Making a submission of an iron disk (8)
I believe the answer is:
offering
'making a submission' is the definition.
I can't tell whether this definition defines the answer.
'of an iron disk' is the wordplay.
'an iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'disk' becomes 'ring' (I can't justify this - if you can you should give a lot more credence to this answer).
'of'+'fe'+'ring'='OFFERING'
Can you help me to learn more?
(Other definitions for offering that I've seen before include "Tendering - sacrifice" , "Present" , "making a bid" , "Religious sacrifice" , "Money contributed at a religious service" .)