Development of Li₄SiO₄ sorbents from Argentine diatomite for high-temperature CO₂ capture

Although Li₄SiO₄-based sorbents show great potential for high-temperature CO₂ capture, conventional formulations derived from pure SiO₂ suffer from high synthesis costs and kinetic limitations. This work proposes a sustainable alternative by utilizing raw, unpurified natural diatomite from Río Negro (Argentina) as the silicon precursor. A series of Li₄SiO₄ sorbents were prepared via a two-step mechano-thermal method, optimizing the initial nLi₂CO₃-SiO₂ molar ratio to 1.7-1.8 to maximize yield and performance. Physicochemical, thermodynamic, and kinetic properties were evaluated and contrasted against a commercial reagent reference (LS). The diatomite-derived sorbent (LD) achieved remarkable experimental CO₂ capture capacities of 27 wt% under pure CO₂ (at 650 °C) and 22 wt% under a diluted 10% CO₂ atmosphere (at 575 °C) demonstrating excellent cyclic stability over 10 cycles. Thermodynamic and kinetic studies via the van 't Hoff and Kissinger equations yielded a reaction enthalpy of 135 kJ mol^-1 and a decarbonation activation energy of 210 kJ mol^-1, outperforming the commercial benchmark. Structural and morphological analyses suggest that native impurities in the diatomite likely induce a beneficial lattice contraction, while promoting the in situ formation of a stable LiFeO₂ secondary phase alongside an alkali-metal eutectic molten phase. Rather than hindering performance, these built-in dopants act synergistically to prevent sintering and bypass solid-state diffusion barriers. These findings validate Argentine diatomite as a strategically advantageous, low-cost regional precursor for manufacturing highly efficient Li₄SiO₄ sorbents tailored for practical carbon capture application.