The flotation process of lead-zinc ore is one of the important means to extract lead-zinc ore, mainly because its mineral composition elements are more, and the floatability has obvious differences. Flotation can obtain better lead and zinc minerals, but many factors affect the flotation effect, including non-adjustable factors and adjustable factors. This article will explore the influence of different factors on the flotation process of lead-zinc ore from six aspects: flotation particle size, pulp concentration, reagents, foam, temperature, and water quality.
Flotation Particle Size
Flotation particle size is often expressed by grinding fineness. During flotation, not only are the mineral monomers required to be dissociated, but also the minerals are required to be ground to a suitable fineness. If the mineral particles are too coarse, even if the minerals have been dissociated, they will not float because they exceed the floating capacity of the bubbles. The upper limit of the flotation particle size of various minerals is different. For example, sulfide ores are generally 0.2-0.5mm, and non-sulfide ores are 0.25-0.3mm. If the mineral particles are ground too fine, such as those smaller than 0.01 mm, they will not float well. Therefore, the requirements of flotation for grinding are that the mineral monomers are dissociated, but not too coarse or "over-crushed". For impregnated ores with excellent interbedded particle sizes, since the monomer dissociation degree requires very fine grinding, it is usually necessary to add a sludge dispersant, or use selective flocculation flotation (adding selective flocculants) or perform "mud and sand separation" (i.e., fine mud and coarse sand are treated separately).
Pulp Concentration
The adjustment of slurry before flotation is an important part of the flotation process. Before the slurry enters the flotation machine, it must be reasonably adjusted (i.e., "slurry adjustment") so that the flotation machine can fully play its role. In most cases, the concentration of slurry adjustment and roughing operation is almost the same as the concentration of classification overflow. The adjustment of slurry concentration is limited by fineness. When the fineness is required to be fine, the classification overflow is thinner; when the fineness is required to be coarse, the classification overflow is thicker. In actual production, the roughing operation uses a thicker slurry to save reagents; the use of a thinner concentration of ore for the fine selection is conducive to improving the concentrate grade; the concentration of the scavenging operation is affected by the roughing operation and is generally not controlled separately. The slurry concentration of the roughing and scavenging operation also affects the flotation time, because when the flotation machine is configured to a certain extent, its effective volume is a determined slurry concentration, and the flow time (i.e., flotation time) is longer; the thinner the slurry, the shorter the flow time.
Reagents
The adjustment of reagents during flotation includes exerting the efficacy, reasonable addition, mixed use, adjusting the concentration of reagents in the slurry, and controlling the pH value.
1. Exerting the efficacy of reagents
The dosage and effect of the same reagent are different when used in different ways. This is especially obvious for reagents that are insoluble in water or have low solubility in water. The main measures to exert the efficacy of the reagents are:
Preparation with solvent
Neutral oil collectors that are insoluble in water appear as large droplets in water, which not only have poor effects, but also increase the dosage. If they are dissolved in special solvents, such as oleic acid dissolved in kerosene, the collection effect can be improved.
Prepared into emulsions
Some solid reagents that are not easily soluble can be prepared into emulsions for use. For example, lime has a very low solubility in water, so it can be ground to 0.1~0. 01mm, mixed with water to form lime milk, and added.
Saponification
For fatty acid collectors, saponification is the most commonly used method. For example, in iron ore flotation, when preparing tar oil (collector), in order to saponify it, about 10% sodium carbonate is added, and it is heated to make a hot soap solution for addition.
2. Mixed use of drugs
Mixed use of drugs has been widely used in practice. The mixed use of various collectors is based on the uneven surface of the mineral and the synergistic effect between the agents. For example, the mixed use of xanthate with different warp chain lengths improves its efficacy. When different types of collectors are mixed, one collector is often used as the main one, and the other is used as an "auxiliary collector" or "enhancer". The mixed use of inhibitors is even more common. For example, hydride is mixed with zinc sulfate, sulfite is mixed with zinc sulfate, sulfur dioxide is mixed with starch, etc. The purpose is to enhance the inhibitory efficiency of these agents. Mixing frothers can also improve their efficiency.
3. Reasonable addition of agents
The purpose of a reasonable addition of agents is to ensure that the optimal concentration of agents is maintained in the ore pulp. According to the characteristics of the ore, the nature of the reagents, and the requirements of the process, appropriate dosing points can be selected, and different dosing methods can be used to achieve the purpose of maintaining the optimal reagent concentration in the slurry. There are often many types of flotation reagents added to the slurry, plus the various original components of the slurry, the interactions between them are very complex, and they are mutually restricted. When a reagent system is selected, it is often when these interactions reach a certain balance. Improper use of reagents, sometimes as long as one reagent is added more or less, it may break the balance and cause chaos in the entire process.
