حمض الأوليك المكرر (قاعدة نباتية وحيوانية): عامل السطحي وعامل التعويم
Refined Oleic Acid (Vegetable & Animal Base): Surfactant & Flotation Agent identifies a distilled C18:1 monounsaturated fatty acid stream with CAS registry number 112-80-1 and molecular weight 282.46 g mol−1. The product is obtained by continuous hydrolytic fat splitting of high-oleic vegetable oils—typically high-oleic sunflower, olive, or canola—or rendered animal fats such as beef tallow, followed by vacuum distillation and, where low saturated fatty acid carryover is required, fractional crystallisation. Commercial refined grades are specified by acid value, iodine value, saponification value, titre, and C18:1 purity. These values differ between vegetable and animal sources because of residual saturated fatty acid profile: tallow-derived material retains higher palmitic and stearic acid, while high-oleic vegetable grades contain greater linoleic carryover. Refined oleic acid functions as an anionic surfactant precursor after neutralisation to sodium or potassium oleate and as a direct fatty acid collector in froth flotation of oxidized minerals. Production is typically based on continuous high-pressure fat splitting at 250–260 °C and 50–60 bar, followed by vacuum distillation at 0.5–2.0 kPa with column bottom temperature below 220 °C to limit thermal isomerisation. The refined product is filtered and may be stabilised with tocopherol or citric acid at 50–200 ppm, depending on iodine value and expected storage duration.
Chemical Identity and Source-Dependent Composition Limits
The carboxylic acid content is titrated by ISO 660:2020; commercial refined oleic acid typically shows an acid value of 196–204 mg KOH/g for tallow-derived material and 196–202 mg KOH/g for high-oleic sunflower or canola material. Iodine value by ISO 3961:2018 commonly spans 85–95 g I2/100 g for animal-base refined oleic acid and 90–95 g I2/100 g for high-oleic vegetable material. Saponification value by ISO 3657:2020 is typically 196–206 mg KOH/g. Unsaponifiable matter by ISO 3596:2000 is limited to ≤1.0 % in refined grades, and moisture by ISO 662:2016 is specified below 0.1 % for flotation reagent use. Gas chromatographic profiling under ISO 12966-4:2015 confirms cis-9 C18:1 contents of 75–85 area% in high-oleic vegetable material and 70–80 area% in tallow-derived material. Linoleic acid is commonly 5–12 area% in vegetable grades and 2–6 area% in animal grades. The residual palmitic and stearic acid content explains the titre difference: animal-base refined oleic acid often has titre 3–8 °C, while vegetable-base material with lower saturated acid content has titre 6–12 °C. The distinction is not cosmetic; it controls pumpability, saponification kinetics, and low-temperature dispersibility in unheated reagent preparation lines.
Refined oleic acid for flotation is not a single-molecule product but a specification envelope. Purchasers should request fatty acid profile by ISO 12966-4:2015 rather than relying exclusively on acid value and iodine value, because two lots with identical acid value can differ in C18:1:C18:2 ratio and alter froth drainage rate. Batch-to-batch variance in tallow titre can shift the cloud point of the sodium soap by 4–5 °C, requiring adjustment of saponification water temperature. Vegetable high-oleic material may contain naturally occurring tocopherols at 50–300 mg/kg; these act as antioxidants but can be reduced by bleaching if not specified. The table below provides representative specification ranges used in industrial reagent procurement.
| Parameter | Test method | Refined vegetable base | Refined animal base |
|---|---|---|---|
| Acid value | ISO 660:2020 | 196–202 mg KOH/g | 196–204 mg KOH/g |
| Iodine value | ISO 3961:2018 | 90–95 g I2/100 g | 85–95 g I2/100 g |
| Saponification value | ISO 3657:2020 | 196–205 mg KOH/g | 196–206 mg KOH/g |
| C18:1 cis-9 | ISO 12966-4:2015 | 75–85 area% | 70–80 area% |
| Titre | ISO 935:1988 | 6–12 °C | 3–8 °C |
| Moisture | ISO 662:2016 | ≤0.1 % | ≤0.1 % |
Why Does Alkaline Saponification Govern Surfactant Efficiency?
