How to remove stuck chisel

Did you try aiming compressed air into the chuck to push away the grit, try spraying WD40 or other penetrating oil to hopefully lube the detent latch holding the bit. Then lastly using a freeze spray (likely need a few cans) to cool the bit which in turn ever so slightly will cause the bit to shrink but you need to be quick! As you don't want the chuck to get cold too!

As an example in Chicago the other day a major draw bridge got stuck as the super hot day cause the deck panel to expand preventing it to lock together about two feet up. They had to use a fire boat to hose the deck to get the panel to drop down.