Chapter 10: Coupling of Competitive Sorption and Membrane Separation for Autonomous Remediation of Radionuclide-Contaminated Areas

The chapter outlines the main provisions of the proposed model of competitive sorption of a microelement by a sorbent placed in a suspension of contaminated material. The simulation results were used to create a new sorption technique for cleaning radioactively contaminated material, in which competitive partitioning of microelements between material suspension and a selective sorbent is coupled with membrane separation of the contaminated material and sorbent. The above coupling is realized in the construction of a minireactor (MR), which consists of a closed container made of a semi-permeable membrane material, inside which there is a suspension of the adsorbent. As an example, the results of an experimental study of the statics and kinetics of material purification from trace amounts of Cs(I) ions pre-sorbed by the material are presented. Silica gel and soil samples in the form of an aqueous suspension were taken as materials contaminated with cesium ions. It was found that the limiting stage of sorption mass transfer of cesium ions from the material to the sorbent (particles of the suspension of Prussian blue, PB, separated from the suspension of the material by the wall of the membrane MR) is diffusion inside the pores of the membrane. The distribution of Cs(I) ions between the material, the aqueous solution, and the sorbent is determined using the difference in the chemical potentials of cesium ions in the material and the sorbent. It is found that the flow of Cs(I) ions from the suspension of the material inside the MR can be regulated by changing the pore diameter of the membrane, the size of the membrane surface of the MR, and the composition of the solution, including pH and the concentration of humic acids. The construction of the membrane MR allows its simple mechanical separation from suspensions. By using this property, it is shown that the ratio between the equilibrium concentrations of Cs(I) ions in an aqueous solution and in each of the solid phases represented by the material and the competing sorbent is additive in nature and can be described by the sum of two Langmuir isotherms for the material (silica gel, the soil reference sample, SRS) and for the sorbent (PB). In conclusion, the methods of controlling the mass transfer of sorbed ions inside a MR with a sorbent and the possibility of scaling up the technique of sorption purification of materials using sorbent-filled MRs as part of future technologies for directed and autonomous remediation of radioactively contaminated areas are discussed.