Iron oxide nanoparticles/nanocomposites derived from steel and iron wastes for water treatment: A review

Iron oxide nanoparticles (IONPs) are characterized by superior magnetic properties, high surface area to volume ratio, and active surface functional groups. These properties aid in removal of pollutants from water, through adsorption and/or photocatalysis, justifying the choice of IONPs in water treatment systems. IONPs are usually developed from commercial chemicals of ferric and ferrous salts alongside other reagents, a procedure that is costly, environmentally unfriendly and limits their mass production. On the other hand, steel and iron industries produce both solid and liquid wastes which in most cases are piled, discharged into water streams or landfilled as strategies to dispose them off. Such practices are detrimental to environmental ecosystems. Given the high content of iron present in these wastes, they can be used to generate IONPs. This work reviewed published literature through selected key words on the deployment of steel and/or iron-based wastes as IONPs precursors for water treatment. The findings reveal that steel waste-derived IONPs have properties such as specific surface area, particle sizes, saturation magnetization, and surface functional groups that are comparable or sometimes better than those synthesized from commercial salts. Furthermore, the steel waste-derived IONPs have high removal efficacy for heavy metals and dyes from water with possibilities of being regenerated. The performance of steel waste-derived IONPs can be enhanced by functionalization with different reagents such as chitosan, graphene, and biomass based activated carbons. Nonetheless, there is need to explore the potential of steel waste-based IONPs in removing contaminants of emerging concern, modifying pollutant detection sensors, their techno-economic feasibility in large treatment plants, toxicity of these nanoparticles when ingested into the human body, among other areas.

Low-Cost Goethite Nanorods for As (III) and Se (VI) Removal from Water

Arsenite (As(III)) and Selenate (Se(VI)) are universally touted as extremely toxic oxyanions in natural and industrial water systems. Thus, the production of low-cost adsorbents that are scalable and toxic-free is of great importance today. In this work, a large-scale goethite nanorods (α-FeOOH NRs) is synthesized using a modified rapid hydrolysis method. The obtained powder is characterized using different multidisciplinary techniques. Accordingly, the results showed uniform and straight nanorods (length ~400 nm and diameter ~40 nm) resembling cigar-like morphology while the structure is confirmed to be of orthorhombic α-FeOOH phase. The potential application of this material to adsorb As (III) and Se (VI) ions in water is explored. In particular, for initial adsorbate concentrations (~500 µg/L), the removal efficiencies are found exceptional with α-FeOOH doses of 0.33 g/L and ~0.5 g/L for As (III) and Se (VI), respectively. Attractively, the adsorption capacities were estimated using trusted isotherms and then experimentally verified at ultimately high concentrations. Besides, a pH-controlled adsorption study showed that a pH of 5–8 is a favored range for higher ionic uptake, which meets the World Health Organization (WHO) benchmarks of drinking water. To conclude, the α-FeOOH NRs are potential adsorbent for the sustainable removal of toxin ions in water systems.