Salt-based melting process

摘要

PCT No. PCT/US88/02374 Sec. 371 Date Oct. 13, 1989 Sec. 102(e) Date Oct. 13, 1989 PCT Filed Jul. 19, 1988 PCT Pub. No. WO89/06291 PCT Pub. Date Jul. 13, 1989.A continuous salt-based process is provided for melting and reclaiming aluminum from aluminum scrap containing impurities including heating a molten salt in a heat bay, mixing the heated salt with aluminum scrap or skim in a charge bay to form a molten charge mixture, separating aluminum from impurities in the charge bay by coalescing aluminum to form a molten aluminum metal pad, chlorinating a portion of the charge mixture from the charge bay to form a chlorinated salt mixture and metal chlorides, removing metal chlorides from the salt mixture, and feeding the salt mixture back to the heat bay. In one aspect, the chlorinating step of the present invention includes introducing carbon monoxide or, preferably, solid carbon to control oxide concentration. The process further comprises adding fluorides and removing metal chlorides from the salt to maintain a preferred salt composition. The metal chlorides can be removed by withdrawing volatile metal chloride gases and electrolytically reducing metal chlorides in the molten salt. A further aspect of the invention permits direct reduction of oxide impurities in the salt by electrolysis. In another aspect of the invention, the scrap itself is used as a consumable heating electrode (i.e., disappearing as the scrap melts) for heating the molten salt. An additional aspect of the invention provides that the molten salt is pumped past heating electrodes, which reduces hot spots that otherwise would lead to fuming and cause instability in the molten bath composition. Yet another aspect of the invention permits removal of carbon impurities, which can be introduced to the molten salt when melting of the scrap causes pyrolysis of organic material associated with the scrap, for example, the lacquer coating on beverage cans.