Mineral processing | Selection of grinding and grading equipment

(1) Ball milling and rod grinding process

For beneficiation, one or two stages of grinding can be used to economically grind the ore to any particle size required for beneficiation. Two or more stages of grinding are usually determined by the requirements for stage selection.

Compared with the two-stage process, the main advantages of a grinding process are: less equipment, low investment, simple operation, no work due to one grinding section shutdown to another grinding section, and less downtime. However, the mill has a wide range of grain size, reasonable ball loading, and it is difficult to obtain a fine final product, and the grinding efficiency is low. When the final product is required to have a maximum particle size of 0.2 to 0.15 mm (i.e., 60% to 79% to 200 mesh), a grinding process is generally employed. For small plants, to simplify the process and equipment configuration, a grinding process can be used when the grinding fineness requires 80%-200 mesh.

The outstanding advantage of the two-stage grinding is that it can obtain a finer product, which can be coarsely ground and finely ground in different grinding sections, especially suitable for stage treatment. In large and medium-sized factories, when the grinding fineness is less than 0.15mm (ie 80%-200 mesh), it is economical to use two-stage grinding, and the product has uniform particle size composition and less over-grinding. According to the different connection modes of the first section of the mill and the classifier , the two sections of the grinding process can be divided into three types: the first section is open; the second section is fully closed; the first section is partially closed, and the second section is always closed. Grinding process.

(2) Self-grinding process

The self-grinding process has two types: dry grinding and wet grinding. Wet grinding is often used in the concentrator. In order to solve the problem of difficult-to-grind particles in self-grinding and improve the grinding efficiency, a small amount of steel balls are added to the self-grinding machine, which is called semi-self-grinding.

Self-grinding often works in combination with crushing equipment such as fine crushing, ball milling, gravel grinding, etc., and can form a variety of processes according to the coupling method.

Grinding equipment widely used in concentrators is a ball mill and a rod mill. In ball mills, only lattice type and overflow type are currently used. Cone ball mills are not manufactured because of their low productivity, but some old concentrators still use them. The specifications of the ball mill and the rod mill are expressed by the simplified inner diameter D and the barrel length L.

The ball mill produced by a company is a horizontal cylindrical rotating device, an external gear transmission, two bins, and a lattice ball mill. The material is uniformly fed into the first chamber of the mill by the feeding device through the hollow shaft of the feeding material. The chamber has stepped lining or corrugated lining, which is filled with steel balls of different specifications. The rotation of the cylinder generates centrifugal force to bring the steel ball to a certain height. After falling, it will hit and grind the material. After the material reaches the rough grinding in the first warehouse, it enters the second warehouse through the single-layer compartment board. The warehouse is provided with a flat lining plate with steel balls inside to further grind the material. The powder is discharged through the discharge raft to complete the grinding operation. Dry ball mills and wet lattice ball mills, etc.

(1) Lattice ball mill

The structure of various specifications sub-type ball mills is basically the same. The cylinder of the ball mill is rolled and welded with a steel plate with a thickness of about 18 to 36 mm. The two ends of the ball mill are welded with a flange made of cast steel, and the cylinder body is provided with a lining plate. It is made of manganese steel, chrome steel, wear-resistant cast iron or rubber. Among them, high manganese steel is widely used, and rubber is still in the trial stage. The lining is about 50-130 mm thick and has a gap of 10-14 mm from the shell. It is paved with plywood, asbestos mat, or plastic pole or rubber to slow the impact of the steel ball on the simplified body.

(2) Overflow ball mill

The overflow ball mill overflows by the mine itself by the lower edge of the hollow shaft because it does not need to install a heavy grid plate. Further, in order to prevent the small balls and the coarse ore nuggets in the ball mill from being discharged together with the slurry, the inner surface of the hollow journal bush is provided with a reverse spiral blade.

(3) Rod mill

At present, the rod mill used in the concentrator has only two types of overflow type and open type. The former is more commonly used, and the latter has been stopped. The structure of the rod mill is approximately the same as that of the overflow type ball mill. The grinding medium used is a long round bar.

Rod mills are available in both dry and wet versions and can be selected according to your actual situation. Henan Hongxing Mining Machinery Co., Ltd. adopts advanced controllable feeding and discharging technology. The actual grinding material should be matched with the appropriate grinding body to change the traditional surface contact to line contact, so that the discharge granularity is more uniform and the output is higher. It is widely used in the refractory industry, chemical industry, metallurgy, glass and other industries. It has high requirements for the uniformity of finished products after grinding. In recent years, it has also been used in the sand making industry for construction sand.

(4) Centrifugal mill

Centrifugal mill is a new type of high-efficiency and ultra-fine equipment. It is divided into vertical and horizontal. According to the number of tubes, the former can be divided into single-tube and three-tube (planetary) centrifugal mills.

(5) Vibration grinding machine

The vibration mill works at high frequencies, and the high-frequency vibration easily causes cracks in the material, and can generate a relatively high stress concentration in the crack, so it can effectively perform ultra-fine grinding. However, such mechanical springs are prone to fatigue and damage, the lining plate consumption is also large, the amplitude used is small, the ore is not too thick, and it is required to be evenly added, so it is generally suitable for grinding materials of 1 to 2 mm to 85~. 5 microns (dry mill) or 5 to 0.1 microns (wet mill).

(6) Jet mill

Jet mill is a new type of dry grinding equipment that combines fine grinding of materials with grading and drying. Mainly used in the chemical and building materials industries, but recently there is a trend for grinding. The operation of the jet mill is: using high temperature compressed air, or superheated steam, or other preheated gas as the medium. Compared with the ball mill and the gravel mill, the concentrate grade of the jet mill product containing iron-bearing quartzite is about 2 to 3% higher than that of the ball mill and the gravel mill, and the iron recovery rate is about 2 to 15% higher.

(7) Spiral classifier

The spiral classifier is a device matched with a wet ball mill and a ball mill to complete the grinding and grading. The specifications are expressed by diameter, and can be classified into a single spiral classifier and a double spiral classifier according to the number of spirals. According to the level of the liquid separation surface, it can be divided into high-grade, immersed and low-lying.

The classifiers produced by a factory in Henan mainly include four types of sorghum single helix and double helix, sinking single helix and double helix. The classifier is widely used in the concentrating plant to form a closed loop recirculating ore with the ball mill, or to classify the ore and fine mud in the gravity concentrating plant, and to classify the slurry in the metal beneficiation process, and to wash the ore. Desliming, dehydration and other operations during the operation. The classifier has the characteristics of simple structure, reliable operation and convenient operation.

(8) Hydrocyclone

The upper part of the hydrocyclone has a cylindrical shape, and the lower part has a conical shape. The center of the cylinder is inserted into an overflow pipe, and the outer side of the upper part has a feed pipe which is tangential to the outside. The hydrocyclone has been applied for many years in China's concentrator, mainly for fine fractionation, slurry concentration, dewatering and dewatering.

In summary, what kind of mineral processing methods and equipment should be used, combined with the actual situation of the enterprise and the characteristics of each mineral, I hope this article will be helpful to everyone.

Source: Tiandao Research Institute