Abstract
A hybrid (pyro + hydrometallurgical) route is evaluated for the selective removal of zinc from the fine fraction of basic oxygen furnace sludges. The route consists of the following steps: i) thermal decomposition of the franklinite (ZnO. Fe2O3) present in the sludge, in the presence of NaOH, ii) staged leaching of the sludge in NaOH solution in order to selectively remove zinc, and iii) washing of the sludge for the removal of reminiscent alkalis from the treatment. The first two steps are evaluated accordingly to three distinct operating conditions: soft, intermediate and severe. It is verified that the thermal decomposition of franklinite is a crucial step to assure the effective removal of zinc. A maximum of 90% of zinc was removed in the best tested condition with practically no loss of iron content, thus demonstrating that the route is very selective. The washing step is also efficient, with total removal of sodium and potassium. Finally, enrichment around 10 times on the Fe/Zn ratio is obtained, from originally 11.6 to 128.8.
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