Yes, DISCARDED is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, C 3, A 1, R 1, D 2, E 1, D 2.

Is it a valid word?

DISCARDED is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

Also: toss out, toss away, chuck out, cast aside, throw out, cast out, throw away, cast away, put away, cast-off, thrown-away.