## 4 Results and Discussion
### Hydration Product Analysis of RCPB
#### 4.3.3 SEM and EDS  
In order to further explore the composition in the samples, as well as the endowment morphology, characterize the typical morphology and quantity of hydration products, as well as the pore structure and distribution of the four groups of samples maintained for 28d [40], SEM detection BES imaging, as well as the elemental composition of the specific points, were analyzed with energy spectroscopy analysis EDS detection; this study systematically revealed the solid waste doping on the formation of the microstructure of the RCPB system and the efficacy of the pollutant sequestration M = mechanism of action. SEM images magnified to 10 \(\upmu\)m (Figure 8) are shown for four samples, showing a large number of flocculent (C-S-H) gels or (C-A-S-H); the residual strong alkaline components in the RM elevate the initial alkalinity of the specimens, leading to a shortened induction period; Fe ions in the RM intensify the reaction in the accelerated period of the C-S-H gel; meanwhile, Al ions displace C-S-H in the bridging silicon sites, enhancing the macroscopic compressive strength. Lumpy (calcium hydroxide and gypsum): the reaction between soluble SO\({}_{4}\) in PG and the hydration product of C\({}_{3}\)S, which reduces the concentration of Ca ions and prolongs the induction period; the formation of insoluble Ca\({}_{5}\)(PO\({}_{4}\))\({}_{3}\)OH by PO\({}_{4}\) impurities and Ca affects the hydration; gypsum crystallization leads to prolongation of the accelerated period and postponement of the onset of the decay period [41]. Stick (AFt)  
Figure 7: DTG-TG curves for different concentrations of RCPB: (**a**) TG and (**b**) DTG.  
as well as flocculent structures (complexes as well as unreacted material), with specific elemental compositions for each structure, were detected by EDS.  
The flocculent gels (C-S-H or C-A-S-H), with EDS face scans showing Si/Ca molar ratios ranging from 0.45 to 0.62, are consistent with the structural features of low Ca-Si ratio C-S-H; the rod-like AFt crystals, with lengths of 1-3 \(\upmu\)m, with EDS showing S/Al molar ratios of \(\approx\)3.0, corroborate the stoichiometric relationships of the sulfoaluminate phases. Residual gypsum phase: Flaky gypsum dihydrate (S/Ca = 1.02) showed disordered accumulation in the low-doped specimens, and its relative content was positively correlated with the PG/RM ratio, indicating that the RM basicity was not sufficient to completely neutralize the PG acidic component. Sodium hexafluoroaluminate precipitation: Na/Al/F\(\approx\)3:1:6 was detected, confirming the formation of Na\({}_{3}\)AlF\({}_{6}\) crystals (crypite structure) with a specific surface area of 152 m\({}^{2}\)/g, which immobilized F by physisorption.  
The SEM images clearly depicted the different microstructural features of each group of samples. The SEM of each group of samples had unreacted gypsum, indicating that the addition of RM was not sufficient to neutralize the impurities such as the phosphoric acid remaining in the original PG, and thus, there were some flocculated layers of gypsum mis-stacked. According to the EDS analysis, part of the flocculent and powdery structure should be sodium hexafluoroaluminate precipitation, and the precipitation is physically adsorbed with F ions at the same time.  
Combined with XRD and thermogravimetric analysis results, it can be seen that increasing the concentration of RCPB makes the reaction intensify, resulting in more gypsum reaction consumption, and, at the same time, makes the F ions adsorbed and removed, and combined with the results of the pH test, the higher concentration is more friendly to environmental protection.  
Figure 8: Microscopic morphology of different concentrations of RCPB and EDS. (**a**) PR-63, (**b**) PR-65, (**c**) PR-67, (**d**) PR-69, and (**e,f**) EDS.