Abstract
This study investigates the application of a novel fine-grain gravity separator in the copper-lead separation process for a low-grade copper-lead-zinc polymetallic ore from Inner Mongolia. The traditional mixed flotation-separation process faced challenges such as unstable indicators, high reagent costs, and water scarcity. By introducing a new gravity pre-concentration step, the process achieved significant improvements in copper recovery, product quality, and operational stability.
Introduction
Copper-lead separation in Pb-Zn ore beneficiation remains a critical challenge due to fine particle size, reagent interference, and mineralogical complexity. Conventional methods such as selective flotation or combined flotation-magnetic separation often yield suboptimal results with unstable copper grades (typically ~18% Cu) and high lead impurities (>20%). This study evaluates a new fine-grain gravity separator integrated with flotation to enhance separation efficiency in a water-scarce region.
Ore Characteristics
The bulk flotation concentrate from a processing plant in Inner Mongolia contains 1.35% copper and 61.87% lead, with an associated gold content of approximately 0.96 g/t. The primary impurities are SiO₂, organic carbon, and Al₂O₃. Characterized by high lead and low copper content—with a copper-to-lead ratio of only 1:50—the concentrate presents significant separation challenges. Copper in the bulk concentrate exists primarily as sulfides and copper sulfides, with negligible amounts occurring as oxides or other mineral forms.
Mineralogical characteristics
- MLA analysis was used to determine the liberation degrees of galena, chalcopyrite, sphalerite, pyrite, and pyrrhotite in the bulk concentrate. The liberation degree of galena as liberated particles was 87.57%, while the remaining 12.43% existed as composite particles associated with sphalerite, pyrite, pyrrhotite, gangue minerals, and chalcopyrite.
- For both chalcopyrite and sphalerite, the proportion of liberated particles slightly exceeded that of composite particles rich in the target mineral; the combined total of liberated and rich composite particles exceeded 80%, indicating good liberation.
Table 1 presents the chemical composition analysis; Table 2 shows the copper phase analysis; Table 3 lists the liberation degrees of major minerals; and Table 4 details the particle size distribution and metal distribution.
The bulk concentrate is characterized by a fine particle size, with a yield of 78.41% in the -0.025 mm fraction; the high proportion of ultrafine material is the primary reason for the poor stability of the separation indices in a single-stage flotation process. Lead exhibits the highest grade (63.93%) and metal distribution rate (81.06%) in the -0.025 mm fraction. Copper shows the highest grade (1.84%) in the +0.074 mm fraction but the highest distribution rate (78.03%) in the -0.025 mm fraction.
Existing Process Limitations
The original "flotation-only" process (1 roughing-4 cleaning-3 scavenging stages) suffered from:
- The diverse sources of run-of-mine ore and significant fluctuations in ore properties necessitate frequent adjustments to the reagent regime during the bulk copper-lead flotation stage; this results in unstable feed characteristics for the subsequent separation circuit, leading to volatile and difficult-to-control separation performance.
- The single-stage flotation separation process demands high stability in feed characteristics and precision in reagent dosing, making it ill-suited to continuous variations in ore properties and limiting operational flexibility.
- Located in the heart of the grasslands, the processing plant faces severe water scarcity; consequently, the copper-lead separation circuit relies entirely on reclaimed water from the tailings pond, where significant fluctuations in residual reagent concentrations directly impact separation efficiency.
Copper-Lead Separation Laboratory Tests
1. Gravity Pre-Concentration Test
The novel gravity separator for ultra-fine particles is designed primarily for the separation of ultra-fine materials. Its core operating principle relies on the synergistic effect of high-magnitude centrifugal force—generated by high-speed rotation—and fluidized backwash water; under the combined influence of a strong centrifugal field and counteracting hydraulic forces, the material undergoes loosening and stratification based on density and particle size. During this process, high-density particles overcome the backwash hydraulic force to remain in the inner layer of the water film, forming the concentrate, while low-density particles rise with the outer layer of the water film to the overflow outlet, where they are discharged as tailings.
To evaluate the separation performance of this novel gravity separator, comparative tests were conducted against conventional gravity separation equipment. Compared to spiral chutes and shaking tables, the novel separator is capable of effectively processing finer materials. When processing copper-lead mixed concentrates using slime shaking tables or spiral chutes, the resulting lead concentrate exhibits high copper content and significant copper loss, yielding unsatisfactory separation results. In contrast, using the novel gravity separator reduces the copper content in the lead concentrate to 0.28% and limits the copper loss rate to just 10.62%, producing a product suitable as a final lead concentrate.
