Why is it difficult to separate fine-grained lean hematite and how?

Fine-grained lean hematite is a hexagonal oxidized mineral, which is widely distributed in nature. It is an important iron-making raw material and a raw material for red pigments. It has a very low grade and a very fine particle size, leading to much difficulty to separate iron ore. Usually we grind the useful mineral embedding particle size to 74~0μm, and the monomer dissociation degree of hematite mineral can reach more than 90%, which is called fine-grained hematite, and the iron ore that needs to be processed is collectively called lean ore. The fine-grained lean hematite refers to the hematite whose iron grade is less than 25%, and when it is ground to less than 30 μm, the dissociation degree of the iron mineral monomer can reach more than 95, which is called fine-grained lean hematite.

This article will introduce the significance, difficulties and operational suggestions of fine-grained lean hematite separation.

?1.Significance of Fine-grained Poor Hematite Separation

China's iron ore reserves rank fourth in the world. Although the reserves are large, China's iron ore has the characteristics of many small mines and few large mines, many lean ores and few rich mines, many associated ores and difficult mining and separation. There are great disadvantages, so it is of great significance for the development and utilization of poor, lean, fine, miscellaneous, and difficult-to-process fine-grained lean hematite ore.

2. What are the difficulties in the separation of fine-grained lean hematite?

2.1 The grade of the hematite ore itself is very low. China's hematite reserves account for half of the country's iron ore reserves, but the average ore grade is less than 30%, and the rich iron ore (more than 55% iron content) in the reserves only accounts for 2.7% of the world's iron ore. And lean hematite ore (20-40% iron content) accounts for 97% of the national reserves.

2.2 There are many compound ores with multi-element symbiosis, and the ore bodies are complex. The symbiotic iron minerals of hematite in China include magnetite, limonite, siderite, false hematite, specularite and pyrite, etc. Gangue minerals include quartz, amphibole, actinolite, etc.

2.3 Weak magnetic hematite ore embedded with fine grains has small mass, large specific surface area and low specific magnetic susceptibility coefficient. Because the magnetic susceptibility coefficient of ore particles is low, the force in the magnetic field is small. Also, due to the small difference with gangue particles, even under strong magnetic field , it is also easy to be mixed with gangue, causing more difficulty to separation effectively.

2.4 There is a lack of perfect hematite beneficiation technology. At present, the commonly used method for beneficiation of fine-grained lean hematite is weak magnetic separation - strong magnetic separation - reverse flotation process, which is a very classic beneficiation method. The magnetic induction intensity of the strong magnetic separation equipment used in this method is generally 1~1.5T, but the recovery rate of the magnetic separator with this magnetic field strength to the fine-grained hematite with a particle size of less than 30 μm is less than 40%, thus the recovery rate is very low. . In the early days, there was also a magnetization roasting process, which was suitable for processing ores with a particle size below 25mm and fine-grained hematite minerals with a particle size of 3-0mm. However, the reduction speed of this method was slow and uneven, leading to unsatisfactory product quality and high production cost.

3. To increase the beneficiation rate of fine-grained lean hematite, we can refer to the following operation suggestions:

3.1 Selective grinding operation to improve monomer dissociation

The coexistence of under-grinding and over-grinding of hematite is the most prominent problem in the beneficiation technology of fine-grained lean hematite. Therefore, it is targeted to grind the ore, and the worn-out qualified particle size is efficiently recovered in the first time, which is the key to improving beneficiation efficiency. If the degree of dissociation is only increased mechanically by reducing the size of ore particles, it will inevitably result in the coexistence of insufficient dissociation and over-grinding operation.

3.2 Using efficient flotation reagents

Weak magnetic separation - strong magnetic separation - reverse flotation process is a commonly used process for fine-grained lean hematite. The commonly used flotation reagents are NaOH, causticized starch, lime and fatty acid collectors, but these reagents haven’t help in flotation process to achieve ideal recovery, so improvements on reagents can be considered.

3.3 Improving the magnetic properties of the magnetic separator

Strong magnetic separation equipment is the main equipment for processing fine-grained lean hematite. However, the current strong magnetic separation equipment is not ideal for the recovery rate of fine-grained lean hematite less than 30 μm. Thus, the magnetic induction intensity of the magnetic separation equipment can be increased, and the magnetic induction intensity of the magnetic separation equipment can be increased at 1~1.5T to 1.7T or 1.8T, or even higher (this technology already exists, but research and discussion are still needed in practical applications).

?The significance, difficulties and operational suggestions of fine-grained lean hematite separation are listed. In the separation of fine-grained lean hematite, the above methods can be used for reference. In actual beneficiation, it is necessary to find a reliable mining enterprises in the country conduct beneficiation tests to determine the ore composition and properties, and make a reasonable flotation process that meets their own mine conditions based on the analysis results and actual experience.