## 3 Results and Discussion  
### Flotation Experiments  
The impact of STG on the flotation behavior of chalcopyrite and molybden was explored through flotation tests, where the kerosene and terpinol concentrations were fixed at 2.0 \(\times\)\(10^{-4}\) mol/L and at 4.0 \(\times\)\(10^{-4}\) mol/L, respectively. Figure 5a illustrates that STG significantly inhibited the floatability of chalcopyrite, with its recovery progressively decreasing as the STG concentration increased. When the STG concentration reached 1.0 \(\times\)\(10^{-3}\) mol/L, chalcopyrite recovery declined to its lowest point, around 10%. In contrast, molybden recovery remained consistently above 90%, resulting in the largest observed separation between the flotation performances of the two minerals. To evaluate the impact of Cu\({}^{2+}\) on the depressive action of STG on the flotation behavior of chalcopyrite and molybden, additional experiments were performed. The results, illustrated in Figure 5b, indicated that increasing Cu\({}^{2+}\) concentration had little to no effect on chalcopyrite flotation, with its recovery consistently remaining below 10%. This stability suggested that chalcopyrite was already strongly depressed by STG, leaving minimal room for further suppression by Cu\({}^{2+}\). In contrast, molybden exhibited significant sensitivity to Cu\({}^{2+}\) addition. As Cu\({}^{2+}\) concentration increased from 4 mg/L to 10 mg/L, molybden recovery drastically declined from over 90% to below 10%. To further clarify whether the observed decrease in molybden recovery was solely attributed to Cu\({}^{2+}\), various reagent conditions were tested through flotation experiments. Figure 5c shows that the recovery of pure chalcopyrite was 88.02% without metal ions or inhibitors. A slight decrease in recovery to 76.92% was observed following the addition of Cu\({}^{2+}\) alone. However, when only STG was present, chalcopyrite recovery dropped significantly to 11.52%. The sequential addition of Cu\({}^{2+}\) and STG still remained the chalcopyrite recovery below 10%, indicating that Cu\({}^{2+}\) negligibly influenced the depression behavior of STG for chalcopyrite. For molybden, flotation recovery in the absence of metal ions or depressants was 96.41%. When either Cu\({}^{2+}\) or STG was added separately, recovery remained high at 95.41% and 96.26%, respectively, indicating that molybden's floatability was largely unaffected by these reagents individually. However, in the STG system with Cu\({}^{2+}\), molybden recovery dropped sharply to 23.23% when the Cu\({}^{2+}\) concentration was 8 mg/L. These findings revealed that the presence of Cu\({}^{2+}\) in the STG system significantly suppressed the flotation performance of molybden, affecting the separation efficiency between molybden and chalcopyrite. The impacts of Cu\({}^{2+}\) on the flotation behavior of a chalcopyrite-molybdenite artificial mixture was further examined. As depicted in Figure 5d, increasing amount of Cu\({}^{2+}\) resulted in a marked decrease in both recovery and grade of molybden. Notably, the depression of molybden in this mixed mineral system was more pronounced. At a Cu\({}^{2+}\) concentration of 8 mg/L, molybden recovery decreased to 22.28%, with a corresponding grade of 23.87%. In contrast, chalcopyrite recovery remained relatively stable at approximately 10% as Cu\({}^{2+}\) concentration increased, while its grade gradually improved. At 8 mg/L Cu\({}^{2+}\), chalcopyrite recovery was 9.66%, with a grade of 4.73%. These results clearly demonstrated that Cu\({}^{2+}\) exerted differential effects on the floatability of chalcopyrite and molybdenite in the STG system. In the absence of Cu\({}^{2+}\), chalcopyrite exhibited low recovery, and this value did not change significantly with the introduction of Cu\({}^{2+}\). In contrast, molybden recovery sharply declined, indicating that its floatability was heavily suppressed in the STG system containing Cu\({}^{2+}\).