Silver metal (CAS 7440-22-4): storage and disposal
Silver foil and powder sit in school, college and university stores, and a grey or black tarnish on the surface is the first thing anyone notices. Silver metal is classified as suspected of damaging fertility and as potentially causing organ damage through prolonged or repeated exposure. The classification as very toxic to aquatic life with long lasting effects applies to specified particulate forms, including silver powder, rather than automatically to solid foil. That makes it toxic stock and hazardous waste, whatever the foil looks like.
- CAS number
- 7440-22-4
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Warning
- Usual EWC code
- 16 05 06*
Serious health hazard
Hazardous to the environment
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 toxic 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
Hold the jar up to the light and look at the foil: if it has gone dark, something in the air of the store has been reacting with it. Silver goes in a locked toxic cabinet with a stock record, away from food and drink areas, acids and oxidising stock. Keep hydrogen peroxide away, since metals speed its breakdown and release oxygen and pressure. Picric acid, ammonium picrate and Bouin's fluid form shock sensitive picrates with metals, and sodium azide forms shock sensitive azides with several metals, so they need a different cupboard. Foil and powder should be in separate labelled containers.
How to tell it has deteriorated
Silver tarnishes. Bright foil first dulls and then browns or blackens where sulfur compounds in the air reach it, and the change is usually uneven, darker at folds and edges. The tarnish is a surface layer and is normal on old stock, but it shows the jar has been open or poorly sealed. Powder tarnishes more evenly and can look dull grey rather than bright. Beyond the metal, check the container: a faded label, a stained cap, a failed seal, a lost stock record or unexpected caking. Dark marks on the inside of a lid suggest the foil has been kept loose in the jar.
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 toxic laboratory pack with compatible chemicals.
Note whether the silver is foil or powder, how much remains, whether it is tarnished and what the jar and label look like. The laboratory waste classification must reflect the form and composition held. The suspected fertility and repeated-exposure organ hazards remain relevant, but the aquatic classification and any UN number must be confirmed for the particular silver material. It must not go into a sink, a drain, an ordinary bin or a skip, and nobody should try to clean the tarnish off or recover the metal from a mixture. A specialist collector packs it in a compatible group away from oxidisers, acids, hydrogen peroxide and sodium azide.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded inorganic chemical, not a laboratory pack | 16 05 07* |
| 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
- OxidiserToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- AcidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- Acetic acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Ammonium picratePicric acid forms shock sensitive metal picrates with metals.
- Calcium hypochloriteToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Hydrochloric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Hydrogen peroxideMetals speed the breakdown of hydrogen peroxide, releasing oxygen and pressure.
- Nitric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Picric acidPicric acid forms shock sensitive metal picrates with metals.
- Potassium nitrateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
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- Potassium permanganateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Sodium azideAzides form shock sensitive metal azides with lead, copper, brass and similar metals.
- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities we collect
Usually held as: foil, 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
Hazard statements
- H361f Suspected of damaging fertility.
- H373 May cause damage to organs through prolonged or repeated exposure.
- H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
- P203 Obtain, read and follow all safety instructions before use.
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P318 If exposed or concerned, get medical advice.
- P319 Get medical help if you feel unwell.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
- P273 Avoid release to the environment.
- P391 Collect spillage.
Substance as classified, dilutions may differ.
Questions
Does tarnished silver foil need special handling?
Tarnish is a surface layer and does not change the classification. Tarnished foil is still toxic stock, so it stays in its labelled container in the locked cabinet. Do not polish, clean or wash it before collection, and record the condition on the stock sheet.
Can silver from a lab jar go in with the scrap metal?
No. Silver metal carries suspected fertility and repeated-exposure organ hazard classifications. Some particulate forms also carry aquatic toxicity classifications. Laboratory silver waste requires appropriate classification and specialist collection rather than disposal with ordinary scrap. It needs specialist collection and must not be mixed with scrap metal or ordinary waste.
Why must silver be kept apart from acids?
Toxic stock is stored away from acids because several toxic salts release toxic gas on contact with acid. Silver metal is not the worry here, but a shared cupboard puts it beside salts that are. Keeping the toxic cabinet free of acids removes the problem.
