Redemption of Microscale Mill Waste into Commercial Nanoscale Asset

Abstract

Mill-scale is a porous, hard and brittle coating of several distinct layers of iron oxides (predominantly Fe3O4) formed during the fabrication of steel structures. It is magnetic in nature with iron content up to as high as 93%. About 1240 million metric tons of steel was produced in 2006 globally, 1.5 % of which by weight accounts for the mill-scale waste. Thus, 18.6 million metric ton of mill scale waste was produced in one year alone. Most of the steel mill-scale waste (almost 80%) end ups in a landfill; a small fraction of it is also used to make reinforced concrete in Russia and some Asian countries. A purer commercial form of this oxide in combination with nickel and zinc oxide is used in making ceramic magnets (soft ferrites) which are an integral part of all the audio-visual and telecommunication media on this planet as well those in the space. The mill-scale waste could be a valuable technological resource if properly processed and converted into nanoscale species, in particular nanoscale iron particles for hydrogen fuel cell, medical imaging and water remediation applications. In order to achieve the much-discussed and sought-after hydrogen economy via an ‘econo’ viable and ‘enviro’ friendly route, a roadmap for utilizing the mill-scale waste has been developed. The method consists of reacting heated iron with steam, also appropriately called metal-steam reforming (a route well-known to the metallurgists for centuries) generating high purity hydrogen, with a twist. The innovation lies in the conversion of the coarse oxide scale into nanoscale iron by a novel solution-based technique. This produces highly uniform zerovalent iron particles as small as 5 nm. The scope of utilizing the mill-scale waste is broadened several folds as nanoscale iron and nanomagnetite find potential applications in de-arsenification of drinking water, destruction of perchlorate and reduction of hexavalent chromium ions in water sources. In addition, nanoscale iron and magnetite are finding increasing application as the preferred contrasting agents in magnetic resonance imaging - MRI.

A novel paradigm in greenhouse gas mitigation

“…Generation of hydrogen via metal‐steam reforming reaction as per Eq. 9 has been amply demonstrated [21–23]. A comparison of the fuel cell output under engine exhaust conditions with those using other feeds is presented in Figure 5; the fuel cell operated at 83.9% efficiency with the engine exhaust.…”

Hydrothermal Production of H2 and Magnetite From Steel Slags: A Geo-Inspired Approach Based on Olivine Serpentinization

“…The net reaction corresponds to the water-gas shift: COg + H 2 Og ⇒ CO 2 + H 2 (e.g., Murugan et al, 2011), with oxygen being transiently stored in the form of iron oxide. There is therefore the potential to use embarked cartridges of reduced iron to produce H 2 -rich steam for remote production and utilization (e.g., Azad et al, 2008). Whereas, in the early 1900s, H 2 was produced with the Lane producer, which operated at temperatures around 600-800 • C, new versions of steam-iron producers can be operated in the same T range (stable cycle at 900 • C) with gasified biomass using sponge iron with a high surface area to yield high-purity H 2 , compatible with fuelcell applications (Hacker et al, 2000).…”

“…Another approach would consist in using a low-value ferrous starting material to achieve water splitting without considering further reduction steps. The steel industry does produce such potential starting materials (waste, byproducts, mine tailing), the H 2 -production capacity of which has already been investigated in a few experimental studies (Azad et al, 2008;Matsuura and Tsukihashi, 2012;Malvoisin et al, 2013;Michiels et al, 2015Michiels et al, , 2018Shatokha et al, 2016;Crouzet et al, 2017b;Kularatne et al, 2018 for olivine-bearing mine tailings of nickel extraction). The steam-iron process can be categorized as a thermochemical water-splitting method which uses iron as reducing agent.…”

An Innovative Method of Converting Ferrous Mill Scale Wastes into Superparamagnetic Nanoadsorbents for Water Decontamination

“…These oxides are formed during the fabrication of steel structures and the wastes can be converted into a valuable secondary material due to its high iron content (up to as high as 93%), low impurities, and stable chemical composition [ 9 , 10 ]. Usually, a reduction process is applied due to the high content of iron, either via hydrogen, by microwave heating, or by applying solution-based techniques [ 6 , 11 ].…”