Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

Abstract

Mitigation of hazardous and radioactive waste can be improved through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. However, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granular samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.

Recent progress in low-carbon binders

“…The effective immobilization of cesium in Portland cement-based matrices is well known to be challenging, and so the availability of a cementing system that can restrict its movement is highly desirable. There have been important recent investigations of the potential for compatibility of AAM matrices with complex waste streams containing multiple radioisotopes [265,266], with oily wastes [267,268], with ion exchange media [269,270], and with graphitic or metallic wastes [271][272][273]. AAM matrices have also been demonstrated to show generally good stability under irradiation [274][275][276], and a hydrogen radiolytic yield that depends on water content and pore structure [274].…”

Evidence of technetium and iodine release from a sodalite-bearing ceramic waste form

“…The third material was produced using the SRNL BSR using feed from actual radioactive Hanford waste (Tank SX-105) and is referred to as LAW1. More details on the processing of this material, also known as Module C, is found in a report by Jantzen et al(2013) Further information on mineralogical studies conducted with the P1BG and BSRG materials is provided elsewhere (Jantzen et al, 2013;Williams et al, 2016).…”

“…Na + , Cs + , K + ) and X = a 1anion (e.g. Cl -, Br -, OH -)], as well as a significant amorphous fraction (Williams et al, 2016).…”

“…The quantitative results, when combined with results obtained through other test methods, can then be used as input values to performance assessment models that describe the long-term impacts on public health and environmental resources of disposing of the FBSR waste form in a facility. Previous tests that have been performed on similar FBSR products are the static product consistency test (PCT) (Williams et al, 2016) and the pressurized unsaturated flow (PUF) test, which simulate dissolution in a water-unsaturated environment (Neeway et al, 2014;Pierce et al, 2014). Previously, similar SPFT tests have been run on FBSR products (Jantzen et al, 2007;Lorier et al, 2005;McGrail et al, 2003) and glass-bonded sodalite (Jeong et al, 2002;Morss et al, 2000); however, these studies were run on samples that did not contain Tc, and the systems were not run long enough to achieve a steady-state release of species from the products.…”

Inorganic Waste Forms for Efficient Immobilization of Radionuclides

“…The physical characteristics of geopolymers such as their compressive strength and others are either similar or superior to the PC . Particularly, its resistance to highly reactive and hazardous chemicals, including concentrated inorganic acids (nitric, sulfuric, and hydrochloric), and organic acids is much better than that of PC, which in turn, proves the suitability of the geopolymer as one of the promising alternatives for radioactive waste stabilization and immobilization. , Moreover, because of their cation-binding sites, mechanical properties (compressive strength), and chemical resistance, geopolymers have received considerable attention as suitable solidifying materials for the long-term immobilization of radioactive wastes. , …”