Views: 0 Author: Site Editor Publish Time: 2026-05-28 Origin: Site
Unstable grinding fineness is a prevalent technical problem troubling most mineral processing plants in daily production. A typical abnormal operating phenomenon is widespread across concentrators: continuous steel ball replenishment fails to boost mill throughput, but instead causes a gradual decline in processing capacity. Meanwhile, the mill operating current keeps rising steadily, while grinding fineness fluctuates randomly without stable qualification. This abnormal operation further accelerates liner wear, leading to uncontrollable steel ball consumption and high production costs. In the closed-circuit grinding system, the classifier overflow particle size alternates between coarse and fine fractions, triggering sticky flotation froth, severe concentrate entrainment, and sudden rises in tailing metal loss, which seriously restricts overall mineral processing economic indicators.
When facing such process fluctuations, on-site technicians usually focus on conventional influencing factors, including increased ore hardness, coarse particle overflow failure of hydrocyclones, and mismatched flotation reagent systems. These inspection directions are essential for troubleshooting process abnormalities. However, most production teams ignore a core and long-term neglected key factor: the deviation of grinding media filling rate and ball load gradation structure from the optimal operating range.
In recent years, mining resources have gradually presented characteristics of low ore grade, fine mineral dissemination size and high slime content. To meet the target grinding fineness, most plants adopt the empirical operation of excessive and frequent steel ball replenishment. Although this method can raise mill current and enhance grinding energy input in the short term, it will cause irreversible imbalance of ball load structure in the long run. Excessive media occupation reduces the mill’s effective grinding volume, deteriorates internal slurry fluidity, and aggravates over-grinding and ore sliming problems. Ultimately, the whole grinding and classification system becomes unstable, severely weakening the recovery efficiency of subsequent flotation operations. It is worth clarifying that grinding fineness fluctuation is caused by multiple coupled factors such as ore hardness variation, feed size fluctuation, unstable grinding density, liner wear and hydrocyclone parameter deviation. This paper mainly focuses on the critical yet easily overlooked influencing factors: grinding media filling rate and ball load structure.
Grinding media filling rate refers to the volume ratio of steel balls or steel rods occupying the internal space of the mill to the effective working volume of the mill, which is the core basic parameter of mill operation. Its standard calculation formula is: Grinding media filling rate φ = Vb / Vm × 100%. In the formula, Vb represents the bulk stacking volume of internal grinding media, and Vm refers to the effective working volume of the ball mill.
On-site professional terms such as 30% ball load, 35% filling rate and excessive ball level all correspond to this parameter. It is crucial to distinguish that the on-site measured ball load volume is the bulk volume of stacked steel balls containing internal gaps, rather than the solid volume of steel ball entities. Multiple field conditions including liner structure, mill model, residual slurry volume and shutdown state will affect the accuracy of filling rate measurement.
The filling rate determines the overall operating state of the mill, rather than simply representing the total amount of grinding media. It directly controls the motion trajectory of steel balls, the proportion of cataracting and cascading movements, the intensity of impact crushing and abrasive grinding, the effective slurry flow space, grinding volume utilization rate and energy conversion efficiency. A substandard filling rate will break the balanced grinding state. A low filling rate leads to insufficient impact and abrasive force, making it difficult to fully grind coarse ore particles and resulting in unqualified fineness. An excessively high filling rate compresses the effective grinding space, hinders slurry circulation, and generates a large number of invalid collisions between steel balls, which greatly reduces effective grinding efficiency and increases unit energy consumption. Therefore, the optimal filling rate is not blindly high or low, but needs to be dynamically matched with ore properties, feed particle size, grinding fineness targets, classification efficiency and downstream separation process requirements.
Filling rate and ball load structure are two independent core indicators, which are frequently confused in on-site operation and management. Essentially, the filling rate reflects thetotal quantity of grinding media inside the mill, while the ball load structure refers to the size gradation matching of grinding media, which determines whether the media can adapt to actual grinding tasks.
