PNNL

Abstract

Natural colloids were generated from zeolitized tuffs from the Nevada Test Site (NTS) and the effects of colloids on the transport of a strongly sorbing metal, lead (Pb(II)), were investigated in column experiments under different geochemic al conditions. Because of the high sorption affinity of Pb(II) for zeolitized t uffs, the migration of Pb(II) without colloids was strongly retarded. The prese nce of mobile colloids, however, enhanced the mobility of Pb(II). Approximately 75-90% of the eluted Pb(II) was transported as a colloid-associated phase. T he migration of colloids was closely related to the geochemical conditions in th e background solution. Immobilization of colloids increased as the ionic streng th of the background electrolyte solution increased, because of double layer com paction. Remobilization of initially deposited colloids occurred when the ionic strength of the background electrolyte solution was reduced. The mobility of c olloids increased with increasing pH and increasing flow rates. These results h ave significant implications for the migration of strongly sorbing radionuclides and other metals at nuclear testing facilities and metal-contaminated sites and are consistent with the hypothesis that inorganic contaminant migration in the subsurface is a function of geochemical conditions.