Biochar produced from mineral salt-impregnated chicken manure: Fertility properties and potential for carbon sequestration

[Display omitted] •Biochars were produced from chicken manure pretreated with mineral salts.•Mineral salt pretreatment reduced biochar N and P availability.•Addition of mineral salts enhanced biochar’s carbon sequestration potential.•Ferric chloride is the most effective additive to improve biochar stability. In this study, nutrient properties and carbon sequestration potential of biochars derived from chicken manure (CM) impregnated with mineral salts (calcium chloride, magnesium chloride, ferric chloride) were evaluated. Pretreatment with mineral salts reduced phosphorus (P) availability via the formation of insoluble metal phosphate minerals. Less carbon was lost during the pyrolysis of pretreated CM, and the produced biochars (BCCa, BCMg, and BCFe) were more stable (i.e., reduced C loss during chemical oxidation and less CO2 release during incubation) than pristine biochars. Spectroscopic evidence indicated that enhanced biochar stability via metal salt pretreatment before pyrolysis was related to increased aromatization and enhanced physical protection due to the metal-oxygen interaction, together with the formation of metal mineral phases on biochar surfaces. Moreover, ferric chloride was the optimal additive, as it significantly decreased biochar P leachability and increased carbon sequestration potential.