Environmental Application of Biogenic Magnetite Nanoparticles to Remediate Chromium(III/VI)-Contaminated Water

Yumi Kim,Yul Roh

doi:10.3390/min9050260

Abstract

The physicochemical characteristics of biogenic minerals, such as high specific surface areas and high reactivity and the presence of a bacterial carrier matrix, make them promising for various applications. For instance, catalysts, adsorbents, oxidants, and reductants. The objective of this study is to examine the efficiency of biogenic magnetite nanoparticles (BMNs) that are produced by metal-reducing bacteria for removing chromium. Interactions between ionic chromium (Cr III/VI) and BMNs were examined under different pH values (ranging from pH 2 to pH 12) by using different doses of BMN (0–6 g/L). Chemically synthesized magnetite nanoparticles (CMNs) were used in the experiments for the purpose of comparing them to the BMNs. The results showed that the BMNs had higher Cr(VI) removal efficiency (100%) than the CMNs (82%) after a two-week reaction time. A lower pH and longer reaction time in the Cr-contaminated solution led to a higher Cr(VI) removal efficiency. The Cr(VI) removal efficiency by the BMNs in the Cr-contaminated groundwater was about 94% after a reaction time of two weeks. The BMNs that were coated with organic matter were more effective than the CMNs in leading to adsorption of Cr(III) with electrostatic interactions (82% versus 13%) and in preventing Fe(II) oxidation within the magnetite structure. These results indicate that the BMNs could be used to decontaminate ionic Cr in environmental remediation technologies.

Highlights

Chromium (Cr) is primarily present in the environment in two oxidation states: Cr(III) and Cr(VI).While the trivalent Cr(III) is only toxic at high concentrations, the hexavalent Cr(VI) is a strong oxidizer that is toxic to humans and the environment at μg/L concentrations
The biogenic magnetite nanoparticles (BMNs) synthesized by bacteria were coated with organic materials that had a functional group, such as carboxyl (-COO− ) in the previous study [11]
They were regarded as extracellular polymeric substances (EPSs) that resulted from microbial metabolism [11]

Summary

Introduction

Chromium (Cr) is primarily present in the environment in two oxidation states: Cr(III) and Cr(VI). While the trivalent Cr(III) is only toxic at high concentrations, the hexavalent Cr(VI) is a strong oxidizer that is toxic to humans and the environment at μg/L concentrations. Cr(III) exists primarily as a cation (e.g., Cr3+ , Cr(OH)2+ ) in solution, while the Cr(VI) exists primarily as an anion (e.g., HCrO4 − , CrO4 2− , Cr2 O7 2− ), depending on the pH [1]. Iron-containing minerals are considered to be beneficial in chromium treatment in aqueous solutions because the minerals are predominantly available in nature. They play key roles in elemental recycling in the environment.

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