Tetrachloroauric acid (CAS 16903-35-8): storage and disposal
Gold chloride is kept in university and histology laboratories as tetrachloroauric acid, either as the solid or as a gold toning solution. It is classified as causing severe skin burns and eye damage, as harmful if swallowed, as a skin sensitiser and as harmful to aquatic life with long lasting effects. It belongs with the acids but behaves like no other acid on the shelf.
- CAS number
- 16903-35-8
- Form
- Solid
- Storage class
- Acid
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Corrosive
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
Because it is an acid it goes low down on an acid-resistant tray in a ventilated corrosive store, and it should be kept apart from alkalis, from oxidisers and from salts that give off gas with acid. Metal caps and shelf fittings do not last next to it, so use a plastic-lined cap and check the shelf. The crystals are yellow and take up water from the air, so keep the bottle sealed and away from damp. Light matters as well, so a dark or amber bottle in a closed cupboard suits it better than a clear bottle on a bench. A histology lab should keep toning solution in a labelled container with its date.
How to tell it has deteriorated
A normal bottle holds yellow to orange crystals or a clear yellow solution. The first change usually seen is dampness, where the crystals clump, cake or form a syrup at the base because they have drawn water from the air. Light and contact with organic matter can reduce gold salts to a purple, brown or dark deposit, so a bottle with a purple film on the glass or a dark sediment in a toning solution has been spoilt. Corroded caps, a crust round the neck and stained shelving point to a leak. Skin that has touched a bottle may show a purple stain.
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.
Look at the code that matches the setting. A laboratory pack uses 16 05 06*, discarded inorganic stock outside a laboratory pack uses 16 05 07*, and a human healthcare setting such as a hospital histology service uses 18 01 06*. Describe the solid and any toning solution separately and give a volume for the liquid. This corrosive acid must never go down a sink and nobody should try to neutralise it or reduce the gold out of solution. Keep it in a sealed container on a resistant tray away from alkalis, and the carrier packs it with compatible acids on a specialist collection.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded inorganic chemical, not a laboratory pack | 16 05 07* |
| 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.
Show 7 more
- 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: gold toning solution.
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
- H302 Harmful if swallowed.
- H314 Causes severe skin burns and eye damage.
- H317 May cause an allergic skin reaction.
- H412 Harmful to aquatic life with long lasting effects.
Precautionary statements
- P234 Keep only in original packaging.
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
- P264 Wash hands and exposed skin thoroughly after handling.
- P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
- P270 Do not eat, drink or smoke when using this product.
- P272 Contaminated work clothing should not be allowed out of the workplace.
- P273 Avoid release to the environment.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P301+P317 IF SWALLOWED: Get medical help.
- P301+P330+P331 IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P302+P361+P354 IF ON SKIN: Take off immediately all contaminated clothing. Immediately rinse with water for several minutes.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P305+P354+P338 IF IN EYES: Immediately rinse with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P316 Get emergency medical help immediately.
- P317 Get medical help.
- P319 Get medical help if you feel unwell.
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- P333+P317 If skin irritation or rash occurs: Get medical help.
- P362+P364 Take off contaminated clothing. And wash it before reuse.
- P363 Wash contaminated clothing before reuse.
- P390 Absorb spillage to prevent material damage.
- P391 Collect spillage.
- P405 Store locked up.
- P406 Store in corrosive resistant container with a resistant inner liner.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Why has our gold toning solution gone purple or dark?
Gold salts can be reduced by light or organic matter, leaving a purple or dark deposit. The stock has been spoilt. Do not try to filter it. Record the change and arrange collection.
Why do the crystals turn into a wet lump?
Tetrachloroauric acid draws water from the air, so a poorly closed bottle will cake or form a syrup. It is still corrosive. Keep it closed on a tray and send an enquiry.
What should we do with small amounts of used toning solution?
It must never be poured away, because it is a corrosive acid and harmful to aquatic life. Collect it in a labelled container and include it with the volume in your collection request.
Which waste code does a hospital histology lab use?
A human healthcare setting uses 18 01 06*. A university laboratory pack uses 16 05 06*, and discarded inorganic stock outside a pack uses 16 05 07*.
