# Research on a Reductive Deep Chlorine Removal Process for Breaking Through the Solid Film Barrier
## 3 Results and Discussion
### Ascorbic Acid Denlorination Reaction Mechanism  
#### 3.6.1 Analysis of Products of Dechlorination  
The effect of different reaction factors on the reductive dechlorination reaction of ascorbic acid was investigated, and the optimized experimental conditions were determined to be as follows: an initial pH of 3.6, a molar ratio of n(Cu\({}^{2+}\))/n(Cl\({}^{-}\))/n(H\({}_{2}\)A) = 1.25:1:0.75, a reaction temperature of 20 \({}^{\circ}\)C (room temperature), and a reaction time of 20 min. Under  
Figure 12: Effect of different reaction times on dechlorination effect. these optimized conditions, 90.8% removal of chloride ions was achieved, and the chloride concentration was reduced from an initial value of 1 g/L to 0.0917 g/L. Under this condition, the slag samples of dechlorination products were characterized by XRD, XPS, XRF, and SEM-EDS. In order to investigate the substance type and composition of the precipitate product in the dechlorination of ascorbic acid, the precipitate product was analyzed for its physical phase using X-ray diffraction (XRD). The XRD technique is an effective analytical method that can provide information about the crystal structure in the precipitate product and help to identify its main physical phase. The XRD pattern of the precipitate is shown in Figure 13. By comparing this pattern with the standard cuprous chloride pattern (JCPDS NO.06-0344), it can be found that the characteristic diffraction peaks in the XRD pattern match well with the diffraction peaks of the standard cuprous chloride pattern, which proves that the precipitation product produced during the experiment is mainly cuprous chloride (CuCl). An additional diffraction peak was generated at the 20 position at 36.7\({}^{\circ}\), and this peak corresponds to basic copper chloride. This indicates that the effects of exposure to air and water during precipitate washing resulted in the conversion of a small amount of cuprous chloride to basic copper chloride through oxidation. To further explore the reaction mechanism of ascorbic acid dechlorination, we analyzed the precipitation products formed during the reaction using X-ray photoelectron spectroscopy (XPS), as illustrated in Figure 14. The XPS spectra were corrected for surface charge by taking the carbon C1s peak (284.8 eV) as a reference. From the 2p3/2 XPS spectrum of Cu, it can be observed that the binding energy peak at 932.4 eV corresponds to monovalent copper Cu(I) (from CuCl). In addition, satellite peaks of Cu\({}^{2+}\) were detected at 938.4 eV and 945.2 eV, and the presence of the satellite peaks indicates the presence of copper in an oxidized state (Cu\({}^{2+}\)) in the sample. This suggests that the generated precipitation product came in contact with air during washing as well as drying, resulting in oxidation of the generated CuCl to basic copper chloride. To investigate the surface morphology and elemental distribution of the precipitate produced in the ascorbic acid dechlorination process, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were employed for analysis, as shown in Figure 15. From the image, it can be observed that the precipitate exhibits an irregular morphology. Further analysis using the EDS spectrum reveals that the main constituent elements of the precipitate are Cu and Cl. According to the EDS elemental mapping, the atomic percentage of Cu is 43.51% and the mass percentage is 60.88%, while the atomic percentage of Cl is  
Figure 13: XRD analysis of ascorbic acid dechlorination products. 44.90% and the mass percentage is 35.04%. Oxygen (O) is also present with an atomic percentage of 11.59% and a mass percentage of 4.08%. The distribution of Cu and Cl elements is nearly identical, indicating that these elements are uniformly distributed within the precipitate. Based on this distribution pattern, it can be inferred that the precipitate is primarily CuCl. This conclusion is further supported by the elemental composition ratios of the dechlorination product in Table 4, where Cu and Cl are the dominant elements.