Comparing the Microstructural Changes of Mechanically Activated Hematite During Nano Zero-Valent Iron Preparation

This investigation presents a new method for preparing nano zero-valent iron (NZVI) from mechanically activated hematite. The XRD analysis indicated that even after 240 min mechanical activation (MA), the constituent phase of hematite could be detectable without any phase change. Regarding peak broadening and reduction of peak intensity, MA generally changed the microstructural properties of hematite with more intensity during the first 60 min of intensive planetary ball milling. The microstructural study performed by the Rietveld method also proved that all microstructural parameters changed in favor of the reactivity promotion of hematite. The amorphization degree and microstrain were increased to 83% and 0.16 (%), respectively, while crystallite size was reduced to 9.2 nm after 240 min MA. Therefore, MA could promote the hematite leachability where iron extraction was increased from 14% in initial hematite to 61% in 240 min mechanically activated hematite. Leaching efficiency increased even after surface area reduction and agglomeration in 240 min mechanically activated hematite. Consequently, the surface area parameter would not be the main factor in hematite reactivity promotion, as microstructural parameters changed in favor of hematite reactivity during MA. Among the microstructural parameters, the amorphization degree and crystallite size were the predominant parameters in the reactivity promotion of 60 min mechanically activated hematite and replaced with microstrain after 240 min MA. Also, NZVI was synthesized with titrating NaBH₄ through chemical precipitation from the iron-bearing solutions obtained during mechanically activated hematite leaching tests. The XRD and FE-SEM analyses also revealed that NZVI was synthesized and fairly oxidized.

Graphical Abstract