2.4.1. Material Adsorption Stability
The adsorption stability of the material was assessed by experimentally determining the desorption of adsorbed phosphorus elements from La-EPRC particles in room temperature water, high-temperature hot water, and sulfuric acid solution.
- 1.
Room Temperature Water Desorption
The following amounts of 1 g P/L phosphorus standard reserve solution were taken: 1.25 mL, 2.5 mL, 5 mL, 12.5 mL, 25 mL, 37.5 mL, and 50 mL. These were diluted with deionized water to 250 mL, creating concentrations of 5 mg P/L, 10 mg P/L, 20 mg P/L, 50 mg P/L, 100 mg P/L, 150 mg P/L, 200 mg P/L. A total of 3 g of La-EPRC particles was weighed into each conical flask and placed in a shaker (25 ± 1 °C, 150 ± 5 r/min). After 48 h of continuous shaking, the samples were taken and filtered through a 0.45 μm filter, and absorbance was measured using ammonium molybdate spectrophotometry to calculate residual phosphorus concentration and the adsorption amount of the adsorbent.
After adsorption, La-EPRC particles were washed 3–5 times with water and air-dried. The dried particles were placed in seven 250 mL conical flasks sequentially, with 250 mL of deionized water added simultaneously. The particles were subjected to constant shaking in a shaker (25 ± 1 °C, 150 ± 5 r/min) for 48 h to desorb the material. After the reaction was halted, samples were collected, and after filtration for absorbance determination, the desorbed material amount and desorption rate were calculated.
- 2.
Desorption in High-Temperature Water
The following amounts of 1 g P/L phosphorus standard reserve solution were taken: 1.25 mL, 2.5 mL, 5 mL, 12.5 mL, 25 mL, 37.5 mL, and 50 mL. These were diluted with deionized water to 250 mL, creating concentrations of 5 mg P/L, 10 mg P/L, 20 mg P/L, 50 mg P/L, 100 mg P/L, 150 mg P/L, and 200 mg P/L. A total of 3 g of La-EPRC particles was weighed for each flask, placed in a shaker (25 ± 1 °C, 150 ± 5 r/min), and sampled after the adsorption reaction reached equilibrium at 48 h. The samples were filtered, absorbance was measured, and phosphorus concentration and the adsorption amount of the adsorbent were calculated.
After adsorption, La-EPRC particles were rinsed 3~5 times with water and dried naturally indoors. The dried particles were placed into 7 sets of 250 mL conical flasks, adding 250 mL of deionized water simultaneously. The particles were placed in a shaker with constant shaking (25 ± 1 °C, 150 ± 5 r/min), desorption was conducted for 48 h, the reaction was stopped, the supernatant was sampled, the samples were filtered, absorbance was determined, and the material desorption amount and desorption rate were calculated.
- 3.
Desorption in Sulfuric Acid Solution
A total of 5 mL of 1 g P/L phosphorus standard reserve solution was taken and distributed into five conical flasks. Each flask was diluted to 250 mL with deionized water to create a 20 mg P/L dilute solution. A total of 3 g of La-EPRC particles was weighed into each flask, placed in a shaker with constant shaking (25 ± 1 °C, 150 ± 5 r/min), and sampled after the 48 h adsorption reaction reached equilibrium. The samples were filtered, absorbance was measured, and phosphorus concentration and the adsorption amount of the adsorbent were calculated.
After adsorption, La-EPRC particles were rinsed 3~5 times with water and dried naturally indoors. Sulfuric acid solutions with concentrations of 0.01 mol/L, 0.1 mol/L, 0.5 mol/L, and 1.0 mol/L were prepared. The dried particles were sequentially placed into five 250 mL conical flasks and desorbed in a shaker for 48 h. The reaction was stopped, sampled, absorbance after filtration was measured, and the amount of material desorbed and desorption rate were calculated.
2.4.2. Adsorbent Regeneration Experiment
A total of 5 mL of 1 g P/L phosphorus standard reserve solution was taken, diluted to 250 mL with deionized water, and mixed well to create a 20 mg P/L phosphorus dilute solution. A total of 3 g of La-EPRC particles was weighed, added to a conical flask, and placed in a shaker with constant shaking (25 ± 1 °C, 150 ± 5 r/min). After stopping the reaction for 48 h, the samples were filtered and measured to calculate the adsorption capacity of the adsorbent.
After adsorption, 250 mL of NaOH solution was reintroduced to the La-EPRC particles, with concentrations ranging from 0.01 mol/L to 4 mol/L. They were continuously placed in the shaker for 24 h to achieve full desorption. At the end of the reaction, a supernatant sample was taken to determine absorbance using a spectrophotometer and the phosphate desorption rate was calculated.
- 2.
Desorption Time
A total of 3 g of La-EPRC particles was added to 250 mL of 20 mg P/L phosphorus solution, placed in a shaker with constant shaking (25 ± 1 °C, 150 ± 5 r/min), and sampled after the reaction stopped at 48 h. The samples were filtered and measured to calculate the adsorption capacity of the adsorbent. After adsorption, 250 mL of 2.5 mol/L NaOH solution was reintroduced into the La-EPRC particles and shaking was continued to fully desorb them. Samples were taken at 2 h, 4 h, 8 h, 12 h, 18 h, 24 h, and 48 h intervals, and the absorbance of the phosphorus solution was measured using a spectrophotometer after sample removal to calculate the phosphate desorption rate at different time points.
- 3.
Three Successive Adsorption–Desorption Experiments
A total of 3 g of La-EPRC particles was added to 250 mL of 20 mg P/L phosphorus solution and placed in a shaker (25 ± 1 °C, 150 ± 5 r/min). Sampling was conducted after 48 h, followed by filtration for absorbance determination and calculation of adsorption capacity. Subsequently, 250 mL of 2.5 mol/L NaOH solution was reintroduced for 24 h to fully desorb the La-EPRC particles. This adsorption–desorption cycle was repeated twice more, and absorbance was measured to calculate adsorption capacity and removal rate.