Enhancing zero-valent iron (ZVI) pulverization during mechanical milling: FeSx as milling aids

A critical problem in the production of ultrafine zero-valent iron (ZVI) using mechanical milling is that the metallic iron (main component of ZVI) is ductile and can withstand severe plastic deformation, which leads to the slow pulverization of ZVI during its milling. In this work, we introduce non-ductile particle solids (FeSx) as milling aids to enhance the pulverization of the ductile ZVI, and find that the addition can improve the pulverization. The result is verified in three different ways through which the milling aids (FeSx) are introduced, namely, the addition of the FeSx solid directly, the use of the FeSx that is formed during the milling using aqueous sulfide solution as milling solvent with and without the addition of ferrous ion. The ZVI particles are pulverized to hundreds of nanometers using the milling aids, while the particles are deformed to flakes of a few microns without the milling aids. Such size difference is quantified using two sizing technologies independently and is verified by the study of the hydrodynamic performance at three flow conditions that are of practical interest for the environmental applications of ZVI. Mechanism of the FeSx as milling aids for the pulverization enhancement may relate to its wedge effects, its non-ductile texture that inhibits the cold welding and its fine bead function. The study provides a method to improve the efficiency of the production of ultrafine iron particles for environmental applications and it is also the 1st work reporting the enhancement of the pulverization of ductile ZVI.