Nickname for bits of soot on lots of lumps of coal (9)
I believe the answer is:
sobriquet
'nickname' is the definition.
(I know that nickname can be written as sobriquet)
'bits of soot on lots of lumps of coal' is the wordplay.
'bits of' indicates taking the first letters.
'lots of lumps of coal' becomes 'briquet' (I can't justify this - if you can you should give a lot more credence to this answer).
The first letters of 'soot on' is 'so'.
'so'+'briquet'='SOBRIQUET'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for sobriquet that I've seen before include "dubious name" , "Another handle" , "Nickname -- Boers quit (anag)" , "one's assumed" , "Another name" .)