| HS Code | 249631 |
| Product Name | Sodium Ferrocyanide |
| Chemical Name | Sodium hexacyanoferrate(II) |
| Synonyms | Sodium ferrocyanide; Tetrasodium hexacyanoferrate; Yellow prussiate of soda; E535 |
| Chemical Formula | Na4Fe(CN)6 |
| Cas Number | 13601-19-9 (anhydrous); 14434-22-1 (decahydrate) |
| Ec Number | 237-081-9 |
| E Number | E535 |
| Molecular Weight | 303.91 g/mol (anhydrous); 484.06 g/mol (decahydrate) |
| Appearance | Pale yellow crystalline solid or powder |
| Physical State | Solid |
| Odor | Odorless |
| Solubility In Water | Soluble |
| Solubility In Organic Solvents | Insoluble in ethanol |
| Density | 1.458 g/cm3 (decahydrate) |
| Melting Point | Decomposes; loses water at about 81.5°C (decahydrate) |
| Ph | Neutral to slightly alkaline in aqueous solution |
| Purity | Typically ≥98% |
| Grade | Technical, food, and photographic grades available |
| Storage | Store in a cool, dry, well-ventilated area away from acids |
As an accredited Sodium Ferrocyanide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium Ferrocyanide is packaged in 25 kg polyethylene-lined, moisture-resistant fiber drums with sealed lids and clear regulatory labels. |
| Container Loading (20′ FCL) | Container Loading (20′ FCL): Sodium Ferrocyanide loaded in 20-foot FCL, palletized bags/drums, secured, sealed, shipped as non-hazardous chemical cargo. |
| Shipping | Sodium ferrocyanide is not classified as dangerous goods for transport under DOT, IATA, or IMDG. Ship in sealed, labeled containers away from acids, moisture, and oxidizers. No UN number, hazard class, or packing group is assigned. Follow applicable local, national, and international regulations. |
| Storage | Store sodium ferrocyanide in a cool, dry, well-ventilated area in tightly closed, labeled containers. Keep away from strong acids, oxidizers, and moisture to prevent decomposition and possible hydrogen cyanide release. Avoid dust generation; use appropriate PPE. Separate from incompatible materials and foodstuffs. Ensure secondary containment and follow local regulations. Protect from sunlight and elevated temperatures. Maintain inventory records. |
| Shelf Life | Sodium ferrocyanide is stable; stored sealed in a cool, dry place, it has an indefinite shelf life. |
On continuous vacuum salt crystalliser lines, sodium ferrocyanide decahydrate is injected as a filtered aqueous solution. The injection point is between the pusher centrifuge discharge and the fluidised-bed dryer inlet. The dosing rate is maintained between 5 mg/kg and 15 mg/kg of dry sodium chloride. The European Union maximum for food-grade salt is fixed at 20 mg/kg calculated as anhydrous Na₄[Fe(CN)₆] under Regulation (EC) No 1333/2008 Annex II category 12.1.1. At these levels the hexacyanoferrate ion adsorbs selectively on the {100} cleavage planes of sodium chloride. This adsorption blocks the formation of intercrystalline salt bridges during final drying at 120 °C to 160 °C bed temperature. The dried salt is screened through ISO 3310-1 test sieves. A mean particle size shift above 400 µm generally requires dose reduction because the available crystal surface area falls. Terminal products include free-flowing table salt, low-sodium salt substitutes, and dry seasoning bases. For export documentation the FCC monograph for sodium ferrocyanide decahydrate is the principal purity reference. Release laboratories measure residual free cyanide and water-insoluble matter for each production batch. Warehouses with relative humidity above 60% require polyethylene-lined multiwall packaging with moisture vapour transmission below 5 g/m²·24 h. This packaging maintains free-flow character through declared shelf life. The combination of potassium iodate and ferrocyanide in iodised salt is not fully described in public supplier data. Published data for this specific configuration is limited.
Addition of sodium ferrocyanide to highway de-icing salt is performed on bulk rock salt after coarse dry screening. The additive is applied either by spraying a 5% to 10% aqueous solution onto the salt surface or by metering dry decahydrate crystals into a rotary drum conditioner. Typical dosage for winter maintenance salt ranges from 60 mg/kg to 125 mg/kg of sodium chloride. Final product gradation is verified against AASHTO M 143 sieve limits, and sodium chloride content is measured per ASTM D632. The additive functions only when residual surface moisture is below 0.25% by weight. Above this threshold dissolved ferrocyanide recrystallises during stockpile settling and contributes to crust formation instead of preventing it. Treated salt is discharged into covered salt domes at angles of repose between 32° and 38°. Bridging in conveyor transfer chutes is reduced by maintaining discharge belt speed below 2.5 m/s. Terminal product is specification-grade highway rock salt for pre-wet spreading and direct dry application. At salt shed temperatures below −20 °C, caking tendency declines because brine films freeze and crystal bridge growth stops. The higher ferrocyanide dose is therefore reserved for transitional freeze-thaw cycles. Published data for this specific configuration is limited where quarried rock salt contains chloride-based impurities above 2%.
