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.

Study on Effect of Nano-CaCO3 on Properties of Phosphorus Building Gypsum.

Phosphogypsum is an industrial by-product from the wet preparation of phosphoric acid. Phosphorus building gypsum (PBG) can be obtained from phosphogypsum after high-thermal dehydration. Improving the mechanical properties of PBG is of great significance to extending its application range. In this paper, PBG was modified by adding nano-CaCO3. Specifically, this study, conducted on 0.25-2% nano-CaCO3-doped PBG, tested effects on the fluidity, setting time, absolute dry flexural strength, absolute dry compressive strength, water absorption and softening coefficient of PBG, followed by its microscopic analysis with SEM and XRD. The experimental results showed that, with an increase in nano-CaCO3 content, the fluidity and setting time of PBG-based mixes were decreased. When the content was 2%, the fluidity was 120 mm, which was 33% lower than that of the blank group; the initial setting time was 485 s, which was 38% lower than that in the blank group; the final setting time was 1321 s, which was reduced by 29%. Nano-CaCO3 evidently improved the absolute dry flexural strength, absolute dry compressive strength, water absorption and softening coefficient of PBG to a certain extent. When the content was 1%, the strengthening effect reached the optimum, with the absolute dry flexural strength and absolute dry compressive strength being increased to 8.1 MPa and 20.5 MPa, respectively, which were 50% and 24% higher than those of the blank group; when the content was 1.5%, the water absorption was 0.22, which was 33% lower than that of the blank group; when the content approached 0.75%, the softening coefficient reached the peak of 0.63, which was 66% higher than that of the blank group. Doping with nano-CaCO3 could significantly improve the performance of PBG, which provides a new scheme for its modification.

Strength Prediction of Ball-Milling-Modified Phosphorus Building Gypsum Based on NSGM (1,4) Model.

Phosphogypsum is an industrial byproduct from the wet preparation of phosphoric acid. Phosphorus building gypsum can be obtained from phosphogypsum after high-thermal dehydration. This study aimed to analyze the influence of ball milling with different parameters on the strength of phosphorus building gypsum. In this paper, the absolute dry flexural strength and the absolute dry compressive strength of phosphorus building gypsum were compared under different mass ratios of material to ball, ball-milling speed, and ball-milling time, and the NSGM (1,4) model was applied to model and predict the strength of phosphorus building gypsum modified by ball milling. According to the research results, under the same mass ratio of material to ball and ball-milling speed, the absolute dry flexural strength and absolute dry compressive strength of phosphorus building gypsum firstly increased and then decreased with the increase in milling time. The NSGM (1,4) model established in this paper could effectively simulate and predict the absolute dry flexural strength and the absolute dry compressive strength of the ball-milling-modified phosphorus building gypsum; the average relative simulation errors were 12.38% and 13.77%, and the average relative prediction errors were 6.30% and 12.47%.

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.