Tim Lamb wrote:

My use was feed racks for
housed cattle and, now this activity has finished, I am wondering how to
dispose of the residue.

If it cannot be re used then land fill at a permitted facility or a fully
WID compliant burner are the only two options I can think of, with the
latter all the ash would be considered hazardous.

Most wood fire retardants seem to be simple salts of sodium potassium and
boron and silica, rather than the bromine based stuff, so the products of
combustion shouldn't be too bad. I guess they act by farminng a skin over
the wood which prevents the air getting to char, which then is self
limiting to an extent as char is a good insulator. So the wood self
extinguishes in the same way a match does once the volatiles have burned
off. Any such coating will fail if the wood it protects gets above ~270C,
as one might expect in a good, hot wood burner.

AJH