Impact of Alumina Balls on Copper Rough Concentrate Grinding and Flotation

1. Introduction

In the complex realm of copper ore processing, the grinding and flotation stages play pivotal roles in determining the overall efficiency and profitability of the operation. The traditional choice of grinding media, such as steel balls, has long been the norm. However, with the increasing demand for higher efficiency, lower costs, and more sustainable practices in the mining industry, alternative grinding media are being explored. Alumina balls, with their unique properties, have emerged as a potential game-changer. This comprehensive study delves deep into the impact of using alumina balls instead of steel balls for regrinding copper rough concentrate, analyzing various aspects from grinding efficiency and wear rate to energy consumption and flotation performance.

2. Enhancing Grinding Efficiency with Alumina Balls

2.1 Filling Rate Experiments

The use of alumina balls for regrinding copper rough concentrate was meticulously evaluated under different filling rates: 20%, 25%, 30%, 33%, and 35%. These rates were chosen to comprehensively understand how the proportion of grinding media in the mill affects the grinding process. The results were remarkable. When the filling rate reached 35%, it provided the highest grinding efficiency. At this rate, an astonishing 95.32% of particles were ≤76μm and 71.36% were ≤38.5μm. Comparing these figures to those obtained with steel balls, it was clear that alumina balls at a 35% filling rate marked significant improvements. There was a 3.63% increase in the proportion of particles ≤76μm and a 7.45% increase in the proportion of particles ≤38.5μm. This indicates that alumina balls, when optimally filled, can achieve a more fine - grained product, which is crucial for subsequent flotation processes.

2.2 Wear and Energy Consumption Advantages

In addition to the enhanced particle size distribution, alumina balls demonstrated other remarkable advantages. Their wear decreased by a staggering 82.14% compared to steel balls. This reduction in wear is of great significance as it directly impacts the operational costs. Steel balls, due to their mechanical and electrochemical corrosion during the wet grinding process, tend to degrade over time. This degradation not only affects their grinding efficiency but also requires frequent replacements. With alumina balls, the need for such frequent replacements is drastically reduced.
Moreover, energy consumption was reduced by 56.70% when using alumina balls. In an industry where energy costs can be a substantial portion of the overall expenses, this reduction is a major boon. The lower energy consumption not only leads to cost savings but also aligns with the growing global emphasis on sustainable mining practices. Thus, alumina balls prove to be a highly efficient and cost - effective alternative to steel balls in the grinding of copper rough concentrate.

3. Challenges in Copper Rough Concentrate Regrinding

3.1 Steel Ball - Related Issues

Traditional wet grinding methods that rely on steel balls face numerous challenges. The mechanical forces at play during grinding, combined with the electrochemical corrosion in the wet environment, cause significant wear to the steel balls. As time passes, the continuous wear and tear lead to a degradation in the shape and size of the steel balls. This, in turn, has a detrimental effect on the grinding efficiency. The irregularly shaped and worn - out steel balls are no longer able to grind the copper rough concentrate as effectively as when they were new.
To maintain a certain level of grinding efficiency, steel balls need to be replaced frequently. This frequent replacement not only involves the cost of purchasing new balls but also the labor and time required for the replacement process. Additionally, the downtime during the replacement period further disrupts the production flow, leading to overall increased operational costs.

3.2 The Promise of Alumina Balls

To address these challenges and improve grinding efficiency while cutting costs, alternative grinding media such as alumina ceramic balls have been the subject of extensive study. Alumina balls are renowned for their high strength, hardness, wear resistance, and chemical stability. These properties make them highly suitable for various industries. In the ceramics industry, their wear - resistant nature ensures long - lasting performance in grinding ceramic materials. In the glass industry, they can efficiently grind glass raw materials without contaminating the product due to their chemical stability. In the chemical industry, they can withstand harsh chemical environments during grinding processes.
In the mining sector, the adoption of alumina balls is gradually increasing. Their durability and superior performance offer a viable solution to the problems associated with steel balls. This study specifically focuses on how 95% alumina balls can enhance the grinding efficiency and flotation performance in the regrinding of copper rough concentrate, providing a sustainable and economical alternative for the mining industry.

