Molybdenum metal has the characteristics of high temperature resistance, high melting point, and high rigidity. Most of the molybdenum ores currently developed and utilized are molybdenite, which is recovered by flotation process. The embedded particle size of molybdenite is relatively fine, and it is often associated with minerals such as pyrite, chalcopyrite, and galena.
The difficulty in molybdenite flotation lies in chalcopyrite and galena. The three have similar floatability, and galena is difficult to suppress after dissociation. Therefore, how to separate chalcopyrite and galena has become a research focus.
1.Crushing and grinding
Before the flotation of molybdenite, crushing and grinding are extremely critical preparation links. Generally speaking, two-stage or three-stage crushing and two-stage grinding operations are generally used in practice. The current trend is to use a gyratory crusher for coarse crushing and then use a semi-autogenous mill and a cyclone to form a closed-circuit grinding.
The purpose of crushing is to reduce the particle size of the original ore, making it more conducive to the subsequent grinding and flotation process. The focus of the grinding operation is to make the molybdenite dissociate as much as possible and achieve a suitable fineness to create good conditions for flotation. For example, it is generally necessary to grind to a certain particle size as much as possible before flotation, first obtain the waste tailings and coarse concentrate to ensure a higher recovery rate, and then a series of regrinding and selection are carried out to select the final concentrate.
For unevenly embedded molybdenite, if the waste tailings cannot be obtained during coarse grinding, stage flotation can be used. Moreover, practice has proved that when regrinding molybdenite concentrate, the recovery rate is better when using pebbles than when using steel balls, because pebbles have no harmful effect on flotation. Different grinding methods will affect the subsequent flotation. Insufficient grinding fineness may lead to insufficient dissociation of molybdenite monomers, affecting the flotation effect and recovery rate; while too fine grinding particles may produce sludge, interfere with the flotation process, and reduce the quality of the concentrate.
2.Molybdenite flotation
Molybdenite flotation has clear operating procedures and condition control requirements for each link from roughing, concentrating to scavenging.
(1) Roughing stage
In the roughing stage, attention should be paid to controlling the pulp concentration. Generally, a thicker pulp is used for roughing to ensure a high recovery rate and save reagents. Collectors such as kerosene and frothers such as 2# oil are usually added, and the flotation time is about 3-4 minutes. For example, a common operation is to grind the raw ore to a certain fineness and then put it into the mixing tank, control the pulp concentration within a suitable range (such as 33-35%), add lime to adjust the pulp pH to 8-9.5, and then start the roughing process.
(2) Concentration stage
The roughing concentrate usually undergoes 1-2 rounds of concentrating, and then undergoes multiple rounds of concentrating, with the total number of concentrating times reaching more than 6 times. The pulp concentration during concentrating is relatively thinner than that during roughing, which is beneficial to improving the quality of the concentrate. In addition, if there are other impurities such as sulfides in the ore, inhibitors must be added to remove most of the sulfides from the concentrate, and other sulfides suppressed during concentrating cannot be returned to the roughing circuit. At the same time, in order to improve the recovery rate of molybdenum in the concentrate (obtained from an ore containing a small amount of other sulfides), it is also appropriate to add kerosene to stir the rough concentrate before concentrating and the scavenged concentrate before returning to the roughing operation.
(3) Scavenging stage
It is mainly to further process the roughing tailings and recover the remaining molybdenite as much as possible. The concentration of scavenging is always thinner than that of roughing, and its flotation time is roughly 3-4 minutes. The scavenging concentrate returns to the roughing operation, and the scavenging tailings are the final tailings discharged.
In the entire flotation process, the stirring intensity of the slurry should also be reasonably controlled to ensure that the reagent can be fully mixed with the slurry, the mineral particles can be well contacted and attached to the bubbles, etc., to ensure that the flotation process is carried out smoothly and efficiently, and finally obtain high-quality molybdenum concentrate that meets the requirements.
