In China, molybdenum resources are extremely abundant, accounting for approximately 37% of the world’s total reserves. These resources are primarily concentrated in regions such as Henan, Shaanxi, Liaoning, and Hebei, with the vast majority originating from porphyry-type copper-molybdenum deposits. Currently, as economic development continues to drive increasing demand for copper and molybdenum, the available resources face several challenges: there are relatively few high-grade ores but many low-grade ones; significant co-occurrence of other valuable minerals; a wide variety of useful components present; fine grain sizes of mineral particles; and close floatability between molybdenite and copper sulfide minerals—all of which make copper-molybdenum separation particularly difficult. Consequently, research into and application of copper-molybdenum separation technologies have become especially important.

　　1. Copper-molybdenum flotation separation technology

　　Currently, flotation is widely used for processing copper-molybdenum ores. The associated process technology is well-established and delivers excellent performance indicators. In principle, there are three main flotation methods for copper-molybdenum ores: mixed flotation, preferential flotation, and isomorphic flotation. In industrial practice, mixed flotation is the most commonly chosen method; however, preferential flotation or isomorphic flotation are sometimes also employed.

　　2. Copper-molybdenum mixed flotation technology

　　Most copper-molybdenum ores employ a mixed flotation-copper-molybdenum separation process because molybdenite and chalcopyrite have similar floatability and occur in close association. This process is cost-effective and features a relatively simple flow sheet.

　　3. Mixed flotation stage

　　In general, mixed flotation collectors typically consist of xanthates (such as butyl xanthate), hydrocarbon oils (such as kerosene) as auxiliary collectors, pine oil as a frother, and lime and water glass as adjusting agents. Ye Lijia conducted experimental studies on a low-grade copper-molybdenum ore in Anhui Province and found that when kerosene was used as the primary collector and BK301C as the auxiliary collector for the simultaneous flotation of copper and molybdenum, a dosage of only 59 g/t enabled copper and molybdenum recovery rates of 93.01% and 73.2%, respectively—far superior to the performance achieved with other auxiliary collectors.

　　4. Copper-molybdenum separation pretreatment stage

　　Generally, copper-molybdenum separation processes fall into two main approaches: depressing molybdenum to float copper and depressing copper to float molybdenum. Given that molybdenite is more readily floated, the majority of operations adopt the approach of depressing copper to float molybdenum. However, when processing ores with high copper content and low molybdenum content, it becomes necessary to consider the approach of depressing molybdenum to float copper, as depressing copper can lead to significantly higher reagent costs. Moreover, molybdenite exhibits excellent floatability, making it difficult for small inorganic or organic molecules to act as effective inhibitors. This has paved the way for the use of certain macromolecular inhibitors, such as dextrin, starch, humic acid, and tannic acid.

　　Copper-molybdenum separation primarily involves pretreatment before separation, inhibition of copper minerals during the separation process, and subsequent re-enrichment after copper-molybdenum separation. The main pretreatment methods are as follows:

　　1) Concentration of mixed concentrates. This process primarily aims to remove residual reagents and frothers from the flotation concentrate of copper-molybdenum mixtures. During the second-phase reconstruction of the Unugtushan copper-molybdenum concentrator, Liu Zilong and his team intensified the application of this pretreatment method, using a ceramic filter as the concentration equipment following copper-molybdenum mixed flotation. This approach effectively addressed the longstanding challenge of separating molybdenum minerals, yielding a molybdenum concentrate with a grade of 57.75%. Meanwhile, Lei Guichun employed hydrocyclones to concentrate and de-foam the mixed copper-molybdenum concentrate from the Dexing copper mine, resulting in a 0.63% increase in the grade of the molybdenum concentrate, an 11.14% improvement in recovery rate, and a 32.17% reduction in sodium sulfide consumption.

