Crushing of ore

Crushing is the process of reducing the size of pieces of minerals by breaking them down using external forces that overcome the internal cohesive forces that bind the particles of solid matter together.

Technologically, crushing processes are divided into:

• Independent – in which the crushing products are final (commercial), that is, they are not subject to further processing (coal crushing).
• Preparatory – obtain minerals of a given size for subsequent processing.
• Selective – one of the components of the material has low strength and is destroyed more effectively than the other, with their subsequent separation.

In the enrichment processes of ore and other minerals, crushing and grinding processes are used to open up intergrowths of rock, with the purpose of facilitating and increasing the "efficiency" of further enrichment processes. The limits of crushing size are determined by the size of the inclusions of the extracted elements. This size is determined empirically.

The following crushing methods are distinguished:

• Mechanical – through the use of mechanical forces;
• Pneumatic – using steam or compressed air energy;
• Aerodynamic (jet) – use of the energy of a gas jet;
• Ultrasonic – through the use of ultrasound energy.

The most widespread method of crushing minerals due to its simplicity is the mechanical method. To characterize the crushing process and to understand in advance what energies will be used to crush various materials, the concept of crushability is introduced . Crushing is a generalizing parameter of many mechanical properties of rocks, expressing the energy intensity of the rock crushing process.

The intensity of the crushing process is characterized by the degree of crushing.

The degree of crushing is a characteristic that indicates how many times the size of the largest pieces of rock has decreased as a result of crushing. The degree of crushing i is defined as the ratio of Dmax - the size of the largest pieces of rock in the material entering crushing, to dmax - the size of the largest pieces after crushing.

i = Dmax/dmax

In turn, the crushing process is divided into stages of crushing in a crushing machine:

• large – from 1200 to 300 mm;
• average – from 300 to 75 mm;
• small – from 75 to 10-15 mm.

Crushing efficiency E% is the ratio of the amount of a class of a given size formed during crushing to the amount of material in the initial feed that requires additional crushing: E = 100 (b _{l - s} – a _{l - s} )/a _{> s} where s is the given crushing size; a _{l - s} and b _{l - s} are the content of class ls in the initial feed and crushed product, respectively, in %; a _{> s} is the content of class greater than s in the initial feed, %.

Let's consider the main theoretical foundations of fragmentation . The main methods include:

a) Crushing - destruction as a result of compression

b) Splitting – splitting between the tips of the crushing surfaces

c) Fracture – destruction as a result of bending.

d) Shearing - destruction occurring through shear deformation

d) Abrasion – destruction of pieces by a sliding working surface (removal of layers from the surface).

A visual representation of this classification is shown in Figure 1.

Fig. 1. Methods of crushing rocks

Methods of crushing ore

The crushing method is selected depending on the properties (viscosity, strength, elasticity) of the rocks, to achieve the greatest crushing efficiency. For example, for strong and non-brittle rocks, the best method of destruction may be crushing or impact. The choice of crushing method is also influenced by the value of the input material, as well as the requirements for the final product.

Thus, the crushing process is an integral part of the enrichment processes, and most importantly, the process that sets the pace and efficiency of subsequent enrichment.