Herein is disclosed a flue gas scrubbing composition, a method of using the flue gas scrubbing composition, and a method of entombing mercury collected with the flue gas scrubbing composition. The flue gas scrubbing composition includes an admixture of a mercury sorbent material that comprises a clay, copper, and sulfur; and lime that comprises calcium oxide and/or calcium hydroxide. The method of collecting mercury from a flue gas includes injecting the flue gas scrubbing composition of any one of the preceding claims into a flue duct comprising the flue gas; reacting the mercury sorbent material with mercury in the flue gas to form a mercury-sorbed material and thereby reducing the concentration of mercury in the flue gas; reacting the lime with SO2, SO3, and/or HCl in the flue gas to form a calcium sulfate and/or a calcium chloride; and collecting a mixture that includes the mercury-sorbed material. The method of entombing mercury includes mixing the collected mixture of any one of claims 6 to 9 with water to form a freshly mixed concrete; and casting the freshly mixed concrete into a form.