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A novel method for metal recovery from zinc & lead slags Zhang, Yanjun

Abstract

Conventional zinc fuming from lead blast furnace slags cannot continue when zinc and lead contents are below 1.5-2.5 wt.% and 0.1-0.5 wt.% respectively, because of solid iron formation, which also causes the formation of accretions, foaming of slag, and contamination of the fume. A new method, electroreduction, was developed in a previous study to recover the heavy metals zinc, lead, indium and germanium from final zinc fumer slag. A series of experiments was also conducted in this study using two types of fumer slag from COMINCO. Zinc content was 4.5wt% in one slag and 1.5wt% in another slag. Experimental data indicated that about 50% of the zinc and most of the lead could be removed from both slags by 90 minute of electrorefining. Following the work on the fumer slags, a study was conducted on the potential to reduce lead and zinc directly from COMINCO's Kivcet slag (containing about 16 wt% zinc and 10 wt% lead) and potentially obviate the need for slag fuming. Metal recovery from the Kivcet slag was examined using the three methods used for the fumer slag study: holding at temperature to allow the divalent iron to reduce the metal ions into the gas phase; equilibration with a copper "getter"; and electroreduction into a liquid copper cathode using a graphite anode. The presence of metallic lead and carbon in the Kivcet slag has a significant influence on the recovery of metal from the slag in subsequent processing. Holding of the slag at temperature permitted the recovery of much of the metallic lead as vapor and some small recovery of zinc as fume. When copper was used as a getter, more zinc and lead were recovered. In electrorefining, lead recovery was much higher than that in equilibrating with copper, but there was no obvious enhancement in zinc recovery. A series of experiments were also conducted in which the Kivcet slag was treated to remove some of the zinc and the lead and then was electro-refined three times. Zinc and lead contents in the final slag decreased to 5.9% and 0.3% respectively. Although most of the lead was recovered, further refining would still be required to capture the remaining zinc metal.

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