Subsequent redeposition may occur in process equipment, in pollution control equipment, or in the environment. Minerals dissolved in naturally occurring geothermal waters typically plate out as the temperature drops. Deposits of scale containing substantial concentrations of radionuclides may result. As the water comes to the surface and the partial vapor pressure drops, radon dissolved in water partitions into the air. In open air, dilution, convection, and diffusion minimize increases in concentration, but in caves or buildings, higher concentrations of radon and its progeny may result.
Brines exhibit similar behavior.
Mechanical reduction in particle size enhances the potential for mobilization of material, such as erosion, movement of alluvial or glacial particles, bulldozers, mining, and construction. In addition, radionuclide concentrations can increase when part of the matrix is removed, leaving radionuclides behind in increased concentrations in the residue. Combustion of coal leaves uranium in the ash and slag. Suspended materials settle out of material streams as the velocity decreases. Fines settle out where the current is slowest, with successively coarser material settling out in the faster sections.