The novel gravity separator can recover a high-quality lead concentrate from the mixed concentrate with a yield of 51.23% and a copper content of 0.28%. Compared to an all-flotation process, pre-separation using this novel device reduces the throughput for subsequent flotation stages and increases the copper-to-lead ratio in the feed, thereby lowering the difficulty of flotation separation and saving on reagent costs. Furthermore, combining the copper rougher concentrate and middlings followed by thickening and dewatering significantly reduces the residual collector content in the mixed concentrate, effectively removing reagents.
The magnitude of centrifugal force is a critical factor influencing the separation efficiency of light and heavy minerals. Generally, the finer the particle size, the greater the separation difficulty, requiring a correspondingly higher centrifugal force. Centrifugal force tests indicate that copper minerals primarily concentrate in the lower-density product fraction, whereas lead concentrate accumulates in the higher-density fraction. As the centrifugal force gradually increased, both the copper grade and recovery rate of the copper rougher concentrate rose; the higher the centrifugal force, the better the copper-lead separation performance. When the centrifugal force increased from 90g to 120g, the copper grade improved slightly, while the copper recovery rate rose significantly from 44.87% to 89.38%; however, when the centrifugal force exceeded 120g, there were no significant changes in copper grade or recovery rate. Therefore, a centrifugal force of 120g was selected.
2. High-Gradient Magnetic Separation Pre-enrichment Tests
Chalcopyrite is a weakly magnetic mineral; high-intensity magnetic separation can be employed to concentrate copper minerals from the mixed concentrate into the magnetic product, while the majority of lead minerals report to the magnetic separation tailings, thereby achieving preliminary copper-lead separation. Additionally, the high-intensity magnetic separation process removes most residual reagents from the mixed concentrate, creating favorable conditions for subsequent flotation separation. The copper-lead mixed concentrate is characterized by a fine particle size, with 78.41% of the material being finer than 0.025 mm; recovering ultrafine copper minerals via high-intensity magnetic separation is challenging, and magnetic flux density is the primary factor influencing recovery efficiency. The test procedure involved one roughing stage and one scavenging stage, with the magnetic products from both stages combined to form the copper rougher concentrate.
As the magnetic flux density increased, the copper grade of the magnetic product decreased while its lead content rose; simultaneously, both copper recovery and lead loss increased. However, increasing the magnetic flux density from 1.3 T to 1.4 T resulted in negligible changes in copper recovery. Therefore, a magnetic flux density of 1.3 T was selected for the high-intensity magnetic separation process.
3. Comparison of Test Results for Different Approaches
| Separation Process | Cu Grade (%) | Pb Content (%) | Cu Recovery (%) | Pb Loss Rate (%) | Key Advantages |
| Single Flotation Process | ~18.00 | >20.00 | <66.00* | - | Simple operation |
| HGMS-Flotation Combined Process | 26.81 | 4.38 | 66.54 | 0.24 | Lower cost, stable production |
| Gravity-Flotation Combined Process (Novel Separator) | 26.63 | 4.56 | 79.10 | 0.30 | 12.56% higher Cu recovery, 54% reagent cost saving |
Note: The single flotation performance is implied from context (~18% Cu grade with low recovery).
Abbreviations: HGMS = High Gradient Magnetic Separation
Key Findings:
- Both combined processes significantly improve Cu grade (from ~18% to 26+%) versus single flotation.
- Gravity-flotation delivers 56% higher Cu recovery than HGMS-flotation.
- Pb loss rates remain similarly low (<0.5%) in combined processes.
Conclusions
This study demonstrates that integrating a novel fine-grain gravity separator into the copper-lead separation process effectively addresses the limitations of traditional flotation methods. The gravity preconcentration step achieved superior performance, yielding a 26.6% copper grade with 79.1% recovery while reducing lead contamination to 4.56% and slashing reagent costs by 54%. The technology's ability to process ultrafine particles (<0.025 mm) and mitigate water scarcity constraints makes it particularly suitable for challenging polymetallic ores. These results establish gravity-flotation hybridization as a sustainable solution for complex Cu-Pb separation, with immediate industrial applicability in water-scarce regions.