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Does finer grinding improve the flotation effect, and what are the requirements for grinding fineness for different minerals?

In the field of mineral processing, particularly during the flotation process, the particle size of the ore plays a crucial role in the separation effect. Although finer grinding can generally improve flotation performance, excessively fine grinding may also have negative impacts. Below is a detailed analysis

1. Particle Size and Specific Surface Area

Specific Surface Area to Volume Ratio: The finer the grinding, the larger the ratio of specific surface area to volume of the particles. This increased specific surface area enhances the contact between the mineral surface and flotation reagents, potentially improving the adhesion of valuable minerals to bubbles. Studies have shown that reducing the particle size from 100 micrometers to 10 micrometers can increase the specific surface area by an order of magnitude.

2. Mineral Liberation

Degree of Liberation: Grinding to a finer particle size can increase the degree of liberation of valuable minerals from the gangue. The degree of liberation is a measure of how well valuable minerals are separated from the surrounding matrix, and it is a key factor in flotation recovery. Research indicates a positive correlation between mineral liberation degree and flotation recovery rate, with higher liberation degrees typically enhancing flotation recovery.

For example, grinding to 80% passing 75 micrometers (P80 of 75 micrometers) usually achieves better liberation effects than coarser grinding.

3. Energy Consumption and Cost

Energy Requirements: Fine grinding requires more energy, described by the Bond Work Index. Energy consumption increases exponentially as particle size decreases.

For example, reducing the particle size from 100 micrometers to 50 micrometers may require double the energy input.

4. Reagent Consumption

Reagent Usage: The finer the ore is ground, the greater the specific surface area of the mineral particles, necessitating more flotation reagents to cover the mineral surfaces, increasing reagent consumption. However, excessive reagent use not only increases costs but may also reduce the selectivity of the reagents, affecting the grade of the flotation concentrate, and thus impacting the overall cost and efficiency of the flotation process.

For example, when grinding is finer, the consumption of collectors and frothers may increase by 20-30%.

5. Slurry Re-grinding and Slime Formation

Fine Particle Inclusion: Excessively fine grinding can lead to re-grinding and slime formation in the slurry. This results in a large number of fine particles (slime), with particles finer than 20 micrometers more easily entrained and carried over in the froth phase, potentially reducing the selectivity of the flotation process. This can lead to increased recovery of gangue minerals, with excessive slime entrainment in the flotation concentrate, reducing concentrate grade.

6. Slurry Concentration and Viscosity

Excessively fine grinding increases the concentration and viscosity of the slurry, affecting the distribution of bubbles and the suspension state of particles in the flotation cell. This may lead to excessive bubble loading during flotation, reducing flotation efficiency.

7. Flotation Time and Cell Capacity

The flotation rate of finely ground mineral particles is slower, requiring longer flotation times to achieve desired recovery rates. This demands higher processing capacity from the flotation cells, possibly necessitating larger flotation equipment or an increased number of flotation cells.

Below are examples for several common mineral types:

1. Copper Ore

Optimal Grinding Fineness: 200 mesh (approximately P80 of 75 micrometers)

Recovery Rate: About 85%

Concentrate Grade: 20-25%

Data Support: A study of a copper mine showed that controlling grinding fineness at 200 mesh achieves the optimal mineral liberation degree, resulting in high flotation recovery rates and better concentrate grades.

2. Iron Ore

Optimal Grinding Fineness: 325 mesh (approximately P80 of 44 micrometers)

Recovery Rate: About 92%

Concentrate Grade: 65-70%

Data Support: In magnetite flotation, grinding to 325 mesh can achieve full liberation of iron minerals, enhancing flotation recovery and concentrate grade.

3. Lead-Zinc Ore

Optimal Grinding Fineness: 100 mesh (approximately P80 of 150 micrometers)

Recovery Rate: Lead about 90%, Zinc about 85%

Concentrate Grade: Lead 45-50%, Zinc 50-55%

Data Support: For lead-zinc ore flotation, controlling grinding fineness at about 100 mesh can effectively increase lead and zinc recovery rates while maintaining high concentrate grades.

4. Gold Ore

Optimal Grinding Fineness: 150 mesh (approximately P80 of 100 micrometers)

Recovery Rate: About 85%

Concentrate Grade: 50-60 grams/ton

Data Support: In the flotation of gold-bearing ores, grinding to 150 mesh ensures sufficient liberation of gold minerals, achieving high recovery rates and concentrate grades.

Mineral Type Optimal Grinding Fineness (Mesh) P80 (Micrometers) Recovery Rate (%) Concentrate Grade
Copper Ore 200 mesh 75 85 20-25%
Iron Ore 325 mesh 44 92 65-70%
Lead-Zinc Ore 100 mesh 150 Lead 90, Zinc 85 Lead 45-50%, Zinc 50-55%
Gold Ore 150 mesh 100 85 50-60 grams/ton
Although finer grinding can generally enhance mineral floatability and improve flotation performance, excessively fine grinding for certain ores may alter the properties of mineral surfaces, reducing their floatability. It also increases energy consumption, reagent usage, and the risk of fine gangue particle entrainment. It is necessary to balance these factors to optimize flotation performance. Therefore, finer grinding can improve flotation to a certain extent, but beyond a certain limit, the disadvantages may outweigh the advantages.

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