•Dissolved Hg decreases by >90% with high-T biochars (600 and 700°C).•Elevated SO42− (up to 1000mgL−1) is released from manure-derived biochar.•XRF results indicate Hg is distributed heterogeneously throughout biochar particles.•S XANES indicates presence of reduced and oxidized S species in biochar.•Hg EXAFS indicate Hg is bound to S atoms in biochar particle when S content is high. Thirty-six biochars produced from distinct feedstocks at different temperatures were evaluated for their potential to remove mercury (Hg) from aqueous solution at environmentally relevant concentrations. Concentrations of total Hg (THg) decreased by >90% in batch systems containing biochars produced at 600 and 700°C and by 40–90% for biochars produced at 300°C. Elevated concentrations of SO42− (up to 1000mgL−1) were observed in solutions mixed with manure-based biochars. Sulfur X-ray absorption near edge structure (XANES) analyses indicate the presence of both reduced and oxidized S species in both unwashed and washed biochars. Sulfur XANES spectra obtained from biochars with adsorbed Hg were similar to those of washed biochars. Micro-X-ray fluorescence mapping results indicate that Hg was heterogeneously distributed across biochar particles. Extended X-ray absorption fine structure modeling indicates Hg was bound to S in biochars with high S content and to O and Cl in biochars with low S content. The predominant mechanisms of Hg removal are likely the formation of chemical bonds between Hg and various functional groups on the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications for stabilization of Hg in surface water, groundwater, soils, and sediments.