# Low-Cost RSAC and Adsorption Characteristics in the Removal of Copper Ions from Wastewater
## 2 Materials and Methods  
### RSAC Preparation  
The fly ash used in this study was obtained from a power plant in Nanjing, China, and the steel slag was from a steel mill in Nanjing, China. Table 1 presents the main physical properties of the fly ash and the steel slag, Table 2 provides the particle size distribution of the fly ash and the steel slag, and Table 3 provides the chemical composition of the fly ash and the steel slag as measured by X-ray fluorescence analysis (XRF). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Waste Substrates**} & \multirow{2}{*}{**Density (g/cm\({}^{3}\))**} & \multicolumn{2}{c}{**Specific Surface**} & \multirow{2}{*}{**Particle Size (\(\upmu\)m)**} & \multirow{2}{*}{**Color**} \\  & & & & \\ \hline Fly ash & 2.91 & 580 & 150 or more & Grey \\ Steel slag & 2.10 & 3653 & 210 or more & Brown \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of waste substrates. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Chemical Composition**} & \multicolumn{1}{c}{**Fly Ash**} & \multicolumn{1}{c}{**Steel Slag**} \\ \hline CaO & 1.31 & 55.0 \\ Fe\({}_{2}\)O\({}_{3}\) & 4.39 & 21.5 \\ Al\({}_{2}\)O\({}_{3}\) & 45.9 & 1.51 \\ SiO\({}_{2}\) & 44.4 & 13.4 \\ MgO & 0.261 & 3.65 \\ MnO & 0.026 & 1.75 \\ SO\({}_{3}\) & 0.666 & 0.512 \\ V\({}_{2}\)O\({}_{5}\) & 0.038 & 0.417 \\ TiO\({}_{2}\) & 1.26 & 0.296 \\ Na\({}_{2}\)O & 0.094 & 0.077 \\ ZnO & 0.021 & - \\ CuO & 0.02 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of waste substrates (%). Additionally, the physical properties and the chemical composition of the activated white clay used in this experiment are presented in Tables 4 and 5. The binder used in the experiments was 525R ordinary silicate cement, which has the characteristics of a slow thickening rate, fast setting, and high strength. It can significantly improve the early strength of the composites [17]. The porogenic agent used in the experiment was a plant-based foaming agent. It is made by a saponification reaction with rosin and sodium hydroxide as the main raw materials, and it has a light yellow-brown viscous liquid appearance. The use of a plant-based foaming agent makes the adsorbent structure lose and porous, which can enhance the adsorption performance of RSPRC particles [18]. After comprehensive consideration of the adsorption and mechanical properties, the following substrate proportioning methods were set, which are shown in Table 6.  
After the groups of adsorbents were maintained and shaped, static adsorption tests were performed. The results of the experiments are shown in Table 7 and Figure 1. The RSAC particle morphology and the residual liquid shape were observed after the completion of static adsorption experiments. The properties of the RSAC particles in each group were observed after the adsorption of copper ions. The residuals of Groups I, II, and III were clear, the RSAC particles were not abnormal, and the hardness did not change significantly. The residuals of group IV were somewhat turbid, with slight precipitation, the surface of RSAC particles showed signs of shedding, and the hardness decreased. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Groups** & **Fly Ash** & **Steel Slag** & **Activated White Clay** & **Bonding Agent** \\ \hline Group I & 65 & 15 & 10 & 10 \\ Group II & 70 & 10 & 10 & 10 \\ Group III & 65 & 10 & 15 & 10 \\ Group IV & 60 & 10 & 20 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Ratio of base material to binder for different groups (%). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ingredients** & **Density** & **Particle Size** & **Moisture** & **Free Acid** \\  & **(g/cm3)** & **(Through 75 \(\mu\)m Sieve)** & **(\%)** & **(as H2 SO4)** & **Color** \\ \hline Activated white clay & 0.7–1.1 & \(\geq\)95\% & 12 & \(\leq\)0.2\% & pale \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physical properties of activated white clay.