Comparison of Hanford Colloids and Kaolinite Transport in Porous Media

Abstract

Understanding colloid transport at the Hanford site in Washington State is critical in assessing migration of radionuclides because colloid transport is a potential means for facilitated off‐site migration of radioactive wastes. In this study, eight saturated column experiments were conducted to investigate transport of Hanford colloids and a model colloid (kaolinite) through two types of porous media (Hanford sediments characteristic of 2:1 clay minerals and silica Accusand). Experiments were conducted at a pH value of 10 to mimic the conditions at the Hanford site. The Hanford colloids used were obtained by reacting Hanford sediments with simulated tank waste solutions. The results show that factors influencing transport of Hanford colloids and kaolinite include flow velocity, solution ionic strength, medium type, and colloid properties. Hanford colloids exhibited higher deposition rates than kaolinite in both Hanford sediments and Accusand. Likewise, Hanford sediments retained more colloids than did the silica Accusand. Comparison of transport behaviors of the two colloids through two sands supports the assumption that chemical heterogeneity is important in controlling particle–particle and particle–collector interactions in colloid retention and transport.