# Enhanced Phosphorus Removal from Wastewater Using RSPRC and a Novel Reactor
## 2 Materials and Methods
### RSPRC Preparation  
The raw materials of RSPRC were divided into two types: substrate and auxiliary material. The substrate consisted of steel slag, fly ash and activated clay. The auxiliary material was cement as binder and the foaming agent to increase the specific surface area [15]. The steel slag and fly ash used in this experiment were taken from a steel plant and a power plant in Nanjing. The chemical composition of the steel slag and fly ash was analyzed by wavelength dispersive X-ray fluorescence analyzer (XRF-1800) produced by Shimadzu, Kyoto, Japan. Table 1 shows the chemical composition and content of the waste residue substrate and Table 2 presents the particle size distribution of the waste residue substrate. The preparation of activated clay is divided into original soil treatment and modification treatment [16]. This experiment adopted acid modification treatment [17]. The bentonite was taken from Tangshan, Jiangning District, Nanjing, China. For the acid modification treatment, the bentonite was immersed in a 3 mol/L sulfuric acid solution, activated for 30 min, and stirred at a speed of 1000 r/min in a constant temperature environment of 100 \({}^{\circ}\)C. After the activation was completed, it was washed with distilled water to neutrality, dried, ground, and passed through a 100-mesh sieve to obtain experimental activated clay. Respectively, the principal oxides SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), MgO, Fe\({}_{2}\)O\({}_{3}\), and CaO in the activated clay account for 64.23%, 16.88%, 0.76%, 2.05% and 2.45%. The preparation of the adsorbent was carried out according to the different proportion of various substrates. The specific percentages of substrate and binder are presented in Table 3. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Oxide** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **MgO** & **MnO** & **SO\({}_{3}\)** & **V\({}_{2}\)O\({}_{5}\)** & **TiO\({}_{2}\)** & **Na\({}_{2}\)O** & **ZnO** & **CuO** \\ \hline
**Composition of fly ash (\%)** & 1.31 & 4.39 & 45.9 & 44.4 & 0.261 & 0.026 & 0.666 & 0.038 & 1.26 & 0.094 & 0.021 & 0.02 \\
**Composition of steel slag (\%)** & 55.0 & 21.5 & 1.51 & 13.4 & 3.65 & 1.75 & 0.512 & 0.417 & 0.296 & 0.077 & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Percentage of oxides in waste residue substrate. Figure 1: (**a**) The concentric circular diversion wall adsorption reactor schematic; (**b**) the concentric circular diversion wall adsorption reactor. A schematic flow chart of the RSPRC preparation process is provided in Figure 2. At first, the selected substrate (fly ash and steel slag) was mechanically pulverized. After that, an appropriate amount of activated clay, binder and foaming agent were blended and thoroughly mixed. Later, an appropriate amount of tap water was added to the materials and these materials were stirred evenly. Then, all the materials were poured into the drum granulator. After the granulation was completed, the water was sprinkled after 6-8 h. Finally, RSPRC was maintained for several days under normal temperature and pressure to keep certain humidity on the surface of the particles. According to the experimental conclusion of [PERSON] et al. (2018), the composite adsorbent with a particle size of 5 mm had a more efficient phosphorus removal effect than that with particle sizes of 10 and 20 mm. Therefore, the particle size selected for this experiment was 5 mm. [PERSON] (2019) pointed out in their research on Efficient Phosphorus Removal Composite (EPRC)that the use of a plant-type foaming agent in the preparation process made it more difficult to cause secondary pollution, and that the optimal dosage was 8 mL/kg. RSPRC and EPRC are basically the same in terms of material physical properties. Consequently, the preparation of the adsorbent was carried out with an 8 mL/kg foaming agent. The plant-type foaming agent was bought from Shanghai Fangbao Building Material Technology Co., Ltd., Shanghai, China.