Magnesium hydroxide (CAS 1309-42-8): storage and disposal

In a school prep room magnesium hydroxide usually shares a shelf with other white powders such as magnesium oxide and calcium carbonate, so the label does the work and not the look of the powder. Keep it in a dry, closed, labelled tub, dated on arrival and apart from food grade supplies. Any suspension made from it should be in a capped bottle labelled with the name and date made, since a settled white slurry looks like milk of magnesia. University stores should list powder and suspension separately and keep the tub away from damp.

Good magnesium hydroxide is a fine white powder, soft and free of lumps. Caking or a damp, clumped feel means moisture has entered. The powder gives few other visible signs. Suspensions are different: the solid settles to a layer at the base, and that is normal, but a film, floating specks, a smell or a change from white to something else suggests growth in the bottle. A crust at the cap, a cracked tub or an unreadable label counts as a problem. Anything unlabelled should be left closed and recorded.

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.

Do not wash it down the sink because it is a white powder that looks inert: magnesium hydroxide must not go into a sink, a drain, a general waste bin or a skip, and nobody should try to treat it first. Not being classified as hazardous on the sources we checked does not change that. It leaves by specialist collection with compatible solids, and a waste transfer note covers it under entry 16 05 09. Say whether the stock is powder or suspension, give the container size, and mention anything added to a suspension.

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.