Calcium carbonate (CAS 471-34-1): storage and disposal

Most calcium carbonate stock is marble chips or fine powder, held in school and college prep rooms, university labs and pathology and histology stores. It is not classified as hazardous on the sources we checked, but it remains a chemical waste and has to be described accurately. Which neighbours sit on the shelf and what the chips have been used for matter more than the substance itself.

CAS number: 471-34-1
Form: Solid
Storage class: General
Usual EWC code: 16 05 09

What to do this week

Check the label is readable and write down the opened date if it is not already there.
Check it is stored as general stock and apart from the items listed under "Do not store with".
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

Keep calcium carbonate away from picric acid, ammonium picrate and Bouin's fluid, because picric acid forms sensitive picrate salts with lime, plaster and concrete, and away from hydrofluoric acid, which reacts with calcium carbonate to produce calcium fluoride, water and carbon dioxide gas. In a histology store that is a real concern, since picric acid fixatives sit a few shelves from general powders. It is otherwise general class stock, kept in a dry, labelled, well organised store and dated on arrival. School prep rooms usually hold marble chips in a tub and the powder in a bottle, and each should carry its own label.

How to tell it has deteriorated

Few visible signs of ageing show up in this solid, so the checks are mostly about the container. Powder that has caked or clumped has taken in damp, and a faded label or an unknown date of receipt is a more common problem than any change in the solid. In schools the thing to look for is the marble chips tub: chips returned after a practical may be pitted, wet or mixed with residue and with unrelated bits from the bench. Keep used chips apart from clean ones and label them as used. A bottle with a cracked cap or a stained shelf beneath it should be put forward for collection with its condition noted.

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.

Used marble chips are the awkward case. A tub that has been through acid practicals holds wet, pitted chips mixed with residue, and the collection team needs to know what they sat in. Clean chips and powder go under waste code 16 05 09, or 18 01 07 in a human healthcare setting. Neither marks the stock as hazardous waste, but it is still chemical waste that must be described accurately, so a transfer note accompanies it. Keep used chips apart from clean stock and label the tub as used. Chips and powder do not go into a sink, a drain, a general waste bin or a skip, and no one should try to treat them first.

Waste codes and transport details for Calcium carbonate
EWC code, laboratory chemicals	16 05 09
Human healthcare setting	18 01 07
Hazardous waste	No

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

Do not store with

Named chemicals to keep apart

Ammonium picratePicric acid forms sensitive picrate salts with lime, plaster and concrete.
Hydrofluoric acidHydrofluoric acid attacks glass and silicates, releasing toxic gas.
Picric acidPicric acid forms sensitive picrate salts with lime, plaster and concrete.

Common quantities we collect

Usually held as: marble chips, 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

Do old marble chips still need specialist collection?

Yes. Chips and powder are still chemical waste and go by specialist collection, not into a bin or skip. The waste code is 16 05 09. Describe whether they are clean or used, and keep used chips apart.

Is calcium carbonate classed as hazardous?

It is not classified as hazardous on the sources we checked. That does not remove the duty to describe it accurately. A waste transfer note applies, and your own supplier safety data sheet remains the reference for your stock.

What should it not be stored next to?

Keep it away from picric acid, ammonium picrate, Bouin's fluid and hydrofluoric acid. Picric acid can form sensitive picrate salts with calcium-containing materials. Hydrofluoric acid reacts with calcium carbonate, releasing carbon dioxide and forming calcium fluoride.

Does calcium carbonate go off over time?

It gives few visible signs of ageing. The usual problems are caked powder from damp, a faded label or no date. Check the container and the record rather than the solid, and put forward anything undated or damaged.