Does impurity disappear by drying the mattress in the sun, and does impurity transfer through water or sweat, knowing that the questioner follows the Maliki school of thought?

The drying of urine without washing it does not purify the ritually impure spot. If the unwashed spot where urination occurred comes into contact with something wet, the impurity transfers to it. Sheikh al-Islam Ibn Taymiyyah held the view that drying by the sun and wind purifies the earth and other things, and this is a position within the Hanbali school of thought.