Urium remains are an item found and used in the Shades of Mort'ton minigame. To obtain these remains, the player must kill an Urium Shade, located behind the gold door in the Shade Catacombs.
To burn the Urium remains, first place redwood pyre logs on a funeral pyre, followed by the Urium remains, then ignite the pyre with a tinderbox. This will grant the player 500 Firemaking experience (750 with Morytania Diary 4 complete), and 120.5 Prayer (180.7 with Morytania Diary 3 complete) experience.
Urium remains will always reward the player with a gold shade key, or some coins. Gold keys give unrestricted access to all areas of the shade tombs and opens the gold chests in the Urium area of the tombs, which give the best rewards out of all the chests.
Completing the Morytania Diary 3 offers 50% more Prayer experience, and completing the Morytania Diary 4 offers 50% more Firemaking experience. The Pyromancer's/Zealot's outfit does not increase Firemaking/Prayer experience gained from burning shade remains.
The following drop rates are provided by Jagex, unless otherwise specified.
There is a 79/100 chance to roll for a key. If the roll fails, players receive coins instead.
For an exhaustive list of all known sources for this item, see here