4. Regrinding - Flotation Process for Copper Rough Concentrate

4.1 The Dexing Copper Mine Sizhou Processing Plant (Phase II) Process

The Dexing Copper Mine Sizhou Processing Plant (Phase II) is a large - scale operation that processes 20,000 tons of ore per day. The regrinding process here is a multi - step and highly coordinated operation.
The first - stage rough concentrate undergoes pre - classification. This initial step is crucial as it separates the coarse and fine particles in the rough concentrate. The underflow, which consists of the coarser particles, is then directed into the ball mill for regrinding. The ball mill is where the actual size reduction of the particles takes place. The discharge from the regrinding process, along with the concentrates from two scavenging stages, enters the inspection classification. This stage further refines the particle size distribution, ensuring that only the optimally sized particles move forward in the process. The overflow from the inspection classification then merges with the pre - classification overflow before advancing to the copper - sulfur separation stage. This copper - sulfur separation is a critical step in obtaining the final copper concentrate.
This multi - step process is designed to ensure optimal particle size distribution for subsequent flotation and metal recovery. Each step is carefully orchestrated to maximize the efficiency of the overall process and the quality of the final copper concentrate.

5. Experimental Setup

5.1 Steel Ball Grinding Media Performance

Steel grinding balls, with their high density, have certain characteristics that affect the grinding process. Their density increases the mill load, which can initially seem beneficial for grinding. However, over time, they experience significant wear and deformation. Data from the study shows that the average wear rate of steel balls is 28g/t.
In the steel ball grinding test, 35mm balls were used at a 35% filling rate. The results of this test were as follows: In the pre - classification overflow, 95.06% of particles were ≤76μm and 75.95% were ≤38.5μm. In the inspection classification overflow, 85.43% of particles were ≤76μm and 52.44% were ≤38.5μm. The total overflow had 91.69% of particles ≤76μm and 63.91% ≤38.5μm. The grinding efficiency was measured at 0.887 t/(mm°·h).
Steel balls, due to their high density, tend to overgrind materials. This overgrinding leads to the generation of excessive fine particles. These excessive fine particles can have a negative impact on the flotation performance. Additionally, the corrosion of steel grinding media results in the release of iron ions. These iron ions can alter the slurry chemistry, which in turn reduces the flotation efficiency.

5.2 Alumina Ball Grinding Test

For the alumina ball grinding test, alumina grinding balls of 15mm, 25mm, and 35mm sizes were used with an initial charge ratio of 3:4:3. Once the optimal filling rate was determined, only 35mm alumina balls were replenished. The test conditions for both steel and alumina grinding balls were kept identical to ensure an accurate and fair comparison.
Alumina balls, with their lower density and higher wear resistance, create a unique grinding environment. Their lower density means that they do not overgrind the materials as much as steel balls, reducing the generation of unnecessary fine particles. Their high wear resistance ensures that they maintain their shape and size for a longer period, providing more consistent grinding performance. This combination of properties helps in ensuring optimal regrinding conditions for the copper rough concentrate.

6. Key Findings

6.1 Effect of Filling Rate on Grinding Efficiency

The study tested alumina ball filling rates of 20%, 25%, 30%, 33%, and 35%, while keeping steel balls at a 35% filling rate for comparison. The results clearly demonstrated the impact of the filling rate on grinding efficiency.
At a 20% filling rate, the performance of alumina balls was slightly lower than that of steel balls. As the filling rate increased but remained below 35%, the fine particle content in the overflow of alumina balls was lower than that of steel balls. However, when the filling rate reached 35%, the overflow fineness of alumina balls was superior to that of steel balls. With 95.32% of particles ≤76μm and 71.36% ≤38.5μm, alumina balls at this filling rate achieved a more fine - grained product.
These findings suggest a positive correlation between increasing alumina ball filling rates and enhanced grinding efficiency. Additionally, the chemical stability of alumina balls plays a crucial role. It prevents the release of unwanted metal ions, which helps in maintaining a more stable slurry environment for the subsequent flotation process. A stable slurry environment is essential for efficient flotation as it allows the flotation reagents to interact more effectively with the copper particles.

