High pressure decomposition of a sandwich compound

While it is widely recognized that purely organic molecular systems with multiple bonds undergo chemical condensation at sufficiently high pressures (from tenths to tens of GPa), the fate of organometallics at extreme conditions remains largely underexplored. We have investigated the high pressure (up to 41 GPa) chemical transformations in a simple molecular system known as nickelocene, (C5H5)2Ni, which serves as a representative example of a class of organometallics called sandwich compounds. Nickelocene decomposed above 13 GPa, at room temperature, while lower pressure thresholds have been observed at higher temperatures (295-573 K). The products were identified as nanocomposite materials, primarily composed of disordered, nickel-rich nanoparticles segregated within an extended, amorphous matrix of hydrogenated carbon (a-C:H). The investigation was conducted by means of diamond anvil cells in combination with optical spectroscopies and microscopy, synchrotron x-ray absorption spectroscopy and diffraction, as well as transmission electron microscopy. Our findings have the potential to stimulate further research into the high-pressure chemical reactivity of organometallics and open up new synthesis routes for the production of metal-based nanoparticles, which find a wide range of applications.

Influence of Sodium Sulfate Addition on Iron Grain Growth during Carbothermic Roasting of Red Mud Samples with Different Basicity

Red mud is an iron-containing waste of alumina production with high alkalinity. A promising approach for its recycling is solid-phase carbothermic roasting in the presence of special additives followed by magnetic separation. The crucial factor of the separation of the obtained iron metallic particles from gangue is sufficiently large iron grains. This study focuses on the influence of Na2SO4 addition on iron grain growth during carbothermic roasting of two red mud samples with different (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21, respectively. Iron phase distribution in the red mud and roasted samples were investigated in detail by Mössbauer spectroscopy method. Based on thermodynamic calculations and results of multifactorial experiments, the optimal conditions for the roasting of the red mud samples with (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21 were duration of 180 min with the addition of 13.65% Na2SO4 at 1150 °C and 1350 °C followed by magnetic separation that led to 97% and 83.91% of iron recovery, as well as 51.6% and 83.7% of iron grade, respectively. The mechanism of sodium sulfate effect on iron grain growth was proposed. The results pointed out that Na2SO4 addition is unfavorable for the red mud carbothermic roasting compared with other alkaline sulfur-free additives.