Abstract
During the pyrolytic production of biochar, only 50% of carbon (C) could be retained in biochar, and about 10% C would be mineralized after biochar is amended into soil. In this study, we aim to search a material to pretreat the biomass and improve carbon sequestration along biochar production and application. Alkaline minerals are widely reported to have catalytic effect on biomass pyrolysis and alter the liquid and gas products, while few studies have focused on their influence on biochar C sequestration. This study selected KCl, NaCl, MgCl2, and CaCl2 to dope in a biomass, cow manure, to explore their influence on the carbon sequestration based on carbon retention before and after pyrolysis and the carbon stability assessed by K2Cr2O7 oxidation and biological mineralization in real soil. Results showed that dosage of these minerals with a mineral/biomass ratio of 1: 5 (w/w) increased C retention in biochar from 49.8% (without minerals) to 52.5% (KCl), 53.7% (NaCl), 64.1% (MgCl2), and 60.7% (CaCl2), respectively. However, only MgCl2-fixed C in the produced composite biochar (Mg-BC) exhibited significant C stability both for bulk C (about 60.0%) and surface C (5.0 mg CO2·kg−1 soil). Addition of CaCl2 also could retain more C in biochar during pyrolysis, while the C in this composite biochar was not stable indicated by K2Cr2O7 oxidation and biological mineralization. Crystals of MgO and MgO3(CO3)2 were detected on the surface of Mg-BC by X-ray diffractometer (XRD), which could sorb small organic molecules such as C3–C7 compounds from the thermal decomposition verified by thermogravimetry-mass spectrum analysis (TG-MS). Moreover, a physical barrier was formed covering on biochar surface and enhance its capacity against oxidation and biological mineralization. This study offers a potential strategy to strengthen biochar-carbon sequestration by Mg-doping from the production of biochar to the application in soil environment.
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