How Ore Type Affects Grinding Ball Wear

Grinding balls operate in an extremely aggressive environment, but not all ores affect their service life in the same way. In practice, the same batch of grinding balls may demonstrate significantly different wear rates depending on the mineralogical composition of the ore, its abrasiveness, hardness, and grinding conditions.

Therefore, when evaluating the quality of grinding balls, it is important to consider the characteristics of the material being processed.

During operation, grinding balls are subjected to several types of degradation:

• abrasive wear;
• impact wear;
• corrosive-abrasive wear;
• surface fatigue failure.

The contribution of each mechanism depends on the ore type, pulp parameters, and mill operating conditions.

Iron Ores

Many iron ore processing operations are characterized by the presence of quartz, one of the most abrasive minerals found in ores.

Quartz has a hardness of 7 on the Mohs scale; therefore, its presence significantly affects the wear rate of grinding media.

Consequences include:

• intensive abrasion of the ball surface;
• gradual reduction of ball diameter;
• predominance of the abrasive wear mechanism.

In many cases, relatively uniform wear is observed without severe surface deterioration.

Copper Ores

Copper ores often contain:

• quartz;
• pyrite;
• chalcopyrite;
• magnetite.

Under such conditions, grinding ball wear becomes more complex.

In addition to abrasive action, the presence of sulfide minerals and oxygen may intensify electrochemical processes, accelerating the corrosive-abrasive wear of steel grinding balls.

This may lead to:

• accelerated corrosion;
• localized surface damage;
• increased overall grinding media consumption.

For this reason, many copper concentrators experience higher grinding ball wear rates compared with operations where abrasive wear is the dominant mechanism.

Gold-Bearing Ores

Gold deposits vary significantly in mineralogical composition. However, many gold-bearing ores are characterized by a high quartz content.

Under such conditions:

• abrasive wear increases;
• the load on the ball surface layer becomes higher;
• the hardness of the working surface becomes particularly important.

For efficient operation, it is often necessary to achieve an optimal balance between hardness and impact toughness of the grinding ball material.

Ores with High Magnetite Content

Magnetite generally exhibits lower abrasiveness than quartz. Therefore, magnetite ores with a low quartz content often cause less abrasive wear of grinding balls.

Under such conditions:

• abrasion rates may be lower;
• the role of impact loading increases;
• resistance to crack formation becomes more important.

In some cases, excessively hard grinding balls may perform worse due to a greater tendency toward brittle fracture.

Influence of Feed Size

The service life of grinding balls depends not only on ore composition. The size of the material entering the mill is also important. The coarser the feed size:

• the higher the impact loads;
• the greater the risk of microcrack formation;
• the higher the requirements for steel impact toughness.

As a result, identical grinding balls may perform differently even at operations processing ores of similar composition.

Other important factors include:

• pulp pH;
• dissolved oxygen content;
• pulp density;
• mill rotational speed;
• mill filling degree;
• ratio of balls of different diameters.

In practice, there is no steel grade that is equally effective for all ore types and grinding conditions.

For highly abrasive ores, the most critical properties are:

• hardness;
• surface wear resistance.

For conditions involving high impact loads, greater importance is placed on:

• impact toughness;
• structural homogeneity;
• resistance to crack initiation and propagation.

Therefore, the performance of grinding balls should be evaluated only under specific operating conditions.

Conclusion

The service life of grinding balls is determined not only by manufacturing quality. Significant influence is exerted by the mineralogical composition of the ore, its abrasiveness, feed size, pulp characteristics, and mill operating conditions.

When selecting grinding balls, it is important to consider the characteristics of a specific deposit and beneficiation process. A solution that performs well with magnetite ores may prove less effective when grinding quartz-bearing or sulfide ores.

Therefore, the modern approach is not to select the “hardest” grinding ball, but to choose grinding media that are optimally matched to specific grinding conditions.