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Click to add WeChatAs an important metal in modern industry, lithium is widely used in many fields such as batteries, ceramics, and glass. Spodumene is one of the main mineral raw materials for extracting lithium. Since it often coexists with a variety of gangue minerals, efficient mineral processing methods are required for separation and enrichment. Spodumene flotation technology plays a key role in this process.
Spodumene (LiAl (SiO₃)₂) does not exist in a pure state in nature, and often coexists closely with gangue minerals such as mica, feldspar, and quartz. Although these gangue minerals differ from spodumene in physical and chemical properties, the differences are not significant enough, and it is difficult to achieve efficient separation through simple physical methods such as gravity separation and magnetic separation. For example, the density of spodumene and quartz is relatively close, and the effect of gravity separation is not good; and spodumene itself is non-magnetic, and magnetic separation cannot effectively enrich it. Flotation can utilize the subtle differences in the physical and chemical properties of the mineral surface, and with the help of flotation agents, achieve efficient separation of spodumene and gangue minerals, thereby obtaining high-grade lithium concentrate, providing high-quality raw materials for subsequent lithium extraction and processing.
Spodumene has a unique crystal structure and surface properties. The lithium, aluminum, silicon and other atoms on its surface form specific chemical bonds and surface active sites. Compared with common gangue minerals, the wettability and charge distribution of spodumene surface are different. When in aqueous solution, the surface of spodumene will carry a certain charge due to hydrolysis and other effects, and this charge characteristic affects the adsorption behavior of flotation agents on its surface. The surface properties of gangue minerals such as quartz are different. Through the selective action of flotation agents, the hydrophobicity of the surface of spodumene and gangue minerals can be changed, thereby achieving separation. The role of flotation agents in the process is as follows:
Collector: Commonly used are oleic acid, oxidized paraffin soap, etc. Taking oleic acid as an example, in an alkaline slurry environment, oleic acid will dissociate into oleate ions. Lithium, aluminum and other metal ions on the surface of spodumene can react chemically with oleate ions to generate insoluble metal soaps, such as lithium oleate and aluminum oleate. These metal soaps form a hydrophobic film on the surface of spodumene, which greatly enhances the hydrophobicity of the surface of spodumene, making it easy to attach to bubbles, thereby achieving flotation.
Adjuster: The adjuster is mainly used to adjust the properties of the pulp and the activity of the mineral surface in spodumene flotation. Sodium carbonate is commonly used, which can not only adjust the pH value of the pulp, but also eliminate the influence of harmful ions (such as calcium and magnesium ions) in the pulp to prevent them from interfering with the effect of the collector and spodumene.
Frothing agent: The function of the frother is to generate a large number of stable and uniform bubbles in the pulp, providing a carrier for the flotation of minerals. Pine alcohol oil is a commonly used frother in spodumene flotation, and its molecular structure contains hydrophilic and hydrophobic groups. In the ore pulp, the foaming agent molecules will be arranged in a directional manner at the gas-liquid interface, with the hydrophilic group facing the water phase and the hydrophobic group facing the gas phase, thereby reducing the surface tension of the gas-liquid interface and promoting the formation and stability of bubbles.
Chemical adsorption and surface chemical reaction: During the flotation of spodumene, the collector undergoes chemical adsorption and surface chemical reaction with the spodumene surface. Taking fatty acid collectors as an example, their reaction with metal ions on the surface of spodumene is a typical chemical adsorption process. This adsorption not only changes the charge distribution on the surface of spodumene, but also forms a hydrophobic metal soap film. From a microscopic point of view, the metal ions and collector molecules are combined through chemical bonds, which significantly changes the surface properties of spodumene. Studies have shown that through analytical methods such as X-ray photoelectron spectroscopy (XPS), changes in the elemental composition and chemical state of the spodumene surface after the adsorption of the collector can be detected, further confirming the occurrence of chemical adsorption and surface chemical reactions.
The influence of double layer theory and electrokinetic potential: According to the double layer theory, when spodumene particles come into contact with aqueous solution, a double layer structure will be formed on their surface. In alkaline slurry, the surface of spodumene is negatively charged due to hydrolysis and other effects, and the cations in the solution will form a diffusion layer near the surface. When flotation reagents are added, the reagent ions will participate in the formation and change of the double layer. For example, collector ions will change the charge density on the surface of spodumene during adsorption, thereby affecting its electrokinetic potential (ζ potential). When the absolute value of the potential reaches a certain level, the hydrophobicity of the spodumene surface is enhanced, and the adhesion to the bubbles is increased, which is conducive to flotation. Through electrophoresis experiments and other means, the potential changes of spodumene particles under different reagent conditions can be measured to gain a deeper understanding of the flotation mechanism.
