PNNL

Abstract

A method was developed to measure trace noble gas element adsorption to the surfaces of geologic materials in the presence of a background gas that could potentially compete for surface adsorption sites. Adsorption of four noble gas elements (Ne, Ar, Kr, and Xe) at a concentration of 100 µg/g in helium and nitrogen were measured on a sample of crushed tuff at 0, 15, 30, and 45°C. In addition, Ne, Ar, Kr, and Xe at 250 µg/g and 500 µg/g in nitrogen at 15°C were measured. Noble gas adsorption was found to increase with increasing atomic mass and decreasing temperature. It was also observed that the relative increase in noble gas element adsorption with decreasing temperature tends to increase with increasing atomic mass. Noble gas adsorption from nitrogen was approximately an order of magnitude greater than for the noble gases in helium. As the noble gas concentrations in nitrogen increased, adsorption increased in a slightly non-linear fashion which could be modeled using a Freundlich isotherm. For noble gas concentrations that were =100µg/g linear sorption equations were calculated.