Systems, compositions, and methods for removing a substance or substances from a material, such as a gas or liquid material, are described. The compositions can comprise composite removal particles. In some embodiments, the composite removal particles can be comprised of support particles made from an inexpensive carrier material, and a reactive particle borne on the support particle. The reactive particle reacts with the substance or substances in the material. The reacted composite removal particles can then be removed from the material, which reduces the amount of the substance or substances present in the material. The composite removal particles are useful for removing pollutants, such as mercury, from exhaust gases, such as flue gas from a power plant combustion unit, and from other materials such as natural gas, liquefied natural gas, fuels, hydrocarbons, petrochemicals, and refinery streams.