Technological measure of fine flotation

　　Fine often means slime less than 18 or 10 micron. Because fine-sized ore grain (slime) has the feature of light quality and big specific surface area, which causes ore grain to have a seires of special actions during pulp conditioning and flotation.
　　Seen from the action between fine and fine, because surface energy can increase greatly, different ore grains are easy to produce mutual setting effect and form non-selective aggregation and fines are easy to adhere to the surface of coarse fines and form slime shroud on a certain condition. Seen from the action between fine and medium, fine has great specific surface area and surface energy, therefore it has high agent absorption capacity, bad absorption selectivity and big surface solubility, which makes mine pulp hard to ion and increasing quality small and easily mechanical entraped t by water and foam. Seen fron the action between fine and foam, contact efficiency and adhesion efficiency decrease, which makes capture rate of foam to fine decrease and at the same time have the slime “armor” phenomenon of foam and affect the carrying capacity of foam.
　　 The above actions are the main resons which cause flotation speed of fine to become slow,selectivity to become bad, recovery rate to reduce and flotation index to become obviously serious.. in order to reduce and prevent the harmful effect of slime and intensify the flotation of fine, the following measures are often taken in the flotation practice in modern times: (1) eliminate and prevent slime from interrupting the flotation process and the main measures include:
　　 1)Desliming This is a method to eliminate the impact of slime. Classification is the commonly used method, for example classify slime wiith some size by using hydrocyclone before flotation or abandon it or treat slime and grit separately, that is separation of slime and sand. As to some slimes easy to flotate, add a little foaming agent before flotation to flotate ahead of time to remove.
　　 2)Add slime dispersant Dispersing slime fully can eliminate “phenomenon of slime covering ” and the harmful effect of non-selectivity and mutual setting between fines. The commonly used slime dispersants include: water glass, sodium carbonate and sodium hexametaphosphate and so on.
　　 3)Adding agent step by step. Adding collector step by step can keep the effective concentration of agent and improve selectivity.
　　 4)Reduce the pulp density.Reducing the pulp density can reduce slime pollution concentration foam on the one hand, and also reduce pulp viscosity on the other hand.
　　 (2) Selecting collector with chemiabsorption or chelation to fine minerals to improve the selectivity of flotation.
　　 (3) Apply chemical or physical method to increase the appearance size of fine mineral, improve flotation speed and selectivity of minerals waiting for separating. New processes which have been developed according to this principle in modern times include:
　　 1)Select ocfloatation Use flocculating agent to select purpose mineral or gangue slime of flocculable fine, then separate with flotation method. This method has been used in the flotation of fine hematite (United States Tilden separation factory).
　　 2)Carrier flotation. Use mineral partical with common size as carrier, make fine particle cover on the carrier, and then flotate with carrier. Carrier can be carrier (mineral) of the same kind and also be carrier (mineral)of different kind.
　　 3)Aggregation is slao called emulsion flotation Fine mineral is treated by collector, acted by neutral oil and form oily foam with mineral. This method has been used to separate fine manganese ore, ilmenite and phosphorite and so on. Its operating process condition is divided into two kinds: one kind is that collector and neutral oil mix and form emulsion and add it; the other kind is that add neutral oil and collector at first and stir violently in the mine pulp with high intensity (70% solid).
　　 (4) Reduce the size of bubble to realize micro-bubble flotation On a certain condition, reducing the size of bubble can increase the interface of gas and liquid, and at the same time increase colliding rate and sticking probability of fine, both of which are advantageable to the flotation of fine mineral. Main processes include:
　　 1) Vacuum flotation
　　 Use dropping equipment to separate out vacuum flotation of micro-bubble from liquid. The size of bubble is 0.1～0.5 micrometer. As the research shows, separating out barite, fluorite and quartz of micro-bubble flotation fine is very effective. When the other conditions are the same and using normal flotation, grade of barite concentrate is 54.4%, recovery rate is 30.6%, but grade can be increased to 53.6%～63.6% by using vacuum flotation and the corresponsing recovery rate is 52.9%～45.7%. 2）Electrolytic floatation
Using the method of brine electrolysis to get micro-bubble. Commonly, the size of micro-bubble is 0.02～0.06 micrometer. When it is used to flotate fine tin ore, only using electrolysis hydrogen bubble to flotation, recovery rate of rougher flotation is obviously higher than normal flotation, increasing from 35.5% to 79.5%, at the meantime, grade increases by 0.8%. Besides that, other new process research has been done in recent years, for example, control dispersion flotation and offtake flotation are used for the flotation of iron ore and black tungsten slimes, and both of them have a good effect.