Synthesis of Nanoscale Zerovalent Iron (nZVI) Supported on Biochar for Chromium Remediation from Aqueous Solution and Soil.

Haixia Wang,Hongyi Li,Mingliang Zhang

doi:10.3390/ijerph16224430

Abstract

Maize straw biochar-supported nanoscale zero-valent iron composite (MSB-nZVI) was prepared for efficient chromium (Cr) removal through alleviating the aggregation of zero-valent iron particles. The removal mechanism of MSB-nZVI was investigated by scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). Cr(VI) removal from aqueous solution by MSB-nZVI was greatly affected by pH and initial concentration. The removal efficiency of Cr(VI) decreased with increasing pH, and the removal kinetics followed the pseudo-second-order model. XRD patterns of MSB-nZVI before and after reaction showed that reduction and precipitation/co-precipitation (FeCr2O4, Fe3O4, Fe2O3) occurred with the conversion of Cr(VI) to Cr(III) and Fe(0) to Fe(II)/Fe(III). The produced precipitation/co-precipitation could be deposited on the MSB surface rather than being only coated on the surface of nZVI particles, which can alleviate passivation of nZVI. For remediation of Cr(VI)-contaminated saline–alkali soil (pH 8.6–9.0, Cr 341 mg/kg), the released amount of Cr(VI) was 70.7 mg/kg, while it sharply decreased to 0.6–1.7 mg/kg at pH 4.0–8.0, indicating that the saline–alkali environment inhibited the remediation efficiency. These results show that MSB-nZVI can be used as an effective material for Cr(VI) removal from aqueous solution and contaminated soil.

Highlights

Chromium is a highly toxic contaminant in industrial wastewater that is discharged from metallurgy, leather tannery, electroplating process, and dyeing, etc
70.7 mg/kg, while it sharply decreased to 0.6–1.7 mg/kg at pH 4.0–8.0, indicating that the saline–alkali environment inhibited the remediation efficiency. These results show that maize straw biochar (MSB)-nZVI can be used as an effective material for Cr(VI) removal from aqueous solution and contaminated soil
MSB-nZVI samples were synthesized as follows: 1 g MSB sample was added into the solution (5 g analytical grade FeSO4 ·7H2 O dissolved in 500 mL deionized water) for 24 h at room temperature (20–25 ◦ C)

Summary

Introduction

Chromium is a highly toxic contaminant in industrial wastewater that is discharged from metallurgy, leather tannery, electroplating process, and dyeing, etc. Hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) are the main valence states present in the wastewater and contaminated soil, and Cr(VI) is much more soluble, mobile, and toxic than Cr(III) [1]. The Cr(VI) species including chromate (CrO4 2− , HCrO4 − ) and dichromate (Cr2 O7 2− ) can cause serious health issues. According to the World Health Organization (WHO) guidelines and Chinese standards (GB5749-2006), less than. The efficient removal of Cr(VI) from wastewater in recent years has become an urgent environmental issue. NZVI has been successfully used for the treatment of many contaminants from wastewater and contaminated soil, including inorganic pollutants (e.g., Cr(VI), As(V), Cu2+ , NO3 − ), and organic pollutants (e.g., Polychorinated biphenyls (PCBs), Int. J. Public Health 2019, 16, 4430; doi:10.3390/ijerph16224430 www.mdpi.com/journal/ijerph

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