When sodium ferrocyanide is used in pigment reactors, the decahydrate is dissolved in demineralised water at 40 °C to 60 °C. The solution is then reacted with ferrous sulfate heptahydrate in a baffled stirred vessel. The primary molar ratio is 1 mol ferrocyanide to 2 mol Fe(II), producing a pale white ferrous ferrocyanide intermediate. The intermediate is oxidised with sodium chlorate or air in the presence of sulfuric acid. Oxidation is held at pH 1.5–2.5 and temperature 85–95 °C. This step determines the particle size and tint strength of the resulting C.I. Pigment Blue 27. The oxidised slurry is washed through filter presses until filtrate conductivity falls below 1,000 µS/cm. It is then dried in belt or spray dryers at inlet air below 180 °C. Terminal products include offset printing inks, solvent-borne and water-borne decorative coatings, paper coatings, and masterbatch concentrates. Compliance for pigment use is governed by REACH registration for the substance and by the Colour Index classification C.I. 77510. Finished pigment batches are tested for matter volatile at 105 °C and sieve residue at 45 µm according to ISO 787-2 and ISO 787-7. The processing window is narrow because over-oxidation at pH above 3 shifts the shade toward greenish blue and increases coarse aggregate formation.
For potassium ferrocyanide production, sodium ferrocyanide decahydrate is dissolved in recycled mother liquor at 70 °C. It is reacted with potassium chloride at a chloride-to-ferrocyanide molar ratio of 4.05:1 in a continuous draft-tube-baffle crystalliser. Potassium ferrocyanide trihydrate precipitates selectively. The crystal slurry is centrifuged, washed with chilled demineralised water, and dried at 50–60 °C to restrict loss of crystallisation water. Terminal material is potassium ferrocyanide trihydrate intended for food additive E536 in salt and for metal finishing bath make-up. Compliance for the food-grade derivative follows Regulation (EC) No 1333/2008 and the FCC. The sodium salt feedstock is specified by assay, cyanide impurity profile, and water content. The main processing bottleneck is mother liquor accumulation of sodium chloride. Operators purge a bleed stream when sodium chloride concentration exceeds 300 g/L to prevent co-precipitation on cooling surfaces.
Copper hexacyanoferrate granular sorbents are prepared by displacing sodium from sodium ferrocyanide with a soluble copper nitrate stream. The precipitation occurs in a continuous loop fitted with an in-line high-shear rotor-stator mixer. The feed ferrocyanide concentration is held at 0.05 mol/L to 0.2 mol/L. The copper-to-ferrocyanide molar ratio is maintained at 2.1:1 to produce a flowable slurry. The precipitate is agglomerated on open-cell polyurethane foam or silica gel carrier particles. It is cured at 60 °C for 24 h. The resulting sorbent is used for selective removal of Cs-137 from alkaline nuclear wastewater streams and for analytical preconcentration of cesium in environmental samples. Operational boundaries include pH 3–11 for continuous column loading, with column bed volumes of 50–100 per cycle depending on competitor sodium and potassium concentration. International validation for radiochemical separations is expressed through IAEA proficiency-test methods and analytical quality assurance programmes. Published data for this specific configuration is limited when treating high-organic decommissioning wastes.
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Sodium ferrocyanide, CAS 13601-19-9, is the decahydrate of tetrasodium hexacyanidoferrate(II), Na₄[Fe(CN)₆]·10H₂O. The anhydrous form has the formula Na₄[Fe(CN)₆] and a molar mass of 303.91 g/mol; the commercial decahydrate has a molar mass of 484.06 g/mol and contains 37.22% w/w water of crystallization. The product appears as pale yellow to yellow crystals or crystalline aggregates, is readily soluble in water, and is practically insoluble in ethanol. Industrial supply is separated into food-grade material meeting Food Chemicals Codex criteria, technical-grade material used in pigment synthesis and metal treatment, and analytical reagent grade used for iron detection. The iron centre is in the +2 oxidation state, coordinated by six cyanide ligands. The [Fe(CN)₆]⁴⁻ complex is stable in neutral and alkaline media, but prolonged contact with strong mineral acids at elevated temperature can liberate hydrogen cyanide.