　　2) Heating methods. Heating the mixed concentrate can cause the collector on the mineral surfaces to decompose, breaking down the hydrophobic film and evaporating the frother from the slurry. As a result, the surface of copper minerals becomes oxidized, reducing their floatability and leading to inhibition, while having minimal impact on molybdenite, thereby achieving separation. Currently, the main heating methods include heaters, roasting, and steam blowing. It has been confirmed that approximately 40% of copper-molybdenum concentrators worldwide adopt thermal treatment methods. This not only reduces the consumption of sodium sulfide but also significantly improves beneficiation performance.

　　3) Add reagents—primarily oxidizing agents such as peroxides, ozone, chlorine, potassium permanganate, and oxygen—to oxidize the surface of copper minerals, rendering them hydrophilic and causing the adsorbed collectors to be oxidized and decomposed. At a pH of 10–11, dissolved O2 in the slurry can oxidize chalcopyrite into S2O3²⁻, thereby inhibiting its flotation. Natarajan et al. used electrochemical tests to confirm that ozone effectively oxidizes and decomposes the collectors on the chalcopyrite surface, with ozone proving more effective than oxygen.

　　Therefore, by controlling pulp conditions—such as introducing oxygen and adjusting the pH—it is possible to suppress chalcopyrite and achieve selective flotation of molybdenum while suppressing copper. However, one point that should be noted is that the dosage of oxidizing agents should not be excessive; otherwise, an excess amount could impair the inhibitory effect of sodium sulfide—a strongly reducing agent—in the subsequent stage of copper suppression and molybdenum flotation.

　　5. Copper-molybdenum separation inhibition stage

　　After pretreatment, the copper-molybdenum separation process can be carried out. An important aspect of this process is the selection of flotation inhibitors. Commonly used inhibitors can be categorized into two types: inorganic and organic. Inorganic inhibitors mainly include Knox compounds, cyanides, and sodium sulfide compounds, while organic inhibitors primarily consist of mercaptoacetates. These inhibitors can be used individually or in combination.

　　1) Cyanides. These include cyanide complexes such as sodium zinc cyanide and sodium ferrocyanide. They are primarily used as inhibitors for copper and iron sulfide ores, with the aim of decomposing xanthates and forming stable cyanide complexes. The effect is highly pronounced and remarkably efficient even at low dosages. In production applications at the Jinduicheng Concentrator, adding 0.05 to 0.06 kg of sodium cyanide per ton during the molybdenum flotation stage can yield a molybdenum concentrate containing less than 0.5% copper. However, due to their extreme toxicity—especially when used in ores containing gold, silver, or other precious metals—their application in mineral processing plants has been gradually declining.

　　2) Sulfide-based reagents. These primarily include sodium hydrosulfide, sodium sulfide, and ammonium sulfide. Research has confirmed that the primary inhibitory effect is exerted by the SH⁻ ions generated from the hydrolysis of sulfides. In actual production, sodium sulfide and sodium hydrosulfide are the most widely used. For example, at the Dexing Copper Mine, Na₂S is employed to suppress copper during molybdenum flotation, yielding excellent beneficiation results. However, sodium sulfide is prone to oxidation and loses its effectiveness relatively quickly. Moreover, when used in excessive amounts—ranging from 80 to 100 kg per ton—the cost of the reagent becomes extremely high, accounting for as much as 85% of the total molybdenum flotation costs.

　　Domestically, the Beijing Nonferrous Metallurgy Design and Research Institute also conducted an industrial trial using nitrogen injection at the Dexing Copper Mine, reducing the amount of sodium sulfide by 60.55%. It is worth noting that sodium sulfide and sodium cyanide can effectively inhibit chalcopyrite, but they exhibit relatively poor inhibition effects on large quantities of covellite and secondary covellite.

　　4) Thioglycolate salts. In particular, thioglycolic acid exhibits excellent inhibition performance, requires a small dosage, causes minimal pollution, and demonstrates high selectivity. Wan Shenghui et al. synthesized thioglycolic acid via the sodium sulfide method and conducted industrial trials at the Dexing Copper Mine, achieving remarkable inhibition results: the molybdenum concentrate grade reached 51.53%, the molybdenum recovery rate was 79.89%, and the copper content was only 0.32%.

