Cadmium Isotope Fractionation during Adsorption and Substitution with Iron (Oxyhydr)oxides

Abstract

Cadmium (Cd) isotopes have great potential for understanding Cd geochemical cycling in soil and aquatic systems. Iron (oxyhydr)­oxides can sequester Cd via adsorption and isomorphous substitution, but how these interactions affect Cd isotope fractionation remains unknown. Here, we show that adsorption preferentially enriches lighter Cd isotopes on iron (oxyhydr)­oxide surfaces through equilibrium fractionation, with a similar fractionation magnitude (Δ114/110Cdsolid‑solution) for goethite (Goe) (−0.51 ± 0.04‰), hematite (Hem) (−0.54 ± 0.10‰), and ferrihydrite (Fh) (−0.55 ± 0.03‰). Neither the initial Cd2+ concentration or ionic strength nor the pH influence the fractionation magnitude. The enrichment of the light isotope is attributed to the adsorption of highly distorted [CdO6] on solids, as indicated by Cd K-edge extended X-ray absorption fine-structure analysis. In contrast, Cd incorporation into Goe by substitution for lattice Fe at a Cd/Fe molar ratio of 0.05 preferentially sequesters heavy Cd isotopes, with a Δ114/110Cdsolid‑solution of 0.22 ± 0.01‰. The fractionation probably occurs during the transformation of Fh into Goe via dissolution and reprecipitation. These results improve the understanding of the Cd isotope fractionation behavior being affected by iron (oxyhydr)­oxides in Earth’s critical zone and demonstrate that interactions with minerals can obscure anthropogenic and natural Cd isotope characteristics, which should be carefully considered when applying Cd isotopes as environmental tracers.

Cadmium Isotope Analysis Of Environmental Reference Materials Via Microwave Digestion–Resin Purification–Double-Spike MC-ICP-MS

“…13 Researchers have identified the main Cd sources and their contribution to Cd pollution by determining the Cd isotope ratios of various sources and contaminated receptors (e.g., soil and sediments). [14][15][16][17] Cd isotope fractionation also occurs during its adsorption-desorption between the solid and liquid phases [18][19][20] and translocation to different plant tissues (e.g., roots, shoots, and grains). 21,22 These observations have demonstrated that Cd isotope analysis is a promising tool for tracing the sources of Cd in contaminated sites and can also be used as an indicator for probing the behavior of Cd in the environment.…”

Facet-dependent adsorption of aluminum(iii) on hematite nanocrystals and the influence on mineral transformation

“…Goethite nucleation and growth occur mainly through the dissolution-recrystallization, while that for hematite primarily via a solid-state transformation through internal dehydrationrearrangement. 57,59,60 The existence of a relatively high concentration of remaining AlIJIII) anions in solution of the HNP systems may favor the transformation of the primary ferrihydrite particles immediately formed after OH − addition to hematite rather than goethite, through adsorption onto ferrihydrite to inhibit the mineral dissolution but promote the ferrihydrite aggregation and further structure rearrangement, similar to the effect of phosphate on the ferrihydrite transformation. 61 And this effect decreases in the order HNPs > HNCs > HNRs.…”

Sorption behavior and mechanisms of thallium to microplastics

“…in soils and natural waters have been mostly reported (Zhuang et al, 2021). Manganese oxides are the strongest natural mineral oxidants in the environments (Peacock and Moon, 2012;Yan et al, 2021). Many studies on soils and sediments have found very high correlations between Tl and Mn in the reducible mineral fraction (Cruz-Herna ́ndez et al, 2019).…”