Gravity beneficiation

1. What is gravity beneficiation?

Gravity separation, known as gravity beneficiation, is a mineral processing method that separates minerals according to their different densities. In addition to various gravity concentration equipment, there must be a medium (air, water, heavy liquid or heavy suspension) when conducting gravity separation. In the gravity concentration process, mineral particles will be applied force by gravity (if in the centrifugal force field is mainly centrifugal force), the mechanical force exerted by the equipment and the force of the medium, the proper combination of these forces will make the different density of the particles produce different movement speed and trajectory, and ultimately they can be separated from each other.

2. What are the characteristics and applications of gravity beneficiation?

Gravity separation method has the characteristics of simple equipment structure and low operating cost, so it can widely be used when the conditions are suitable. The main applications of gravity concentration are,
1. The separation of gold, platinum and other precious metals.
2. Sorting of tungsten and tin ores.
3. In the treatment of rare metal elements containing minerals in the sand ore is very common, such as zirconium, titanium minerals containing the separation of the seashore sand ore;
4. Hematite, limonite separation
5. Separation of manganese ore.
6. Separation of fine coal and gangue in coal processing plant.
7. Separation of some non-metallic minerals and veinstones, such as the separation of asbestos, mica, kaolin, seafoam and diamond, etc.
8. For non-ferrous metal ores such as copper, lead and zinc, which are mainly treated by flotation, preenrichment by gravity concentration is also a common method.
9. Gravity concentration by particle size sorting process such as classification, desliming, etc., almost in all mineral processing plants are indispensable operations.

3. How many forces are applied to the settling of mineral grains in the medium?

The gravity of the grains in the medium is applied by two forces: one is the gravity of the grains in the medium, the gravity of the grains in a certain medium is certain; the other is the resistance of the medium, the resistance and the settling speed of the grains related. The initial stage of the particle begins to settle, because the resistance of the medium is very small, so the particle in the role of gravity to do acceleration settlement. With the increase of settling speed, the resistance of the medium also increases. As the resistance of the medium gradually increases, the acceleration of the particle settling gradually decreases. After a certain time, the acceleration is reduced to zero. At this point, the particles will settle at a certain speed, the speed is called the final velocity of settlement. Settling velocity is affected by several important factors, including: the density, particle size and shape of the particles; the density and viscosity of the medium.

4. Why is it necessary to crush and grind the ore sufficiently before gravity beneficiation?

In order to separate the particles as much as possible by density, the ore must be sufficiently crushed and ground before gravity beneficiation to dissociate the useful minerals from the vein minerals and to reduce the bulk size entering the gravity beneficiation process. Ore particles must be sieved and graded into a variety of particle size, in order to enter the different gravity beneficiation machinery. Because the narrower the gravity beneficiation, the more can reduce the size of the impact on the sorting, and the more accurate sorting of the particles by density, and can improve the productivity of the gravity beneficiation machinery, reduce the useful minerals in the sorting process of mud.

5. How many types of operations according to the principle of different gravity separation?

According to the form of media movement and different purposes of operation, gravity separation can be divided into six types of operations.

1. Heavy media beneficiation. Gravity beneficiation must be carried out in the media, the media used are air, water, heavy liquid or heavy suspension, the most commonly used is water, with air is called wind beneficiation, with a density greater than the heavy liquid or heavy suspension is called heavy media beneficiation. Heavy media beneficiation is a method of sorting strictly according to the density of minerals.
2. Classification. Shattered materials in the air or water settlement, different particle size and shape of the particles due to the different resistance of the medium and have different settling speed, at this time can be separated by size, this gravity separating operation is called classification.
3. Ore washing. When the ore is clay agglutination and interfere with the subsequent operations need to use washing operations, it is with the water impulse and mechanical force to make the clay and ore block from the operation.
4. Jigging beneficiation. The use of periodic vertical variable speed media flow, so that the group of particles repeatedly loose, dense and stratified by density of the gravity separation process is called jigging beneficiation.
5. Shaking table beneficiation. The use of shaking table surface asymmetric reciprocating motion generated by the inertial force and water rinsing effect, so that the particles located on the table surface loose stratification and transported to separate the belt, so as to achieve the sorting operation.
6. Spiral chute beneficiation. It is the method of beneficiation by means of the water flowing in the inclined chute.

6. What is the feeding size range of commonly used gravity separation equipment?

The size range of the commonly used gravity separation equipment is shown in the table

7. How to determine the difficulty of the gravity separation of two minerals?

The gravity beneficiation is based on the different density of minerals for mineral separation, gravity beneficiation must be carried out in the media. Therefore, the density of the minerals and the density of the medium are the most important factors affecting the gravity beneficiation process. The degree of difficulty of the gravity separation of two minerals can be roughly judged by the following formula.


In the formula A1, A2, P refers to the densities of light minerals, heavy minerals and media respectively.

E value is called the gravity selectivity judgment criterion, the larger the E value, the easier to separate. It is customary to divide the E value into several grades as shown in the table.

Taking the separation of metallic and non-metallic minerals as an example, the density of metallic minerals is generally greater than 4.6 g/cm3 and the density of non-metallic minerals is generally less than 2.8 g/cm3, when separating them in an aqueous water medium (P=1.0 g/cm3), then.


This shows that it is easy to separate.

As can be seen from the above equation, for two specific minerals, i.e., when A2, A1 are certain, the greater the dense P value of the medium, the greater the E value, and the easier the separation becomes. For example, when P = 1.8 g/cm3, separating metallic and non-metallic minerals, the E=(A2-P)/(A1-P)=(4.6-1.8)/(2.8-1.8)=2.8>2.5

The separation is extremely easy at this point.

Of course, the particle size, shape of the mineral particles, the state of motion of the medium, etc. are also important factors affecting the gravity beneficiation process, so the E value as a criterion to determine the ease of gravity separation is only preliminary and rough.

8. What are the definitions of free sedimentation, interference sedimentation, equiparticle sedimentation and equiparticle sedimentation ratio?

The settling of a single particle in a wide medium space is called free settling, and the settling of individual particles in a cluster is called interference settling. In the free settling process, the particles are only affected by their own gravity, medium buoyancy and resistance and are not affected by other factors. In the process of interference settlement, individual grains are subject to their own gravity, medium buoyancy and resistance, in addition to the role of friction, collision and suspension of other grains, thus changing the settling speed and trajectory of individual grains. As can be seen, the interference settling process is much more complex than free settling. All sedimentation in the practice of gravity separation is interference sedimentation, but when the distance between the particles in the particle group is large, that is, the volume concentration (the ratio of the total volume occupied by the particles to the total volume of the suspension) is very small (generally less than 3%), the interference between the particles becomes very weak, which can be regarded as free sedimentation.

In free settling, the settling velocity of mineral particles is related to the density, size and shape of the particles at the same time. When settling in the same medium, particles with different densities, particle sizes and shapes can have the same settling final velocity under specific conditions, and these different particles with the same settling final velocity are called equal-drop particles. Obviously, there is a small density of large particles (set its size as d1) and large density of small particles (set as d2), d1 and d2 ratio is called the ratio of equal fall.