Where does most of the sulfur in coal originate from?
Mainly from sulphur content of the original vegetation from which coal was formed.
It originates from the sulphur content of the vegetation from which coal was formed millions of years ago.
Dead vegetation, in time covered over with sediments, was exposed to high pressure over very long time periods, and eventually turned into what we know as coal. However, sea water in coal beds also contains sulphates which can undergo bacterial reduction to hydrogen sulphide. Over extended time this can react with iron ions in water to form pyrite, and also with the organic material or with reducing bacteria to form the organic sulfur structures found in coal.