Citric acid (CAS 77-92-9): storage and disposal
Citric acid is held as a white solid in school and college prep rooms, university labs, pathology stores and pharmacies. It is classified as causing serious eye irritation and may cause respiratory irritation, so it is still a chemical waste despite its everyday reputation. Damp, dust and food grade tubs that wander onto laboratory shelves are what holders most often get wrong.
- CAS number
- 77-92-9
- Form
- Solid
- Storage class
- Acid
- Signal word
- Warning
- Usual EWC code
- 16 05 06*
Harmful or irritant
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 acid 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
Bicarbonate, carbonates and other alkalis, along with bleach compounds, should not share a shelf with a tub of citric acid. Alkalis react with acids, and many oxidisers release toxic gas or become unstable in contact with acid. Dust is what irritates the eyes and airways, so a tight lid matters for the loose solid. A tub bought as a food grade ingredient should be kept apart from laboratory stock and labelled, and in a pharmacy it should not sit with the dispensing supplies. Date every tub on arrival, keep it dry, and put it on a labelled laboratory shelf rather than a kitchen cupboard.
How to tell it has deteriorated
Free-flowing white crystals or powder is what normal looks like. Caking is the usual sign that damp has got in, and a tub that has set into a solid block has been open or poorly sealed for a long time. Weak solutions kept for a long time can grow mould, a cloudy film or floating threads. Look for stained or faded labels, a cracked lid and an unknown date of receipt. A tub with no label is the most common problem, because plain white powder gives no clue to what it is and cannot be described accurately for collection.
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 corrosive acid laboratory pack with compatible chemicals.
Note whether each container holds free powder, caked lumps or a made-up solution, roughly how much is left and whether the label is readable. Citric acid is classified for eye and airway irritation, so it must never be put in a sink or drain, a kitchen bin or a skip because it looks like a food ingredient. It must not be diluted or neutralised first. A pharmacy or pathology store describes it under 18 01 06*. The collector groups it with other acids and keeps it away from alkalis, so list any bicarbonate or carbonate stock separately.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded organic chemical, not a laboratory pack | 16 05 08* |
| Human healthcare setting | 18 01 06* |
| Hazardous waste | Yes |
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
- FlammableOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- AlkaliAcids and alkalis react with strong heat and spattering if they meet.
- OxidiserMany oxidisers release toxic gas or become unstable in contact with acid.
- ToxicToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- AcetoneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Ammonia solutionAcids and alkalis react with strong heat and spattering if they meet.
- Calcium hypochloriteMany oxidisers release toxic gas or become unstable in contact with acid.
- EthanolOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- FormalinToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- HexaneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Hydrogen peroxideMany oxidisers release toxic gas or become unstable in contact with acid.
- Mercury(II) chlorideToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
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- MethanolOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Potassium hydroxideAcids and alkalis react with strong heat and spattering if they meet.
- Potassium nitrateMany oxidisers release toxic gas or become unstable in contact with acid.
- Potassium permanganateMany oxidisers release toxic gas or become unstable in contact with acid.
- Sodium cyanideToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Sodium hydroxideAcids and alkalis react with strong heat and spattering if they meet.
- TolueneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
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
Hazard statements
- H319 Causes serious eye irritation.
- H335 May cause respiratory irritation.
Precautionary statements
- P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
- P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
- P271 Use only outdoors or in a well-ventilated area.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P319 Get medical help if you feel unwell.
- P337+P317 If eye irritation persists: Get medical help.
- P403+P233 Store in a well-ventilated place. Keep container tightly closed.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Can a school put old citric acid out with the kitchen waste?
No. It is classified for serious eye irritation and may irritate the airways, and a tub from a prep room is chemical waste even though the same substance is sold as a food ingredient. It goes by specialist collection.
Why has the citric acid in the tub set solid?
Damp has got in. The solid cakes when the lid is left loose or the store is humid. It is still the same irritant. Keep the lid on, do not break the block up, and list it for collection if it is old or unlabelled.
Can food grade citric acid stay on the laboratory shelf?
Keep food grade supplies separate from laboratory stock, clearly labelled and out of the lab store. Once a tub has been in a lab environment it should be treated as laboratory stock and should not go back into the kitchen.
