Abstract: Described here is a free-standing composite particle with a large surface area. The particle is capable of adsorbing heavy metal contaminants from water. The particle itself is comprised of a granular activated carbon particle to which are attached one or more carbon nanotubes, the combination of which is covered by at least a partial thin film of polydopamine or other polymeric material derived from dopamine-like compounds. The composite particles are mixed with contaminated water, after which the water and particle mixture is injected into a hydrocyclone separator specifically designed for use with the composite particle. The hydrocyclone separator removes the particles from the water, allowing the particles holding the contaminants to be extracted for treatment, while the purified water flows out of the separator for reuse. The separated particles can be treated to remove all the adsorbed contaminants, after which the reclaimed particles may be reused.