Potash alum (CAS 10043-67-1): storage and disposal

School prep rooms usually hold potash alum as a tub of clear crystals, bought for crystal growing projects, and sometimes the grown crystals themselves in jars. Keep the stock in a dry, labelled, well organised store, dated on arrival, with the full name on the label, since other alums look similar. Histology labs that keep it as a mordant should shelve it with stain components and away from food supplies. It is not classified as hazardous on the sources we checked, so no cabinet is needed, but a stock record still counts. Grown crystals belong in a lidded container, not on an open shelf where dust collects.

Good alum crystals are clear and glassy. A dodecahydrate holds a lot of water, and in dry air it can turn dull and powdery on the surface, while damp air can leave a tub caked. Grown crystals left in a window may cloud, crack or stick together. This substance gives few other distinctive signs, so the container carries the evidence: a faded or lifted label, a cracked tub, a crust at the neck and no date of receipt. Made up solutions that have gone cloudy or mouldy have stood too long.

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.

Before asking for collection, say what the stock really is: loose crystals, crystals grown by students, mordant stock or a bottled solution, with container size and amount left. School and university holders quote 16 05 09. A histology lab in human healthcare quotes 18 01 07 instead. Not being classified as hazardous on the sources we checked does not open up a sink, a drain, a bin or a skip, and staff should leave the stock untreated. Transfer note paperwork is all the movement needs, though the description still has to be accurate.

Usually held as: dodecahydrate, mordant.

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.