Hydrothermal decomposition of K-feldspar with Cs enrichment into pollucite in Cs-included alkaline solution

Hydrothermal decomposition of K-feldspar in Cs-included NaOH (2.2 mol/kg) and KOH (3.0 mol/kg) solu-tions with initial Cs/(Cs + Na) and Cs/(Cs + K) ratios varying from 0 to 1 was investigated. Results showed that the solid products exhibited high selectivity for Cs with respect to Na and K, where pollucite crystals instead of analcime and kalsilite in cubic and trioctahedra morphologies with less than 5 mol% Na or K replacement were obtained from Na-Cs (220 degrees C) and K-Cs (240 degrees C) solutions respectively. The distribution of Cs between the final solid and solution exhibited as liner relations in similar slops (about 0.06) for the two mixed mediums, and an extremum Cs/(Cs + Na + K) value of about 0.95 in solid phase was derived. Present work indicated that Cs was enriched during the hydrothermal processing on K-feldspar, almost pure pollucite was synthesized even in mixed ion systems, and radioactive Cs could be immobilized from vast polluted silicates including feldspar minerals.(c) 2022 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved.

Automated summary

The hydrothermal decomposition of K-feldspar in Cs-included NaOH and KOH solutions was studied. The solid products showed high selectivity for Cs, resulting in the synthesis of pollucite crystals with low substitution of Na or K. Cs distribution between solid and solution followed a linear trend, indicating Cs enrichment during hydrothermal processing. This study demonstrates the immobilization of radioactive Cs from polluted silicates, including feldspar minerals.