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

Manganese(II) sulfate (CAS 7785-87-7): storage and disposal

Manganese(II) sulfate monohydrate is a pale pink crystalline salt that school, college and university prep rooms often hold on the general salts shelf. The shelf is not the whole story. It is classified as possibly causing organ damage through prolonged or repeated exposure and as toxic to aquatic life with long lasting effects, so surplus stock is hazardous waste even though the crystals look mild.

CAS number
7785-87-7
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Serious health hazard pictogramSerious health hazard
  • Hazardous to the environment pictogramHazardous to the environment

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

On a school prep-room shelf this tends to sit beside other sulfates and nitrates, and that is acceptable provided the container is tightly closed and labelled with its full name and form. The repeated-exposure classification is a reason to avoid dusty handling, so keep the jar where it will not be opened casually, and keep a stock record. It does not need a fire cabinet or a corrosive store. Standing it on a tray near the bottom of the unit protects the shelf below from spilt crystals. Because it is the monohydrate, check the label says so, since the hydrated forms of manganese salts look alike and are easily confused.

How to tell it has deteriorated

A technician will see the colour first. Good stock is pale pink and crystalline, so a jar that has turned brown or darker on the surface has met air and moisture over a long time, and manganese(II) salts can slowly darken that way. Lumps and caking point to damp, while powder round the cap shows the lid has not been closing properly. A faded label or a crust on the thread are the other things to record. Apart from those changes, this salt gives few visible signs of age, so the label and the stock record matter as much as the crystals.

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.

Start with the code: 16 05 06* applies in a laboratory pack and 16 05 07* for discarded inorganic stock outside a pack. That is the route for stock jars as well as for leftover solutions from a practical, which should be bottled and described separately with an approximate volume. Because the aquatic classification applies at low levels, never put any of it into a sink, a floor drain or the ordinary bin, however pale the solution looks. Keep the original jar if the lid seals, record any browning or caking on the label, and request a specialist collection so it is grouped with compatible inorganic salts.

Waste codes and transport details for Manganese(II) sulfate
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Hazardous wasteYes

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: monohydrate.

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

  • H373 May cause damage to organs through prolonged or repeated exposure.
  • H411 Toxic to aquatic life with long lasting effects.
Precautionary statements
  • P260 Do not breathe dust, fume, gas, mist, vapours or spray.
  • P273 Avoid release to the environment.
  • P319 Get medical help if you feel unwell.
  • P391 Collect spillage.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Why is manganese(II) sulfate hazardous waste?

It is classified as possibly causing organ damage through prolonged or repeated exposure, and as toxic to aquatic life with long lasting effects. That combination makes surplus stock hazardous waste, so it should be collected.

Why has the pink colour turned brown?

Manganese(II) salts can darken slowly with air and moisture. The change tells you the jar has been poorly closed or kept a long time. It remains hazardous waste and should be recorded before collection.

What happens to leftover solution from a practical?

It must never go down a drain. The aquatic classification applies even to dilute solutions. Collect it in a labelled bottle, give an approximate volume, and include it with the solid in the collection request.

Does it need a special cabinet?

No. A general shelf is acceptable if the jar is closed, labelled and recorded. Keep it away from dusty handling because of the repeated-exposure statement.

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 MnO4S. EC number 232-089-9.

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