C CHEMISTRY; METALLURGY
C22 METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
C22B PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
11/00 Obtaining noble metals
C22B11/02 by dry processes
C22B11/021 Recovery of noble metals from waste materials
C22B11/023 from pyrometallurgical residues, e.g. from ashes, dross, flue dust, mud, skim, slag, sludge