Alkali aluminosilicate geopolymers as binders to encapsulate strontium-selective titanate ion-exchangers

Abstract

Geopolymer cements can be used to solidify strontium-contaminated ion exchanger particles, forming a stable monolith potentially suitable for final disposal.

Encapsulation of Sr-loaded titanate spent adsorbents in potassium aluminosilicate geopolymer

“…The Ti-rich regions are the adsorbent particles, with the clearly distinguished distribution boundary between adsorbent and matrix, indicating the absence of any interaction that could lead to a breakdown and release of Ti from the titanates between adsorbent and geopolymer 10 matrix during the manufacturing (geopolymerization) and leaching processes. This is consistent with the results of Ke et al [18]. There Al-and Si-rich areas consistent with geopolymer regions have no Ti, also indicating no specific interaction.…”

“…The XRD patterns of the titanate adsorbent before and after loading with Sr 2+ are shown in Figure 2. The titanate adsorbent is identified as a long-range disordered (X-ray amorphous) material, with the broad feature at around 9 2 indicating the interlayer spacing of the main edge-sharing TiO 6 sheets [18,30]. With no significant difference in XRD patterns before and after Sr adsorption, this indicates that no new phases have formed, and there are no identifiable crystallographic changes occurring as a result of the adsorption processes.…”

“…The alkaline activator solution was prepared by dissolving KOH (Wako Pure Chemical Industries, Ltd., Osaka, Japan) pellets into a commercial potassium silicate solution (Wako Pure Chemical Industries, Ltd., Osaka, Japan) to reach a final SiO 2 /K 2 O molar ratio of solution equal to 1.0, and adding distilled water to give a constant H 2 O/K 2 O ratio in each sample. The final stoichiometry of sample is K 2 OAl 2 O 3 3SiO 2 11H 2 O, which is followed by our previous studies to achieve a dense and stable gel matrix [18][19]. The same activator was used for all samples.…”

“…The titanate adsorbent is an inorganic ion exchanger which has a layered structure of titanium-oxygen octahedral sheets. Between the sheet layers there is sodium which forms a hydrous sodium titanate structure [18,21]. These sodium ions are readily exchangeable, and the layered structure gives a large surface area with the high amount of interlayer water and relatively open layered structure.…”

“…Recently, Ke et al [18] determined the distribution of Sr in a geopolymer with embedded titanate adsorbents at high Sr concentrations. The formation of SrCO 3 from high concentrations of Sr was observed to play an important role in immobilizing the Sr inside the waste form generated.…”