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Chemical collection and stock control for UK schools, universities and hospitals

Calcium chloride (CAS 10043-52-4): storage and disposal

Calcium chloride is a white solid held as anhydrous granules or as the hexahydrate in school, college and university stores, pathology labs and pharmacies. It is classified as causing serious eye irritation, and it is treated as hazardous waste. Its habit of drawing water from the air shapes both how it is stored and how its condition is described when a bottle is put forward for collection.

CAS number
10043-52-4
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Harmful or irritant pictogramHarmful or irritant

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as general stock and apart from the items listed under "Do not store with".
  3. If you no longer need it, add it to your disposal list so it goes on the next collection.

Safe storage in a school or lab

Near the drying tubes and desiccator supplies, on a general shelf, is where school prep rooms usually keep calcium chloride, because anhydrous granules are kept as a drying agent. They are only useful while dry, so the cap goes straight back on after every use. It is general class stock: dry, labelled, well organised store, dated on arrival, and apart from food grade supplies. Hexahydrate and anhydrous bottles should be shelved and labelled as separate items. In pathology and pharmacy settings, any made-up solutions should carry their own label and date rather than being kept alongside the solid.

How to tell it has deteriorated

Anhydrous calcium chloride takes up moisture, so a bottle that was once free-flowing gradually clumps, then fuses into a hard lump, and in a poor seal can end up as a wet mass or even a pool of liquid at the base. Hexahydrate crystals can also go damp and stick together. Corroded or stuck caps and staining on the shelf below show that liquid has escaped. A faded label and an unknown date of receipt count as well. Stock that has absorbed water is still calcium chloride and is described that way. Do not try to dry it out, and keep the container upright and closed.

How it must be disposed of

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

Two forms turn up in school and university stores and they are not interchangeable on a waste list: dry anhydrous granules and the hexahydrate. Each bottle should be described as it is now, including any that have fused into a lump or sit in their own liquid, because a leaking bottle is packed differently from a sound one. Waste code 16 05 06* is the entry for this hazardous waste in a lab pack. Pathology and pharmacy holders with made-up solutions should list those as solutions, apart from the solid. Do not dry out a wet bottle, empty it into a sink or drain, or put it in a general waste bin or skip.

Waste codes and transport details for Calcium chloride
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Human healthcare setting18 01 06*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Common quantities we collect

Usually held as: anhydrous, hexahydrate.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.

Where it is commonly held

Hazard statements

  • H319 Causes serious eye irritation.
Precautionary statements
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P337+P317 If eye irritation persists: Get medical help.

Substance as classified, dilutions may differ.

Questions

Why has our anhydrous calcium chloride turned into a solid lump?

It takes water from the air, so a bottle with a poor seal clumps and can fuse or turn wet. That is its normal behaviour, not a sign of a different substance. Keep it closed and upright, and put it forward for collection.

Can calcium chloride that has gone to liquid be collected?

Yes. Describe it as calcium chloride that has absorbed water, keep it in the original container, closed and upright, and say if the container is cracked or leaking. A leaking bottle is packed differently from a sound one, so the condition matters.

Can we keep the anhydrous and hexahydrate bottles together?

They can share a general shelf, but label each as its own item and date it. Mixing the two in one bottle makes the description unclear. If stock has absorbed water, record that on the label.

How do we describe a bottle that has gone wet?

Name it as calcium chloride, say which form it started as if you know, and note that it has absorbed water or become a lump or liquid. Keep it in the original container, closed and upright, with no attempt to dry it.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula CaCl2. EC number 233-140-8.

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