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Introduction
Calcium ferrocyanide (Ca₂[Fe(CN)₆]·nH₂O) is a calcium salt of the ferrocyanide complex. It is used as an anticaking agent in table salt, particularly in some European countries, and as a firming agent in some applications. It is less common than the sodium and potassium salts because it has lower solubility and may form insoluble residues. It is approved as a food additive (E538) in the EU.
Calcium ferrocyanide provides the same anticaking effect but also contributes calcium ions, which can be beneficial for nutritional fortification. However, the lower solubility can lead to turbidity in brines and solutions.
CAS Number
14434-26-5 (anhydrous). Hydrated forms exist with varying water content.
Synonyms
Calcium hexacyanoferrate(II), Calcium ferrocyanide, E538.
Topic Headings
1. Comparison of solubility with other ferrocyanides (neutral list, no superiority claims)
• Solubility in water at 20°C — Sodium ferrocyanide: 17.5 g/100 mL; Potassium ferrocyanide: 29 g/100 mL; Calcium ferrocyanide: approximately 0.5 g/100 mL (low solubility).
• Effect in salt solutions — Calcium ferrocyanide is less effective in dry salt because it does not disperse as easily.
• Advantage for specific applications — Low solubility means that calcium ferrocyanide is less likely to migrate in salt products stored under damp conditions.
• Calcium contribution — Provides calcium (about 15% Ca by weight), which may be a secondary benefit in some dietary supplements.
2. Physical and chemical properties (list form)
• Appearance — Pale yellow to yellow powder.
• Odor — Odorless.
• Molecular weight — 292.10 g/mol (anhydrous, approximate).
• Melting point — Decomposes before melting.
• Solubility in water — 0.5-1.0 g/100 mL at 20°C (sparingly soluble).
• Solubility in other solvents — Insoluble in ethanol.
• Stability — Stable; decomposes in strong acids.
• Density — Approximately 1.8 g/cm³.
3. Food applications and typical usage levels (list form)
• Anticaking agent in table salt — 10-30 mg/kg; used in some European countries (e.g., Germany, Austria).
• Salt for meat processing (curing salts) — Prevents caking in brining mixes.
• Wine fining (less common) — Used in combination with potassium ferrocyanide.
• Calcium-enriched salt — As a dual-purpose additive (anticaking + calcium fortification).
4. Regulatory status and considerations (paragraph form)
Calcium ferrocyanide is approved as E538 in the EU with the same maximum level for salt: 20 mg/kg as ferrocyanide ion. It is not specifically listed in the USA CFR; however, sodium and potassium ferrocyanides are GRAS, and calcium ferrocyanide would likely be considered GRAS if used under similar conditions (though it is not commonly used in the US). The same safety profile applies: the ferrocyanide complex is non-toxic. The lower solubility means that it may leave a slight residue in brine solutions, which is generally not a problem. Some salt manufacturers prefer calcium ferrocyanide because it is less likely to cause yellow discoloration in the final product (the sodium and potassium salts can impart a faint yellow tint at high concentrations, though at 20 ppm this is usually invisible). Overall, calcium ferrocyanide is a safe and effective anticaking agent, though it is the least common of the three ferrocyanides.
