Alkali and alkaline earth metals promoted chemisorption of CO2

https://doi.org/10.1016/j.ccst.2022.100059

“Biomass is composed of carbon, hydrogen, oxygen, sulfur, nitrogen, and small amounts of other elements, including alkali metals, alkaline earth metals, and heavy metals, depending on the type or type of biomass (Gezae Daful et al., 2022). Alkali elements and alkaline earth metals (Ca, Mg, K, Na, etc.) can enhance the alkalinity of biochar, and in turn increases the affinity for acidic CO₂, manifesting itself in the enhanced adsorption capacity for CO₂ (Walton et al., 2006; Yuan et al., 2011). And these unique properties of biochar can facilitate the chemical adsorption of acid CO₂ to form carbonates, bicarbonates, carbonates, or minerals. CO₂ chemisorption via chemical reactions between absorbents and CO₂ is available on metal oxides and amine containing materials. Through zwitterion mechanisms, two amine functional groups on biochar can chemically combine with one CO₂ molecular, yielding carbamate and ammonia pairs (Choi et al., 2009; D’Alessandro et al., 2010; Rashidi and Yusup, 2016).

Xu et al. (Xu et al., 2016) produced biochar from pig manure, sewage sludge and wheat straw for CO₂ adsorption. The alkali metals and alkaline earth metals on the surface of three biomasses were different, while chemisorption was closely related to the minerals in the biochar. Xu suggestd that the sorption of CO₂ all started with the dissolution of CO₂ in an aqueous film on the surface of the biochar, followed by gradual dissociation into HCO (Köne and Büke, 2019– and CO₃^2–, followed by reaction with the mineralogical components of the biochar to form carbonate, bicarbonate or subcarbonate products. It was claimed that chemical adsorption possibly plays a major role in CO₂ adsorption (K. Li et al., 2022).”