During the last several decades considerable research effort has been expended to identify suitable "getter" materials that can immobilize or delay the transport of anionic radionuclides (such as 129I and 99TcO4) that would be released from physically and chemically degrading waste packages. Several investigators have identified a number of important performance characteristics such as adsorption potential and chemical/physical stability that getter materials should possess for effective deployment in repository environments. A review of published literature indicated that various minerals and synthetic adsorbent materials such as, oxides, hydroxides, natural and modified aluminosilicates, sulfides, carbonates, phosphates, carbon, and functionalized novel sorbents have been tested for their getter properties. Oxide/hydroxide solids and many silicate minerals have poor capacity and selectivity for iodide (Kd : 0 – 10 ml/g) and release iodide with increasing pH. A few silicate minerals such as illite exhibit better selectivity for iodide (Kd : ~30 ml/g). Significantly improved iodide selectivity (Kd : 5,000 ml/g) has been observed with organically-modified silicate minerals such as montmorillonite and vermiculite. Sulfide minerals such as cinnabar and argentite typically adsorb iodide with very high selectivity (Kd : 3,000 – 80,000 ml/g). Synthetic materials such as calcium monosulfate aluminate and hydrotalcite show moderate iodide selectivity (Kd: ~25 – 300 ml/g). A new class of specially-designed synthetic getters when tested in groundwater and simulated waste package leachate adsorbed iodide with very high specificity (Kd: 100,000 – 1,000,000 ml/g). The long-term stability of these mineral and synthetic getters in post-closure environment needs further evaluation. Under oxic conditions and in groundwater or background salt solution, many of the oxide/ hydroxide solids and silicate minerals exhibit relatively poor capacity and selectivity (Kd:
Revised: January 12, 2012 |
Published: September 24, 2003