Experimental Investigation of Oxide Leaching Methods for Li Isotopes. Issue 3 (20th July 2022)

• Record Type: Journal Article
• Authors: Liu, Chun‐Yao; Pogge von Strandmann, Philip A. E.; Tarbuck, Gary; Wilson, David J.
• Is Part Of: Geostandards and geoanalytical research. Volume 46:Issue 3(2022)
• Page Start: 493
• Page End: 518
• Publication Date: 2022-07-20
• Subjects: Li isotopes -- oxides -- sequential leaching -- hydroxylamine hydrochloride -- BCR‐2 -- SGR‐1b -- Yellow River sediment; Analytical geochemistry -- Periodicals; Géochimie analytique -- Périodiques; 551.9
• DOI: 10.1111/ggr.12441
• Languages: English
• ISSNs: 1639-4488

Abstract

Abstract : To examine the applicability of different leaching methods used to extract secondary oxides from silicate solids for lithium isotope (δ 7 Li) measurement, this study has conducted leaching experiments on five different types of silicate solids, including a fresh basalt, two weathered basalts, a Yellow River sediment (loess‐dominated) and a shale. Four factors were assessed in the experiments: the concentration of the leaching reagent hydroxylamine hydrochloride (HH), the leaching temperature (20 °C vs 95 °C), the leaching time and the reagent/solid ratio. Based on elemental concentrations and Li isotopes, 0.04 mol l −1 hydroxylamine hydrochloride (HH) in 25% v/v acetic acid at room temperature for 1 h with 40 ml g −1 reagent/solid ratio is recommended. At high temperatures, low δ 7 Li and high magnesium/iron ratios indicate that minerals other than secondary oxides are dissolved. With increased leaching time, there is no evidence for Li isotopic fractionation at room temperature. However, longer leaching time or increased reagent/solid ratios may increase the risk of leaching from non‐oxide phases. Meanwhile, results suggest that low concentrations of HH are not sufficient to target the secondary oxides evenly, while high concentrations of HH can leach out more non‐oxides. We also examined the optimal oxide leaching method within a full sequential leaching procedure (i.e., exchangeable, carbonate, oxide, clay and residual phases). Elemental concentrations show that no elements exist exclusively in oxides, so it is essential to analyse multi‐elemental concentrations to verify that the leaching has accessed this phase in a given sample. Comparing secondary oxides with their corresponding solutions, we estimate the isotopic fractionation (Δ 7 Lioxide‐solution ) is −16.8‰ to −27.7‰. Key Points: Different extraction methods for Li isotope ratios in oxides were examined. It is essential to determine element mass fractions in leachates to verify that the extraction is effective. We estimate that the isotopic fractionation between oxide and the corresponding solution (Δ 7 Lioxide‐solution ) is −16.8‰ to −27.7‰.