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.