Removal of CL-20 from waste acid using macroporous resin: Stabilization of waste acid and recovery of CL-20.

Hexanitrohexaazaisowurtzitane (CL-20) is a powerful explosive with significant environmental and ecotoxicological concerns. Industrial production of CL-20 generates acidic effluents containing residual CL-20, posing treatment challenges and resource loss. This study investigated four macroporous resins (DA201-C, NKA-2, D730, and D121) for CL-20 removal and recovery. Under the conditions of a 10 g/L dosage and 360 min NKA-2 showed over 90 % removal efficiency. Adsorption followed the Freundlich isotherm (R > 0.98) and pseudo-second-order kinetics (R > 0.99), indicating heterogeneous chemisorption. Thermodynamic analysis confirmed the process was spontaneous and exothermic. Ethyl acetate enabled 95 % desorption within 15 min, also fitting pseudo-second-order kinetics. XPS and molecular dynamics identified hydrogen bonding and π-π interactions as key mechanisms. NKA-2 demonstrated stability over four cycles, and CL-20 was recovered as a solid with 91.4 % efficiency, yielding an economic return of $892.14/kg. This work offers an effective method for CL-20 recovery with broader applications.