Refined oleic acid as delivered is a weak acid with aqueous carboxylic acid pKa near 4.8. In mineral flotation and surfactant formulations, the active interfacial species is the carboxylate anion. Neutralisation with sodium hydroxide at pH 9.0–9.5 converts more than 99 % of the acid to sodium oleate; potassium hydroxide is used where lower soap viscosity or higher cloud point is required. The sodium soap has an HLB value near 18, while the protonated acid has HLB below 2. Reported critical micelle concentration for sodium oleate in pure water at 25 °C is approximately 1.0 mmol/L, and it decreases to below 0.2 mmol/L in 0.1 M sodium chloride because counterion binding reduces head-group repulsion. This micellisation behaviour is used to control wetting in mineral conditioning: below CMC, oleate adsorbs onto hydrophobic surfaces; above CMC, excess micelles can strip collector from bubble surfaces and lower froth recovery.
High-shear emulsion preparation in an IKA Magic LAB rotor-stator mixer at 15,000 min−1 or a Silverson batch mixer at 3,000 min−1 is needed when the acid is not fully saponified. The resulting droplet size measured by laser diffraction is typically 10–25 µm D50 at pH 9.5, whereas incomplete neutralisation at pH 7.0 produces coarse globules larger than 100 µm that adhere to pH electrode housings and transfer lines. Plant-scale saponification vessels with pitched-blade turbine impellers at 90–120 min−1 and jacket temperature 70–80 °C maintain conversion; however, over-neutralisation above pH 10.5 increases soap viscosity and can form liquid-crystalline phases, particularly in hard water. The surfactant efficiency of refined oleic acid is therefore not governed solely by C18:1 content but also by the degree of neutralisation, ionic strength, and shear history before the collector contacts the mineral pulp.
In apatite flotation from siliceous ore, refined oleic acid is pre-mixed as a sodium soap and dosed at 0.35–0.70 kg/t of dry feed. Batch selectivity tests are commonly conducted in a 2.5 L Denver D12 flotation cell with impeller speed 1,200 min−1, air flow 4 L/min, and pulp density 25 % solids. Conditioning time of 3–6 min at pH 9.3–9.8 is required for adsorption onto calcium sites on apatite surfaces. Tallow-derived oleic acid generally produces a slightly denser froth and slower flotation rate than high-oleic sunflower material; the difference is attributed to residual saturated C16:0 and C18:0 content, which increases collector film cohesion but reduces low-temperature dispersibility. Production phosphate operations frequently blend the fatty acid collector with fuel oil at a fatty acid-to-oil ratio between 1:1 and 2:1 to extend collector distribution and stiffen the froth. Transfer temperatures are maintained at 40–50 °C for tallow-based material and 20–30 °C for certain vegetable grades to avoid solidification in uninsulated lines.
For fluorspar, sodium oleate additions of 0.15–0.50 kg/t at pH 8.5–9.5 are used with sodium silicate depressant at 0.3–0.8 kg/t to reject quartz and calcite. Hematite flotation with refined tallow oleic acid is typically evaluated at 0.50–1.00 kg/t and pH 9.0–10.0; published data for this specific configuration is limited, and starch depressant at 0.2–0.5 kg/t is required to control quartz recovery. The vegetable-base collector can give slightly higher selectivity against carbonate gangue in fluorspar circuits because the higher linoleic content lowers the melting range and improves dispersion at conditioning temperatures below 20 °C. The following comparative process windows are representative of reported bench-scale flotation evaluations using refined oleic acid collectors.
