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

Magnesium carbonate (CAS 546-93-0): storage and disposal

Light white magnesium carbonate sits in school, college and university stores, typically as a solid powder or block used in thermal decomposition and gas evolution practicals. It is not classified as hazardous on the sources we checked, but it remains a chemical waste that has to be described accurately. Because the solid shows very little change as it ages, what a holder sees is mostly the container and its record.

CAS number
546-93-0
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

An open tub on a prep room bench is the usual problem. The powder is light and fine, so it spreads dust over the shelf and into neighbouring bottles whenever it is scooped, and a tub left open also picks up damp. Keep it in a closed container in the general store, dry and labelled, with the date of receipt on the label and away from food grade supplies. Where it is issued in small tubs for practicals, collect part-used tubs back to the store rather than leaving them with the class set. A label that gives only 'carbonate' is not enough, because a school stock often holds several.

How to tell it has deteriorated

Few visible signs of ageing show up in this solid, so the checks are about the container. Powder that has clumped has taken in damp, and a film of white dust on the shelf shows a lid that is not seating properly. A faded label, an unknown date of receipt and a tub with no name beyond a vague 'carbonate' are the more common faults than any change in the powder. Where blocks are held they can crumble at the edges when handled. Mould is not expected on a mineral solid, so any growth points to contamination from something else in the tub, and the contents should be described accordingly.

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.

Light dust is the awkward feature of this item. Containers that are loosely closed shed powder inside a lab pack, so keep the lid fitted and the tub upright, and do not tip loose powder into a different container to tidy it. The entry is 16 05 09, which is not a hazardous waste entry, but the stock is still chemical waste and must be described accurately. It does not go down a sink or drain, into general waste or a skip, and nobody should try to treat it first. Give the form, which is powder or block, and the approximate amount in each container, and keep different carbonates in separate tubs.

Waste codes and transport details for Magnesium carbonate
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: solid.

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 magnesium carbonate classed as hazardous?

It is not classified as hazardous on the sources we checked. It remains a chemical waste and goes by specialist collection under waste code 16 05 09, with an accurate description. Your supplier's information for the exact product you hold is still the reference.

Does magnesium carbonate degrade on the shelf?

It gives few visible signs of ageing. Look at the container: caking from damp, a loose lid, white dust around it, a faded label or no date. Put forward any tub that is undated or whose contents are uncertain.

Why is light powder a problem for collection?

A fine powder escapes from a poorly closed tub and contaminates the pack. Keep it in its own sound container with the lid on and upright. If the tub is cracked, say so when you request a 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 CMgO3. EC number 208-915-9.

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