# Research on a Reductive Deep Chlorine Removal Process for Breaking Through the Solid Film Barrier
## 3 Results and Discussion
### Initial Reaction pH
The Equation (13) is obtained through the following calculation. \[\varphi=\text{ }\varphi^{0}+0.0591\text{lg }\left(\text{H}^{+}\right) \tag{13}\]  
According to the calculations based on the Nernst equation, when the initial reaction pH value is low, the concentration of hydrogen ions is high, which leads to the high electrode potential of ascorbic acid, thus weakening the reducing ability of ascorbic acid, which is unfavorable for the reduction reaction to take place. When the pH value gradually increases, the electrode potential of ascorbic acid decreases, which enhances the reducing ability of ascorbic acid and, thus, is more conducive to the removal of chloride ions. Additionally, as shown in Figure 9. the pH of the solution significantly affects the species and concentration of ascorbic acid. As the pH increases, ascorbic acid dissociates into  
Figure 8: Images of experimental phenomena at different initial reaction pHs levels. Figure 7: Influence of different initial pH levels on dechlorination effect. ascorbate ions and hydrogen ions, which increases the concentration of ascorbate ions in the solution. This promotes greater binding of divalent copper ions to their ligands, enhancing the reduction efficiency and ultimately improving the chloride ion removal rate. The removal of chloride ions from the solution gradually decreases as the reaction pH was further increases. When the initial reaction pH increases to 4.2, the removal rate of chloride ions is only 79.8%. According to the experimental observations in Figure 8, the color of the precipitate changes from white to yellow. This suggests that when the pH reaches 4.2, the following side reactions may occur, as shown in Equations (14) and (15). Additionally, the resulting cuprous chloride product reacts with OH\({}^{-}\), leading to the re-dissolution of chloride ions, as shown in Equation (18), which decreases the chloride ion removal efficiency. \[\mathrm{Cu^{2+}+C_{6}H_{8}O_{6}+3 OH^{-}\to CuOH\downarrow+2H_{2}O+C_{6}H_{6}O_ {6}} \tag{14}\]  
\[4\mathrm{CuOH+O_{2}+2H_{2}O=4 Cu(OH)_{2}} \tag{15}\]  
\[2\text{Cu}^{2+}+\text{ C}_{6}\text{H}_{8}\text{O}_{6}=\text{ 2 Cu}^{+}+\text{C}_{6}\text{H}_{6}\text{O}_{6}+ \text{2H}^{+} \tag{10}\]0  
\[2\text{Cu}^{2+}+\text{ C}_{6}\text{H}_{8}\text{O}_{6}=\text{ 2 Cu}^{+}+\text{C}_{6}\text{H}_{6}\text{O}_{6}+ \text{2H}^{+} \tag{10}\]1  
\[2\text{Cu}^{2+}+\text{ C}_{6}\text{H}_{8}\text{O}_{6}=\text{ 2 Cu}^{+}+\text{C}_{6}\text{H}_{6}\text{O}_{6}+ \text{2H}^{+} \tag{10}\]2  
Based on the equilibrium concentration distribution of copper ions at different pH levels shown in \[2\text{Cu}^{2+}+\text{ C}_{6}\text{H}_{8}\text{O}_{6}=\text{ 2 Cu}^{+}+\text{C}_{6}\text{H}_{6}\text{O}_{6}+ \text{2H}^{+} \tag{10}\]3 It can be observed that as the pH increases, the concentration of OH\({}^{-}\) ions rises, enhancing the hydrolysis of copper ions. This leads to the gradual conversion of divalent copper ions into copper hydroxide. This conversion competes with the target reaction (i.e., the reduction of copper ions), causing more copper ions to form insoluble copper hydroxide, which hinders the formation of cuprous ions (Cu\({}^{+}\)). Therefore, when the initial reaction pH exceeds 3.6, according to Equations (16) and (17), insoluble impurities such as cuprous hydroxide, copper metal, and cuprous oxide may form in the solution, resulting in a decrease in chloride ion removal efficiency. To optimize the experimental results, an initial reaction pH of 3.6 was selected for subsequent experiments.