Influence of biochar pyrolysis temperature and post-treatment on the uptake of mercury from flue gas

•Slow pyrolysis was performed at four temperatures using four biomass materials.•The biochars were washed with a weak acid or left unwashed to change properties.•The biochars were used to remove mercury from a simulated flue gas stream.•Washed biochars created at 650–800 °C from poultry manure performed the best.•The sorbed mercury could not be thermally removed from the manure-based biochar.

Thermal processing, or pyrolysis, of plant and animal waste under oxygen limiting conditions results in a carbonized material called biochar. Most often, the proposed use for the biochar is in soil applications as a conditioner or for the purpose of carbon sequestration. In this paper we demonstrate that this material can also be used as mercury sorbent in flue gas applications. Four different raw materials (almond shells, cottonseed hulls, lignin, and chicken manure) were pyrolyzed at four different temperatures (350, 500, 650, and 800 °C) and washed or left unwashed. These materials were systematically evaluated for their potential to sorb mercury from a simulated flue gas. The materials that performed the best were washed biochars made from poultry manure at 650 and 800 °C, and these materials sorbed over 95% of the mercury from the flue gas. It was also shown that the majority of mercury sorbed to the biochar at 150 °C was stable and was not thermally desorbed at 450 °C, suggesting the presence of sorbed oxidized mercury species such as HgSO4 or HgO.