Removing Fe is an essential step to obtain target metals from minerals in various industries. The most typical example is to remove Fe from Fe−Zn mixed mineral leachate in zinc hydrometallurgy. Current removal methods that precipitate Fe as Fe-poor phases (e.g., ferric hydroxide, jarosite, and goethite) generate massive Fe-bearing wastes, which results in land occupation, resource loss, and environmental risk. To handle this problem, the present work innovatively precipitated Fe in Fe−Zn mixed solution as magnetite (the mineral with the highest stoichiometric Fe content) with reduced Zn coprecipitation, simply by slowing the addition of Fe−Zn mixed solution into alkali. We uncovered that slower addition of Fe−Zn mixed solution destabilized Fe-bearing intermediates and then promoted the rapid and direct formation of magnetite. Coprecipitation of ZnO and Fe-bearing intermediates, as well as the resulting Zn retention, was thereby circumvented. Compared to conventionally generated Fe-bearing waste, magnetite obtained by the slow addition method had less mass amount (reduced from 1.67 to 0.89 g), lower Zn/Fe ratio (reduced from 0.214 to 0.158), and superior magnetic separation performance (enhanced from 38.8 to 88.2 emu/g). This study proposed a facile strategy to efficiently precipitate Fe as magnetite and elucidated the underlying mechanism, which sheds light on the minimization of Fe-bearing wastes and elimination of corresponding environmental risks.
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