2.The Logical Interplay and Application of Crushed Particle Size, Dissemination Size, and Degree of Liberation

In the preceding article, we defined crushed particle size, dissemination size, and degree of liberation individually. In practice, however, clients are most concerned with one overarching question: How do these concepts actually affect beneficiation performance, and how can they be used to guide decision‑making?

This article addresses that question directly.

The Complete Logical Chain Among the Three Concepts

These concepts form a clear causal sequence:

• Dissemination size is the root cause – an intrinsic property of the ore, not subject to modification.
• Crushed particle size is the means – the dimensional target achieved through mechanical comminution.
• Degree of liberation is the outcome – the extent to which the target mineral has been set free.

For a given ore, crushing to 30 mm may result in inadequate liberation; reducing to 10 mm may bring marked improvement; and at 5 mm, the ore may already reach favourable separation conditions. Consequently, the selection of an appropriate comminution particle size must always be based on the dissemination characteristics and the resultant liberation at each size fraction.

Why Does Degree of Liberation Directly Affect Separation Performance?

All beneficiation methods exploit differences in physical or chemical properties between minerals – such as density, magnetic susceptibility, surface wettability, electrical conductivity, and optical characteristics.

• A free particle of the target mineral fully exhibits the mineral's intrinsic properties, making it readily identifiable and separable;
• A locked particle – for example, one composed of 50% target mineral and 50% gangue – exhibits an apparent property that is an average of the two constituents, falling somewhere between them.

Locked particles pose a significant challenge in separation:

• Locked particles with high target mineral content, if directed to the concentrate, will introduce gangue impurities, lowering concentrate grade;
• Locked particles with low target mineral content, if directed to the tailings, will carry valuable mineral values, reducing overall recovery.

This is the fundamental reason why insufficient liberation inevitably compromises both separation precision and metallurgical recovery.

How Does Dissemination Size Determine the Complexity of the Process Flowsheet?

Conclusion: The finer the dissemination size, the more complex the process flowsheet, and the higher the associated capital and operating costs. This is a critical factor in evaluating the economic viability of an ore deposit.

Why Are Locked Particles of Particular Concern?

Locked particles are the primary obstacle to achieving a high degree of liberation. In practice, a portion of locked particles tends to accumulate as middlings. Many beneficiation circuits therefore incorporate a middlings regrinding and re‑treatment stage, designed to break down locked particles and provide a second opportunity for the target mineral to be liberated.

A high proportion of locked particles in the comminuted product indicates that the current particle size is insufficient to achieve adequate liberation, necessitating further size reduction or the addition of a middlings recirculation loop.

Interim Summary

• Dissemination size defines the objective;
• Crushed particle size defines the method;
• Degree of liberation defines the result.

Together, these three parameters determine the complexity, efficiency, and economic performance of the downstream beneficiation circuit. In the final article of this series, we address the most practical question of all: How fine should the ore be comminuted, and how can over‑grinding be avoided?