Calcium Hypochlorite, Calcium Oxychloride, Calcium Dihypochlorite, Chlorinated Lime, Bleaching Powder, 7778-54-3

Calcium Hypochlorite, Calcium Oxychloride, Calcium Dihypochlorite, Chlorinated Lime, Bleaching Powder, 7778-54-3

CALCIUM HYPOCHLORITE

1. PRODUCT DEFINITION AND CHEMICAL IDENTITY

Note: Commercial calcium hypochlorite typically contains 65–70% available chlorine. It is a strong oxidizing agent and is widely used as a disinfectant and bleaching agent. Its high reactivity requires careful handling and storage.

2. PHYSICAL AND CHEMICAL PROPERTIES

3. REACTION MECHANISM AND MODE OF ACTION

When dissolved in water, calcium hypochlorite hydrolyzes to release hypochlorous acid (HOCl) , the active biocidal and bleaching species, and calcium hydroxide, which imparts an alkaline pH:

Ca(ClO)₂ + 2 H₂O → 2 HOCl + Ca(OH)₂

• Disinfection and Oxidation: Hypochlorous acid (HOCl) is a powerful, broad-spectrum oxidizing biocide. It penetrates microbial cell walls, denatures proteins, and disrupts enzyme systems, effectively destroying bacteria, viruses, fungi, and algae.

• Bleaching Action: HOCl oxidizes coloured organic compounds (chromophores), breaking their chemical bonds and rendering them colourless. This property is fundamental for textile and pulp bleaching.

• Alkaline pH: The co-produced calcium hydroxide gives the solution an alkaline character, which can aid in certain cleaning and disinfection processes but must be considered for pH-sensitive applications.

• Instability: Unlike stabilized chlorine sources (isocyanurates), calcium hypochlorite does not contain a UV stabilizer. In outdoor applications, free chlorine is rapidly degraded by sunlight unless a stabilizer (like cyanuric acid) is added separately.

4. ALTERNATIVE NAMES AND SYNONYMS

• Calcium Hypochlorite

• Bleaching Powder

• Calcium Oxychloride

• Chlorinated Lime

• Calcium Dihypochlorite

• Cal Hypo

5. PRODUCTION METHODS (Summary)

Calcium hypochlorite is produced industrially by two main processes:

A. Lime Process:
Chlorine gas is passed into slaked lime (calcium hydroxide). The reaction produces calcium hypochlorite along with calcium chloride as a by-product.
2 Ca(OH)₂ + 2 Cl₂ → Ca(ClO)₂ + CaCl₂ + 2 H₂O

B. Sodium Process:
Calcium oxide is slaked with water and mixed with sodium hydroxide. Chlorine gas is then introduced into this slurry. After separation, filtration, and vacuum drying, high-purity calcium hypochlorite crystals are obtained.
General reaction: Ca(OH)₂ + 2 NaOH + 2 Cl₂ → Ca(ClO)₂ + 2 NaCl + 2 H₂O

6. SECTORAL APPLICATIONS AND USAGE RATES

7. MANDATORY / IRREPLACEABLE APPLICATIONS

• Large-Scale Municipal Water Treatment: Calcium hypochlorite is an economical and effective disinfectant for treating large volumes of drinking water where on-site generation of chlorine is not feasible.

• Field Decontamination: In military and emergency response scenarios, its solid, portable form and high available chlorine content make it indispensable for decontaminating chemical and biological hazards.

8. ALTERNATIVES AND COMPARISON

9. REGULATORY STATUS, SAFETY, AND STORAGE

• GHS Classification (CLP Regulation):

  • Signal Word: Danger

  • Hazard Statements: H272 (May intensify fire; oxidizer), H302 (Harmful if swallowed), H314 (Causes severe skin burns and eye damage), H400 (Very toxic to aquatic life).

  • Supplementary Hazard (EUH): EUH031 (Contact with acids liberates toxic gas).

  • Precautionary Statements: P210, P220, P260, P280, P301+P330+P331, P303+P361+P353, P304+P340+P310, P305+P351+P338, P310, P405.

• Transport: UN 1748, Class 5.1 (Oxidizing substance), Packing Group II.

• Toxicity:

  • Acute oral toxicity (LD50, rabbit): 850 mg/kg.

  • Acute dermal toxicity (LD50, rabbit): >2000 mg/kg.

• Storage:

  • Store in a cool (15–25 °C), dry, and well-ventilated area, away from direct sunlight.

  • Keep containers tightly closed. The product is hygroscopic; contact with moisture causes decomposition, chlorine gas release, and loss of activity.

  • Strictly segregate from all combustible materials, reducing agents, acids, organic materials, oils, and greases. Contact with these can cause violent reactions or fire.

• Personal Protective Equipment (PPE): Wear chemical-resistant gloves, safety goggles/face shield, and protective clothing. Use a respirator with an acid gas/inorganic vapour cartridge if ventilation is inadequate. Avoid breathing dust.

• First Aid:

  • Eye contact: Rinse immediately with plenty of water for at least 15 minutes and seek medical attention.

  • Skin contact: Remove contaminated clothing, wash skin with plenty of water.

  • Ingestion: Rinse mouth, do not induce vomiting, seek immediate medical attention.

• Packaging: Typically 45–50 kg plastic drums or pails with inner PE liners.

10. FREQUENTLY ASKED QUESTIONS

Q1: Why does calcium hypochlorite leave a residue?
Upon dissolution, it releases calcium ions which can react with carbonates in the water to form insoluble calcium carbonate (scale) or simply remain as a turbid residue. This is a key difference from organic chlorine donors like TCCA, which dissolve cleanly.

Q2: Can I use calcium hypochlorite in a swimming pool?
Yes, it is widely used in commercial and public pools. However, because it does not contain a UV stabilizer, you must add cyanuric acid (stabilizer) separately to protect the chlorine from being rapidly destroyed by sunlight.

Q3: Is it safe to mix with other cleaning products?
No. Never mix calcium hypochlorite with acids, ammonia, or other cleaning agents. Mixing with acids releases toxic chlorine gas. Mixing with ammonia or amines can form explosive nitrogen trichloride.

Q4: What is the shelf life?
Under ideal storage conditions (cool, dry, sealed), it can be stored for up to 12–24 months with minimal loss of chlorine content. Exposure to heat, moisture, or sunlight will rapidly degrade the product.

11. QUICK REFERENCE TABLE