How can I remove a cordless drill chuck?
Prop the drill upside down in a glass filled with warm muriatic acid for a few hours to dissolve the packed calcium sulfate, followed by a couple of whacks on the chuck with a hammer; repeat as necessary. Rinse and dry thoroughly afterwards as muriatic acid is a strong oxidizer that will quickly rust high-carbon steels if left metal surfaces exposed in air. 

USE CAUTION as muriatic acid is actually hydrochloric acid and can burn you and your clothes; wear gloves and eye protection. You can find muriatic acid in the pool cleaning section of the big-box hardware stores.

I use this technique to dissolve impacted gypsum dust from my Dremel chucks.