Radium depletion and 210Pb/226Ra disequilibrium of Mar^|^iacute;taro hydrothermal deposits, Los Azufres geothermal field, Mexico

Exploring 222Rn as a tool for tracing groundwater inflows from eskers and moraines into slope peatlands of the Amos region of Quebec, Canada

“…The highest 226 Ra 617 activity is found in clay sediments (i.e., sample SMB.no3(m)), where the adsorption capacity 618 of radium is the highest. However, SMB peat water is very acidic (pH = 3.9-4.4; Ferlatte 2014) 619 and the sorption capacity of radium is likely inhibited in this sample, as observed in other acidic 620 environments (Pickler et al, 2012). 621…”

Competitive ion-exchange reactions of Pb(II) (Pb2+/PbCl+) and Ra(II) (Ra2+) on smectites: Experiments, modeling, and implication for 226Ra(II)/210Pb(II) disequilibrium in the environment.

“…Thus, the aqueous ratios of activities of 226 Ra and 210 Pb measured at thermodynamic equilibrium of the exchange reaction, normalized to the ratio of initial activities of both elements, allowing to discuss their relative behavior with respect to adsorption at the smectite surface, are reported as a function of pH for two ionic in Figure 6. and then to date geological mechanisms as hydrothermal deposits (Pickler et al, 2012) and to age or determine the growth rate of marine organisms (Andrews et al, 2005;Sabatier et al, 2012). In a wider use, the "excess" of 210 Pb with regard to 226 Ra in soils and surface sediments is used for tracing and dating purposes (Mabit et al, 2014).…”

“…Early decay chain isotopes ( 238,235,234 U, 231 Pa, 234,232,230,228 Th, 226 Ra) are generally used for dating and highlighting geochemical processes (Grozeva et al, 2022;Milena-Pérez et al, 2021;Vigier et al, 2001). For example, the use of end members of the U decay chain, such as 226 Ra (half-life 1600 y) and 210 Pb (half-life 22.2 y), constrains shorter durations of geological events, such as volcanic eruptions or coral growth (Berlo and Turner, 2010;Ghaleb, 2009;Love et al, 2007;Mabit et al, 2014;Moore and Krishnaswami, 1972;Pickler et al, 2012;Rihs et al, 2021;Wang et al, 2019). In this approach, the assumption is made that geological systems are closed, leading to secular equilibrium between 226 Ra and 210 Pb (i.e., their activities are equal).…”

“…In most studies related to date geological processes, no chemical reactivity (or at least the same chemical reactivity) is assumed for both elements (Pb(II) and Ra(II)) (Berlo and Turner, 2010;Ghaleb, 2009;Love et al, 2007;Mabit et al, 2014;Moore and Krishnaswami, 1972;Pickler et al, 2012). This last assumption has to be assessed especially because: (i) in oxidizing conditions, Pb(II) can easily form insoluble carbonate and sulfate minerals at high Pb aqueous concentrations (10 -5 M), while it is not the case for Ra(II), which is only radiogenic and then presents only at very low concentrations in rocks or soils (usually <0.88 ppt) and in natural waters (<10 -15 M) (Fesenko et al, 2014), and (ii) aqueous speciation of both elements is generally significantly different in natural waters (Fesenko et al, 2014;Powell et al, 2009).…”