Water Flow Rate And The Influence Of Water Content Of Strontium Block Effect Research

Transport of Strontium in soil is a complex process along with variousphysical-chemical reactions. In this study, sorption and retardation of Sr inChinese loess at various water flow rates and different water content wereinvestigated in batch and column experiments.First, a sorption equilibrium test was carried out to measure the soilsorption capacity for Sr in the loess at room temperature （25±1℃）.The resultsshowed that the loess has a strong sorption capacity for strontium. The linearFrenudilich isotherm model was able to adequately interpret the equilibrium data,which resulted in a distribution coefficient （K_d） of39.97cm³/g. Based on this K_dvalue and the other measured parameters, the retardation factor （R_d） wascalculated to be112.6.Secondly, experiments with repacked soil columns were also used todetermine Rdvalues of Sr in Chinese loess under different flow conditions andwater content. Bromide （Br^-） was used as a non-reactive tracer, and Strontium(Sr²⁺) as the reactive tracer. And then we can get the breakthrough curves ofbromine and the retention profiles of Sr in the loess column.Finally, The CXTFIT2.1model was used to estimate the parameters byinversion from the breakthrough and retention curves of Br and Sr, respectively.In this work, we applied both the local equilibrium assumption （single region）model and the non-equilibrium （two-region or two-site） model to simulate thesolute retention profiles. The results showed1) In saturated conditions, the observed Br^-breakthrough curves （BTCs）appeared symmetrical and can be well fitted with both the local equilibriummodel and the two-site model. And the Sr retention profiles in the loess columnshowed that the two-site model offered much improved fitting to theexperimental data than the local equilibrium model. Our results also revealedthat R_d value was not a constant, but decreased with increasing pore-watervelocity.2) The breakthrough curves （BTCs） obtained from Br^-experiments exhibited earlier initial arrival and a weaker degree of tailing under unsaturated conditionsin the study. Sr retention curves exhibited non-equilibrium characteristics,particularly at the low moisture condition for the soil. In general, the two regionmodel fitted the Sr profiles more closely than the local equilibrium model inconsidering more factors and parameters. The R_d values decreased with theincrease of average water content in the soil column, and the dispersioncoefficient （D） is proportional to the water content. The relations between the R_dof Sr and water content （θ） can be described by R_d=22.071θ^-1.2945.