Useful metal compounds are recovered from dust, largely fe2o3, collected in steel plants to prevent atmospheric pollution, by mixing it with about an equal weight of aqueous h2so4 of preferably 50 pct concentration, baking for sulfate formation at 130 deg. C, and roasting 4-8 h to convert most of the fe2(so4)3 to fe2o3, with collection of so3 to produce acid for leaching of sulfates of cu, mn, and zn from this oxide. The concentration of the acid can be 1- 10 pct, and 1.5X the oxide weight is used. The oxide and pbso4 are filtered from the leach solution, dried, and pelletized, and the pellets are roasted in a producer or other reducing gas unit mixture at approximately 1,150 deg. C to volatilize pbo and so2 for condensation and recovery from the gas, leaving a partly metallized residue sufficiently free from cu, etc. to be usable in steel melting. A pb-free oxide could be further reduced to a >99 pct pure fe powder if desired. The filtered sulfate solution at ph 2-4 is treated with zn dust to precipitate cu, and it can then be electrolyzed to recover zn on an al cathode, and mNO2 at a pb-ag anode. From dusts containing 0.25-4.4 pct cu, 94-98 pct of the cu was recovered.
U.S. Pat. 3,676,107; July 11, 1972; Chem. Abstr. 77:104,263U