Zinc Residue

(also zinc slag), the part of a zinc agglomerate that is formed in horizontal or vertical retorts after zinc distillation. Zinc residue is a friable or semisintered mass, which consists of nonvolatile metals, waste rock, and unburned coal dust. It contains 5–15 percent Zn, 2–5 percent Pb, 1–3 percent Cu, 15–20 percent Fe, 20–25 percent C, 18–20 percent SiO₂, 1–2 percent CaO, as well as a certain amount of noble metals.

Zinc residue is processed in rotary kilns for the complete extraction of zinc. If the zinc residue contains significant quantities of lead, copper, and noble metals, it is subjected to reduction smelting along with the lead agglomerate.