To remove from a mixture, separate out, withdraw or set apart.
In scientific terms, to sequester a mineral or molecule is to remove it from it's environment, whether that be air, soil, water or other media. Removal can be based on chemical or biological reactions and may be reversible or irreversible. However, the ultimate result is that the sequestered compound or molecule is made unavailable to interact with the surrounding environment.
One of the many types of phytoremediation involves sequestering of metals from soil. This bioremediation approach makes use of plants that draw metals from the environment into their tissues, thus removing, or sequestering, them from soil. Sequestering of metals from soil, or chemical contaminants from water results in concentrated amounts being present in plant or animal tissues and is known as bioaccumulation.
Sequestered carbon dioxide from the atmosphere is converted chemically into other forms of carbon to generate biomass, thus the process is irreversible except through further chemical conversions or combustion of the biomass.