Abstract
Zero-valent iron (Fe0) nanoparticles (NPs) have shown excellent ability to remove contaminants hexavalent chromium (Cr(VI)) from aquatic systems. Use of support materials can help to prevent oxidation and aggregation of Fe0NPs, and thus enhance their remediation efficiency. However, most previous studies were conducted using artificially synthetic wastewater, and little is known on the remediation effects of supported Fe0NPs on actual wastewaters containing Cr(VI). Here, bentonite-supported Fe0NPs (BFe0NPs) with 1–5% of bentonite were prepared and characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Batch experiments were performed to study Cr(VI) removal by the selected BFe0NPs from a simulated wastewater and a leachate wastewater originating from a Cr slag heap-polluted soil. The results show that Fe0NPs were uniformly dispersed on the bentonite, leading to a decreased aggregation of NPs, and the optimal mass ratio of bentonite was 4%. Batch experiment results show that lower pH values favored Cr(VI) removal by BFe0NPs. The removal percentage of Cr(VI) was higher than 90% for both wastewaters when the pH value was 2.0, but decreased significantly as pH value increased. Cr(VI) removal reaction was quite fast within the initial 10 min, and at least 85% of Cr(VI) was removed for both wastewaters. Cr(VI) removal percentage increased with increasing BFe0NPs dosages ranging from 30 to 60, but remained almost unchanged when the Fe/Cr mass ratio increased to above 60. The reaction of BFe0NPs to remove Cr(VI) followed the pseudo second-order reaction model. In most cases, the removal rates of Cr(VI) were higher in simulated wastewater than in leachate wastewater, but all approached 100% at the optimal conditions. Our present results show that BFe0NPs with 4% bentonite are efficient for treatment of Cr(VI)-containing wastewaters.
Highlights
The compounds containing chromium (Cr) are among the most common pollutants in soil and groundwater [1,2]
When loaded on the bentonite, Fe0 NPs were found to disperse on the surface and edges of bentonite (Figure 1b–f)
Some Fe0 NPs on the bentonite appeared to aggregate into chain-like conformations, the degree of aggregation decreased with the increase of the mass ratio of bentonite, and the BFe0 NPs with 4% and 5% of bentonite appeared to have less chain-like conformations than other BFe0 NPs with less bentonite
Summary
The compounds containing chromium (Cr) are among the most common pollutants in soil and groundwater [1,2]. Cr(III) and Cr(VI) are two main fractions in Cr-containing compounds. Cr(VI) is generally more toxic than Cr(III) for both acute and chronic exposures [3]. Cr(VI) can enter human bodies via ingestion, inhalation, or even directly from skin and move to organs such as liver, kidney, and lung, inducing genotoxicity, carcinogenicity, mutagenicity, and teratogenicity [4,5]. Cr(VI) compounds have been classified as a class I carcinogen for humans by IARC and listed as one of the priority contaminants [6]. Effective techniques need to be developed for remediation of Cr(VI)-contaminated soils and groundwater
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