Ulrich, the cheapest wire wool* is used for silver recovery from fixer and has been for a great many years, the sludge is normally just left to dry before smelting. *From your local home improvement store.

When I worked in precious metal recovery our factory plated out as much silver as it could overnight then the residual silver was recovered by passing the fixer through normal wire wool. Commercial cartridges for bleach fix use a different grade because bleach fix rots the wire wool, it's this that can be very messy.

Ron, my comments were really an addition to yours to a previous poster.