Pyrolysis temperature-dependent carbon retention and stability of biochar with participation of calcium: Implications to carbon sequestration

Hongyan Nan; Jianxiang Yin; Fan Yang; Ying Luo; Ling Zhao; Xinde Cao

doi:10.1016/j.envpol.2021.117566

Pyrolysis temperature-dependent carbon retention and stability of biochar with participation of calcium: Implications to carbon sequestration

Environ Pollut. 2021 Oct 15:287:117566. doi: 10.1016/j.envpol.2021.117566. Epub 2021 Jun 9.

Authors

Hongyan Nan¹, Jianxiang Yin², Fan Yang³, Ying Luo¹, Ling Zhao⁴, Xinde Cao⁵

Affiliations

¹ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
² China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai, 201306, China.
³ School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai, 200093, China.
⁴ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China. Electronic address: wszhaoling@sjtu.edu.cn.
⁵ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China; China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai, 201306, China.

PMID: 34153610
DOI: 10.1016/j.envpol.2021.117566

Abstract

Converting biomass waste into biochar by slow pyrolysis with subsequent soil amendment is a prospective approach with multiple environmental benefits including soil contamination remediation, soil amelioration and carbon sequestration. This study selected cow manure as precursor to produce biochar under 300 °C, 400 °C, 500 °C and 600 °C, and a remarkable promotion of carbon (C) retention in biochar by incorporation of exogenous Ca was achieved at all investigated pyrolysis temperatures. The C retention was elevated from 49.2 to 68.3% of pristine biochars to 66.1-79.7% of Ca-composite biochars. It was interesting that extent of this improvement increased gradually with rising of pyrolysis temperature, i.e., doping Ca in biomass promoted pyrolytic C retention in biochar by 16.6%, 23.4%, 29.1% and 31.1% for 300 °C, 400 °C, 500 °C and 600 °C, respectively. Thermogravimetric-mass spectrometer (TG-MS) and X-ray photoelectron spectroscopy (XPS) showed that Ca catalyzed thermal-chemical reactions and simultaneously suppressed the release of small organic molecular substances (C₂-C₇) via physical blocking (CaO, CaCO₃, and CaClOH) and chemical bonding (CO and OC-O). The catalyzation mainly occurred at 200-400 °C, while the suppression was more prominent at higher temperatures. Raman spectra and 2D FTIR analysis on biochar microstructure showed that presence of Ca had negative influence on carbon aromatization and thus weakened biochar's stability, while increasing pyrolysis temperature enhanced the stability of carbon structure. Finally, with integrating "C retention" during pyrolysis and "C stability" in biochar, the maximum C sequestration (56.3%) was achieved at 600 °C with the participation of Ca. The study highlights the importance of both Ca and pyrolysis temperature in enhancing biochar's capacity of sequestrating C.

Keywords: Biochar; Carbon retention; Carbon sequestration; Carbon stability; Mineral Ca; Pyrolysis temperature.

MeSH terms

Calcium
Carbon
Carbon Sequestration*
Charcoal
Pyrolysis*
Soil
Temperature

Substances

Soil
biochar
Charcoal
Carbon
Calcium