Transport and retention of strontium in surface-modified quartz sand with different wettability

Instead of radioactive ⁹⁰Sr, common strontium chloride was used to simulate the migration of radioactive strontium chloride in surface hydroxylated, silanized, and common quartz sand. The sorption and retardation characteristics of strontium (Sr²⁺) in these surface modified quartz sands were studied by batch tests and column experiments. The equilibrium sorption data for Sr²⁺ on different wettability sands were described by the Langmuir and Freundlich isotherm models, and the Langmuir model has been found to provide better correlation for hydrophilic sand. The breakthrough curves (BTCs) of Sr²⁺ in these media were analyzed with the equilibrium convection–dispersion equation (CDE) and a non-equilibrium two-region mobile–immobile model (TRM) using a nonlinear least square curve-fitting program CXTFIT. The TRM model showed better fit to the measured BTCs of Sr²⁺, and the parameters of the fraction of mobile water indicated that significant preferential flow effected the non-equilibrium transport of Sr²⁺. Although TRM model could not fit the Sr²⁺ BTCs very well, the parameter estimated by TRM model may be more reliable than those obtained from batch experiments because the transport of Sr²⁺ in these kind of sand is non-equilibrium processes.