　　5) A novel inhibitor. Jiang Yuren and colleagues synthesized a new inhibitor, DPS. Experimental results show that DPS can significantly inhibit chalcopyrite and galena, yet has minimal effect on molybdenite. Its dosage is only 1/5 of that required for sodium mercaptoacetate and 1/10 of that required for sodium sulfide. Moreover, DPS exhibits excellent stability, features a simple synthesis route, and uses inexpensive raw materials. Yuan Zengwei, on the other hand, studied a new inhibitor, CM1. Compared with sodium mercaptoacetate, CM1 demonstrates a more pronounced inhibition effect, requires a lower dosage (reduced by 20 g/L), acts more rapidly, and also effectively inhibits galena.

　　6. Copper-molybdenum separation and selective concentration stage

　　After copper-molybdenum separation, the next steps involve further molybdenum and copper beneficiation. Typically, molybdenum requires six stages of beneficiation to meet smelting specifications. Sometimes, a portion of molybdenum in the mixed flotation concentrate remains incompletely liberated, making regrinding an essential step. Zhang Hengwang carried out process improvements at the Xiaosigou copper-molybdenum mine by introducing an additional regrinding stage prior to molybdenum beneficiation. As a result, the grade of the final molybdenum concentrate reached 46.49%, with a recovery rate of 92.26%, representing increases of 0.5% and 3.97%, respectively, compared to the situation without regrinding.

　　Copper beneficiation is relatively straightforward and usually requires only a single stage of concentration. However, the asynchronous mixed flotation technique is worth noting: first, float the easily floatable copper minerals; then, intensify the flotation of the more difficult-to-float copper minerals (by adding mixed xanthates). After combining the concentrates from these two stages, the mixture is ground and subjected to further separation.

　　7. New Technologies and Equipment for Copper-Molybdenum Separation

　　1) Application of flotation columns

　　One of the advantages of flotation columns is their excellent recovery performance for fine particles that are difficult to float and for ores with high fine-silt content. Copper-molybdenum ores are characterized by fine-grained mineral inclusions, low-grade raw ore, and significant coexisting minerals, which necessitate fine grinding particle sizes. Moreover, overgrinding is a serious issue, making separation increasingly challenging. Therefore, flotation columns can be used to replace some flotation machines, thereby enhancing the separation efficiency. Currently, many types of flotation columns are in use, such as the hydrocyclone-static microbubble flotation column, the Jameson flotation column, and the SFC-type packed static flotation column. In a renovation project at a copper-molybdenum concentrator in Xinjiang, Ma Zilong and his colleagues adopted the hydrocyclone-static microbubble flotation column as the primary equipment for mixed copper-molybdenum flotation, copper-molybdenum separation, and molybdenum concentrate refining. Meanwhile, flotation machines were employed for roughing and scavenging in the copper-molybdenum separation stage as well as for the mixed copper-molybdenum flotation itself, forming a combined machine-column flotation system. The resulting recovery indicators were as follows: the molybdenum concentrate grade reached 50.59%, with a molybdenum recovery rate of 55.96%; the copper concentrate grade was 21.39%, and the copper recovery rate was 91.57%.

　　2) Application of potential regulation technology

　　Electrochemical flotation has also played a significant role in the separation of copper and molybdenum. By controlling the potential of the slurry, sequential flotation of different sulfide minerals can be achieved. Chander et al. conducted experiments using externally controlled potentiometry to electrochemically separate molybdenite from chalcocite. Krishnaswamy et al. found that molybdenite exhibits naturally good floatability because of its poor ability to conduct electrons—meaning that changes in slurry potential have little effect on it. In contrast, chalcocite flotation requires an oxidizing slurry environment. Therefore, by externally controlling the pH and potential of the slurry, chalcocite can be suppressed under a reducing atmosphere, while molybdenite remains floatable, thus enabling their effective separation.

