Influence of pH and Cations Contained in Rainwater on Leaching of Cd(II) from Artificially Contaminated Montmorillonite. Issue 5 (October 2020)

• Record Type: Journal Article
• Authors: Suzuki, Tasuma; Nakase, Kisyo; Tamenishi, Tomohiro; Niinae, Masakazu
• Is Part Of: Journal of environmental chemical engineering. Volume 8:Issue 5(2020)
• Publication Date: 2020-10
• Subjects: soil contamination -- cadmium(II) -- leaching -- acid rain -- ion exchange; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2020.104080
• Languages: English
• ISSNs: 2213-2929

Abstract

Graphical abstract: Highlights: Influence of pH and cations in rainwater on leaching of Cd(II) was investigated. At pH < 6.0, montmorillonite (Mt) sorbs Cd(II) via outer-sphere complex formation. At pH > 6.0, Mt sorbs Cd(II) via inner-sphere complex or CaCO3 formation. Leaching of Cd(II) from contaminated-Mt increased by cations contained in rainwater. Cations except Na + (e.g., Mg 2+ ) are main contributors to enhanced Cd(II) leaching. Abstract: The objective of this study was to investigate the influence of pH and ions contained in rainwater on leaching of Cd(II) from artificially-contaminated montmorillonite, with the final objective of deepening the understanding of the leaching mechanism of Cd(II) from soils. Batch Cd(II) sorption experiments were performed before performing leaching experiments, and the obtained results were modeled using a surface complexation model coupled with ion exchange reactions. The results showed that at a pH below 6.0, the sorption of Cd(II) onto montmorillonite was not significantly influenced by pH but was strongly hindered by NaNO3, showing that the dominant Cd(II) sorption mechanism was ion exchange at the permanent charge. These results indicate that for the typical pH range for rainwater (< 6.0), the concentration of background ions in rainwater may be an important factor controlling the leaching level of Cd(II) from contaminated montmorillonite. The result of leaching experiments using leaching solutions with different pH and background ions demonstrated that as expected, the addition of cations contained in rainwater significantly enhanced Cd(II) leaching. For instance, for the montmorillonite with the Cd(II) content of 5.36 mmol-Cd kg -1, the leaching level of Cd(II) at pH range between 5.0 and 6.0 increased twofold by adding cations contained in rainwater. It was also shown that Na + only slightly contributes to enhanced Cd(II) leaching, and other cations including K +, NH4 +, Ca 2+, and Mg 2+ are the main contributors to enhanced Cd(II) leaching.