A high efficiency and high capacity mercury adsorbent based on elemental selenium loaded SiO2 and its application in coal-fired flue gas

•The millimeter-grade Se/SiO2 adsorbent can be used as a filler in a fixed bed reactor.•The saturated adsorption capacity of mercury is up to 101.04 mg/g.•HgSe is the main product of mercury removal from adsorbent under flue gas conditions.•The carrier of Se/SiO2 is soluble SiO2, and high purity of HgSe can be recovered.