The food-grade product is designated E 535 in European Union additive law and is covered under Regulation (EC) No 1333/2008. In sodium chloride and salt substitutes, the maximum permitted level is 20 mg/kg, singly or in combination with potassium ferrocyanide and calcium ferrocyanide, expressed as anhydrous potassium ferrocyanide. The EFSA Panel on Food Additives and Nutrient Sources added to Food established a group acceptable daily intake of 0.03 mg/kg body weight per day for ferrocyanides expressed as ferrocyanide ion in its 2018 re-evaluation. At the permitted dose, the additive adsorbs onto the crystal faces of sodium chloride during brine evaporation or recrystallisation, modifying crystal habit and reducing solid-bridge formation between adjacent crystals.
Anti-caking performance is conditional on moisture control in the salt. Vacuum salt operations typically target final free-moisture values below 0.10% w/w before the additive is introduced as a dilute aqueous solution into the brine stream, because dry blending at low addition levels produces concentration heterogeneity. Salt with a mean particle diameter in the range 0.45–1.0 mm and storage at relative humidity below 75% shows measurable caking reduction at the regulated dose; published data for specific plant configurations is limited to equipment-vendor studies and internal process records. The operational boundary is pH. At pH below 4, the ferrocyanide complex may dissociate and release free cyanide species; food-grade salt processes therefore maintain brine pH above 6.5 from the addition point until crystalliser discharge. The Food Chemicals Codex monograph establishes the assay on the anhydrous basis, and commercial food-grade certificates of analysis typically report assay not less than 99.0%.
In pigment manufacturing, sodium ferrocyanide is metered as an aqueous solution into a glass-lined or 316L stainless steel precipitation vessel containing an iron(III) salt. The reaction produces iron(III) hexacyanoferrate(II), CI Pigment Blue 27, CAS 14038-43-8. The precipitation is typically run at pH 2.0–3.0 and 60–80°C with controlled residence time before filtration and washing; the ferrocyanide feed is maintained at 10–20% w/w to prevent localised supersaturation. In this reaction environment, the hydrated sodium salt delivers a lower [Fe(CN)₆]⁴⁻ fraction per unit mass than potassium ferrocyanide trihydrate, but the anhydrous sodium salt delivers a higher fraction; this distinction must be accounted for when converting a pigment recipe from potassium to sodium chemistry. Technical-grade sodium ferrocyanide used for pigment synthesis is specified with assay not less than 98.5% w/w on the anhydrous basis, chloride not more than 0.02% w/w, sulfate not more than 0.02% w/w, and water-insoluble matter not more than 0.005% w/w. These values appear on manufacturer certificates of analysis and are aligned with in-house methods under ISO 9001 systems rather than a single harmonised standard. The main operational boundary is hydrogen cyanide release if the acidic reaction mass is overheated. Exhaust gas scrubbers charged with sodium hydroxide solution are installed on precipitation vessels where headspace hydrogen cyanide monitoring is required, and the pH of the scrubber liquor is kept above 12 to convert gaseous hydrogen cyanide to sodium cyanide in solution.
The water of crystallization in sodium ferrocyanide decahydrate creates a dosing distinction that is not present with anhydrous sodium ferrocyanide or potassium ferrocyanide trihydrate. The decahydrate contains 37.22% w/w water; consequently, 1.00 kg of decahydrate supplies only 0.628 kg of anhydrous sodium ferrocyanide. To achieve the same quantity of ferrocyanide ion as 1.00 kg of potassium ferrocyanide trihydrate, a formulator requires 1.146 kg of sodium ferrocyanide decahydrate. This conversion is structurally embedded in EU additive law, where the maximum use level is expressed as anhydrous potassium ferrocyanide.
| Property | Sodium ferrocyanide decahydrate | Anhydrous sodium ferrocyanide | Potassium ferrocyanide trihydrate |
|---|---|---|---|
| Formula | Na₄[Fe(CN)₆]·10H₂O | Na₄[Fe(CN)₆] | K₄[Fe(CN)₆]·3H₂O |
| Molar mass | 484.06 g/mol | 303.91 g/mol | 422.39 g/mol |
| Water of crystallization | 37.22% w/w | 0% w/w | 12.80% w/w |
| [Fe(CN)₆]⁴⁻ content | 43.79% w/w | 69.74% w/w | 50.18% w/w |
| Typical assay on anhydrous basis | 99.0% minimum | 98.5% minimum | 99.0% minimum |
The anhydrous product is hygroscopic and is not normally handled as a dry solid in open systems. It is either supplied in moisture-proof packaging or produced from the decahydrate by vacuum drying at temperatures not exceeding 120°C under a low-oxygen atmosphere. Drying must be carried out with dust extraction because the fine particulates contain cyanide complex and are subject to workplace exposure limits for cyanide-containing particulates. The decahydrate grade is preferred where stable storage and easy aqueous solution make-up outweigh the freight cost of its water content.
