RECOVERING ZINC FROM STEEL SCRAP WHEREBY THE METAL SCRAP MOVES COUNTERCURRENTLY TO THE CAUSTIC LEACHING SOLUTION IN A PLURALITY OF TANKS; APPARATUS THEREFOR

摘要

Caustic dezincing galvanized steel scrap. A dezincing plant includes a plurality of tanks (14, 16, 18) interconnected in series with steel scrap sequentially being moved through each of the tanks. The tanks (14, 16, 18) contain a caustic leaching solution including an oxidant with the leaching solution being circulated through each of the tanks (14, 16, 18) in a direction opposite to the movement of the scrap. Fresh scrap initially is exposed to a partially depleted leaching solution with the oxidant concentration of the leaching solution increasing as the scrap moves through the series of tanks (14, 16, 18). Leaching solution depleted of its oxidant is transferred to an electrolytic cell (22) where zinc is removed and plated as metallic zinc powder onto a cathode. The leaching solution is recycled by removing zinc. The chemistry of the leaching solution is controlled so that sufficient free caustic is present to prevent passivating zinc coating on the scrap. Oxidant is added to the recycled solution and the caustic concentration is adjusted, if necessary, to have a total caustic concentration of at least 5 M and the recycled solution is returned to the last tank (18). Compressed scrap bales are dezinced and ready for use as a melting furnace charge material. IMAGE