The fabric of the steel wool is gradually replaced by silver and the steel wool also rusts, therefore the entire mess, sludge plus crumbly wool residue, is a mixture of silver, iron and iron salts. This mass (mess) is what can be recovered, but is by no means 'rather pure'. It does have monetary value.
I had a description (a report) on the various processes of silvery recovery some years ago and remember the recovered silver was described as a "relatively pure form". But I may have read it wrong and I trust your knowledge on the subject.
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