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Environmental problems - Chemical approaches
RESEARCH ARTICLE

Can polymeric surface modification and sulfidation of nanoscale zerovalent iron (NZVI) improve arsenic-contaminated agricultural soil restoration via ex situ magnet-assisted soil washing?

Daoheuang Keochanh A B , Saranya Tongkamnoi A B and Tanapon Phenrat https://orcid.org/0000-0003-2179-042X A B *
+ Author Affiliations
- Author Affiliations

A Department of Civil Engineering, Faculty of Engineering, Research Unit for Integrated Natural Resources Remediation and Reclamation (IN3R), Naresuan University, Phitsanulok, Thailand.

B Center of Excellence for Sustainability of Health, Environment and Industry (SHEI), Faculty of Engineering, Naresuan University, Phitsanulok, Thailand.

* Correspondence to: pomphenrat@gmail.com

Handling Editor: Jason Unrine

Environmental Chemistry 20(7) 302-318 https://doi.org/10.1071/EN23078
Submitted: 14 August 2023  Accepted: 12 December 2023  Published: 8 January 2024

© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing.

Abstract

Environmental context

Arsenic (As) contamination in agricultural soil threatens safe agricultural production. Therefore, an ex situ magnet-assisted soil washing, using different types of nanoscale zerovalent iron was tested as a remediation option in soil restoration. Uncoated nanoparticles was the best tested option, with As removal at 45.5% and the nanoparticles were reusable up to four times.

Rationale

Arsenic (As) contamination in agricultural soil threatens safe food and medicinal herb production for millions of people.

Methodology

Therefore, ex situ magnet-assisted soil washing of metal-contaminated soil using bare nanoscale zerovalent iron (NZVI) is proposed as a novel remediation alternative. Conceptually, metal-contaminated soil is mixed with water and bare NZVI, and metals in the soil are transferred to the bare NZVI. The metal-sorbed NZVI is then retrieved from the soil slurry through magnetic separation, leaving behind treated soil. This study evaluated if advanced surface modification can improve ex situ soil restoration efficacy including polymeric coating and sulfidation of NZVI, proven beneficial in situ NZVI application. Sulfur and carboxymethylcellulose (CMC) at various S/Fe and CMC/NZVI ratios were used to modify NZVI via sulfidation and physisorption.

Result

Results revealed that sulfidised NZVI (S-NZVI) performed poorer (41.0%) than bare NZVI (45.5%) in As removal, even at the optimised S/Fe ratio of 0.31. This could be due to acid release via oxidative dissolution of FeS2 on the S-NZVI surface driven by O2. The incidental acid-dissolved NZVI sorption sites decreased As removal efficacy. Similarly, CMC-modified NZVI failed to improve As removal efficacy (11.0%) because it reduced NZVI reactivity and blocked As accessibility to NZVI sorptive sites.

Discussion

Nevertheless, S-NZVI and CMC-modified NZVI promoted non-phytoavailable As fractions in the treated soil. Overall, bare NZVI performed the best for As removal but moderately transformed As into more non-phytoavailable fractions. Bare NZVI can be reused for four cycles of soil washing. In every case, mobile As in treated soil was lower than the maximum contamination level.

Keywords: arsenic contamination, arsenic immobilisation, ex situ soil remediation, food safety, magnet-assisted soil washing, magnetic separation, nanoscale zerovalent iron, polymeric surface coating, sulfidation.

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