Recovery of Carbon Values from Horizontal Zinc Retort Residues

Abstract

Old horizontal and vertical retort Zn smelter sites are being examined by Federal and State environmental agencies because the residues and other wastes contain Pb and Cd. Residues at some of the sites have been declared hazardous wastes. Conservative estimates place the amount of these wastes at 36 Mmt. There are a number of sites with up to 0.4 Mmt of wastes in Kansas, Illinois, and West Virginia and one in Pennsylvania with 27 Mmt of wastes. In addition to their C content (20–30%), the residues represent a possible resource for Ge, Ga, In, Ag, Mn, Pb, and Zn. Samples obtained from several sites near Gas, Kansas are being used in research attempting to recover the unburned C and the metal values as separate products, leaving a nonhazardous residue that could be disposed of safely and economically. The residue was ground to liberate the C. Initial efforts to recover the C used oil agglomeration. This method recovered 67–781% of the C at grades of 66–79% but required large quantities of oil; the absence of agglomeration made separation difficult. Froth flotation has recovered 64–85% of the C in concentrates grading 54–84%.