticism of the people running those plants. Coalescing and activated carbon are mature, well understood, and cheap to specify. The difficulty is that they were never designed to attack an interfacial film, and no amount of extra media area or longer contact time changes that. Once the film is understood as the actual target, the design question shifts from how much media to install to how the film gets broken, which is a different problem entirely.

The CDOF chain, step by step

SINOKLE developed the CDOF (Cyclonic Dissolved Ozone Flotation Unit) around a single sequence: break the membrane, capture, then separate. Each step solves a different question, and skipping one breaks the chain.

Step one, make hydroxyl radicals efficiently

The unit drives ozone to hydroxyl radicals through four parallel routes: homogeneous catalysis, heterogeneous catalysis, hydrodynamic cavitation catalysis and pressurised catalysis. Hydroxyl radicals carry an oxidation potential of 2.8V. Ozone utilisation reaches 99.98%, and the dosing ratio is only 1/5~1/2 of what traditional ozone catalytic oxidation needs, so the oxidant bill for the same duty falls sharply rather than marginally.

Step two, oxidative film breaking

At 2.8V the radical attacks and destroys the oil-water interfacial film on the emulsified droplet surface. Once the film is oxidised away the droplet loses its stable form, the armour comes off, and physical separation becomes possible. No demulsifier and no flocculant enters the stream at any point. The process is purely physicochemical and introduces no secondary pollution, which matters when the stream is a product you intend to sell.

Step three, capture and separation

Destabilised droplets meet ultrafine nano-bubbles smaller than 10um across in the cyclonic dissolved-air flotation section. Against conventional micron-sized bubbles these have a larger specific surface area, a longer residence time and a higher collision probability, so capture is more thorough rather than just faster. Loaded bubbles rise to the surface and the oil leaves with them. The unit runs fully enclosed under pressure with an effective residence time under 15 minutes, where traditional processes need at least 90 minutes, so the throughput gain is sixfold or better.

Where CDOF sits against the conventional train

• Principle: ozone multi-path catalytic oxidation plus cyclonic dissolved-air flotation, replacing coalescence separation plus adsorption plus filtration.
• Oil-removal efficiency: 99%min, against 60%~80%.
• Effluent oil content: 3mg/L after CDOF, 1mg/L after the adsorption column, against an unstable and widely fluctuating figure.
• Chemicals: none, versus dosing with secondary-pollution risk.
• Footprint: under 10% of the baseline.
• Operating cost: under 30% of the baseline.
• Automation: fully automatic and unattended, versus manual or semi-automatic operation.
• Hazardous-waste discharge: minimal, versus relatively high.

What the tests actually showed

Nickel sulfate solution, Zhejiang, 2023 pilot

Treatment scale was 24m³/d on a CDOF integrated unit with 300g/h ozone output. Influent oil content ran at or below 30mg/L; CDOF effluent came in at or below 3mg/L; the adsorption column downstream brought it to at or below 1mg/L. TOC moved from 200mg/L at the inlet to 100mg/L after adsorption, and viscosity dropped from 50 to 28. Those numbers cleared what the downstream process demanded, which in the end is the only test that matters.

Ammonium sulfide solution, bench test

Raw-water oil content 400mg/L, ozone dosed at 250mg/L, effluent oil at 125mg/L, a removal rate of 68.75% under bench conditions. Read it honestly. It shows CDOF can work on a high-oil-load ammonium sulfide stream, and it also shows the bench result did not reach 99%. The gap is a dosing and parameter optimisation margin, not a ceiling; engineering scale-up with tuned parameters still has room to close it, and pretending otherwise would be misleading.

Reading the result as a system

A 99%+ oil-removal rate is not one clever component. Radical film-breaking answers whether separation is possible at all. Nano-bubbles answer how clean it can be. The cyclonic flotation section answers how fast. Take any one away and the other two stop mattering. Add 99.98% ozone utilisation, unattended automatic operation and a skid-mounted frame, and CDOF presents a generational option for product-liquid deoiling in new-energy raw materials, along with a path other plants can copy and verify rather than take on faith.