Microsphere zeolite materials derived from coal fly ash cenospheres as precursors to mineral-like aluminosilicate hosts for 135,137Cs and 90Sr

Hollow microsphere zeolite materials with a bilayered zeolite/glass crystalline shell bearing NaP1 zeolite were synthesized by the hydrothermal treatment of coal fly ash cenospheres (Si/Al = 2.7) in an alkaline medium. Cs+ and/or Sr2+ of zeolitized cenospheres with the different Cs+ and/or Sr2+ loading were prepared by the ion exchange from nitrate solutions. The resulted (Cs,Na)P1, (Sr,Na)P1 and (Cs,Sr,Na)P1 bearing microsphere zeolites were converted to glass ceramics by heating at 900-1000 degrees C. The differential scanning calorimetry and quantitative phase analysis were used to monitor the solid-phase transformation of the initial and ion exchanged zeolite materials. It was established that the final solidified forms of Cs+ and/or Sr2+ are glass-crystalline ceramic materials based on pollucite-nepheline, Sr-feldspar-nepheline and Sr-feldspar-pollucite composites including similar to 60 wt.% of the major host phases (pollucite, Sr-feldspar) and 10-20 wt.% of glass. The Cs-137 leaching rate of 4.1 x 10(-7) g cm(-2) day(-1) was determined for the pollucite glass-ceramic according to Russian State Standard (GUST) No. 52126 P-2003 (7 day, 25 degrees C, distilled water). (C) 2013 Elsevier B.V. All rights reserved.