The chemical exchange between the atmosphere, crust and mantle depends on sediment recycling via subduction. However, it remains unclear how atmospherically modified sediment may affect mantle oxygen fugacity through time. The Great Oxidation Event, among the most important atmospheric changes on Earth, offers an opportunity to investigate changes in magmatism related to surface–mantle interactions. Here we use sulfur K-edge micro X-ray absorption near-edge structure spectroscopy to measure the relative abundances of S⁶⁺, S⁴⁺ and S²⁻ state in apatite inclusions hosted in 2.4–2.1-billion-year-old igneous zircons from the Mineiro Belt, Brazil. The host magmas record intracrustal melting of juvenile crust and the involvement of recycled sediments in the sub-arc mantle wedge. Unaltered apatite inclusions reveal a change from reduced to more oxidized magmas from pre- to post-Great Oxidation Event during the early Proterozoic. We argue that this change is a direct result of deep subduction of oxidized sediments and thus evidence of mantle–atmosphere interaction across the Great Oxidation Event. This suggests that the onset of sediment recycling in the Archaean provided atmospheric access to the mantle, and early ‘whiffs’ of oxygen may have already contributed to a localized increase of calc-alkaline magmatism and related ore deposits on Earth.

Structural repair is a vital step in the direct recycling of spent LiNi _x Co _y Mn _z O ₂ lithium‐ion batteries, yet its underlying mechanisms remain insufficiently clear. Herein, the thermal solid‐state structural repair of spent LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622) layered cathode material is systematically investigated. Through multiscale techniques combining XRD, XAS, and ⁶ Li solid‐state NMR, we identify the structural degradation in spent NCM622 and monitor both long‐ and short‐range structural evolution during repair. Our findings reveal that degradation predominantly occurs through Ni migration into Li octahedral sites, while Co and Mn demonstrate relatively lower occupancies in the Li layer. Such occupancies are primarily responsible for structural disorder and cubic‐symmetry domain formation within the spent material. The repair process is demonstrated to involve re‐lithiation, oxygen capture, increased transition metal (TM) oxidation states, and the migration of TM ions from the Li layer back to the TM layer, followed by cation diffusion. Both temperature and lithium compensation ratio are identified as critical factors promoting these processes. Capacity recovery studies show a strong correlation between reduced TM occupancy in the Li layer and improved electrochemical performances. These insights allow us to move beyond conventional phase‐transition perspectives, offering an atomic‐level understanding of structural degradation and repair mechanisms in spent layered cathode materials.

Mn_xZn_1-xFe₂O₄ (x = 0–1) solid solution was prepared using the TREG-mediated solvothermal method. 10–12 nm spherical superparamagnetic particles (except for ZnFe₂O₄) were obtained. At room temperature, the ferrites have lower magnetic saturation (Ms) than magnetite. However, at 10 K, it is precisely the opposite. DRX and EXAFS showed that incorporating Zn²⁺ ions in tetrahedral A-sites provokes a redistribution of Mn and Fe ions in octahedral B-sites of the mixed spinel structure. For Zn concentrations from x = 0.5 and below, the Mn and Fe ions are almost equally distributed between A and B-sites. Therefore, at low Zn concentrations, the small migration of Fe and Mn ions to B-sites increases the magnetic moment of B sub-lattices and, consequently, the total magnetic saturation. In addition, Mn²⁺ oxidized to Mn³⁺ and, simultaneously, Fe³⁺ reduced to Fe²⁺, affecting the magnetic properties. The increment of Zn concentration severely reduces the magnetization.

Environmental context: Cobalt is a technologically critical element due to its uses in the green energy transition, but its cycling is poorly constrained in surface environments. We determined the form of cobalt in naturally enriched soils and found that it is commonly associated with manganese as mixed oxide nanoparticles. These findings demonstrate that the behaviour of critical elements such as cobalt in the environment is in part governed at the nanoscale. Rationale: Cobalt (Co) faces increasing demand for use in batteries and alloys, but its environmental behaviour in terrestrial surface environments is poorly constrained. This study analyses cobalt regolith mineralogy and nanoparticulate phase transitions to address this knowledge gap. Methodology: We studied Co-enriched environments across six localities and four distinct deposit types in arid and semi-arid Australian regolith environments to analyse its environmental behaviour. We used a combination of single particle inductively coupled plasma–mass spectrometry (SP ICP-MS) and synchrotron X-ray techniques (fluorescence microscopy, X-ray flouresence microscopy and X-ray absorption spectroscopy). Results: We discovered the presence of Co oxide-based nanoparticles in soils surrounding cobalt-rich rocks at all of our studied locations, to our knowledge the first detection of terrestrial Co oxide-based nanoparticles. The extractable concentration of Co in the nanoparticles varied from 0.7 ng of nanoparticulate Co per gram of soil (ng Co g–1), up to 1390 ng Co g–1, the latter soil containing 1 × 109 extractable Co-based nanoparticles per gram of soil. Discussion: Nanoparticulate cobalt was typically closely associated with manganese (Mn) in the form of natural Co–Mn oxide phases, with only two of the studied locations not showing a close Co–Mn association. We discuss the environmental drivers that may facilitate formation of Co–Mn oxide nanoparticles. Our study suggests that Co may be more mobile in surface environments than previously thought, with Co–Mn oxide nanoparticles found around all four analysed types of Co-rich outcrops.