On the mechanism of Ca(OH)2 structure modulation by surfactants: Experimental and calculative studies

Surfactants are widely used for structure modulation of calcium-based materials. However, the modification mechanisms underlying the CaO digestion improved by surfactants for Ca(OH)2 production remain unclear. This study employed experiment methods, Density Functional Theory (DFT), and Molecular Dynamics methods (MD) to reveal the mechanism of surfactant modulation at a molecular level. The adsorption energy of Primary Alcohol Ethoxylate (AEO), Sodium Dodecyl Sulfate (SDS), H2O, and Dodecyl Trimethyl Ammonium Bromide (DTAB) on CaO(0 0 1) surface were −52.62, −51.98, –23.79, and 3.96 kcal/mol, respectively. The strong chemisorption of AEO and SDS on the surface of CaO improved its structure stability. AEO and SDS weakened the diffusion of H2O to CaO surface, thus causing the reaction between CaO and H2O to be suppressed. After being modulated by SDS and AEO, better crystallinity of Ca(OH)2 and finer crystalline grains were observed with the formation of developed pore structure. AEO has a longer molecular chain, giving better modification performance. On the contrary, DTAB accelerated the diffusion of H2O to CaO surface, leading to more energy released and causing the fast growth of Ca(OH)2 crystals, as evidenced by the much larger particle size compared to that of AEO and SDS. This process led to the creation of a larger pore structure. Desulfurization was used as a performance indicator to evaluate the surfactants modulation efficacy. The sulfur capacity of Ca(OH)2 regulated by 1 % AEO was 100.05 mg/g, being the highest among the used surfactants. For comparison, the sulfur capacity without additives was 49.64 mg/g. This study shows that nonionic surfactants are an ideal choice for regulating the structure of Ca(OH)2, as they can effectively inhibit crystal growth.