Even with a fixed standard filling rate (such as 35%), different ball size gradations will produce completely different grinding effects. A high proportion of large-diameter steel balls provides strong impact crushing force, which is suitable for grinding coarse and hard ore particles. However, the reduced number of single balls per unit volume leads to insufficient fine grinding capacity and high coarse particle circulating load. In contrast, a high proportion of small-diameter steel balls forms dense contact points, significantly improving abrasive grinding performance, which is applicable to fine grinding and regrinding processes. Nevertheless, excessive small balls will lack effective impact force, failing to crush coarse particles and locked minerals thoroughly.
Accordingly, the judgment of insufficient or excessive mill media cannot only rely on the total filling quantity. It is necessary to comprehensively verify whether the ball gradation matches the feed size, target product fineness, ore hardness and process objectives. A scientific and reasonable ball load structure realizes precise matching between multi-grade mineral particles and diversified grinding energy modes. The primary grinding stage focuses on impact crushing to dissociate bulk ores, while fine grinding and regrinding stages prioritize abrasive grinding and selective mineral liberation. For high-slime and sliming-prone ores, optimized ball gradation is required to avoid over-grinding and excessive fine slime generation.
The imbalance of ball load structure can be preliminarily identified through multiple on-site operating symptoms. It should be noted that mill current, operating sound and load status are only preliminary reference bases. Final confirmation requires comprehensive verification combining particle size detection, process mineralogy analysis, laboratory grinding tests and closed-circuit process debugging.
First, sustained high current with insignificant fineness improvement. If steel ball replenishment leads to rising mill current but no obvious optimization of discharge and overflow fineness, the increased electric energy fails to convert into effective grinding work. At this time, it is necessary to inspect and optimize the ball load structure, slurry density, liner operating state and classification efficiency.
Second, elevated coarse particle content and circulating load. Excessive coarse particles in mill discharge, increased hydrocyclone underflow and rising system circulating load indicate insufficient coarse crushing capacity or abnormal classification equipment operation. Simply adding steel balls cannot solve the problem; instead, feed particle size composition, ball gradation and hydrocyclone operating parameters should be checked synchronously.
Third, abnormal growth of ultra-fine slimes. A sharp increase in 10 μm or 20 μm fine slimes, accompanied by sticky flotation froth and aggravated concentrate entrainment, is a typical over-grinding symptom. The core problem is excessive grinding rather than insufficient grinding capacity.
Fourth, abnormal rise of steel and liner consumption. Significantly increased steel ball and liner wear without corresponding improvement in grinding efficiency proves abnormal steel ball movement, a large number of invalid collisions and serious ball load structure imbalance.
Fifth, synchronous fluctuation of grinding and flotation indicators. The synchronized variation of grinding fineness, flotation froth state, concentrate grade and tailing grade indicates that grinding and classification fluctuations have interfered with downstream separation. System linkage diagnosis of grinding-classification-flotation is required, rather than simple flotation reagent adjustment.
Empirical steel ball replenishment has obvious limitations, and data-based ball load structure optimization is the core of stable grinding operation. Grinding media filling rate and ball gradation determine energy utilization efficiency, grinding dynamics, product particle size composition, mineral monomer liberation degree and final flotation indicators. For concentrators plagued by high energy consumption, high steel consumption, unstable fineness and fluctuating flotation recovery, ball load imbalance is a key troubleshooting priority.
Systematic process diagnosis and grinding tests are recommended for plants with deteriorating indicators despite continuous ball replenishment, unstable fineness under high current, long-term high unit ore consumption, fluctuating hydrocyclone load, sticky flotation froth, low recovery and severe over-grinding of high-slime ores. Relying on rich industrial experience in complex ore grinding optimization, fine particle recovery and grinding-flotation linkage diagnosis, Huihe conducts systematic analysis based on ore properties, mill parameters, ball replenishment records, operating data and flotation indicators to formulate customized filling rates and ball gradation schemes. Stable grinding production is always verified by data calculation, laboratory tests and field production practice, rather than blind empirical operation.
