Organic ligands and CO2 unlock the potential for energy relevant metals recovery and carbon mineralization from mafic rocks

The need to meet the rising demand for energy relevant metals (e.g., Fe, Mn, Al, Cr, Ni) motivates the development of sustainable chemical pathways to recover these metals from earth abundant and unconventional resources such as mafic rocks. Mafic resources such as olivine gabbro (OG) and picrite basalt (PB) are harnessed for coupled carbon mineralization and metal recovery, and contrasted with ultramafic resources such as serpentinized peridotite (SP). The carbon mineralization extents of Ca, and Mg species in SP, OG, and PB are 71%, 39%, and 11%, respectively, at 185 °C, pCO2 of 50 bar, and a reaction time of 10 h in a mixture bearing 2 M NaHCO3 and 0.1 M Na2H2EDTA·2H2O. Higher carbon mineralization extents are directly related to olivine and pyroxene contents. Magnesite is observed as the dominant carbonate phase in OG, while magnesian calcite and dolomite are consistently formed in PB. The presence of metal chelating solvents such as Na2H2EDTA·2H2O is reported to enhance metal dissolution (Fe: ~2692 & 2606 ppm, Al: 2753 & 2670 for OG and PB respectively). These results unlock the possibility of harnessing mafic rocks such as OG and PB as resources for the co-recovery of energy relevant metals coupled with carbon mineralization.

Microbial-mineral interaction experiments and density functional theory calculations revealing accelerating effects for the dolomitization of calcite surfaces by organic components

Carbonates represent major sedimentary rocks in on the continental and oceanic crust of Earth and are often closely related to microbial activities. However, the origin of magnesium-containing carbonates, such as dolomites, has not yet been fully resolved and was debated for many years. In order to reveal the specific role of organic components and microbes on the precipitation of magnesium ions, different dolomitization experiments were carried out with various setups for the presence of eight amino acids and microbes. The Gibbs free energy for dehydration of Mg[6(H2O)]2+ and organic‑magnesium complexes (OMC) at the calcite (101¯4) step edges were calculated by density functional theory (DFT). Combined results of X-ray diffraction (XRD), scanning electron microscope-energy disperse spectroscopy (SEM-EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) indicated that magnesium ions were incorporated into the crystal lattice of calcite after calcite reacting with organic‑magnesium solutions (OMS). Dolomite was formed on the surface of calcite under the presence of microbes. The Gibbs free energy barrier of asp, glu, gly, thr, tyr, lys, ser, and ala bonding to Mg[6(H2O)]2+ were 17.8, 16.2, 14.8, 16.5, 19.2, 14.5, 19.0, 17.0 kcal/mol, those are lower than that of the direct dehydration of Mg[6(H2O)]2+ of 19.45 kcal/mol. The Gibbs free barrier of OMC bonding at the acute step ([481¯] and [4¯41]) of 29.7/34.25 kcal/mol are lower than that of Mg[6(H2O)]2+ of 32.45/36.7 kcal/mol and the Gibbs free barrier of OMC bonding at the obtuse step ([481¯] and [4¯41]) of 42.07/47.6 kcal/mol are lower than that of Mg[6(H2O)]2+ of 55.4/60.34 kcal/mol. The enhancing effects of organic components and microbes on the precipitation of magnesium ions were collectively determined through experimental and theoretical calculation, thus setting up a new direction for future studies of dolomitization with a focus on microbial- mineral interactions.

Calcium isotope fractionation by intracellular amorphous calcium carbonate (ACC) forming cyanobacteria

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC-forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC-forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to -0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC-forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC-forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach.

Ocean Warming Amplifies the Effects of Ocean Acidification on Skeletal Mineralogy and Microstructure in the Asterinid Starfish Aquilonastra yairi

Ocean acidification and ocean warming compromise the capacity of calcifying marine organisms to generate and maintain their skeletons. While many marine calcifying organisms precipitate low-Mg calcite or aragonite, the skeleton of echinoderms consists of more soluble Mg-calcite. To assess the impact of exposure to elevated temperature and increased pCO2 on the skeleton of echinoderms, in particular the mineralogy and microstructure, the starfish Aquilonastra yairi (Echinodermata: Asteroidea) was exposed for 90 days to simulated ocean warming (27 °C and 32 °C) and ocean acidification (455 µatm, 1052 µatm, 2066 µatm) conditions. The results indicate that temperature is the major factor controlling the skeletal Mg (Mg/Ca ratio and Mgnorm ratio), but not for skeletal Sr (Sr/Ca ratio and Srnorm ratio) and skeletal Ca (Canorm ratio) in A. yairi. Nevertheless, inter-individual variability in skeletal Sr and Ca ratios increased with higher temperature. Elevated pCO2 did not induce any statistically significant element alterations of the skeleton in all treatments over the incubation time, but increased pCO2 concentrations might possess an indirect effect on skeletal mineral ratio alteration. The influence of increased pCO2 was more relevant than that of increased temperature on skeletal microstructures. pCO2 as a sole stressor caused alterations on stereom structure and degradation on the skeletal structure of A. yairi, whereas temperature did not; however, skeletons exposed to elevated pCO2 and high temperature show a strongly altered skeleton structure compared to ambient temperature. These results indicate that ocean warming might exacerbate the skeletal maintaining mechanisms of the starfish in a high pCO2 environment and could potentially modify the morphology and functions of the starfish skeleton.

Modulation of the CaCO3 phase and morphology by tuning the sequence of addition: an insight into the formation of monohydrocalcite

Detailed study on the formation of monohydrocalcite as well as the modulation of the CaCO3 phase and morphology.