Alkaline leaching of galvanized steel scrap

Details Alkaline leaching of galvanized steel scrap Alkaline leaching of galvanized steel scrap

C - Chemistry, Metallurgy

23

F

C23F 1/40 (2006.01) C22B 7/00 (2006.01) C22B 19/30 (2006.01)

Patent

CA 2052849

Caustic dezincing galvanized steel scrap. A dezincing plant includes a plurality of tanks interconnected in series with steel scrap sequentially being moved through each of the tanks. The tanks contain a caustic leaching solution including an oxidant with the leaching solution being circulated through each of the tanks 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. Leaching solution depleted of its oxidant is transferred to an electrolytic cell 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. Compressed scrap bales are dezinced and ready for use as a melting furnace charge material.

Dézincification alcaline de riblons d'acier galvanisé. Installation de dézincification comprenant de nombreuses cuves, reliées en série; les riblons d'acier passent séquentiellement à travers chacune des cuves. Les cuves renferment une solution de lixiviation alcaline, incluant un oxydant; on fait circuler la solution de lixiviation à travers chacune des cuves dans le sens opposé au déplacement des riblons. Les riblons frais sont exposés à une solution de lixiviation partiellement appauvrie, la concentration d'oxydant de la solution de lixiviation augmentant à mesure que les riblons progressent à travers la série de cuves. La solution de lixiviation appauvrie en oxydant est transférée à une cellule d'électrolyse, où le zinc est extrait et plaqué sous forme de poudre de zinc métallique sur une cathode. Après extraction du zinc, la solution de lixiviation est recyclée. Les caractéristiques chimiques de la solution de lixiviation sont contrôlées de telle façon qu'il y ait présence de suffisamment de produit alcalin libre pour empêcher la passivation du revêtement de zinc sur les riblons. L'oxydant est ajouté à la solution recyclée et la concentration alcaline est ajustée au besoin pour obtenir une concentration alcaline totale d'au moins 5 M; la solution recyclée est retournée à la dernière cuve. Après dézincification, les paquets comprimés de riblons sont prêts à alimenter le four de fusion.

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