In mineral processing production lines, grinding is often the first critical watershed that determines success or failure. When it comes to grinding fineness on-site, the common intuition is usually “the finer, the better, the finer, the safer”. However, anyone with actual production experience knows: if the grind is too coarse, the minerals remain undissociated; no matter how you adjust reagents, water, or electric fields in subsequent magnetic separation, flotation, or electrostatic separation, it is like “dancing with shackles”. If the grind is too fine, it will cause a series of side effects such as sliming, coating, entrainment, and adhesion, making separation even more difficult, and ultimately lowering both recovery and concentrate quality.

There is a simple yet crucial saying in the mineral processing industry:No matter what ore you process, once grinding is involved, you must first get the ore’s “fineness” right.

Why Particle Size Matters: Mineral Liberation Is the Prerequisite of Mineral Processing

Whether subsequent separation uses magnetic separation, flotation, or electrostatic separation, they all essentially serve the same purpose:to create distinct physical or chemical differences between target minerals and gangue, thereby achieving separation.

For these differences to be effective and reliable, there is one strict requirement:mineral liberation.

Magnetic separation relies on differences in magnetic properties.If magnetite and gangue remain as locked particles, the magnetic fraction will “drag” gangue along with it, resulting in low concentrate grade.

Flotation relies on differences in surface properties.The surface of a locked particle contains both valuable mineral and gangue; even with highly selective reagents, the “mixed surface” weakens performance, causing contamination in concentrate and loss to tailings.

Electrostatic separation relies on differences in electrical conductivity or dielectric properties.The electrical response of locked particles becomes averaged, widening the separation window and significantly reducing separation sharpness.

Therefore, the core objective of grinding is never “the finer the better”,but rather to liberate minerals to a sufficient degreeto create favorable conditions for subsequent separation.

What Determines Grinding Fineness? Mineral Liberation Size Is the Decider

Ore processing always starts with comminution.The question is: what particle size is appropriate?

The answer does not come from guesswork or experience alone,but from the ore’s inherent structural characteristic:its liberation size.

Liberation size can be understood asthe natural grain size at which valuable minerals occur within the gangue.Some minerals have coarse grains and large crystals,which can be liberated with mild grinding.Others are finely disseminated and tightly interlocked,requiring finer grinding to “liberate” them from the gangue.

This is why, even for the same separation process,the required grind varies greatly:

For flotation, some plants only need 70% passing -74 μm,while others require 80% passing -38 μm for stable performance.

For magnetic separation, some magnetite ores achieve high gradewith moderate fineness,whereas some vanadiumtitanium magnetite oresrequire precise control at the threshold of sliming.

On-site determination of liberation sizetypically relies on process mineralogy:optical microscopy, MLA/SEM, particle-size chemical analysis,liberation measurement, and more.

All these data ultimately lead to one core principle:Achieve sufficient liberation for separationwith minimum energy consumption and minimum sliming.

Finer Is Not Always Better: Over-Grinding Causes Sliming and Separation Difficulties

Many losses in concentrators occur not during coarse grinding,but after overgrinding.Excessively fine grinding leads to severe sliming (often referred to onsite as “pulping” or “slime formation”):

Slime coating and nonselective adsorptionSlimes readily adhere to coarse particle surfaces, forming a slime layer that prevents reagents from acting effectively on target minerals.Meanwhile, slimes strongly adsorb reagents, increasing consumption and reducing selectivity.

Entrainment and froth contamination (especially in flotation)Ultrafine particles are easily entrained into the froth,raising gangue content and lowering concentrate grade.To reduce entrainment, plants must weaken frothing or increase wash water,which in turn reduces recovery.

Reduced classification efficiency and deteriorated circulating loadUltrafine particles blur the cut size in hydrocyclones,causing more fine material to report to the underflow.The circulating load rises, and effective grinding work is wasted on “unproductive circulation”,increasing both energy and reagent costs.

Diminished separation efficiencyExcessively fine particles weaken the physical separation forces in magnetic and electrostatic separation.In flotation, particlebubble collision and attachment stability decrease.The final result is lower recovery.

Therefore, the optimal grinding fineness is always a “window”:Too coarse → no liberation;Too fine → difficult separation.

A truly highlevel process does not aim for the finest possible grind,but keeps the system operating within the most profitable particle size range.

Regrinding–Classification–Separation as an Integrated System: Use Data to Locate the Optimum Point

Grinding is not an isolated process.It is tightly coupled with classification, pulp density, reagent regime, and slurry chemistry.For plant optimization, we recommend focusing on three core lines:

1.Liberation LineAnalyze liberation and recovery contribution of different size fractions to identify where the “effective fineness” lies.

2.Particle Size Distribution LineFocus on the full particle size distribution (not just the percentage passing -74 μm),including slime content, d80, d50, and the shape of the particle size curve.

3.Separation Response LineCorrelate concentrate grade, recovery, and tailings grade with particle size, pulp density, and reagent consumption.Conduct comparative tests to locate the performance peak.

4.When these data are combined, a clear pattern emerges:The optimum grinding fineness corresponds to the point whereliberation is sufficient, slime content is controlled, classification efficiency is stable, and reagent consumption is minimized.

At this point,both the grade–recovery balance in magnetic separationand the selectivity–kinetics balance in flotationbecome easier to regulate and more stable.

From "Proper Grinding" to "Precision Dosing": Reagent Preparation Also Defines the Upper Limit

While grinding establishes the fundamentals of mineral liberation and particle size distribution,the reagent regime dictates the selectivity and stability of the separation process.Especially in flotation systems,the dosage and addition method of collectors, modifiers, depressants, and frothersdirectly influence froth mineralization, entrainment, and fluctuations in concentrate quality.To truly translate the "right grinding fineness" into tangible gains inrecovery and grade,the reagent link must evolve from"experience-based dosing"to meterable, traceable, and close-loop controlled precision management.

The application of electro-differential reagent feeders in reagent preparation and dosing for flotation enablesmore stable flow output and finer adjustment of reagent addition,meeting the dynamic requirements of complex ore conditions. High-precision dosing reduces fluctuations in reagent consumptionand non-selective adsorption caused by over-dosing,while improving process stability and production controllability. Grinding liberates the minerals,and electro-differential reagent feeders deliver reagents precisely to the point of action.The combination of the two is the key pathfor continuously improving recovery and concentrate quality in mineral processing systems.