Since contamination is a concern, my first suggestion would be along the lines of the one offered by @johnpowell, to heat the bucket of the loader in some non-injurious way. Perhaps the outside of the bucket can be lined with the kind of 12V de-icing wire that people use to keep roof eaves ice-free. It could run off the vehicle’s own electrical system, keeping the bucket “just warm enough” to prevent icing. (And lining the outside away from areas where it will scrape against the product and against the ground, to prevent damage to the wiring. Alternatively, it may be possible to line the inside of the bucket, and then cover the wiring with sheet metal to protect it from wear.)
Or is it possible to re-route some of the plant’s waste heat (closed cycle cooling water for plant equipment, for example) into or around the pile of pulp fiber, to keep it warmer? Even a temporary shed with waste heat inside would help a lot to keep the product itself warmer.
Either way, warm bucket or warm product, will prevent freezing.
As an even quicker alternative, what are the chances of having an assistant with a warm-water hose to spray the bucket – while empty – between loads? You wouldn’t really want a person to hand-hold a steam hose, but “warm water” can be plenty warm; the person should be wearing gloves and a face shield for thermal protection.