For the recycling of zinc-containing residues, Befesa Zinc Óxido S.A.U. operates two plants in the region of Bilbao, Spain.
Galvanizing residues, i.e. galvanizing ashes, top- and bottom dross (hard zinc) as well as other zinc-containing materials are recycled. The feed materials are delivered to the plants as bulk material, on pallets, in big bags or drums.
At Befesa Zinc Óxido S.A.U. several processes for the production of metallic zinc and zinc oxide from the aforementioned residues are applied. Zinc containing residues with relatively high zinc content like zinc ashes or zinc scraps are remelted to obtain there metallic zinc content. Furthermore the so-called American (direct) process is applied for zinc oxide production. With this technology, mainly oxidic zinc-containing residues are charged to a rotary kiln jointly with carbon which acts as a reducing agent. At the process temperatures prevailing in the kiln, the zinc content is reduced, vaporizes and is discharged from the kiln via the gas phase. The zinc vapor is oxidized to zinc oxide and reclaimed from the off-gas stream by means of filter systems. Furthermore, the French (indirect) process is applied to receive zinc oxide. The metallic residues are first melted in a drum furnace and then transferred to distillation furnaces. In these furnaces, the liquid zinc melt is oxidized to form zinc oxide, discharged with the off-gas stream and separated in filter systems. The zinc oxide produced is sold to the ceramics and tire industries.