Precipitation of crystallized hydrated iron(III) vanadate from industrial vanadium leaching solution

The crystalline Fe4(VO4)4·5H2O was synthesized at normal pressure from mixing vanadium leaching solution with Fe2(SO4)3. We investigated the effects of reaction temperature, pH and alkali type and characterized the precipitate using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the V/Fe molar ratio and vanadium precipitation ratio decreased with the elevation of pH and reaction temperature, but the addition of Ca(OH)2 increased the V/Fe molar ratio and the vanadium precipitation ratio, then a better crystallized precipitate was synthesized. The best conditions obtained are reaction temperature at 90 °C, pH 2–3, reaction time of 72 h and the addition of Ca(OH)2. Under these conditions, the V/Fe molar ratio of precipitate was close to 1.0 and over 98.5% of the vanadium was precipitated. XRD and SEM analysis showed that the precipitate were conformed as crystalline Fe4(VO4)4·5H2O with grain size of 5–15 μm.

Research Highlights
► Avoid producing high concentration ammonia wastewater.
► The formation of calcium vanadium precipitate appears at pH 3.0–5.0.
► The addition of calcium promotes the crystallization of iron vanadate at pH 2.0–3.0.
► It is economical to use the Ca(OH)2 to adjust the pH of the solution in the precipitation process in industry.