Very safe and very expensive
You may dispose every chemical in a separate bottle (which may be the bottle in which it has been delivered). The chemical must be stored safely and labelled correctly.
For a single chemical there is no standard procedure to dispose ist, but the staff in the disposal company will have to check what is the best way instead. The effort for this has to be paid. The price is charged by weight. Consider that the sum of bottle and content counts!
- If possible (and safe!) prefer plastic bottles, because they are lower in weight!
- One big bottle is lower in weight than several smaller bottles with the same sum of volume. But follow directions of the "Materialverwaltung" (=Material Management) about a maximum of sizes. Consider that the bottles have to be lugged!
- For a certain amount of a chemical which should be disposed, the bottle should not be bigger than necessary.
- Take care about a reliable labelling! A single word "waste" - written with a felt tip pen - will never be OK! A lable with the word "mercury" is a cut above. But if the content of the bottle is a lot of dust which you did sweep up from the area under the cupboards because a thermometer did fall down and the spilled mercury did roll under the cupboards, a reliably labelling would be "mercury-containg dust".
- The labelling must also contain the necessary warnings. With a single compound use the correct GHS-labelling used for this kind of chemical. For mixtures use a plausible labelling.
- A lot of adulterated compounds can be recycled. But for example the complete recycling of benzaldehyde may be a lot of effort and you might think this is not worthwhile. Consider that a recycling is done by standard laboratory procedures and since the students all have to learn standard laboratory procedures you may ask the practical course supervisors if the recycling could be done in a student's lab.