The main impregnation techniques are wet impregnation and dry impregnation. During wet impregnation, the porous particles are dissolved in the extractant and allowed to soak with the respective fluid. In this approach, the particles are either contacted with a precalculated amount of extractant, which completely soaks into the porous matrix, or the particles are contacted with an excess of extractant. After soaking, the remaining extractant, which is not inside the pores, is evaporated.
If the wet method is used, the extractant is dissolved in an additional solvent prior to impregnation. The porous particles are then dispersed in the extractant-solvent solution. After soaking the particles, the excess solvent can either be filtered off or evaporated. In the first case, an extractant-solvent mixture would be retained within the pores. This would be of interest for extractants which would be solid at design conditions when pure. In the second case, only the extractant would remain inside the pores. Figure 3 shows porous particles dispersed in an aqueous solution after wet impregnation. The cut-out in Figure 3 shows an enlarge segment of the surface of such an impregnated particle.
An additional, albeit not so frequently used technique is the modifier addition method. This technique relies on the use of an extractant/solvent/modifier system. The additional modifier is supposed to enhance the penetration of the extractant into the particle pores. The solvent is subsequently evaporated, leaving extractant and modifier in the particle pores.
Furthermore, the dynamic column method can be used. The particles are contacted with a solvent until they are completely soaked. This can be done prior or after packing into the column. The packed bed is then rinsed with the liquid extractant until inlet and outlet concentrations are the same. This approach is particularly interesting when particles are already packed in a column and shall be reused for a SIR application.