鉄還元揮発法による亜鉛焙焼鉱からの金属亜鉛回収

鉄還元揮発法による亜鉛製錬の基礎研究 (第2報)

抄録

The iron-reduction distillation process consists of two successive reduction stages for the mixture of iron oxide and zinc oxidewith a Fe/Zn mole ratio of 2 as a starting material. Experimentswere carried out to investigate the reduction stages by using zinc calcine as a zinc oxide source. Thermodynamic estimations on the bahavior of minor elements were also made. The results are summarized as follows:
(1) On the first reduction stage with a CO₂/CO gas ratio of 0.1 at temperatures 973 and 1073 K, iron oxide was preferentially reduced to metal, while zinc oxide was only slightly reduced. Particularly at 973 K, reduction of zinc oxide hardly proceeded, which suggested that 973 K ofa lower temperature was favorable for the first reduction stage. Zinc ferrite, ZnFe₂O₄, was easily decomposed, but other zinc compounds such as ZnS and Zn₂SiO₄were lessreducible than ZnO and remained after the first reduction stage.
(2) On the second reduction stage in a vacuum of 1 Pa at 1173, 1273 and 1373 K, all the zinc compounds were completely reduced to zinc vapor by the metallic iron, which had been previously reduced on the first reduction stage, within 60, 20, and 10 min at the respective temperatures. Zinc recovery of 91-98% was attained on the second stage in successive treatment of the first and second reductions. The iron contents in the residues were 83-86%, which suggested that the residues could be returned to the first reduction stage or sent to the steelmaking process.
(3) From the thermodynamic estimations it was considered that some minor elements which are more noble than iron were reduced to metals on the first reduction stage. Cadmium was found to be volatilized above 70% during the first reduction, and most of lead was vaporized during the second reduction. Since most of coexisting minor metal values such as gold, silver and copper are concentrated in the metallic iron, their recovery with high efficiency can be expected by magnetic separation of the residue.