Biochar aging in contaminated soil promotes Zn immobilization due to changes in biochar surface structural and chemical properties

Abhay Kumar; Stephen Joseph; Ludmila Tsechansky; Karen Privat; Inga J Schreiter; Christoph Schüth; Ellen R Graber

doi:10.1016/j.scitotenv.2018.01.157

Biochar aging in contaminated soil promotes Zn immobilization due to changes in biochar surface structural and chemical properties

Sci Total Environ. 2018 Jun 1:626:953-961. doi: 10.1016/j.scitotenv.2018.01.157. Epub 2018 Feb 19.

Authors

Abhay Kumar¹, Stephen Joseph², Ludmila Tsechansky¹, Karen Privat³, Inga J Schreiter⁴, Christoph Schüth⁴, Ellen R Graber⁵

Affiliations

¹ Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion 7505101, Israel.
² School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia; School of Environmental and Life Sciences, Chemistry, University of Newcastle, Callaghan, NSW 2308, Australia; Nanjing Agricultural University, Nanjing 210095, China.
³ Electron Microscope Unit, University of New South Wales, Sydney, NSW 2052, Australia; PANGEA Research Centre, School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
⁴ Institute of Applied Geosciences, Technische Universität Darmstadt, Schnittspahnstraße 9, 64287 Darmstadt, Germany.
⁵ Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion 7505101, Israel. Electronic address: ergraber@agri.gov.il.

PMID: 29898560
DOI: 10.1016/j.scitotenv.2018.01.157

Abstract

Adding biochar to Zn-contaminated soil can immobilize excess Zn and promote plant biomass growth. This was seen previously over the course of a 180-day planted pot trial involving two types of biochar (cattle manure, CM, and grain husk, GH) in a Zn-contaminated soil. Both biochars alleviated Zn-induced phytotoxicity to Ficus by immobilizing Zn and reducing its uptake by the plant, but to different extents. The aim of the current study was to delve into the in-soil mechanisms involved in biochar-mediated Zn immobilization. Biochar particles were excavated from the pot soils. Fresh and aged biochar particles were examined by high-resolution scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), field-emission electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The physical and chemical properties of the biochars had changed over the 180 days. SEM-EDS and EPMA indicated that organo-mineral micro-agglomerates had formed on biochar surfaces and in pores. Some of the Zn immobilized by the biochars was bound in the organo-mineral complexes of these agglomerates. XPS and FTIR showed that the complexes had a high concentration of oxygenated functional groups which facilitated Zn binding and encapsulation. The micro-agglomerates were similar in structure and composition to those observed on biochars having resided for much longer times in soils, or having been subjected to accelerated aging. Overall, Zn immobilization by the CM biochar was greater than by the GH biochar, due to its higher alkalinity, higher concentration of available negatively charged groups, and greater accretion of organo-mineral layers. These findings are suggestive that biochar-assisted phytorestoration of heavy metal-contaminated soils can be optimized through selection of biochar having such traits. It is hypothesized that metals may be continually taken up in such micro-agglomerates, since they continue to form over the lifetime of the biochar in the soil.

Keywords: Biochar; FTIR; Immobilization; Scanning electron microscopy; X-ray photoelectron spectroscopy; Zinc.

MeSH terms

Biomass
Charcoal / chemistry*
Environmental Restoration and Remediation
Manure
Metals, Heavy / chemistry
Soil / chemistry
Soil Pollutants / chemistry*
Zinc / chemistry*

Substances

Manure
Metals, Heavy
Soil
Soil Pollutants
biochar
Charcoal
Zinc