Stability and Transportability of Water‐Dispersible Soil Colloids

Abstract

AbstractColloid migration in subsurface environments has attracted special attention lately due to its suspected role in facilitating transport of contaminants to groundwater. This study was conducted to evaluate the stability and potential transport of water‐dispersible colloids (WDC) through intact soil columns, and the properties of colloids and soil columns facilitating or retarding colloid stability and transportability. Water‐dispersible colloids were fractionated from six representative soil samples with diverse mineralogy and physicochemical characteristics. Their stability was evaluated from settling‐rate experiments at different pH levels. The results demonstrated that colloid stability was pH dependent. Colloid transportability was assessed by introducing colloid suspensions at a constant flux into intact soil columns representing upper Bt horizons of a Maury (fine, mixed, mesic Typic Paleudalf) and a Loradale (fine‐silty, mixed, mesic Typic Argiudoll) soil and evaluating characteristics of the suspensions that were eluted. After five pore volumes of leaching, colloid recovery in the eluents ranged from 35 to 90% depending on type of colloid, initial concentration in the influent, and soil column. The mineralogical composition of the colloid, which was correlated with particle size, appeared to have a profound effect on colloid transportability, following the sequence smectitic > mixed > kaolinitic. Total exchangeable bases (TEB) and pH of WDC also significantly influenced colloid transport. Increasing colloid concentration in the influent slightly increased colloid transportability. Soil columns with better macroporosity and less surface charge (Maury) transported more colloids than soil columns with less macroporosity and higher surface charge (Loradale).