Natural and engineered nano and colloidal transport: Role of zeta potential in prediction of particle deposition

This study is designed to answer the question of whether the zeta-potential measurement of natural and engineered nano and colloidal particles can be used as a general predictor for their transport and deposition within porous medium. The transport and deposition of engineered zeolite particles and natural colloids (soil and sediment colloids) was studied and evaluated considering their zeta-potential measurement. The zeta-potential of Ca ²⁺ or K ⁺ saturated zeolite particles increased (i.e., became less negative) with increasing bulk ionic strength, independent of the cation species in the bulk solution, while the zeta-potential of Ca ²⁺ or K ⁺ saturated natural colloids was dependent on the cation species in the bulk solution, unexpectedly decreasing with the bulk K ⁺ concentrations while increasing with bulk Ca ²⁺ concentrations (10 ^-5 to 10 ^-2M). The particle deposition rate coefficient (κ) was sensitive to the cation species in the bulk solution and on the cation exchangeable sites of the particle surfaces. The trend of the zeta-potential of the natural colloids, especially with simple electrolytes in bulk solution, was at odds with that of k under the same conditions, indicating that the zeta-potential of these natural colloids could not be used to adequately predict their transport and deposition. The observed anomaly is a direct result of surface heterogeneity and hydrophobicity of natural colloids, and it points out the important difference between natural and engineered nano and colloidal particles in terms of their transport and deposition prediction.