Potassium sulfate (CAS 7778-80-5): storage and disposal

No classified hazard decides where this goes, so the question is mixing up supplies. Potassium sulfate is also sold for gardens, and a tub of it can arrive in a school or college from a gardening club or a horticulture course. Keep laboratory stock in a dry, labelled, well organised store, dated on arrival, and keep food grade or garden supplies apart from it. The label should give the full name, since sulfates of sodium, magnesium and ammonium look identical on a crowded shelf. Because it is not classified as hazardous on the sources we checked, no cabinet is needed, but the stock record still counts.

Crystals or powder that are white, dry and free flowing are what a good tub looks like. This salt gives few distinctive signs of age. Damp can cake it into a hard cake, and a lid left off lets dust in, so look for a lump at the base, a crusted neck, a faded or lifted label and a tub with no date of receipt. A tub that has been topped up from different bags, or has no readable name, is recorded as it is. Anything with an unexpected colour or smell should be described precisely and reported, not guessed at.

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.

Sacks and tubs are grouped by form and size into a lab pack with compatible low hazard solids, and a half tub is described as half full, not rounded. Waste code 16 05 09 is the entry held for it. Even though it is not classified as hazardous on the sources we checked, it never goes to a sink, a drain, a general waste bin or a skip, and staff should not try to treat it first. A waste transfer note covers the movement. Record the full name, the quantity and whether any is garden grade, since that changes how it is described.

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.