For flotation concentrators, ore particle size (also known as grinding fineness) is an important factor affecting the final flotation index. Practice has shown that the appropriate particle size generally means that more than 80% of the useful minerals have been dissociated from the monomers. If the ore particles are too thick or too fine, even if the monomers have been dissociated, the flotation effect is not ideal. Let’s talk about the problems and solutions of the grinding particle size in the beneficiation and flotation process.
1. What is the effect of grinding particle size on flotation?
During flotation, overly coarse ore particles (greater than 0.1mm) and extremely fine ore particles (less than 0.006mm) will cause a poor flotation effect and low recovery rate.
During the flotation of coarse grains, the shedding force of the ore grains increases due to the larger weight. If the ore particles are too coarse, attaching to the air bubbles is difficult, causing metal loss and affecting the improvement of the concentrate grade. Therefore, it is necessary to:
- Use a sufficient amount of the most effective collector;
- Increase the aeration of the pulp to cause larger bubbles and increase the number of microbubbles precipitated in the water;
- The stirring intensity of the pulp should be appropriate;
- Properly increase the pulp concentration;
- When scraping the foam, the scraper should be quick and steady.
In the flotation of very fine particles (usually refers to the slime less than 5~10um),
- If it is too fine, it is easy to adhere to the air bubbles so that the buoyancy of coarse particles is reduced, the selectivity is poor, the sorting effect is poor, the flotation separation is complex, and the concentrate grade is affected;
- Due to the large specific surface of the ore slime, they will absorb a large number of flotation reagents in the pulp, which will reduce the concentration of the reagents in the pulp, destroy the normal flotation process, and reduce the flotation index;
- Because the slime is very fine and has a large surface area, the surface activity is increased, it is easy to work with various chemicals, it is not easy to sort, and it has strong hydration. So the foam is too stable, and it will cause difficulties during selection. Accurate, reduce the quality of the concentrate, and reduce the fluidity and concentration efficiency of foam products.
2. How to prevent and reduce too much slime in the grinding pulp?
Standard methods to prevent and reduce slime are:
- Reduce and prevent the generation of slime: multi-stage grinding process and stage beneficiation process can be adopted. It is necessary to correctly select the grinding and grading equipment to improve the classifier’s efficiency.
- Add agents to eliminate the harmful effects of ore slime: water glass, soda, caustic soda, etc., are commonly used. They can reduce flocculation and cover the effect of ore slime. To alleviate the harmful effects of a large number of adsorbents in the slime, consider adding drugs in stages;
- The ground raw ore is deslimed before flotation and discarded as tailings. If the content of useful components in the slime is high, the removed slime can also be flotation-treated separately or sent to water for treatment.
When desliming, commonly used methods are:
- classifier desliming;
- Hydrocyclone desliming;
- In special cases, a small amount of foaming agent can be added before flotation to remove the easily floating mud by flotation.
3. Why is it difficult for coarse particles to float, and what technological measures should be taken?
Coarse grinding can save grinding costs and reduce costs. In the flotation plant dealing with uneven ore distribution, under the premise of ensuring the recovery rate of roughing, there is a tendency to increase the fineness of rough grinding. However, due to the relatively heavy coarse particles, it is not easy to suspend in the flotation machine, and the chance of colliding with air bubbles is reduced. In addition, after the coarse particles are attached to the air bubbles, they easily fall off from the air bubbles due to their strong shedding force. Therefore, the flotation effect of coarse particles could be better under general process conditions. To improve the impact of coarse flotation, we can take the following technological measures:
- Use a collector with strong collecting power, and add auxiliary collectors such as kerosene and diesel to strengthen the collection of coarse particles, increase the adhesion and fixation strength of ore particles and air bubbles, and reduce shedding.
- Appropriately increase the mass fraction of the pulp to increase the buoyancy of the pulp. Under the premise of ensuring the stability of the foam layer, stir properly to promote the suspension of coarse particles and increase the chance of adhesion with air bubbles.
- Appropriately increase the inflation volume of the flotation machine, resulting in larger bubbles and the formation of “floating clusters” composed of large and small bubbles. This “floating cluster” has a greater buoyancy and can carry coarse grains float up.
- A shallow tank flotation machine is used to shorten the journey of mineralized bubbles to float up and reduce the falling of ore particles from the bubbles. Or use a special flotation machine suitable for coarse-grained flotation, such as ring-type flotation machines and Skenar flotation machines.
- Adopt a rapid and stable foam scraping device to scrape out the floating mineralized foam in time to reduce the re-falling off of mineral particles.
4. What are the reasons for fine particle flotation's difficulty and the technological measures are taken?
The flotation separation of fine-grained materials is difficult, mainly for the following reasons:
- The specific surface area of fine particles is large, and the surface energy is significantly increased. Under certain conditions, non-selective mutual condensation easily occurs between the surfaces of different minerals. On the other hand, due to the large surface energy of the fine particles, although they have a high adsorption force to the drug, their selective adsorption is poor, which makes it difficult to separate the fine particles selectively.
- The fine particles are small and less likely to collide with air bubbles. The quality of fine particles is small, and when colliding with air bubbles, it is difficult to overcome the resistance of the hydration layer between mineral particles and air bubbles, and it is difficult to attach to air bubbles.
The technical measures to solve fine particle flotation are as follows:
- Selective flocculation flotation. The flocculant is used to flocculate the target mineral particles or gangue fine mud selectively and then separate them by flotation.
- Carrier flotation. Use the ore particles of the general flotation size as the carrier so that the target mineral fine particles are covered on the carrier and floated. The carrier can use the same or different kinds of minerals. For example, fine-grained gold can be floated using pyrite as a carrier. Calcite is used as a carrier to float away fine particles of iron and titanium impurities in kaolin.
- Reunion flotation, also known as emulsification flotation. After the fine-grained minerals are treated with collectors, an oily foam with minerals is formed under the action of neutral oil. Collector and neutral oil can be made into emulsion before adding to the slurry. It is also possible to add neutral oil and collector to high-quality fraction (solids containing up to 70%) ore slurry, stir vigorously, control time, and then scrape out the upper layer of foam. This method has been used for fine-grained manganese ore, ilmenite, and apatite.