In modern large-scale mineral processing plants, crushing and grinding operations are a crucial link between mining and beneficiation, and their efficiency and cost directly impact the overall economic benefits of the project. Among numerous crushing and grinding solutions, the SAG mill crushing production line, with its outstanding advantages of simplified processes and reduced operating costs, has become the preferred solution for processing medium-hard and higher hardness ores. Today, we will delve into the secrets of this "core engine."
What is a SAG Mill? A comprehensive analysis of this efficient grinding equipment
Introduction to SAG Mill
Semi-Autogenous Grinding Mill (SAG Mill for short) is a high-efficiency crushing equipment between autogenous mill and ball mill, and is widely used in large-scale ore crushing operations in mining, metallurgy and other industries. It combines the dual advantages of autogenous grinding and ball milling, and can use the ore itself as a grinding medium, and improve the crushing efficiency by adding a small amount of steel balls.
Compared with the traditional multi-stage crushing process of "jaw crusher + cone crusher + ball mill", the SAG mill production line greatly simplifies the process and reduces equipment investment and civil engineering costs in intermediate stages.
Working principle of SAG Mill
The core working principle of SAG Mill is:
• Ore autogenous grinding: large pieces of ore collide and rub against each other in the mill to achieve initial crushing.
• Steel ball assisted grinding: Add a small amount of steel balls (usually 8%-15% of the mill volume) to enhance the impact force and grinding effect.
• Grading discharge: The crushed slurry is discharged through the discharge end, and the ore that does not meet the fineness requirements continues to be circulated and ground.
This design makes it have the characteristics of high processing capacity, low energy consumption, and strong adaptability. It is particularly suitable for the coarse grinding of hard ores such as gold, copper, and iron.
Structural composition of semi-autogenous mill
• Cylinder: a large rotating steel cylinder lined with wear-resistant materials (such as rubber or alloy linings).
• Feed end: ore and steel balls enter the mill from here.
• Discharge end: equipped with screen plates or grating plates to control the particle size of slurry discharge.
• Drive system: motor + reducer + gear transmission to provide stable power.
• Lubrication and cooling system: ensure long-term stable operation of the equipment.
Advantages and disadvantages of semi-autogenous mill
Advantages of semi-autogenous mill
✔ High efficiency and energy saving: compared with traditional ball mills, energy consumption is reduced by 20%-30%.
✔ Large processing capacity: a single device can replace multiple stages of crushing + ball milling processes.
✔ Strong adaptability: can handle ores of different hardness and particle size.
✔ Low maintenance cost: long liner life, low steel ball consumption.
Disadvantages of SAG mills
✖ High initial investment: large equipment size and high installation cost.
✖ Difficult to control: need to accurately adjust the steel ball ratio and speed.
✖ Sensitive to ore properties: too soft or too hard ore may affect efficiency.
Application scenarios of SAG mills
SAG mills are mainly used in:
★ Metal mines: coarse grinding of ores such as gold, copper, iron, lead and zinc.
★ Non-metallic ores: crushing of minerals such as phosphate rock and limestone.
★ Ore dressing plant: as the core equipment of the grinding-classification circuit.
Typical SAG Mill Crushing Production Line Process Flow
Escondida Copper Mine in Chile (one of the largest copper mines in the world)
Boddington Gold Mine in Australia (using SAG+ball milling combined process)
A complete SAG crushing and grinding production line typically includes the following core stages:
1. Feeding: Raw ore from the mine undergoes preliminary screening (e.g., using a grid screen). Oversized ore pieces may require pre-crushing. The ore is then fed evenly into the SAG mill via a belt conveyor.
2. Semi-Autogenous Grinding: This is the core stage. The raw ore is lifted to a certain height by the lifting liner within the SAG mill and then dropped, where it is crushed into smaller particles by the impact and grinding of the steel balls and the ore itself.
3. Classification: The material discharged from the mill (slurry) enters a vibrating screen or hydrocyclone for classification. Qualified fine particles proceed to the next stage, while unqualified coarse particles are returned to the SAG mill as "return sand" for further grinding, forming a closed-loop cycle to ensure the final product particle size.
4. Secondary Ball Milling: To achieve finer separation requirements, qualified products from the SAG mill typically enter a subsequent ball mill for fine grinding.
5. Separation and Dewatering: The slurry ground to the qualified particle size enters the separation operations such as flotation and magnetic separation. Finally, the concentrate is dewatered to become the product.
SAG mill vs. ball mill vs. AG mill
| Comparison items | SAG mill (SAG) | ball mill | AG mill |
| Grinding media | Ore + a small amount of steel balls | Steel balls | Ore itself |
| Crushing ratio | High | Higher | Medium |
| Energy consumption | Low | High | Medium |
| Applicable ores | Medium-hard-hard ores | |Various ores | Softer ores |
| Investment cost | Higher | Medium | Higher |
SAG mills have become the preferred equipment for modern large-scale mining grinding processes due to their high efficiency, low energy consumption and strong adaptability. With the development of intelligent control technology, SAG mills will further improve the level of automation in the future, helping the mining industry to achieve a more efficient and environmentally friendly production model.
If you have any questions about the selection or application of SAG mills, please leave a message!
