Dicalcium phosphate (CaHPO₄) is a compound made of calcium and phosphate. It appears as a white, odorless crystalline powder, nearly insoluble in water but soluble in acids. The compound belongs to the calcium phosphate family, which also includes:
- Monocalcium phosphate – Ca(H₂PO₄)₂
- Tricalcium phosphate – Ca₃(PO₄)₂
Because it holds both calcium and phosphorus in moderate proportions, it is widely used in food, feed, and pharmaceutical products.
1. Chemical Composition and Structure
| Property | Description |
|---|---|
| Chemical name | Dicalcium phosphate |
| Formula | CaHPO₄ |
| Molecular weight | 136.06 g mol⁻¹ |
| IUPAC name | Calcium hydrogen phosphate |
| CAS number | 7757-93-9 |
| Appearance | White crystalline or granular powder |
| Solubility | Slight in water, readily soluble in acid |
| pH (1 % solution) | Around 7 – 8 |
| Forms | Anhydrous (CaHPO₄) and dihydrate (CaHPO₄·2H₂O) |
Natural minerals such as brushite (CaHPO₄·2H₂O) and monetite (CaHPO₄) contain this compound.
2. How It Is Produced
Industries make dicalcium phosphate by reacting phosphoric acid with a calcium source.
A. Wet process
The common route mixes phosphoric acid (H₃PO₄) with hydrated lime (Ca(OH)₂):
Ca(OH)₂ + H₃PO₄ → CaHPO₄·2H₂O
The resulting dihydrate is filtered, dried, and ground. This process gives feed-grade DCP for animal nutrition.
B. Thermal or hydrothermal process
Here calcium carbonate (CaCO₃) reacts with phosphoric acid at high temperature:
CaCO₃ + H₃PO₄ → CaHPO₄ + CO₂ + H₂O
The product is anhydrous DCP, favored in food and pharmaceutical uses for its purity.
C. Neutralization method
Partial neutralization of monocalcium phosphate with lime also forms DCP:
Ca(H₂PO₄)₂ + Ca(OH)₂ → 2 CaHPO₄ + 2 H₂O
This route allows tight control of calcium-to-phosphorus ratio and purity.
3. Main Forms
| Form | Formula | Typical use |
|---|---|---|
| Dihydrate | CaHPO₄·2H₂O | Feed and fertilizer |
| Anhydrous | CaHPO₄ | Food and pharmaceuticals |
| Granular | CaHPO₄ (granular) | Tablet production |
Each form supplies roughly 23 – 28 % Ca and 18 – 21 % P by weight.
4. Uses
A. Animal feed
Dicalcium phosphate supplies calcium and phosphorus for livestock and poultry. It supports bone growth, shell formation, and metabolism. Farmers favor it for its digestibility, steady Ca\:P ratio (~1.3:1), and low impurity level. Typical inclusion: 1–3 % of the feed mix.
B. Food and nutrition
Food-grade DCP functions as:
- a mineral fortifier in cereals and beverages,
- a leavening agent in baking powder,
- a stabilizer or emulsifier in dairy products. In the EU it appears as additive E341 (ii).
C. Pharmaceuticals
Anhydrous DCP is used as a tablet filler and binder and as a source of minerals. It shows good flow and compression behavior, important in direct-compression tablets.
D. Fertilizers
DCP adds calcium and phosphorus to compound fertilizers and helps maintain soil fertility.
E. Other industries
It is also applied in ceramics, glass, toothpaste, water treatment, and polishing products.
5. Comparison with Other Calcium Phosphates
| Compound | Formula | Ca % | P % | Solubility | Main use |
|---|---|---|---|---|---|
| Monocalcium phosphate | Ca(H₂PO₄)₂ | 16 | 22 | High | Fertilizers, baking |
| Dicalcium phosphate | CaHPO₄ | 23–28 | 18–21 | Moderate | Feed, food, pharma |
| Tricalcium phosphate | Ca₃(PO₄)₂ | ≈38 | 18 | Low | Anticaking, supplements |
Dicalcium phosphate lies midway in both solubility and nutrient ratio.
6. Advantages
- Supplies calcium and phosphorus in one material.
- Non-toxic and officially safe (GRAS, FDA).
- Free-flowing and easy to store.
- Suitable for multiple industries.
- Cost-effective, made from common minerals.
7. Health and Safety
DCP is safe at normal intake levels. Large doses of phosphate salts can upset mineral balance.
Possible effects of excess: high blood phosphate, reduced calcium absorption, kidney strain.
Follow international limits (FDA, EFSA, Codex). Keep correct Ca\:P ratios in feeds and supplements. Use ventilation and masks to limit dust exposure.
8. Environmental Aspects
Production can create by-products such as phosphogypsum or fluoride gases. Modern plants reduce emissions by using low-fluorine ores, recycling process water, and recovering phosphates from waste. When managed well, DCP supports nutrient efficiency without serious environmental impact.
9. Quality Control
| Test | Typical value | Method |
|---|---|---|
| Calcium | 23–28 % | EDTA titration |
| Phosphorus | 18–21 % | Spectrophotometry |
| Moisture | < 5 % | Drying test |
| Heavy metals | < 30 ppm | ICP-OES |
| Fluoride | < 0.18 % | Ion-selective electrode |
Consistent results ensure reliable feed- and pharma-grade quality.
10. Key Facts
| Item | Data |
|---|---|
| Formula | CaHPO₄ |
| Also called | Calcium hydrogen phosphate (DCP) |
| Typical content | ≈25 % Ca, ≈20 % P |
| Forms | Anhydrous and dihydrate |
| Main uses | Feed, food, pharmaceuticals, fertilizers |
| Status | GRAS (FDA) |
| EU code | E341 (ii) |
11. Summary
Dicalcium phosphate (CaHPO₄) is a stable, practical calcium phosphate used worldwide. Its balanced calcium-to-phosphorus ratio suits animal feed, human food, fertilizer, and drug formulations. Moderate solubility, safety, and ready availability keep it one of the most common phosphate materials in commerce today.
