In mineral processing operations, the terms "crushed particle size," "dissemination size," and "degree of liberation" are frequently used. While they sound related, they refer to distinctly different concepts. Misunderstanding these terms often leads to flawed assessments of ore treatability and process design.
This article defines each concept individually, providing a clear foundational understanding for non-specialists and practitioners alike.
Crushed particle size describes the overall dimensional scale of ore particles after they have been subjected to crushing.
A typical crushing circuit may proceed as follows:
In this example, 200 mm, 50 mm, and 10 mm all represent crushed particle sizes. When expressed as −10 mm, it indicates that 100% of the material passes through a 10 mm sieve.
It is critical to note: a 10 mm particle may consist entirely of the target mineral, entirely of gangue, or contain a mixture of both. The target mineral may still be intimately locked within the gangue matrix.
Therefore, crushed particle size indicates only the external dimensions of the particle; it does not reveal whether the constituent minerals have been separated from one another.
Dissemination size refers to the grain size at which the target mineral occurs within the ore body. This is an inherent mineralogical attribute of the ore – a characteristic determined by nature, not alterable by processing.
Ores vary widely in this regard:
To distinguish the two:
During crushing and grinding, ore particles fracture preferentially along mineral grain boundaries. As particle size diminishes, the originally intergrown target mineral and gangue gradually separate into individual particles. This extent of separation is termed the degree of liberation.
Comminuted particles generally fall into three categories:
Free target mineral particles – already liberated from gangue, amenable to direct separation;
Free gangue particles – from which the target mineral has been detached;
Locked particles – a single particle containing both target mineral and gangue in intergrown form.
Degree of liberation can thus be understood as follows: the higher the proportion of free target mineral particles, the higher the degree of liberation; conversely, the greater the proportion of locked particles, the lower the degree of liberation.
| Ore Type | Dissemination Characteristics | State After Crushing to −10 mm |
|---|---|---|
| Ore A | Target mineral coarsely disseminated at 5–8 mm | Significant liberation along grain boundaries; numerous free particles present |
| Ore B | Target mineral finely disseminated at only 0.1–0.5 mm | Most 10 mm particles remain locked, with the target mineral still enclosed within gangue |
This comparison demonstrates that identical crushed particle sizes do not imply equivalent degrees of liberation. Crushed particle size alone is insufficient for assessing ore separability.
Crushed Particle Size
How large the crushed ore particle is.
Dissemination Size
How large the target mineral grains are within the ore.
Degree of Liberation
How much of the target mineral has been released from the gangue.
A clear grasp of these three distinctions is the first and essential step toward a correct evaluation of ore amenability to beneficiation. In the following article, we examine how these concepts interrelate and how they guide process design decisions.
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