Permeable reactive barriers based on natural zeolites from Kazakhstan in solving ecological problems: Mathematical model and simulation

In view of ecological problems stemming from the leakage of reservoirs with liquid radioactive wastes (LRW) and groundwater contamination with radioactive Cs⁺ and Sr²⁺, we have estimated the physicochemical (including sorption) characteristics of clinoptilolite-bearing tuff (CBT) from the Chankanai deposit in Kazakhstan. Data were obtained on the chemical and phase composition of CBT, its total cationexchange capacity, and equilibrium (exchange isotherms) and kinetic (diffusion coefficients) characteristics in sorbing radioactive Cs⁺ and Sr²⁺ from 0.07 n CaCl₂ solution (model solutions of groundwaters). We proved that CBT efficiently sorbs Cs from this solution and practically does not sorb Sr and elucidated the reasons for the low selectivity with respect to Sr²⁺. Based on the equilibrium and kinetic characteristics of the process, a mathematical model is suggested for Cs sorption under dynamic conditions. The protection lifetime of the clinoptilolite-based geochemical barrier is evaluated.