Synergistic removal of As(III) and Cd(II) by sepiolite-modified nanoscale zero-valent iron and a related mechanistic study

Meihaguli Ainiwaer; Tuo Zhang; Nan Zhang; Xianxiang Yin; Shiming Su; Yanan Wang; Yang Zhang; Xibai Zeng

doi:10.1016/j.jenvman.2022.115658

Synergistic removal of As(III) and Cd(II) by sepiolite-modified nanoscale zero-valent iron and a related mechanistic study

J Environ Manage. 2022 Oct 1:319:115658. doi: 10.1016/j.jenvman.2022.115658. Epub 2022 Jul 14.

Authors

Meihaguli Ainiwaer¹, Tuo Zhang², Nan Zhang³, Xianxiang Yin⁴, Shiming Su³, Yanan Wang³, Yang Zhang³, Xibai Zeng⁵

Affiliations

¹ College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, China; Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Sciences, Key Laboratory of Agro-Environment, Ministry of Agriculture and Rural Affairs, Beijing, 100081, China.
² Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Sciences, Key Laboratory of Agro-Environment, Ministry of Agriculture and Rural Affairs, Beijing, 100081, China; College of Environmental Science & Engineering, China West Normal University, Nanchong, Sichuan, 637009, China.
³ Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Sciences, Key Laboratory of Agro-Environment, Ministry of Agriculture and Rural Affairs, Beijing, 100081, China.
⁴ College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, China. Electronic address: xqyin@nwafu.edu.cn.
⁵ College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, China; Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Sciences, Key Laboratory of Agro-Environment, Ministry of Agriculture and Rural Affairs, Beijing, 100081, China. Electronic address: zengxibai@caas.cn.

PMID: 35842987
DOI: 10.1016/j.jenvman.2022.115658

Abstract

Arsenic (As) and cadmium (Cd) are two highly toxic elements. In recent years, many newly synthesized chemical materials have been used widely for treatments of As- and Cd-contaminated effluents. However, most materials do not exhibit high efficiencies for simultaneous removal of As and Cd from water systems. Our study established a simple scheme for synthesizing a sepiolite (SEP)-modified nanoscale zero-valent iron (S-nZVI) for simultaneous removal of coexisting As and Cd from water and illuminated a possible underlying mechanism. Batch experiments showed that the maximum capacities for adsorption of As(III) and Cd(II) by S-nZVI were 230.29 mg/g and 11.37 mg/g, respectively, which represented better effects than those of other materials, as reported previously. Removal of Cd(II) depended on pH, but As(III) removal showed little dependence on pH. Coexisting ions such as phosphate (PO₄^3-) and the conjugate base of humic acid (HA) significantly inhibited simultaneous removal of As(III) and Cd(II). In the mixed As(III)-Cd(II) system, the presence of As(III)-pretreated S-nZVI significantly enhanced Cd(II) adsorption by a factor of four over that seen for aqueous solution without As(III). XRD and XPS results showed that CdFe₂O₄ (Fe-O-Cd), Fe₂As₂O₁₄ or FeAsO₄ (Fe-O-As) were formed after As(III) and Cd(II) were captured by S-nZVI. However, a further zeta (ζ) potential analysis showed that the mechanism for As(III) and Cd(II) adsorption by S-nZVI is not just simple formation of the above chemicals, since the adsorbed As(III) increased the negative charge of S-nZVI; this suggested an electrostatic attraction between S-nZVI and Cd(II) and indicated that adsorbed As(III) created new sorption sites for Cd(II), which enhanced Cd(II) sorption via formation of ternary complexes (Fe-As-Cd). These results suggested that S-nZVI is a promising material for in situ remediation of heavy metal-contaminated groundwaters or paddy soils.

Keywords: Arsenic; Cadmium; Coremoval; Nanoscale zero-valent iron; Sepiolite.

MeSH terms

Adsorption
Arsenic* / analysis
Cadmium / analysis
Iron / chemistry
Magnesium Silicates
Water
Water Pollutants, Chemical* / analysis

Substances

Magnesium Silicates
Water Pollutants, Chemical
Cadmium
Water
magnesium trisilicate
Iron
Arsenic