Enhanced carbon retention in Litchi biochar via in-situ limewater coating and self-limited oxygen pyrolysis regulated by water-fire interaction

Abstract

Biochar, a carbon-rich material with a porous structure, holds significant potential for mitigating climate change through carbon sequestration. However, its widespread adoption has been hindered by high production costs, primarily associated with oxygen-restricted systems and energy-intensive production processes. This study introduced a cost-effective, field-adapted strategy to enhance carbon retention in biochar derived from Litchi branches through limewater coating and synergistic water-fire interaction. Litchi branches were pretreated with limewater to create a surface coating, then underwent in-situ carbonization via self-oxygen-limited pyrolysis to form a dark-red char which was then quenched with limewater to produce biochar. Calcium (Ca)-mediated carbon retention during pyrolysis was investigated through Fourier-transform infrared spectroscopy (FTIR) coupled with scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS). The limewater-treated biochar achieved a significantly improved carbon conversion rate (86%) compared to CK (52%), the untreated biochar sample, with an enhanced specific surface area of 280 m² g^–1. FTIR and SEM–EDS analyses revealed that the limewater treatment formed a calcium-enriched protective barrier that effectively suppressed the formation of CO_x during combustion. Additionally, mineral Ca-carbon composites formed during pyrolysis further improved carbon stabilization and retention. This study offers a practical and scalable solution for producing biochar under field conditions by addressing challenges related to cost-effectiveness and process efficiency, thereby promoting the application of biochar for carbon sequestration.

Keywords

Carbon conversion rate / Limewater / Immersion / Coating / Litchi branches

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Funding

Guangdong Basic and Applied Basic Research Foundation(2022A1515110330)

Water Resources Department of Guangdong Province(2020B121201014)

Guangdong Province “Hundreds of Counties, Thousands of Towns, and Tens of Thousands of Villages Initiative” Rural Science and Technology Commissioners Project(KTP20240657)

Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province(2023KTSCX155)

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