## 3 Results and Discussion
### Safety Analysis and Regeneration Study of La-EPRC Particles
#### 3.3.2 Adsorbent Regeneration Experiment  
1. Effect of NaOH Concentration on The Regeneration Effect of Adsorbent  
Figure 16 illustrates the experimental outcomes regarding the impact of varying NaOH concentrations on the desorption rate of the adsorbent. Analyzing the relationship curve between NaOH concentration and phosphate desorption rate reveals that, at low NaOH concentrations, the phosphate desorption rate increases with rising NaOH concentration. Phosphate desorption rate essentially peaks when NaOH concentration reaches 2.5 mol/L, approximately at 87.82%. Subsequent increases in NaOH concentration do not substantially alter the phosphate desorption rate, maintaining a state of desorption saturation. Therefore, for regenerating the adsorbent, a 2.5 mol/L NaOH solution is recommended as the desorption concentration. Subsequent analyses will focus on assessing the impact of desorption time on the regeneration effectiveness of the adsorbent.  
2. Effect of Desorption Time on Regeneration of Adsorbent  
Examining the desorption time versus desorption rate curves in Figure 17, it is evident that the desorption rate of La-EPRC particles experiences a rapid initial increase, reaching  
Figure 16: Effect of NaOH concentration on desorption rate of adsorbent.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sulfuric Acid** & **Adsorption (mg/g)** & **Desorption (mg/g)** & **Desorption Rate (\%)** & **Particle Surface State** \\ \hline
0.1 & 2.160 & 0.123 & 5.694 & No change \\
0.5 & 2.142 & 0.201 & 9.383 & Small portion of surface \\  & & & & material peeling off \\
1 & 2.133 & 0.436 & 20.44 & Further increase in \\  & & & & solution turbidity \\
5 & 2.204 & 0.875 & 39.70 & The particles are eroded to \\  & & & & a greater extent \\
10 & 2.198 & 1.329 & 60.46 & Pellets fall apart \\ \hline \hline \end{tabular}
\end{table}
Table 9: Desorption of La-EPRC particles in sulfuric acid solution.  
67.34% within 8 h. Subsequently, the rate of increase diminishes in the later stages of desorption, stabilizing around 24 h, where the desorption rate reaches approximately 85.38%. At 48 h, the desorption rate further stabilizes at about 87.5%. Considering the potential impact of prolonged impregnation of La-EPRC particles in a strong alkali solution on the material's mechanical properties, the optimal desorption time for La-EPRC particles is determined to be 24 h.  
3. Three successive adsorption-desorption experiments  
The outcomes from the three adsorption-desorption cycles of La-EPRC particles are illustrated in Figure 18. As the number of adsorption-desorption cycles increases, the adsorption capacity of La-EPRC particles gradually diminishes. Although the phosphate removal rate in the second adsorption cycle still exceeds 85%, it decreases to 62.37% in the third adsorption cycle after desorption. This decline could be attributed to incomplete desorption in the adsorption process, where certain binding sites remain occupied. Additionally, the impregnation of the adsorbent in the desorption solution contributes to its own loss, resulting in a reduction in adsorption capacity and phosphorus removal. The findings indicate that the regenerative properties of La-EPRC particles are effective for only a limited number of cycles, allowing for approximately two reuses.  
Figure 17: Effect of NaOH desorption time on the desorption rate of adsorbent.  
Figure 18: Results of adsorption–desorption experiments.