## 2 Materials and Methods
### Research Method  
#### 2.3.1 Comparison of Zr-EPRC Preparation Methods  
In this study, the EPRC composites underwent a vital enhancement process through the introduction of zirconium oxychloride octahydrate. This modification aimed to bolster their adsorption and phosphorus removal capabilities. Given the practicality of large-scale production in future applications, it was imperative that the modification method remain straightforward. Consequently, the impregnation method was selected as the most suitable approach. The specific modification methods were classified into three distinct approaches: direct modification of EPRC particles, concurrent modification of substrates followed by granulation, and separate modification of adsorption substrates followed by granulation. * Direct modification of EPRC to prepare Zr-EPRC A solution with a concentration of 0.1 mol/L of \"ZrOCl\({}_{2}\)-8H\({}_{2}\)O\" was prepared. Subsequently, the EPRC particles were immersed in this zirconium-containing solution and subjected to continuous agitation at a constant temperature of 25 \({}^{\circ}\)C for a duration of 12 h. Following this immersion, the particles were carefully air-dried in a well-ventilated environment. This process resulted in the creation of Zr-EPRC particles, denoted as No.1 Zr-EPRC. * Preparation of Zr-EPRC via co-modification of adsorption substrates To create the zirconium-containing solution with a concentration of 0.1 mol/L, \"ZrOCl\({}_{2}\)-8H\({}_{2}\)O\" was prepared. The substrates, namely steel slag and fly ash, intended for EPRC production, were immersed together in the zirconium-containing solution, following the prescribed proportions. This mixture was then placed in a constant temperature oscillator operating at 25 \({}^{\circ}\)C for a duration of 12 h. Subsequently, the substrates were rinsed with distilled water until neutral, subjected to extraction and filtration under reduced pressure, and finally, they were dried in an oven at 105 \({}^{\circ}\)C. This process yielded substrate powder. The next step involved the creation of Zr-EPRC particles, accomplished by adding cement, a blowing agent, and other necessary materials to the substrate. These modified particles were designated as No. 2 Zr-EPRC. * Preparation of Zr-EPRC via separate modification of adsorption substrates A solution with a concentration of 0.1 mol/L of \"ZrOCl\({}_{2}\)-8H\({}_{2}\)O\" was prepared. Subsequently, steel slag and fly ash were separately immersed in this zirconium-containing solution. After undergoing 12 h of continuous agitation at 25 \({}^{\circ}\)C, the two modified substrates were prepared. This involved washing, drying, and grinding the substrates. Following these steps, cement, foaming agent, and other requisite materials were added in accordance with the specified proportions. This process resulted in the production of Zr-EPRC particles, denoted as No. 3 Zr-EPRC. Static adsorption experiments were conducted on the modified adsorbent materials, as well as the original EPRC adsorbent materials prepared through the three distinct methods. The investigation aimed to assess their respective phosphorus removal efficiencies. The experimental procedure was as follows: 1 g of EPRC particles and three types of Zr-EPRC  
Figure 1: EPRC preparation process flow. particles were measured and placed into separate conical flasks. Subsequently, 200 mL of a 5 mg/L phosphorus solution was introduced into each flask. The flasks were then subjected to an adsorption test within a constant temperature water bath shaker (at 25 \(\pm\) 1 \({}^{\circ}\)C and 150 rpm). Following a specific duration, the supernatant was aspirated from the solution, and the residual phosphorus concentration in the adsorbed liquid was determined. * Investigation of Optimal Modification Conditions  
To determine the optimal loading conditions, five conical flasks were prepared, each containing 100 mL of deionized water.