Aqueous Li⁺/Al³⁺ alkaline solution for CO₂ capture and the massive Li-Al-CO₃ hydrotalcite precipitation during the interaction between CO₂ gas and the Li⁺/Al ³⁺ aqueous solution

The concentrations of Al³⁺ and Li⁺ in an aqueous alkali affect the ability of the solution to capture CO₂. When CO₂ gas was forced into such a solution, CO₂ was captured via the formation of a carbonate-containing compound. The carbonate-containing compound was Li-Al-CO₃ hydrotalcite (Li-Al-CO₃ LDH) or amorphous aluminium hydroxycarbonate. The former compound contained 2.84-3.22 wt% carbon, while the latter contained less carbon (1.52-1.97 wt%). The Li-Al-CO₃ LDH was porous with nanosized pores and had a BET surface area of 114.8-161.8 m² g^-1. The injection of a relatively low CO₂ gas flow rate into the Al³⁺- and Li ⁺-containing aqueous solution favoured the production of Li-Al-CO₃ LDH. For example, forcing CO₂ gas into the aqueous solution at a flow rate of 70 mL min^-1 produced Li-Al-CO ₃ LDH. Injecting CO₂ at a higher flow rate (120 mL min^-1) into the same solution produced amorphous aluminium hydroxycarbonate. A CO₂ capture capacity (mmol per gram AlLi IMC) of up to ∼30 mmol g^-1 (1.30 kg CO₂ per kg of AlLi) was achieved in 120 s. The fall in the pH of the alkaline solution during CO ₂ bubbling was the critical factor that determined whether the final product was Li-Al-CO₃ LDH or amorphous aluminum hydroxycarbonate.