Structural evolution of annealed Cs-exchanged copper hexacyanoferrate (Cs,K)2CuFe(CN)6 loaded on mesoporous silica particles

International audiencePorous silica particles functionalized by potassium copper hexacyanoferrate (CsKCu-HCF@silica) are currently studied as a selective sorbent to remove radioactive cesium from contaminated effluents. After use, these spent particles need to be transformed into a dense waste form. A hot isostatic pressing (HIP) treatment under argon is envisaged to achieve this goal. As a preliminary study to the HIP, this paper reports the thermal behaviour of CsKCu-HCF@silica particles, at a laboratory scale. It was shown that an immediate HIP of spent particles is not possible. As an alternative, a first air annealing prior to HIP leads to (i) decomposition of KCu-HCF (ii) a reduction of the specific surface with closing of the mesoporosity (iii) crystallization of silica into cristobalite (iv) an in-situ formation of a Cs based silicate glass in the siliceous particles leading to no significate Cs loss. The results are discussed and put into a perspective for the upcoming HIP test