The nature of ore and surrounding rock

The properties of ore and surrounding rock mainly include: hardness, firmness, solidity, swell, agglomeration, oxidation, pyrophoricity and water content.

(1) Hardness of ore rock

The hardness of the rock is the property of the rock to resist the intrusion of tools. The hardness of the rock depends on the composition of the rock, that is, depending on the hardness, shape, size, crystal structure and inter-particle structure of the rock. The hardness of the rock has a great influence on the rock. Affect the toughness and solidity of the rock.

(2) Ruggedness of ore rock

In the long-term practice, people realized that some rocks are not easy to break, and some are difficult to break. Rocks that are difficult to break are generally difficult to rock, difficult to blast, and their hardness is relatively large, in general, it is more sturdy. Therefore, people use the concept of rock solidity to indicate the difficulty of rock breaking.

The size of the ruggedness is expressed by the firmness factor (many hardness coefficients in many books, also known as the Platts coefficient f).

Robustness factor (R unit kg/cm2)

Where R is the unidirectional ultimate compressive strength value of the rock standard specimen.

The commonly used Platts rock classification method is to classify rocks according to the solidity coefficient.

Such as:

1 Extremely strong rock f=15～20 (sturdy granite , limestone, quartzite, etc.)

2 Hard rock f=8 ～10 (such as unsturdy granite, strong sandstone, etc.)

â‘¢ medium solid rock f = 4 ~ 6 (such as ordinary sand, iron ore, etc.)

4 not strong rock f = 0.8 ~ 3 (such as loess, only 0.3)

The robustness of the rock is also a property against external forces, but its strength with the rock is two different concepts.

Strength refers to the performance of the rock against unidirectional action such as compression, stretching, bending and shearing. The external force resisted by the sturdiness is a comprehensive external force. (such as resistance to sputum, manuscript, mechanical breakage, the combined force of explosives).

(3) The stability of the ore rock

(1) The concept of rock stability:

Stability refers to the performance of not falling off under a certain exposed area and for a certain period of time. Or, more solidity refers to the size of the area where the rock is allowed to be exposed in space and the length of time allowed for exposure.

The factors affecting the stability are very complex, higher than the composition, structure, structural joint condition, weathering degree, and high water geological conditions of the rock, and also related to the actual situation formed during the mining process (such as roadway). Direction, mining depth, etc.).

Stability has a major impact on the choice of mining methods, the choice of support methods, and the way in which they are driven.
(2) Relationship between stability and robustness

The two are both connected and different. Generally, in the joint development and structural fracture zone, although the solidity of the rock may be good, the stability is greatly reduced. Therefore, stability and robustness cannot be confused. (If the strength is not good, it may not be stable.)

(3) Classification of ore rock stability: roughly divided into five categories

1 extremely unstable

No exposed area is allowed. It is required to support ahead in mining and mining. Otherwise it will go down. (Non-metallic mining conditions);

2 unstable

The area allowed to be exposed is within 50 m 2 . That is, a smaller exposed area is allowed, and with the recovery, support is required immediately.

3 medium stable

It is allowed to have a certain exposed area, that is, 50m2 - 200m2, generally without support, or for temporary support, it can be safely produced.

4 more stable

It is allowed to have a large exposed area of ​​200-500 m2, which is generally not supported.

5 extremely stable

A large exposed area is allowed, that is, 800 m2 or more. You don't have to support it, you can't fall for a long time.

[Note] Stability is not only related to the exposed area and time, but also related to ground pressure, size, joint development, joint direction, and exposed area shape.

(4) The slack of mineral rock

The swell of the ore is the increase in the area after the ore and surrounding rock is broken than the original volume. The bulging property can be expressed by the coefficient of expansion (also called the loose coefficient)

Fragmentation coefficient = volume after crushing / original volume > 1

For general hard rock, the looseness coefficient is 1.4 - 1.6 (or 1.2 - 1.6).

The size of the looseness coefficient mainly depends on the particle size composition and the shape of the blockiness of the ore after crushing. The ore blocks that are initially loaded into the container (mine truck, bucket, etc.), due to the large gap between the ore blocks, the looseness coefficient can reach 1.8 - 2.0 (secondary looseness is generated).

(5) Agglomeration of ore

Agglomeration means that the mined rock is pressed against water and, after a certain period of time, forms a monolithic property.

What we usually see is that clay minerals, talc , or high-sulfur mines are subjected to water pressure, and after a period of time, they are prone to agglomeration. The agglomeration causes difficulties in the production of mining, loading and unloading, transportation, etc., and even affects the smooth use of certain mining methods. The agglomerated ore is in the mining workshop, and the storage time in the sinking well should not be too long.

(6) Oxidation of ore

Oxidation of ore means that the sulfide ore becomes a oxidized ore under the action of water and air. After the oxidized ore is immersed in the sulphide ore, the recovery rate of the beneficiation is reduced. (The chemicals used in mineral processing are different). Therefore, the sulfide ore and oxidized ore should not be mixed.

(7) Spontaneous combustion of ore

Self-ignitability refers to high-sulfurized ore (with a sulfur content of 18-20% or more), and has the property of spontaneous combustion when it has good water permeability and gas permeability.

When high-sulfur ore is oxidized in the well, a large amount of heat is released. After a period of time, the temperature rises, which will cause a fire in the well. The area of ​​contact with the air, especially the powdery high-sulfur ore, is more likely to cause fire.

For the above reasons, high-sulfide deposits must be quickly mined to reduce the loss of ore.

Ore with self-igniting has special requirements in the choice of mining methods. (For example: Xiaoyanlin mine had a big blow in the Cultural Revolution. Because the ore was not released in time, the time was long, the temperature increased, and spontaneous combustion occurred. It burned for a long time without being destroyed, so it was closed. Not taken). It has not been closed yet.

(8) Water content

Water content refers to the nature of water in the cracks and pores of the rock. The water content of the ore directly affects the upgrading of ore, transportation, and storage in the mine. Excessive water content in the ore will increase drainage costs. For mines in this cold area, the icy river will be caused by water content.

(9) Other

(1) Volumetric weight - The bulk density refers to the weight of the original rock in a unit volume.

Generally, the bulk density of rocks is between 2.3 and 3.0 T/m3.

Non-ferrous metal ore contains less metal and its bulk density is similar to or slightly larger than rock. The ferrous metal ore has a high metal content and a bulk density of about 3.5 T/m3. (or larger)

(2) Blockiness - After the original collapse, a nugget, or rock block, is formed, and the size of the block is called the block degree.

The block size is usually expressed in three average sizes in mutually perpendicular directions. (or use the largest dimension)

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That is, the flat fill values ​​of B, L, and H. (Generally, according to the third degree, when using the square method, the second degree is used, and sometimes the second degree is used as a positive coefficient).

For certain shipments, crushing equipment, etc., there are certain requirements for the maximum block size of the ore. In order to ensure the continuous production of the mine, the maximum block size of the ore must be matched with the requirements of equipment such as shipping.

The acceptable block size is usually used to indicate the block size of the mined ore. When the ore block exceeds the acceptable block size, secondary crushing is required.

Qualified block size - the maximum allowable ore block size. Usually the acceptable block size is between 250 and 500mm, and there are also 600mm. It is determined by the process and equipment requirements for mining and processing. As the level of mechanization increases, the degree of acceptable blockiness increases.

(3) Natural Relief Angle - When the loose ore rock is self-combustion and accumulating, it will form an inclined piled slope. The maximum angle at which the natural accumulation slope intersects the horizontal plane is called the natural repose angle of the ore.

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