Impact of Solution Chemistry on Deposition and Breakthrough Behaviors of Kaolinite in Silica Sand

Abstract

Understanding the transport and deposition behavior of particles within porous media is of importance because clogging can degrade the long-term performance of hydraulic infrastructure (e.g., artificial recharge system, cutoff walls, and infiltration structures) due to the reduction of hydraulic conductivity. In addition, the deposition behavior significantly affects the transport of contaminants that are favorably adsorbed to particles. Between the various factors affecting deposition behavior, geochemical conditions can affect both the interaction energy between particles and the porous medium, as well as aggregation behavior of particles; however, the impact of prevailing geochemical conditions on particle transport and deposition is not well understood, particularly when the particles are clay minerals. Therefore, a series of soil column tests was performed to study the transport of kaolinite under variable solution chemistry (pH and ionic strength) and flow rate (low and high). The observed deposition profiles and breakthrough curves of kaolinite particles revealed that the reduction of hydraulic conductivity was most significant at low pH (pH∼3), regardless of flow rate. In addition, the reduction of hydraulic conductivity due to clogging was a stronger function of solution chemistry at low flow rates, which is attributed to the impact of solution chemistry on the size of kaolinite clusters, the interaction energy between sand and kaolinite, as well as the impact of hydrodynamic force on deposition behavior of kaolinite.