| Mineral system | pH window | Collector addition | Modifying reagent | Test cell |
|---|---|---|---|---|
| Apatite/silica | 9.3–9.8 | 0.35–0.70 kg/t | Soda ash if hardness >200 mg/L | 2.5 L Denver D12 |
| Fluorspar/calcite/quartz | 8.5–9.5 | 0.15–0.50 kg/t | Sodium silicate 0.3–0.8 kg/t | 1.5 L Agitair |
| Hematite/quartz | 9.0–10.0 | 0.50–1.00 kg/t | Starch 0.2–0.5 kg/t | 2.5 L Denver D12 |
When Hard Water Cations Depress Collector Activity
Hard mill water with calcium hardness above 200 mg/L consumes sodium oleate as precipitated calcium oleate. The precipitated material is visible as white scum in conditioning tanks and causes erratic froth texture. Magnesium hardness at 50–150 mg/L is more damaging because magnesium oleate films are less hydrophobic and more difficult to displace from quartz gangue. Soda ash addition at 0.2–0.7 kg/t or polyphosphate dosing to reduce free calcium below 10 mg/L is effective only if the softening reaction is completed before collector injection. Contact-angle measurements on apatite conditioned with oleate typically exceed 80° at pH 9.5 but can fall below 40° after magnesium interference, indicating loss of collector film integrity. Operators must therefore monitor both total hardness and magnesium fraction, not simply pH, when diagnosing oleate flotation performance.
Hard water also changes soap phase behaviour. In water containing 500 mg/L calcium carbonate equivalent, sodium oleate may form a gel phase above 25 °C, blocking collector feed lines and rotameter tubes. Online turbidity meters below 20 NTU after the softening step are used to prevent gel carryover. For fluorspar circuits, sodium silicate depressant must be added before oleate collector; reversed addition sequences can suppress recovery by 5–15 percentage points in bench flotation because silicate anions compete with oleate for surface sites. This sequence sensitivity is a frequent plant-scale failure mode during reagent line changeovers. Selectivity against silica gangue depends on maintaining pH above 9.0; at pH 8.0 the protonated form adsorbs more indiscriminately and may increase silica recovery. Sodium silicate at 0.4–0.6 kg/t is the standard depressant in fluorspar circuits, while dextrin at 0.1–0.3 kg/t can depress carbonates but may also reduce oleate adsorption on target minerals.
Storage, Transfer, and Formulation Compatibility Boundaries
Refined oleic acid with iodine value 90–95 g I2/100 g is susceptible to oxidative rancidity; storage in nitrogen-blanketed 316L stainless steel tanks at 20–30 °C is standard for vegetable-base material. Animal-base material with titre 3–8 °C is held at 35–45 °C to maintain pumpability, but heater surfaces should not exceed 60 °C because thermal degradation increases peroxide value and darkens the product. Peroxide value measured by ISO 3960:2017 should remain below 5 meq O2/kg. Unlined mild steel and copper-alloy transfer systems are incompatible: dissolved iron and copper catalyse autoxidation and can produce metal soaps with reduced flotation activity. All transfer lines should be stainless steel or plastic-lined, and pumps should use mechanical seals rated for weak organic acids. Repeated heating and cooling cycles should be avoided because thermal cycling can condense moisture in headspaces and raise free water content above the 0.1 % specification limit.
Saponification is exothermic. Sodium hydroxide at 50 % concentration should be metered under controlled cooling so the reaction mass remains below 85 °C. The resulting soap solution at pH 10.0–10.5 is stable for 24–48 h under continuous slow agitation; storage beyond 72 h can develop rancid off-odour and viscosity drift. Oleic acid should not be blended with primary amine collectors in the same mix tank because fatty acid-amine complexes precipitate at pH 7–9 and blind in-line screens. Reagent day tanks should be flushed with softened water after each campaign to remove calcium oleate scale. At production scale, transfer lines from the saponification vessel to the flotation conditioning tank should be heat-traced only when animal-base material is used; vegetable-base soap can remain pumpable without trace heating if ambient temperature is above 20 °C and excess water is controlled.