Changes in surface energy and wetting contact angle: During flotation, the hydrophobicity of the mineral surface is closely related to the surface energy and wetting contact angle. Before treatment, spodumene has a higher surface energy, stronger hydrophilicity, and a smaller wetting contact angle in water. When the collector is adsorbed on the surface of spodumene, the hydrophobic film formed reduces the surface energy of spodumene and increases the wetting contact angle. When the contact angle is greater than 90°, the mineral surface shows hydrophobicity and is easy to attach to bubbles. Through equipment such as contact angle measuring instruments, the change in contact angle of spodumene under the action of different reagents can be directly measured, which intuitively reflects the change in surface hydrophobicity and provides an important basis for the study of flotation mechanism.
Slurry pH value is one of the key conditions for spodumene flotation. Different pH environments will affect the charge properties of spodumene and gangue mineral surfaces, the degree of dissociation and existence form of flotation reagents, and thus affect the flotation effect. Under alkaline conditions (pH 8-11), fatty acid collectors exist in ionic form, which is more conducive to chemical reaction with metal ions on the surface of spodumene and enhance the collection effect. At the same time, the alkaline environment can inhibit the flotation of some gangue minerals (such as quartz and feldspar) and improve the selectivity of spodumene flotation. However, too high a pH value may lead to the formation of calcium hydroxide and other precipitates in the slurry, affecting the flotation process, so the pH value needs to be precisely controlled. A pH meter is usually used to monitor the pH value of the slurry in real time, and it is regulated by adding adjusters such as sodium carbonate and sodium hydroxide.
Grinding fineness directly affects the degree of monomer dissociation between spodumene and gangue minerals, and thus affects the flotation effect. Spodumene needs to be ground to a suitable particle size so that spodumene can be dissociated from gangue minerals as much as possible, while avoiding over-crushing. Too coarse grinding particle size will lead to incomplete dissociation of spodumene and gangue minerals, affecting the recovery rate; while too fine grinding particle size will produce a large amount of fine mud, which will not only adsorb on the surface of spodumene, hindering the action of the collector, but also increase the viscosity of the slurry, affecting the adhesion of bubbles and minerals, and reducing the flotation selectivity. Generally speaking, the grinding fineness of spodumene is required to reach -0.074mm, accounting for about 60%-80%, and the specific fineness needs to be determined by experiment according to the properties of the ore.
Collector dosage: When using oleic acid as a collector, the general dosage is between 500-1500g/t ore. The specific dosage depends on the content, grade and other mineral composition of spodumene in the ore.
Adjustment dosage: Sodium carbonate dosage is generally 1000-3000g/t ore, mainly used to adjust the pH value of slurry and eliminate the influence of harmful ions; water glass is used as an inhibitor and dispersant, and its dosage is usually 500-2000g/t ore. The specific dosage needs to be adjusted according to the content and properties of gangue minerals to achieve the best inhibition and dispersion effect.
Frother dosage: The amount of frother affects the number, size and stability of bubbles. An appropriate amount of frother can produce uniform, stable and sufficient bubbles, providing a good carrier for the flotation of spodumene. Generally, the dosage of frothers such as pine oil is 50-200g/t ore, and the specific dosage needs to be optimized according to factors such as the type of flotation equipment and the properties of the ore pulp.
The flotation time also has an important influence on the flotation effect of spodumene. Within a certain time range, as the flotation time increases, the contact opportunities between spodumene and the collector and bubbles increase, and the recovery rate gradually increases. However, when the flotation time is too long, the spodumene that has been floated up may fall off for the second time, and the gangue minerals may also be mixed into the foam product due to long-term stirring, reducing the grade of the concentrate. Generally, the flotation time of spodumene is about 15-30 minutes, and the specific time needs to be determined through experiments based on factors such as the properties of the ore, the flotation process and the equipment. In actual production, segmented flotation can be performed by setting different flotation tanks, and the flotation time of each segment can be reasonably controlled to achieve the best flotation index.
Spodumene flotation is a complex physical and chemical process involving the mutual influence of many factors such as the surface properties of the mineral, the action of the flotation agent, and the flotation conditions. In-depth understanding of the principles and mechanisms of spodumene flotation and precise control of flotation conditions are of great significance for improving spodumene flotation efficiency and obtaining high-grade lithium concentrate, and also provide solid technical support for the efficient development and utilization of lithium mineral resources.
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