Optimization Design of Metakaolin-Based Geopolymer Solidification for Potassium Copper Hexacyanoferrate After Cs+ Adsorption Using Response Surface Methodology

This study employed a metakaolin-based geopolymer (GP) to solidify potassium copper hexacyanoferrate after its saturation with adsorbed Cs+. The experiment was designed using response surface methodology (RSM) in the Design–Expert 13 software, targeting the compressive strength and cumulative leaching fraction of the solidified form. A regression model was developed to achieve the multi-objective optimization of the comprehensive performance of the GP solidified product. Regression analysis identified the optimal mix proportion as Na2O/Al2O3 = 0.84, SiO2/Al2O3 = 2.8, and H2O/Na2O = 10.23. Under these conditions, the experimentally measured compressive strength was 23.41 MPa. The 42-day cumulative leaching fractions at 25 °C and 40 °C were 7.906 × 10−4 cm and 1.5923 × 10−3 cm, respectively, both significantly below the national standard threshold (Standard Code GB7023-2011) of 2.6 × 10−1 cm. The percentage error remained within 10%, indicating strong agreement with predicted values. These results suggest that metakaolin-based GP exhibits promising potential for the immobilization of radionuclides.