Selection of dosing points
The dosing point has a great relationship with the effectiveness of the reagents. PH adjusters and inhibitors are mostly added to the mill. Some relatively insoluble collectors can also be added to the mill. Reagents that can react and offset each other are required to be added separately. Generally, the second reagent is added after the first reagent has fully reacted. For example, the addition of copper sulfate and xanthate, calcium chloride and oleic acid, all require a certain order.
Dosing method
The reagents can be added at once or in batches.
When adding at one time, the concentration of the reagent is higher at one point, which can improve the initial flotation speed. It is also convenient to add and is often used. Adding in batches or point by point can maintain the reagent concentration along the flotation line basically consistent.
For the following situations, batch addition is adopted:
- First, reagents that are easily carried away by foam. For example, when oleic acid is used as a collector, it has foaming properties. If it is added at one point, it is easy to be carried away by foam;
- Second, reagents that are easy to react in the slurry, such as carbon dioxide, sulfur dioxide, etc., if only added at one point, the reaction will quickly fail.
- Third, reagents that require strict control of dosage, such as sodium sulfide, will lose their selectivity if the local concentration is too large, so they should be added in batches.
4. Slurry pH control
Slurry pH is an important factor in the flotation process. On the one hand, it affects the flotation properties of the mineral surface; on the other hand, it affects the effects of various flotation reagents. For the flotation of various ores, each has a relatively suitable pH range.
Foam
Froth flotation is a process of sorting at the liquid-gas interface, so foam plays an important role. The size and number of bubbles, the stability of the foam, and the thickness of the foam layer are related to the type of flotation machine used (mainly the amount of aeration and stirring intensity), the nature of the ore, the reagent system, and other factors. Under the condition that other conditions remain unchanged, the thickness of the foam layer is mainly adjusted by controlling the slurry level. Practice has shown that in order to stabilize the flotation operation, it is necessary to maintain a certain thickness of the foam layer, and when the foam layer is thicker, the concentrate grade is higher.
Temperature
The slurry temperature can affect the chemical reaction rate between the mineral surface and the reagents, and often plays an important role in the flotation process. However, most flotation plants currently perform flotation at room temperature, that is, the slurry temperature is not controlled and changes with the air temperature. Heating flotation comes from two requirements. One is the nature of the reagents. Some reagents must be at a higher temperature to play their effective role; the other is that some special flotation processes require the temperature of the minerals to be increased to achieve the purpose of mineral separation. Steam or hot water is commonly used for slurry heating. With the development of complex sulfide ore flotation technology. It is necessary to find a more effective separation method. Therefore, many studies have been conducted on the heating flotation separation of copper-lead, copper-molybdenum, zinc-sulfur, copper-nickel, etc., and they have been applied in some mineral processing plants at home and abroad. For example, in the separation of copper-sulfur mixed concentrates, steam heating can replace lime sulfur suppression to float copper.
Water Quality
Flotation is carried out in water. The "hardness" of water (depending on the content of Ca2+ and Mg2+), the "turbidity" of water (the content of solid impurities per unit volume), and the composition also affect flotation. The water used for flotation varies from place to place and time to time. In the study of flotation technology, attention must be paid to the quality of water used for flotation. In order to save water resources, the utilization of return water is increasingly valued. The characteristic of flotation return water is that it contains more organic and inorganic reagents. The use of return water can save reagents, but due to the complex composition, improper use will affect the sorting effect. Practice has proved that the use of return water for flotation of monometallic ores is relatively simple, while the recycling of return water is more complicated when sorting polymetallic ores. It is necessary to conduct a comprehensive analysis of the water quality of each flotation section before a proper decision can be made on the utilization plan.
Conclusion
In summary, the flotation efficiency of lead-zinc ores is influenced by multiple factors, both uncontrollable and adjustable. Among the key parameters examined—particle size, pulp density, reagents, froth characteristics, temperature, and water quality—each plays a critical role in determining the selectivity and recovery of valuable minerals.
Optimizing particle size ensures proper mineral liberation, while controlling pulp density balances froth stability and kinetic efficiency. The selection and dosage of flotation reagents directly impact mineral selectivity and froth properties. Meanwhile, froth stability and temperature adjustments can enhance or hinder bubble-particle attachment. Lastly, water quality—often overlooked—significantly affects reagent performance and overall process stability.
To maximize Pb-Zn separation and recovery, a holistic approach that systematically optimizes these factors is essential. Future research could further refine reagent systems and automation to adapt to varying ore characteristics and environmental constraints.