## 3 Results and Discussion  
Figure 2a-c shows the XRD patterns of synthesized R1-R3, PR1/24h-PR3/24h, and PR1/48h-PR3/48h granules. Figure 2a illustrates that the XRD results reveal that the synthesis of the R1-R3 granules predominantly led to the formation of CSD as the major crystalline phase. This observation indicates that the CS powder utilized as a precursor underwent a hydration reaction during synthesis in an aqueous environment, resulting in its transformation into the dihydrate form of calcium sulfate. This hydration-induced phase transformation facilitated the transition from a loose powder to a consolidated solid through crystal growth and interlocking, which was subsequently processed into granules [21]. Figure 1: The following schematic diagram illustrates the preparation process of the raw R1–R3 granules, which are later converted into the final product, PR1/24h, PR1/48h, PR2/24h, PR2/48h, PR3/24h, and PR3/48h granules. The XRD patterns of the reaction products, obtained after the R1-R3 precursor granules were immersed in a solution containing Mg\({}^{2+}\), H\({}_{2}\)PO\({}_{4}\)\({}^{2-}\), HPO\({}_{4}\)\({}^{2-}\), and PO\({}_{4}\)\({}^{3-}\) ions for a period of 24 h, are shown in Figure 2b. These include PR1/24h, PR2/24h, and PR3/24h, which are derived from the monophasic R1 granules and the mixed R2 and R3 granules, respectively, along with the standard Mg-WH diffractogram [ICDD #00-070-2064]. The XRD patterns of PR1/24h, PR2/24h, and PR3/24h granules revealed the formation of biphasic materials, with PR1/24h consisting of Mg-WH and calcium deficient hydroxyapatite (CDHA, Ca\({}_{10-x}\)(HPO\({}_{4}\))\({}_{x}\)(PO\({}_{4}\))\({}_{6-x}\)(OH)\({}_{2-x}\), where \(0<x<1\)) phases, while PR2/24h and PR3/24h were composed of Mg-WH and dicalcium phosphate anhydrous (DCPA, CaHPO\({}_{4}\)) phases. Notably, the amount of DCPA in the PR2/24h sample was significantly higher compared to PR3/24h. The formation of CDHA phase is commonly observed at higher pH values, as Mg-WH is thermodynamically more stable than apatite under moderately low pH conditions. In this study, however, all syntheses were performed under nearly identical pH conditions, suggesting that the appearance of CDHA is influenced by variations in the Ca/Mg ratio within the reaction solution, as previously reported in [22]. The presence of the DCPA phase in the PR2/24h and PR3/24h samples can be ascribed to its function as a transient intermediate in the formation pathway of Mg-WH. It is known that DCPA undergoes a gradual conversion into Mg-WH over time, a transformation that is promoted by magnesium-rich conditions and a moderately acidic pH. This observation is consistent with previous findings [6] and underscores the pivotal role of reaction time, precursor composition, and solution composition on the resulting phase. In contrast, the XRD patterns of the products synthesized for 48 h (PR1/48h, PR2/48h, and PR3/48h granules) demonstrated the formation of single-phase materials, as no diffraction peaks corresponding to CDHA, DCPA, or any other secondary phases were observed (see Figure 2c). The broad and low-intensity diffraction peaks indicate the formation of nanocrystallites with moderate crystallinity [23]. The reflection positions identified in the XRD analysis were subjected to careful indexing and were found to correspond with the standard diffractogram for rhombohedral Mg-WH [00-070-2064]. The diffraction peaks observed at 20 values of 10.92\({}^{\circ}\), 13.72\({}^{\circ}\), 17.14\({}^{\circ}\), 28.02\({}^{\circ}\), 31.28\({}^{\circ}\), and 34.70\({}^{\circ}\) can be attributed to the (0 1 2), (1 0 4), (1 1 0), (214), (0 2 10), and (2 2 0) crystallographic planes of the Mg-WH  
Figure 2: XRD patterns of R1–R3 (**a**), PR1/24h–PR3/24h (**b**), and PR1/48h–PR3/48h (**c**) granules synthesized via a dissolution–precipitation reaction. phase, respectively. Additionally, smaller peaks align with the reference data too. A 48 h synthesis duration was sufficient for the complete phase transformation of the raw granules into Mg-WH ones.