Study on the adsorption mechanism of CL-20 in waste acid by silicic acid: adsorption model and DFT calculation

Industrial wastewater pollution has emerged as a significant global environmental challenge, particularly regarding the urgent need to address highly acidic industrial effluents containing organic pollutants. As a novel high-energy explosive, hexanitrohexaazaisowurtzitane (CL-20) inevitably generates strongly acidic wastewater during its production and application processes, posing severe threats to ecological systems and human health. This study systematically investigates the adsorption performance of two silicon-based materials, sodium silicate (Na 2 SiO 3 ) and silicic acid (H 2 SiO 3 ), for the removal of CL-20 from wastewater. Experimental results demonstrate that the Langmuir isotherm model reveals maximum adsorption capacities of 87.21 and 69.97 mg/g for H 2 SiO 3 and Na 2 SiO 3 , respectively. Kinetic studies indicate that the adsorption processes of both materials conform to the pseudo-second-order kinetic model (R 2  > 0.98). Thermodynamic parameter analysis demonstrates reduced spontaneity of the adsorption process with increasing temperature, accompanied by exothermic characteristics and entropy reduction. Through density functional theory (DFT) calculations, the mechanisms underlying electrostatic adsorption and chemical bonding interactions between CL-20 molecules and silicon-based materials are elucidated. This research establishes a novel technical approach for efficient CL-20 wastewater treatment while providing theoretical foundations for developing and optimizing related adsorption materials.