6.2 Alumina Grinding Ball Wear Rate

A half - month tracking test was conducted to determine the wear rate of alumina balls. The results were astonishing. The average wear rate of alumina balls was found to be 4.7g/t, which is significantly lower than the 28g/t wear rate of steel balls. This represents an 83.21% reduction in wear.
This substantial reduction in wear has several implications. Firstly, it leads to significant cost savings. With a lower wear rate, the consumption of grinding media is reduced, meaning less money needs to be spent on purchasing new balls. Secondly, the lower wear rate minimizes the downtime required for ball replenishment. In a continuous mining operation, minimizing downtime is crucial for maintaining high productivity. Thus, the lower wear rate of alumina balls not only reduces costs but also improves the overall process efficiency.

6.3 Energy Consumption of Alumina Grinding Balls

The energy consumption of the grinding process is a major concern in the mining industry. The study compared the energy consumption of the alumina grinding ball mill and the steel ball mill. The alumina grinding ball mill operated for 2738.7 hours and consumed 190,734.48 kWh, with a unit energy consumption of 0.084 kWh/t. In contrast, the steel ball mill operated for 2773.18 hours and consumed 502,208.96 kWh, with a unit energy consumption of 0.194 kWh/t.
The shift to alumina balls led to a 56.70% reduction in energy consumption. This reduction in energy consumption is not only beneficial from a cost - savings perspective but also from an environmental sustainability perspective. Lower energy consumption means a reduced carbon footprint, which is in line with the global efforts to make the mining industry more environmentally friendly.

6.4 Impact on Flotation Performance

A 20 - day study was carried out to compare the flotation indicators before and after switching to alumina balls. The results showed that the switch had a minimal impact on flotation performance. In fact, the final copper concentrate grade and copper recovery rate were slightly improved compared to when steel balls were used.
The improved flotation performance can be attributed to several factors. Alumina balls produce fewer ultrafine particles during grinding. Ultrafine particles can sometimes interfere with the flotation process by causing unwanted agglomeration or by being too small to be effectively captured by the flotation bubbles. Additionally, the chemical stability of alumina balls helps in maintaining stable slurry chemistry. A stable slurry chemistry is essential for the proper functioning of the flotation reagents, which are responsible for selectively separating the copper particles from the gangue.

7. Conclusion

In conclusion, alumina balls have been proven to be an effective replacement for steel balls in the regrinding of copper rough concentrate, offering a multitude of significant advantages.
At a 35% filling rate, alumina balls achieved finer grinding results compared to steel balls. With 95.32% of particles ≤76μm and 71.36% ≤38.5μm, they outperformed steel balls in terms of particle size distribution, which is crucial for efficient flotation.
The grinding media wear rate of alumina balls dropped by 83.21% compared to steel balls. This reduction in wear not only decreases operational costs but also increases the longevity of the grinding media, reducing the frequency of replacements and minimizing downtime.
Energy consumption was reduced by 56.70% when using alumina balls. This reduction in energy usage contributes to both cost efficiency and environmental sustainability, making the mining operation more economically viable and environmentally friendly.
Despite the significant changes in the grinding media, the flotation performance remained stable, with slight improvements in the final copper concentrate grade and recovery rate. This indicates that the switch to alumina balls does not negatively impact the overall copper recovery process.
In summary, the adoption of alumina grinding balls in copper concentrate processing offers superior grinding efficiency, lower operational costs, and enhanced sustainability. Their use in mining operations represents a significant step forward in achieving efficient, cost - effective, and eco - friendly mineral processing solutions. As the mining industry continues to seek ways to improve its processes and reduce its environmental impact, alumina balls are likely to play an increasingly important role in the future.