Facile preparation of high-strength α-CaSO4·0.5H2O regulated by maleic acid from phosphogypsum: experimental and molecular dynamics simulation studies

Abstract

Crystal modifier is a significant factor in preparation of α-hemihydrate gypsum (α-HH) from phosphogypsum (PG). The influence of maleic acid, reaction temperature, time, and solid-liquid ratio on the preparation of high-strength α-HH from PG was systematically studied herein. The optimum condition for α-HH prepared by hydrothermal autoclave method was pH of 4, temperature of 140 °C for 2.0 h with solid-liquid ratio of 4:5. Crystal modifier of maleic acid can effectively regulated the crystal morphology of α-HH. SEM-EDS and FTIR analysis suggested that maleic acid could preferentially absorbed on the top face of α-HH crystals that decreased the growth rate of α-HH along the c-axis, resulting in the morphology of α-HH crystals transformed to hexagonal prisms, and the regulatory mechanism was estimated by molecular dynamics (MD). When maleic acid (0.1%) was added, the obtained α-HH showed aspect ratio of 1.2, and the flexural and compressive strength of the hardened α-HH could reach to 14.79 and 46.24 MPa, respectively. All of these results will help to design long-term effectiveness of phosphogypsum recycling strategies.

Unveiling the organic acids with auxiliary functional groups effect on α‐hemihydrate gypsum: Ab initio calculations

“…The optimized crystal parameters are listed in Table 1. The α‐HH four major crystal planes (002), (200), (110), and (1–10) were predicted by the attachment energy method, 35 which is in good agreement with previous work 36,37 …”

“…The single crystal was prepared by Bezou et al 34 in 1995 using high-purity gypsum mineral as the starting material and subjected to hot-pressurized decomposition for 4 hours at 134 attachment energy method, 35 which is in good agreement with previous work. 36,37 Yan et al 38 studied the adsorption and doping effects of Mg 2+ ions on the growth of calcium sulfate hemihydrate crystals with the (002) top surface and (200) side surface.…”

The study on the effect of flotation purification on the performance of α-hemihydrate gypsum prepared from phosphogypsum

“…The other experimental conditions for the preparation of α-HH were kept consistent, by the preliminary study and literature search, the mixed solution of maleic acid and aluminum sulfate was selected as the crystal transfer agent, and the amount of fixed aluminum sulfate was 0.2% 49 . The amount of aluminium sulfate was fixed at 0.2 wt% of the sample mass.…”

“…The main steps included hydrothermal synthesis reaction, high-temperature drying, and characterization. The specific procedure was as follows: 2 g of PG concentrate (purified phosphogypsum by flotation), solid–liquid ratio 1:1 49 , was weighed and hydrothermally reacted in a 50 ml autoclave at 140 °C under fully closed conditions (the pressure of operation is 3 MPa), and the sample was quickly removed after 2 h of reaction, the upper liquid layer was poured out and dried at 120 °C for more than 12 h. The dried sample was stored in a desiccator and observed under a scanning electron microscope (TM-1000; HITACHI Co. Ltd., Tokyo, Japan) at a magnification of 1000 times to study whether there was any change in the crystal morphology. The effect of the amount of transcrystallizer on the crystal morphology of the prepared products was investigated.…”