Views: 0 Author: Site Editor Publish Time: 2026-07-24 Origin: Site
In the field of mineral processing, grinding serves as the core pre-treatment stage for all separation operations. Its fundamental purpose is to liberate valuable target minerals from gangue and impurity minerals by mechanical crushing and attrition, creating qualified particle size conditions for subsequent flotation, magnetic separation, gravity separation and leaching processes. In actual plant production, a widespread empirical misunderstanding has long prevailed among operators: the finer the grinding fineness, the more thoroughly the minerals are liberated, and thus the higher the final metal recovery rate. Based on this intuitive logic, many concentrators continuously pursue ultra-fine grinding, blindly reducing cyclone overflow particle size and extending mill grinding time in pursuit of better beneficiation indicators.
Nevertheless, actual mineral processing production and academic research have repeatedly proven that grinding fineness and recovery rate do not follow a simple linear positive correlation. Excessively coarse grinding causes insufficient liberation and restricts separation efficiency, while excessive ultra-fine grinding triggers severe slime interference, which instead suppresses flotation response and increases production costs. The optimal grinding state always lies in the balanced “effective liberation interval” between under-grinding and over-grinding, rather than an endless pursuit of finer particle sizes.
Under-grinding refers to the condition where the grinding fineness fails to reach the minimum liberation particle size of target minerals. In this case, valuable minerals and gangue minerals still exist in the form of locked particles, composite aggregates and intergrowth structures, which cannot be effectively dissociated for selective separation.
In flotation circuits, unliberated locked particles present dual defects. On the one hand, gangue components attached to valuable mineral surfaces will be co-floated mechanically, significantly increasing concentrate impurity content and reducing concentrate grade. On the other hand, the incomplete exposed surface of target minerals cannot fully adsorb collectors and activators, resulting in poor floatability. A large number of low-liberation mineral particles cannot be recovered and are eventually discharged with tailings, causing irreversible metal loss.
This negative impact is also prominent in physical separation processes. In gravity separation, locked particles have an intermediate specific gravity between valuable minerals and gangue, failing to achieve effective density-based stratification. In magnetic separation, mineral inclusions and intergrowth structures weaken the magnetic susceptibility difference between target minerals and gangue, greatly reducing the sorting accuracy of magnetic separators. Within a reasonable range, appropriately improving grinding fineness can indeed increase the liberation degree, optimize separation conditions and raise recovery rates. However, this optimization effect has a clear upper limit and will completely reverse once crossing the critical fineness threshold.
Over-grinding is a common wasteful production state in industrial grinding. After the target minerals are fully liberated, the materials still stay in the mill for prolonged mechanical action, and the already qualified monomer minerals are further crushed into ultra-fine slime particles (generally below 10 μm). These ultra-fine particles with huge specific surface area and high surface activity bring a series of irreversible hazards to the flotation system.
First, ultra-fine particles have extremely low bubble collision and adhesion efficiency. Even after surface hydrophobic modification by reagents, their small mass and low inertia make it difficult to stably attach to air bubbles, resulting in extremely low flotation recovery of fine fractions. Second, high-activity fine slimes are prone to non-selective adsorption and coating on the surface of coarse and medium mineral particles, forming slime coating. This physical coverage completely isolates the interaction between conventional particles and flotation reagents, destroying the selective flotation system. Third, massive ultra-fine particles sharply increase the total specific surface area of pulp, leading to a sharp rise in the consumption of collectors, depressants and dispersants. Meanwhile, fine gangue is easily entrained by froth and enters the concentrate, causing continuous decline in concentrate quality.
A 2025 professional study on galena fine grinding systematically verified this mechanism. The experimental data showed that with the continuous increase of sub-10 μm ultra-fine particle yield, the flotation recovery of galena decreased significantly. The research further pointed out that mill media filling rate, steel ball operating trajectory and particle attrition intensity are core factors affecting ultra-fine slime generation. This fully proves that finer grinding does not equal more effective grinding. If increased fineness only produces a large number of difficult-to-recover ultra-fine slimes, the nominal grinding index is improved, but the actual beneficiation economic indicators will deteriorate comprehensively.
Most concentrators traditionally take the ‑0.074mm particle size content as the sole evaluation standard for grinding fineness. This index is simple to detect and convenient for daily production control, but it has obvious one-sidedness and cannot reflect the real grinding quality and liberation status. In actual production, two groups of grinding products with the same 70% ‑0.074mm fineness may show completely different flotation performance.
The core reason lies in the different internal particle size distribution and liberation composition. Some products have a narrow and reasonable particle size composition with uniform liberation; others contain a large amount of invalid ultra-fine slimes while maintaining the same mesh content. Therefore, scientific grinding quality evaluation must abandon single mesh indicators and comprehensively cover four core dimensions: the liberation degree of target minerals in different particle fractions; the proportion of unliberated locked particles in coarse fractions; the abnormal yield of ultra-fine slimes and their mineral composition; and the metal distribution law of each particle size fraction, distinguishing whether metal loss comes from coarse locked particles or fine slime loss.
Accurate evaluation can be realized through sieve classification, graded assay, microscopic liberation observation and MLA process mineralogy detection. A copper-cobalt sulfide ore research shows that taking moderately liberated mineral aggregates as the recovery object can avoid excessive invalid fine grinding. Excessively pursuing full monomer liberation of all particles will instead reduce the overall flotation efficiency. This indicates that the optimal separation unit is not necessarily fully dissociated monomer minerals, but mineral aggregates with reasonable particle size and separation characteristics.
The optimal grinding fineness of each ore type cannot be determined by a single grinding test or rely solely on a single recovery data. It requires multi-group gradient fineness conditioning tests and comprehensive evaluation of the entire process indicators. Enterprises need to set multiple grinding fineness gradients, and conduct particle size analysis, liberation identification and full-condition flotation tests for each group. The final qualified fineness must balance multiple key indicators: concentrate grade and recovery rate, middlings circulating load, unit reagent consumption, grinding energy consumption and mill processing capacity, thickening and filtration efficiency, and index stability under fluctuating ore properties.
For ores with uneven liberation particle size, serious slime tendency and large differences in grindability between valuable minerals and gangue, the traditional single-stage full fine grinding process is completely unsuitable. It is necessary to adopt advanced technological schemes such as stage grinding and stage separation, coarse particle early enrichment and middlings regrinding to avoid uniform over-grinding of all materials. A verification test on microcrystalline graphite ore confirmed that compared with single-stage grinding, the stage grinding-flotation process effectively reduces ultra-fine slime entrainment loss and significantly improves overall separation accuracy and recovery stability.
High-quality grinding evaluation should abandon the simplistic judgment standard of “the finer the better”. The real effective grinding must answer three core technical questions: whether the target minerals achieve the best liberation state matching separation; whether over-grinding-sensitive minerals are effectively protected to avoid slime generation; whether the current particle size distribution maximally adapts to the downstream flotation and separation process.
Conclusion
There is no universal fixed optimal grinding fineness in mineral processing. Different ore properties, different target minerals and different separation processes correspond to unique optimal particle size intervals. The most reasonable grinding standard for concentrators is to find the best balance point among recovery efficiency, product quality, processing capacity, energy consumption and comprehensive economic benefits. Blindly pursuing ultra-fine grinding will only increase energy consumption, reagent cost and slime loss. Only precise and effective grinding that “just meets the separation requirements” can help enterprises achieve long-term high-efficiency and low-cost production.
