Molecular dynamics study on the interaction of phosphorus building gypsum /surfactant composites.

While surfactants are widely used in phosphogypsum, their interactions with the phosphogypsum-water interface remain unclear. This study investigates the impact of three types of surfactants, namely polycarboxylate-based surfactant (PCE-TPEG), naphthalene-based surfactant (NS), and melamine-based surfactant (MS), on the performance of phosphorus building gypsum (PBG). Additionally, a nanoscale model of the PBG-surfactant-water interface is constructed using molecular dynamics to elucidate the mechanisms underlying the interaction between different surfactants and PBG at multiple scales. The results demonstrate that all surfactants enhance the mechanical properties of PBG. PCE-TPEG exhibits the most pronounced improvement. In the model, PCE-TPEG molecules likely undergo comb-like adsorption, while NS and MS molecules tend to adsorb on both ends of the crystal plane. Changes in the potential difference between CaSO4·2H2O and H2O, as well as between CaSO4·2H2O and the surfactant, play a crucial role in adsorption. PCE-TPEG, NS, and MS molecules tend to spread horizontally in a vacuum state. With the addition of water molecules, they transition to spatial adsorption. Ca2+ easily interacts with -COO- and -SO3- groups, leading to reduced migration and flexibility of the main chain. The adsorption process of surfactants at the gypsum-water interface occurs spontaneously and Electrostatic forces are the main driving factor. This study contributes to a more comprehensive understanding on the behaviour of the phosphorus building gypsum/surfactant composites.

Preparation and Pore Structure of Energy-Storage Phosphorus Building Gypsum.

In this study, the pore structure of a hardened phosphorous building gypsum body was optimised by blending an air-entraining agent with the appropriate water-paste ratio. The response surface test was designed according to the test results of the hardened phosphorous building gypsum body treated with an air-entraining agent and an appropriate water-paste ratio. Moreover, the optimal process parameters were selected to prepare a porous phosphorous building gypsum skeleton, which was used as a paraffin carrier to prepare energy-storage phosphorous building gypsum. The results indicate that if the ratio of the air-entraining agent to the water-paste ratio is reasonable, the hardened body of phosphorous building gypsum can form a better pore structure. With the influx of paraffin, its accumulated pore volume and specific surface area decrease, and the pore size distribution is uniform. The paraffin completely occupies the pores, causing the compressive strength of energy-storage phosphorous building gypsum to be better than that of similar gypsum energy-storing materials. The heat energy further captured by energy-storage phosphorous building gypsum in the endothermic and exothermic stages is 28.19 J/g and 28.64 J/g, respectively, which can be used to prepare energy-saving building materials.