## 4 Conclusions  
In this study, porous diatomic granules were prepared by the dropwise granulation of diatomic/sodium alginate dispersions involving sodium alginate cross-linking and subsequent heat treatment ranging from 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C. The dispersions were formulated with solid loadings of diatomic ranging from 3.8 to 30.5 wt.% (4 to 44 g/100 mL H\({}_{2}\)O) while maintaining a fixed sodium alginate content. The assessment of the properties throughout the manufacturing process yielded the following key findings:  
The optimization of the solid content and viscosity of the dispersions to 30.07 wt.% and 1560 mPa.s (\(\sim\)0.3 s\({}^{-1}\) shear rate), respectively, ensured a uniform solid network within the granules, which minimized deformations under fixed granulation conditions and resulted in granules with a maximum sphericity of \(\sim\)0.90. The porous diatomic granules exhibited a decrease in the total porosity from 74.6 \(\pm\) 1.9% to 69.0 \(\pm\) 2.9%, an outcome attributed to the enhanced partial densification as the heat-treatment temperature was increased from 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C. Additionally, these granules displayed a hierarchical structure consisting of macropores ranging from 1.769 \(\upmu\)m to 2.777 \(\upmu\)m and mesopores ranging from 14.83 nm to 35.34 nm. The pore sizes increased due to the facilitated filling and merging of smaller pores with an increase in the temperature. A trade-off relationship was evidenced between the compressive strengths and the specific surface areas of the porous diatomic granules as a function of the temperature. The compressive strengths increased from 0.51 \(\pm\) 0.09 MPa to 5.17 \(\pm\) 0.31 MPa while the specific surface areas simultaneously decreased from 2.45 m\({}^{2}\)/g to 0.49 m\({}^{2}\)/g. However, it is noteworthy that the diatomic granules consistently displayed hierarchical meso/microporosity, independent of the heat-treatment conditions. In summary, the newly developed millimeter-sized porous diatomic granules exhibited high sphericity, hierarchical porosity, and acceptable compressive strengths comparable to those of porous \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) granules derived from sodium alginate gelation and porous diatomic granules, obtained through pan rotation granulation. These characteristics highlight the potential applicability of these granules as support materials for catalytic and adsorption purposes. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13169474/s1](https://www.mdpi.com/article/10.3390/app13169474/s1)]([https://www.mdpi.com/article/10.3390/app13169474/s1](https://www.mdpi.com/article/10.3390/app13169474/s1)), Figure S1: Scheme illustrating the ball-milling conditions and the processed diatomic slurries used to prepare the diatomic/sodium alginate dispersions and, subsequently, the porous diatomic granules; Figure S2: Representative porous diatomic granules (D08-D24) obtained after each step in the processing route: (a) aging (CaCl2 bath) and cleaning (DI water), (b) drying (80 \({}^{\circ}\)C, overnight), and (c) a heat treatment at 1200 \({}^{\circ}\)C for 1 h in air; Figure S3: Representative porous diatomic granules (D28-D40) obtained after each step in the processing route: (a) aging (CaCl2 bath) and cleaning (DI water), (b) drying (80 \({}^{\circ}\)C, overnight), and (c) a heat treatment at 1200 \({}^{\circ}\)C for 1 h in air. **Author Contributions:** [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] and [PERSON] performed the experiments; [PERSON], [PERSON] and [PERSON] analyzed the data; [PERSON] contributed reagents/materials/analysis tools; [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Fundamental Research Program of the Korean Institute of Materials Science (KIMS), through Grant No. PNK8810, and by the Technology Innovation Program (20003782) of the Ministry of Trade, Industry and Energy.