The rate of formation of elemental sulfur on the surface of lignite pa
rticles during leaching by acidic ferric chloride was found to depend
on the concentration and acidity of the ferric chloride, the particle
size of the sample, the temperature and the rate of stirring. Generall
y, S formation increased during the first 40-45 min of leaching and su
bsequently decreases. It was more significant with small particles and
high acidities.