An atomic-scale understanding of the initial stage of nucleation of heavy metal cations on clay edges. (1st March 2019)

• Record Type: Journal Article
• Authors: Zhang, Chi; Liu, Xiandong; Lu, Xiancai; Meijer, Evert Jan; Wang, Rucheng
• Is Part Of: Geochimica et cosmochimica acta. Volume 248(2019)
• Page Start: 161
• Page End: 171
• Publication Date: 2019-03-01
• Subjects: Clay edges -- Complexation -- Heavy metals -- Heterogeneous nucleation -- First principles molecular dynamics; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2019.01.010
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: For the purpose of revealing the microscopic mechanism of the early stage in the nucleation of heavy metals on clay edges, we performed first principles molecular dynamics (FPMD) simulations systematically to characterize the chemistry of the incipient clustering processes by taking Pb 2+ and Ni 2+ as the model cations. We found that Pb 2+ and Ni 2+ have different complexation mechanisms: Pb 2+ cations are adsorbed onto different sites with the similar probability whereas Ni 2+ cations prefer octahedral vacancy to the other sites. The reason is that Pb 2+ does not enter the vacancy due to the large ionic size. p K a calculations indicate that Ni 2+ adions can provide available complexing sites (i.e., OH − groups) for the subsequent cations through hydrolysis and free energy calculations show that the complexation of subsequent cations is thermodynamically favored, which can thus result in nucleation and precipitation eventually. In contrast, the first adsorbed Pb 2+ cannot provide available complexing sites due to the extremely high p K a, thus making nucleation impossible. Our findings, consistent with the experiment, reveal the role of the surface in heterogeneous nucleation, which should also apply to other similar systems. The results derived in this study are directly useful for understanding the mobility and fate of heavy metals in surficial environments.