Improving Cu(II) sorption by biochar via pyrolyzation under CO 2 : the importance of inherent inorganic species

Abstract

Biochar from Spartina alterniflora (SA) and rice straw (RS) under N₂/CO₂ were evaluated for Cu(II) removal from aqueous solution. The result indicates SA biochar prepared at 700 °C under CO₂ can achieve a Cu(II) sorption capacity of 89.12 ± 2.77 mg/g, which is higher than that from N₂ by about 50%. CO₂ can promote the development of multi-porous structure, enhance specific surface area, and increase the amounts of hydroxyl and carboxyl groups on biochar. In addition, CO₂ can inhibit the thermal decomposition of inorganic carbonate, such as MgCO₃ and CaCO₃ in biochar. These matters facilitate Cu(II) removal via the formation of chemical precipitation of Cu₂(OH)₂CO₃. The dissolution of inherent inorganic matter makes Cu(II) transformed into hydrolyzed species or amorphous precipitation, which contributes to about 75% (w/w) of Cu(II) removal. Metal exchange with complexed cations and the formation of basic cupric carbonate are time-consuming and responsible for about 24% (w/w) of Cu(II) removal.

Graphical abstract

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