Journal
APPLIED CLAY SCIENCE
Volume 247, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.clay.2023.107213
Keywords
Pre-treatments; Hydrogen; Stable isotopes; Smectite; Kaolinite; Structural alteration
Ask authors/readers for more resources
This study examined the effects of different pre-treatments on the structural H-isotope composition of clay minerals. The results showed that different pre-treatments had varied impacts on different clay minerals, and the choice of pre-treatment should be based on the specific properties and mineralogy of the samples.
The structural hydroxyl hydrogen (H)-isotope compositions of clay minerals are frequently used as tracers of alteration or change in paleoenvironmental and material science studies. Dissolution pre-treatments are commonly used to remove cements and H-bearing impurities prior to isotopic analysis. These pre-treatments commonly include reactions respectively with: HCl or acetic-acetate buffer, H2O2 or NaClO, and a Na-dithionite-Na-citrate-bicarbonate (DCB) solution in order to remove carbonates, organic matter, and iron (oxy)hydroxides. However, there has been inconsistent data regarding to what extent the structural hydroxyl H-isotope composition of a clay mineral is altered during exposure to these chemical pre-treatments.This study examined the most extreme impacts of each pretreatment on the structural H-isotope composition of reference nontronite, montmorillonite, saponite, and kaolinite samples obtained from the Clay Minerals Society Source Clay Repository. All chemical reagents were isotopically labeled to a delta 2H value approximate to+200 or +570 parts per thousand, to sharply contrast the average clay starting material delta 2H value approximate to-120 parts per thousand. H-isotope compositions were measured before and after pre-treatments by High Temperature Elemental Conversion (TCEA) coupled with an Isotope Ratio Mass Spectrometer (IRMS). TCEA-IRMS measurements were done on potassium (K)-exchanged samples pre-dried under active vacuum at 220 degrees C to mitigate isotopic contamination by adsorbed water vapor.The results showed that only the H-isotope composition of kaolinite was unaffected by all pre-treatments. NaClO and DCB treatments affected the H-isotope compositions of saponite and nontronite, respectively, with the remaining pre-treatments not causing measurable changes for these two clay minerals. The HCl and H2O2 pre-treatments caused massive alteration to the H-isotope compositions for montmorillonite and are considered unadvisable for use with this clay mineral, with respect to H-isotope analysis. The study confirms the possibility of altering the H-isotope composition of clays when using common selective dissolution procedures. The choice of applied pre-treatments before H-isotope measurements for clay-bearing materials should be based on the specific properties and mineralogy of the investigated samples and the amount and type of impurities they contain.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available