Introduction to the method of flake graphite beneficiation

Graphite is one of the crystalline minerals of carbon element. It has the characteristics of high temperature resistance, corrosion resistance, thermal shock resistance, high strength, good toughness, high self-lubricating strength, thermal conductivity, electrical conductivity, plasticity, coating, etc. It is widely used in metallurgy, machinery, electronics, chemical industry, light industry, aerospace and refractory materials and other industries. It is one of the non-metallic materials indispensable for the development of high-tech today.

In addition to the traditional uses of graphite, the fastest growing in recent years is spherical graphite used in the lithium (ion) battery industry. Graphite is divided into two categories according to its crystallization: crystalline graphite (flake) and cryptocrystalline (earthy) graphite.

The characteristic of flake graphite is that its grade is not high. Its fixed carbon content generally does not exceed 10%, and it can reach more than 20% in particularly enriched areas. Because of its flaky structure and good surface properties, it has good natural floatability and is one of the best floatable minerals in nature. However, due to its special properties, the flake structure is easily damaged during the selection, especially during the grinding process, so it has special requirements for the beneficiation process, that is, while ensuring the concentrate grade requirements, the yield of large flake graphite should be increased as much as possible.

Flake graphite is divided into large flake graphite and fine flake graphite according to the size of its flakes. Usually, large flakes refer to flake graphite with mesh sizes of +50, +80, and +100. Flake graphite with mesh sizes below these is called fine flake graphite. Large flake graphite has greater value than fine flake graphite. Therefore, in the beneficiation process, the flakes of graphite should be protected as much as possible. There are many factors that affect the damage of large flakes and the concentrate grade, such as grinding media, grinding fineness, number of regrinding stages, flotation equipment, etc. At present, research work is mainly focused on grinding equipment, number of regrinding stages, and new flotation processes.

Grinding equipment and media

In graphite beneficiation, the quality of grinding directly affects the grade of concentrate and the yield of large flakes. Therefore, it is crucial to choose the regrinding equipment reasonably. Grinding media of different shapes have different effects on the protection of large graphite flakes. The results show that due to the different shapes of grinding media and the different ways of contact between the media and the minerals, the grinding efficiency and the degree of protection of large graphite flakes are also different.

Gravity separation

Gravity separation can also play a role in early recovery of flake graphite and protection of flake structure. According to data, the density of quartz-based gangue is about 2.6, while the density of pure graphite flakes is 2.24. The density difference between the two is not large, and the ratio is small. It is an extremely difficult mineral to be selected, and it is almost impossible to separate it by density difference alone. However, experiments have shown that when the ore is separated by a shaking table, in addition to the role of density difference, minerals of different shapes can also play an enrichment role. Under the premise of similar density, graphite flakes have large water resistance due to their large water-facing area, sink slowly, and stay on the upper layer of the bed surface, while gangue minerals with small water-facing surface have small water resistance, sink quickly, and stay on the bottom layer of the bed surface. Therefore, graphite flakes are subject to large forces from the horizontal water flow on the bed surface and small forces from the vertical water flow, while gangue minerals are the opposite, resulting in obvious zoning and achieving the purpose of sorting.

Grinding-floating new process

Flake graphite has a non-polar mineral surface and is easier to float with neutral oil collectors, which is only for graphite ores with good monomer dissociation. However, graphite itself has lubricity and is difficult to separate from gangue monomers during grinding. Especially for the sorting of fine particles, the sorting efficiency of ordinary flotation machines is low, and the process flow is long (generally three grindings and seven selections), so a simple process or new method that protects large flakes and collects more and earlier should be selected.