　　8. Priority flotation technology for copper and molybdenum

　　For low-grade molybdenum-copper ores, while ensuring the grade and recovery rate of the molybdenum concentrate, it is also necessary to consider the comprehensive recovery of copper. In some cases, preferential flotation is more appropriate.

　　Dai Xinyu and colleagues conducted a study on a copper-molybdenum deposit in Tibet. This deposit exhibits severe secondary enrichment of copper, a high oxidation rate, fine-grained chalcopyrite that is tightly intergrown with gangue minerals, and significant occlusion of molybdenite within the gangue fractures and intergranular spaces. The flotation process adopted was as follows: first, molybdenum was preferentially floated; then, after regrinding, copper and molybdenum were separated. The copper-bearing tailings from the molybdenum flotation stage were further processed to recover copper. The collector used for molybdenite was a mixture of kerosene and diesel oil, while the inhibitor for copper-molybdenum separation was DY08, and the collector for copper was OSN-43. The flotation results showed that the molybdenum concentrate had a molybdenum grade of 56.16%, a copper content of 0.071%, and a recovery rate of 87.58%; the copper concentrate had a copper grade of 21.84% and a recovery rate of 75.93%. Compared to conventional mixed flotation, this approach achieved a cost reduction of 10%.

　　9. Equilibrium flotation technology for copper and molybdenum

　　Generally speaking, both preferential flotation and mixed flotation require high alkalinity (lime) to achieve separation of copper, molybdenum, and sulfur. However, lime has an inhibitory effect on molybdenum, which is detrimental to its recovery. In contrast, equal-floatability flotation can avoid these issues by using selective collectors and either eliminating or minimizing the use of lime, thereby achieving separation of copper, molybdenum, and sulfur with minimal interference to subsequent copper-molybdenum separation and molybdenum concentration processes, thus facilitating the attainment of superior performance indicators. In a process study conducted on a certain copper-molybdenum ore, Hu Zhenfeng adopted the equal-floatability flotation process. This ore has a low molybdenum grade and contains a slightly higher proportion of pyrite.

　　10. Copper-Molybdenum Joint Beneficiation Technology

　　For most porphyry copper-molybdenum deposits where molybdenum and copper occur symbiotically, flotation is an effective processing method. However, for certain refractory copper-molybdenum ores, a combined beneficiation and metallurgical approach can be employed. For example, the Bingham Canyon copper-molybdenum deposit in Utah is a porphyry-type copper-molybdenum deposit whose main minerals are molybdenite and chalcopyrite. The ore contains high levels of talc and sericite, making it prone to slimes formation. The conventional process involves bulk flotation—suppressing copper while floating molybdenum, followed by multiple stages of molybdenum concentration and reverse flotation of talc—yielding a concentrate containing 52.3% molybdenum. Subsequently, this concentrate undergoes oxidative roasting, but the recovery rate remains only at 49.4%.

　　11. Conclusion

　　Mixed flotation is applied to the separation of most copper-molybdenum ores. Sometimes, preferential flotation and isoflotation are also worth considering. The key lies in the fact that the grade and liberation size of copper and molybdenum in the raw ore significantly affect factors such as reagent dosage and grinding operations—thus determining both the economic cost of mineral processing and the quality of beneficiation indicators.

　　Effective pretreatment and the selection of appropriate inhibitors are critical steps in the reseparation of copper and molybdenum after their initial flotation. Concentration, heating, and oxidation can effectively break down and remove reagents; however, these processes must not introduce "secondary pollution" that could compromise the separation of copper and molybdenum. Inhibitors such as Knox compounds, cyanides, and sodium sulfide exhibit good inhibitory effects, but they suffer from drawbacks such as toxicity or the need for excessive dosages. Mercaptoacetate salts, on the other hand, show great promise—they require low dosages yet deliver high efficiency. The development of new reagents and combination formulations remains a worthwhile direction for future research.