Synergistic removal of As(III) and Cd(II) by sepiolite-modified nanoscale zero-valent iron and a related mechanistic study. (1st October 2022)

• Record Type: Journal Article
• Authors: Ainiwaer, Meihaguli; Zhang, Tuo; Zhang, Nan; Yin, Xianxiang; Su, Shiming; Wang, Yanan; Zhang, Yang; Zeng, Xibai
• Is Part Of: Journal of environmental management. Volume 319(2022)
• Publication Date: 2022-10-01
• Subjects: Sepiolite -- Nanoscale zero-valent iron -- Arsenic -- Cadmium -- Coremoval; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2022.115658
• Languages: English
• ISSNs: 0301-4797

Abstract

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 CdFe2 O4 (Fe–O–Cd), Fe2 As2 O14 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. Highlights: A newly sepiolite modified nZVI was synthesized for co removal of As(III) and Cd(II). S-nZVI has high sorption efficiency of As(III) and Cd(II). Pre-treatment with As(III) can significantly promote Cd(II) adsorption by S-nZVI. The mechanism of As–Cd co-removal is suggested by forming a ternary complex Fe–As–Cd.