Baragano, and 4 co-authors, reported in 2020 that the capacity of two iron-based nanomaterials, namely goethite nanospheres (nGoethite) and zero valent iron nanoparticles (nZVI), to immobilize As in a polluted soil was evaluated and compared. The composition and morphology of the products were studied by energy dispersive X-ray analysis and transmission electron microscopy, while zeta potential and average sizes were determined by dynamic light scattering. To assess As immobilization, soil subsamples were treated with nGoethite or nZVI at a range of Fe doses (0.5%, 2%, 5% and 10%) and then studied by the TCLP test and the Tessier sequential extraction procedure. The influence of both nanoparticles on As speciation was determined, as was impact on soil pH, electrical conductivity, Fe availability and phytotoxicity (watercress germination).
For nZVI, notable results were achieved at a dose of 2% (89.5% decrease in As, TCLP test), and no negative effects on soil parameters were detected. Indeed, even soil phytotoxicity was reduced and only at the highest dose was a slight increase in As3+ detected. In contrast, excellent results were obtained for nGoethite at the lowest dose (0.2%) (82.5% decrease in As, TCLP test); however, soil phytotoxicity was increased at higher doses, probably due to a marked enhancement of electrical conductivity. For both types of nanoparticle, slight increases in Fe availability were observed. Thus, our results show that both nZVI and nGoethite have the capacity to effectively immobilize As in this brownfield. The use of lower doses of nGoethite emerges as a promising soil remediation strategy for soils affected by As pollution.
The authors concluded that the application of nZVI and nGoethite to soil samples from a brownfield polluted with As caused a marked reduction in the availability of this heavy metalloid. The effectiveness of the immobilization was significantly higher for nGoethite. However, the marked effect of high doses of this nGoethite on the EC and
phytotoxicity of soil may limit the use of this nanomaterial for remediation purposes. The highest dose of nZVI (10% w/w) tested was observed to cause a slight increase in arsenate reduction to arsenite (lower than 2%).
The authors also concluded that our results demonstrate that both nZVI and nGoethite, at the lowest doses assayed (0.5% and 0.2%, respectively) are efficient, although the former showed poorer As immobilization yields, as revealed by measurements of As availability in the EX and CB fractions of the Tessier method and in TCLP extracts. Moderate doses of nZVI outperformed nGoethite with respect to As immobilization. On the basis of their findings, they also concluded that, at the lowest dose assayed (0.2%), nGoethite is a safe and promising technique for As immobilization. Regarding nZVI, a dose of 2% would show a similar result for the remediation of the brownfield. Pilot or real-scale studies are now required to validate these conclusions in a range of soil types.
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