A direct substitution of sodium ferrocyanide for potassium ferrocyanide is not stoichiometrically neutral when cation loading governs the formulation. The anhydrous sodium salt contains 30.26% w/w sodium, while the decahydrate contains 19.00% w/w sodium. Potassium ferrocyanide trihydrate contains 37.02% w/w potassium and no sodium. For a low-sodium salt substitute, this difference is analytically significant only if the additive is used at levels far above the food additive maximum; at 20 mg/kg of sodium ferrocyanide decahydrate, the added sodium is less than 4 mg/kg, which is below common labelling thresholds for sodium. The selection between sodium and potassium salts is therefore driven by raw material availability, cost of cation removal downstream, and compatibility with the main salt matrix rather than by the anti-caking mechanism itself.
In redox-sensitive applications, sodium ferrocyanide is not a substitute for sodium ferricyanide. The standard reduction potential of the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ couple is +0.36 V versus the standard hydrogen electrode at 25°C. Ferrocyanide is the reduced form and functions as a mild reducing agent or complexing agent; ferricyanide is the oxidised form and acts as an electron acceptor in alkaline photographic developers and in some organic oxidation reactions. Sodium ferrocyanide solutions are stable under alkaline conditions but can oxidise slowly in the presence of dissolved oxygen at pH above 10, forming ferricyanide; this conversion is accelerated by transition-metal catalysts and by ultraviolet light. The ferrocyanide ion also reacts with labile iron(III) ions to form Prussian blue, a reaction used in qualitative analysis for iron detection.
The main incompatibility is acid hydrolysis. Contact with concentrated hydrochloric acid or sulfuric acid at temperatures above 30°C must be avoided because hydrogen cyanide is liberated. Neutral and alkaline process streams are recommended. In electroplating shops using cyanide-based baths, incoming technical sodium ferrocyanide is tested for free cyanide by ISO 6703-1:1984 or an equivalent method before addition to the bath, because batch-to-batch variation can shift the free cyanide background. Waste streams are oxidised by alkaline chlorination to convert cyanide species to cyanate, with treated effluent monitored for total cyanide by the same standard. Published data for specific electroplating formulations using sodium ferrocyanide is limited.
Analytical reagent grade sodium ferrocyanide is used as a 1% w/v aqueous solution for the confirmation of iron(III) in acidified samples. A deep blue precipitate of Prussian blue forms when labile Fe³⁺ is present. The reaction is run in dilute hydrochloric acid at a concentration not exceeding 1 mol/L and at ambient temperature; stronger acid or heating can release hydrogen cyanide. The visual detection limit is approximately 1 mg/L Fe³⁺ under transmitted light, but published data for this specific reagent configuration is limited, and matrices with strong complexing agents can suppress the response. The reagent solution is prepared fresh weekly and stored in a borosilicate reagent bottle protected from direct sunlight to reduce oxidation to ferricyanide.
Commercial packaging for sodium ferrocyanide decahydrate is typically 25 kg multi-wall paper sacks with an inner polyethylene liner for food-grade material, or 1,000 kg flexible intermediate bulk containers for technical salt use. The package should be stored in a dry, ventilated area below 40°C and protected from acids and oxidising agents. Pallets are kept away from direct sunlight to reduce photo-oxidation of surface material. The product is not classified as an oxidiser; however, contact with strong oxidisers such as concentrated nitric acid or permanganate can degrade the cyanide complex and generate toxic gases. Empty containers retain residues and should be managed as cyanide-containing waste according to local regulations. The selection of packaging model is based on the risk of rehydration of anhydrous product or efflorescence of decahydrate, and food-grade lots are segregated from technical-grade lots to prevent cross-contamination.
In bulk de-icing salt, sodium ferrocyanide is applied to prevent storage caking in large stockpiles. The additive is metered as a concentrated aqueous solution onto salt crystals moving on a belt conveyor, with the spray bar positioned after the final dryer and before the stockpile stacking conveyor. The dose is typically maintained at 5–20 mg/kg for non-food salt, and the distribution uniformity is controlled by rotary atomizers or static mixers in the feed line. Caking tendency is evaluated by sieve analysis after a specified storage period under controlled relative humidity, commonly 75% relative humidity at 25°C for 7 days; no harmonised ASTM or ISO method covers this exact evaluation, so equipment vendors and salt producers rely on internal conditioning protocols. The operational boundary for storage is ambient relative humidity above 75%, which can initiate surface dissolution and recrystallisation, reducing the anti-caking benefit. Published data for specific de-icing salt formulations is limited, but the additive is used commercially in regions with seasonal freeze-thaw cycles.
