firing is carried out at a temperature of 960 С
Bakhriddin Tilovkabulovich Berdiyarov
Since ferrites and silicates are formed at high temperatures, therefore, in your enriched concentrate there are iron, zinc oxides and silicates. Typically, for large-scale industries before firing, direct, reverse flotation is used. For small volumes, ion flotation can be used. Separating iron and zinc oxides, you can get zinc ferrite nanoparticles from waste.
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Bakhriddin Tilovkabulovich Berdiyarov Consult the appropriate Ellingham diagrams - I suspect your temperature is way too high. I agree with Yuri Mirgorod - the only route to avoid the formation is to reduce the temperature or to find alternative routes.
Perhaps you could treat under reducing atmosphere (for instance hydrogenated atmosphere) to prevent Fe3+ formation. If you replace the whole Fe3+ ions by Fe2+ ions, spinel ferrite will not be formed.
I agree with Philippe Tailhades Idea is to keep avoiding the formation of Fe3+ by firing under reducing environment.
