Insight into the effect of maleic acid on the preparation of α-hemihydrate gypsum from phosphogypsum in Na2SO4 solution

Effect of Molecular Structure of Organic Acids on the Crystal Habit of α-CaSO4·0.5H2O from Phosphogypsum

“…The x-ray diffraction analysis indicated that the main phase of PG is CaSO 4 •2H 2 O with a little quartz (SiO 2 ) and co-crystallized phosphorus (CaHPO 4 •2H 2 O). The contents of the CaSO 4 •2H 2 O, soluble phosphate and soluble fluorine were 91.32 wt%, 0.18 wt%, and 0.01 wt%, respectively [21]. In order to reduce the influence of soluble impurities on the preparation process and mechanical strength of α-CaSO 4 •0.5H 2 O, the soluble phosphate and soluble fluoride were solidified by adding 0.6 wt% quicklime (mass ratio of lime to PG), and the removal rates were 90.45% and 36.36%, respectively.…”

“…The model of α-CaSO 4 •0.5H 2 O crystal habit regulated by the crystal modifier is shown in Figure 15. In our previous study, the adsorption of the MA molecule on the (111), (110), and (010) crystal faces of α-CaSO 4 •0.5H 2 O were studied using DFT calculations, and the results indicated that the (111) face was the most stable chemical adsorption surface and presented the strongest bonding interaction with MA, and the adsorption of MA on the (110) and (010) faces was relatively weak [21]. Therefore, the crystal modifier can preferentially adsorb on the (111) face and retard its growth in the length direction.…”

“…For instance, the short hexagonal prism α-CaSO 4 •0.5H 2 O, with an aspect ratio of 1.0-1.4, could be obtained by adding succinic acid (C 4 H 6 O 4 ) [15][16][17][18] [20]. In the presence of maleic acid (C 4 H 4 O 4 ), the crystal habit of α-CaSO 4 •0.5H 2 O evolved from a needle-like whisker to a short equiaxial crystal [21]. The crystal habit of α-CaSO 4 •0.5H 2 O crystals can be influenced by adding citric acid (C 6 H 8 O 7 •H 2 O) [22] and sodium citrate (Na 3 C 6 H 5 O 7 •2H 2 O) [12,13]; the aspect ratio of α-CaSO 4 •0.5H 2 O crystal is decreased from 10.3 to 0.6 with the increase in the sodium citrate dosage from 0 to 0.045 wt% [23].…”

Radioactivity of Five Typical General Industrial Solid Wastes and its Influence in Solid Waste Recycling

“…Major components in seven solid wastes were analyzed by using X-ray fluorescence (XRF, PANalytical Axios mA×4 KW, Malvern Panalytical, Almelo, The Netherlands), and the results are illustrated in Table 3. As shown in Table 3, PS, RM, FA are mainly composed of CaO, SiO 2 , Al 2 O 3 , and Fe 2 O 3 [35], PG is composed of CaO, SiO 2 , Al 2 O 3 , and SO 3 [36], while CaO, SiO 2 , Al 2 O 3 , Mn, and S are the main components in EMR, EMR-Na, and EMR-Ca.…”

Hydration Mechanism and Hardening Property of α-Hemihydrate Phosphogypsum

“…Many studies have confirmed that the morphology of HH is one of the most important factors for affecting mechanical strength of hardened paste, and the short hexagonal prism crystal with an aspect ratio of 1:1 is a perfect morphology with high strength [6][7][8][9]. Crystal modifiers such as succinic acid [10][11][12][13], maleic acid [14], citric acid [15], et al can regulate the morphology of HH from a needle-shaped particle to a short columnar crystal. Our previous research indicated that L-Aspartic acid (L-Asp) is an effective crystal modifier for the preparation of short columnar HH [16], but the effects of L-Asp on the hydration process and hardening property of HH are not clear.…”