Comminution Testing: Size Reduction in Mineral Processing
Comminution Testing
The comminution is a mechanical operation of size reduction, resulting in indirect energy consumption. It is considered that in general the relationship energy – downsizing does not define properly the size reduction process. The relationship between diet and the product of a team of reduction is an approximation and can be directly determined. The effects of operational variables, such as solid feed rate, size reduction equipment, etc., are the factors that require a better understanding.
The design of size reduction machines markedly change as you change the size of the particles.
When the particle is large, the fracture energy for each particle is high but the energy per unit mass is small.
A drop in particle size, the fracture energy for each particle decreases, but the energy per unit mass increases more rapidly. Consequently crushers have to be large and structurally stronger while the mills should be capable of dispersing energy over a large area.
Objectives
- Check operations Comminution
- Determine reason for reducing capacity and equipment
- Compare crushing equipment v / s grinding
Basics
Primary Crushing
In most operations, the primary crushing program is the same as mining. When the primary crushing takes place underground, this operation is normally the responsibility of the department of mining, when the primary crusher is on the surface, it is customary to give the department of mining the ore to the crusher and ore processing department and crush handling the ore from this point through the successive unit operations of mineral processing. The primary crushers are typically designed to operate 75% of the time available, mainly due to disruptions caused by insufficient power to the crusher and mechanical delays in the crusher. They are also machines that reduce the size of the mine ore (run of mine) to a size suitable for transport and storage. Always operate in an open circuit, with or without grids
The two main machines are jaw crushers and gyratory.
This type of crusher should be able to support maximum blocks that can get out of the mine according to the method of exploitation.
The inlet port is called “mouth” and download “throat.” In general the size of the mouth is fixed, but the size of the throat varies periodically during the operation.
When the “throat” is at its maximum opening position, is called “open position” (Sa). When there is little talk of “position closed” (So).
Figure 1. Jaw Crusher
Secondary Crushing
The material given to these teams, it is usually less than 15 cm in diameter, so that equipment is much lighter than the previous. Also the material is easier to handle and transport, and does not require large feeding systems for the crushers.
The purpose of this stage is to prepare the material for grinding and in those cases where size reduction is carried out more effectively in crushing, can incorporate a tertiary crushing mill before entering.
The main equipment used in this stage are cone crushers.
It is similar to rotary crushers, the key difference is that the shaft is shorter, and is not suspended, but is mounted on bearings in the swivel head or cone (Figure 2).
Because it does not require a large aperture can be increased crushing area to discharge, with a greater angle in the rotating cone, keeping the same angle between the parts crushers.
Figure 2. Cone Crusher.
A cone crusher is individualized by the cone diameter in feet. This varies from 2 to 7 feet (60 to 210 cm, approximately), with capacity to 1.10 t / h with a discharge setting of 19 mm. (3 / 4 “)
These crushers operate at a higher speed than the rotary. This allows the material chanque faster due to better flow of material through the large opening created by moving the cone.
These teams may have a reduction ratio of between 3:1 to 7:1 and higher in some material particular.
Are constructed of two types, long head and short head or standard, which is characterized by a steeper cone crusher, reducing the size of the product.
Tertiary Crushing
If the ore tends to be slippery and hard, tertiary crushing stage may be replaced by a coarse grinding in rod mills. Usually these tours are accompanied by corresponding stages of classification to avoid excessive production of fines and increase the capacity of equipment
Milling
The last stage in the process of comminution. It is performed in rotating cylinders known as Mills, and there are several types of them that are classified by shape and by their means of grinding. To develop their work grinding machine is provided with grinding elements or pebbles.
This can be done dry or wet. It’s called dry milling where the ore is fed into such a state. If water is added, thus forming a pulp, it is called wet milling.
Grinding, crushing unlike, is a random process, which should join the particle and the grinding media for the size reduction takes place.
Figure 3: ball mill
Reduction ratio
Defined as the ratio between the size of entering a computer (Power) and leaves the team size (product) using the following equation:
R (r) = F80
P80
Where:
F80: Opening of mesh that lets a 80% power.
P80: Opening of mesh that lets in 80% of the product.
Treatment capacity
defined as the amount of ore can be processed by a crusher or mill, this is measured in kg / min; ton / h, tons / day, etc.
Procedure
- First, the material should be homogenized by cone and quartering to obtain a representative sample of 500 g for head size analysis.
- Second, spend the whole sample by the primary jaw crusher, you must record the time it takes for the material to be crushed by the crusher. After that it will homogenize the material and take a representative sample of 500 g for sieve analysis.
- Third, the remaining mineral must pass through the secondary crusher, here also must record the time it takes to crush the material and take a representative sample of 500g for sieve analysis.
- Fourth, the excess material must be passed by the tertiary crusher and repeat the above procedure to record the time and take a representative sample of 500 g AG
- Fifth, the final product of tertiary crushing will take 2 samples of 1 kg for a dry and wet milling, these mills will be held in ball mills.
Figure 1: Flowchart size reduction tests
Inform
- Tabulate granulometric analysis of crushing and grinding.
- P 80 of each stage of reduction in size, variance and standard deviation.
- Plot size distribution curves of feed and product, both crushing and grinding.
- Calculate the rate of reduction at all stages.
- Calculate the treatment capacity of each of the crushers.
- Compare the results of milling including desliming, these data establish the differences between wet and dry milling. To do so is to seek a 60% under 200 mesh Ty.