Which Mineral Grinding Equipment offers the best energy efficiency for hard rock processing

The Critical Role of Mineral Grinding Equipment in Modern Mining

In the complete flow of mineral processing, Mineral Grinding Equipment holds a core position following the crushing stage and preceding the concentration stage. Comminution operations typically account for more than 50% of the total energy consumption in a mining operation, with grinding being the most meticulous and energy-intensive phase.

The primary task of grinding is to achieve monomer dissociation. Valuable minerals in natural ores, such as gold, copper, and iron, are usually tightly bound with gangue minerals. If the particle size is not fine enough, the valuable minerals cannot be exposed, rendering subsequent flotation or magnetic separation ineffective. Conversely, over-grinding not only wastes energy but also produces slimes that are difficult to recover. Therefore, selecting the appropriate Mineral Grinding Equipment and operating it under optimal parameters is key to improving mine recovery rates and economic efficiency.

Fundamental Classification of Mineral Grinding Equipment

Based on grinding media, discharge methods, and process requirements, Mineral Grinding Equipment can be divided into several major categories. Each type of equipment differs significantly in particle size distribution, throughput capacity, and energy efficiency.

Performance Parameter Comparison of Common Grinding Equipment

To visually demonstrate the characteristics of different Mineral Grinding Equipment, the following table lists a comparison of core technical parameters:

High-Capacity Primary Grinding: AG and SAG Mills

In modern large-scale concentrators, to simplify the process and reduce maintenance costs of the crushing section, Mineral Grinding Equipment tends to be large-scale, with Autogenous (AG) and Semi-Autogenous (SAG) mills being the mainstream choices.

Autogenous (AG) Mill

An AG mill relies entirely on the ore being ground as the crushing medium. Its working principle involves the rotation of the shell to lift large chunks of ore to a certain height, after which they fall, creating strong impact and grinding actions. This type of Mineral Grinding Equipment eliminates the need for expensive steel ball media and avoids iron contamination which could interfere with subsequent chemical processes like gold cyanidation. However, it has strict requirements for ore hardness; if the ore is too brittle, grinding efficiency drops.

Semi-Autogenous (SAG) Mill

To compensate for the shortcomings of AG mills when processing ores of uneven hardness, SAG mills add a volume of 8% to 15% steel balls into the shell. The power consumption of a SAG mill is closely related to the ball charge, liner profile, and shell speed. They typically operate at 70% to 80% of critical speed. This is the preferred primary Mineral Grinding Equipment for large-scale open-pit mines, capable of handling massive feed sizes.

The Industry Standard: Ball Mills and Rod Mills

The ball mill is the most representative member of the Mineral Grinding Equipment family. Whether in small mines or ultra-large smelters, it is a constant presence in the circuit.

Structure and Classification of Ball Mills

Ball mills rely on the impact and attrition of steel balls to reduce ore size. Depending on the discharge method, they are classified as Overflow Type, which has a simple structure and relies on the slurry level difference, or Grate Discharge Type, which is equipped with a discharge grate plate that allows for faster discharge and reduces over-grinding.

Uniqueness of Rod Mills

Rod mills use long steel rods as media. Because the contact between rods is linear, large ore particles are first crushed between the rods. This selective grinding characteristic ensures a very uniform product size. The rod length is usually 15 to 30 cm shorter than the shell length to prevent the rods from tangling or crossing during operation within the Mineral Grinding Equipment.

Advanced Fine and Ultra-Fine Grinding Solutions

As global ore grades decline, ores become increasingly poor and complex. Traditional Mineral Grinding Equipment is less efficient when handling extremely fine particles below 20 microns, leading to the rise of stirred mills.

Vertical Stirred Mill (Tower Mill)

These machines do not rotate the shell; instead, an internal stirrer rotates to move the media. In the fine grinding stage, the energy efficiency of a stirred mill is 30% to 50% higher than that of a traditional ball mill. Ceramic balls are often used as media to reduce metal contamination.

High-Pressure Grinding Rolls (HPGR)

While often classified as crushing equipment, HPGR has become an essential pre-treatment link for Mineral Grinding Equipment in modern circuits. It uses high pressure between two rollers to create micro-cracks inside the ore, drastically reducing the energy consumption of subsequent ball milling stages.

Components and Engineering of Mineral Grinding Equipment

A high-performance piece of Mineral Grinding Equipment is composed of thousands of parts. Its core wear components and drive systems determine the equipment's availability.

• Shell Liners: Categorized into manganese steel, rubber, and magnetic liners. Rubber liners are widely used in wet ball mills for their low noise and light weight.
• Bearing Systems: Large mills often use hydrodynamic or hydrostatic bearings to support the massive rotational inertia of several hundred tons.
• Drive Systems: These include Girth Gear drives and modern Gearless Motor Drives, the latter allowing for more precise speed control of the Mineral Grinding Equipment.

FAQ: 

What does Critical Speed mean for a grinding machine?

Critical speed is the minimum speed at which the centrifugal force causes the grinding media to stick to the inner wall of the shell without falling. In actual production, Mineral Grinding Equipment is usually set at 70% to 85% of the critical speed to ensure the media produces impact or attrition effects.

Why is water added during the grinding process (Wet Grinding)?

Wet grinding is the mainstream in mining. Water acts as a carrier to help transport the slurry and prevents fine ore powder from sticking to the liners and media. Additionally, wet grinding eliminates dust pollution and generally has a higher throughput.

How do you determine if steel balls need to be added to the mill?

Operators usually judge by monitoring the motor current or power. As steel balls wear down and become lighter, the motor load decreases. Modern Mineral Grinding Equipment may also use vibration monitors or acoustic sensors to analyze the impact sound of the shell.

Does the shape of the liner affect production?

Greatly. Wave or step liners increase the lift height of the media, creating stronger impact forces. As liners wear flat, the lifting capacity weakens, and the mill's output decreases significantly.

Is finer grinding always better?

No. Grinding should stop at the point of just dissociated. Over-grinding leads to skyrocketing energy consumption, and in subsequent flotation, extremely fine mineral particles can coat the surfaces of valuable minerals, reducing recovery rates.