Magnesium oxide (CAS 1309-48-4): storage and disposal

Keep magnesium oxide away from anything that will wet it. Light grades take up water and carbon dioxide from the air, slowly becoming a lumpy mix with magnesium hydroxide and carbonate, so a tightly closed cap on a dry shelf matters more than separation from neighbours. Nothing about it requires special segregation. Even so, place it away from acids, since it reacts with them, and keep burnt magnesium residues from demonstrations out of the stock jar. A prep room usually holds one large tub and several small ones decanted for classes. Date every tub and write the grade on the label when the supplier names one.

Caking is the telltale change. Fresh magnesium oxide is a very fine, free-running powder, but an old tub that has been opened in humid air forms hard lumps and may feel gritty or slightly damp. The powder can also stick to the inside of the lid and the thread, making the cap difficult to turn. These changes come from reaction with moisture and carbon dioxide, not from any hazard in the material. Watch for a faded label, a split tub and a missing date of receipt. Jars that have been topped up from another source or contaminated by burnt residue should be treated as mixed stock.

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

It is not normally classified as hazardous, but it remains a chemical waste and needs a clear description: the grade if known, the quantity and the tub condition. It does not belong in a bin, a skip or any drain, and a prep room should not tip it out to clear shelf space. A waste transfer note covers the movement. Mixed or contaminated tubs, such as those used for burnt residue, are described as what they may contain. The specialist carrier packs it with other low hazard solids from the same collection.

Usually held as: solid.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.