Mineral Speciation for CO₂ Captured by Potassium Hydroxide

Capture of greenhouse gases, especially CO₂, can reduce the effects of global warming and generate valuable minerals as feedstock for industry. Herein, the mineral products formed by capture of atmospheric CO₂ by potassium hydroxide (KOH) in aqueous, aqueous-ethanol, and aqueous-acetone solutions, and aqueous-acetone enriched using solid CO₂ are studied. A multimodal analysis combining single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), with Pawley and Rietveld refinements, and 850 MHz, 1 GHz, and 1.2 GHz ¹H, as well as ¹³C, and ³⁹K nuclear magnetic resonance (NMR), is used to analyze the composition of the mineral products. SCXRD identifies KHCO₃ in space group P2₁/n (transformable to P2₁/a) as a product from all reactions. PXRD and NMR data show the presence of both crystalline and amorphous phases in products, predominantly as mixtures of KHCO₃ and K₂CO₃ and its hydrates, with KOH as a minor component, except for aqueous-ethanol which gives KHCO₃ in high purity. Analysis of complex ¹H NMR data is aided by 2D nuclear Overhauser effect spectroscopy (1 GHz), which characterizes COH···OC interactions. Revealing K₂CO₃ hydration is aided by deconvolution of ultrahigh-field 28.2 T (56 MHz) ³⁹K spectra. This multimodal approach provides new insights into the speciation of potassium minerals from CO₂ capture.