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

Chromium(III) oxide (CAS 1308-38-9): storage and disposal

Chromium(III) oxide is the dull green powder that school, college and university stores keep for pigment and catalyst demonstrations. It is not classified as hazardous on the sources we checked, so there are no hazard statements to carry on its label, but it is still a chemical waste that has to be described accurately. What goes wrong with it is rarely the powder.

CAS number
1308-38-9
Form
Solid
Storage class
General
Usual EWC code
16 05 09

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

Mistaken identity is the realistic risk. A green powder on a prep-room shelf may be this oxide, a different chromium compound, copper carbonate or an old pigment, and those are classified differently. Keep it away from any chromium stock in other oxidation states and from anything with an uncertain label, on a general shelf in a tightly closed jar. The oxide is stable and insoluble, so no special cabinet is needed, but a fine powder travels, so use a tray and wipe the thread after use. Record the full name, the date opened and the quantity left, and keep a dedicated spatula for it.

How to tell it has deteriorated

The oxide itself gives almost no signs of age. It is a stable green powder, and a jar that has stood for decades usually looks as it did on arrival. What changes is the container: a thread coated with green dust, a lid that sticks, a label that has faded or been over-written and powder lumps from damp storage. If the jar has been topped up from another source, or if the colour looks different from other jars labelled the same, treat the contents as unconfirmed. In that case the record, not the powder, is what has deteriorated.

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.

Grouping starts with identification. Because it is not classified as hazardous on the sources we checked, it travels under a waste transfer note, but it is still a chemical waste and must be described accurately. The code is 16 05 09. Say that it is chromium(III) oxide powder, give the container size and the state of the lid, and keep it separate from any other chromium compound in the same collection. Spilt powder must not be swept into a bin or washed into a sink. Keep the jar upright in a tray with the lid taped, and request a specialist collection.

Waste codes and transport details for Chromium(III) oxide
EWC code, laboratory chemicals16 05 09
Hazardous wasteNo

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: powder.

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

Questions

Is chromium(III) oxide hazardous waste?

It is not classified as hazardous on the sources we checked, but it is still a chemical waste. Describe it accurately, send it with a waste transfer note and arrange a specialist collection.

How do we tell it from other green powders?

Do not rely on colour. Check the label, the date and the stock record, and keep any jar of uncertain green powder closed until its identity is confirmed.

Does it deteriorate on the shelf?

Hardly at all. The powder is stable, so what changes is the label, the lid and the record. Dust on the thread and a worn label are the usual signs.

Can small amounts of spilt powder go in the bin?

No. Spilt powder remains chemical waste. Collect it in a labelled container, keep it separate from other chromium stock, and mention it when you request collection.

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 Cr2O3. EC number 215-160-9.

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