Hallo Fiona, what Khais has said is correct. However, in prose dialogue, poetry and creative thinking 'discard' can be used for people. For example: That poor girl was discarded like a dirty rag and left alone on the streets to rot....:
The word 'abandoned' is used to describe a concept, an idea or a thought as well as a human being. Example: I abandoned the idea of designng this project and instead I will choose that project. OR, I abandoned hope because all seemed lost and no food was ever going to come. Abandoned / Discarded - context.
Think of it this way, Abandon = Letting go of something you already have out of necessity or selfishness or good reason, turning your back on something or someone,
Discard = Throwing something away with the pecific intention that it is of no use to you, it has no more purpose.