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.