The role of flotation agent (1)
1. Surfactant adsorption form (1) Adsorption form 2. The chemisorbed surfactant chemically reacts with the lattice ions (or atoms) on the surface of the mineral, and electron transfer or electron sharing between the particles participating in the reaction forms an ionic bond, a covalent bond or a coordination bond on the surface of the mineral. The adsorption of the bond is chemical adsorption. Since chemisorption is extremely selective and irreversible, it can be carried out with extremely low concentrations of adsorbed particles and does not desorb with a decrease in the concentration of adsorbed ions in the solution. Particles that undergo chemisorption cannot easily move along the surface of the mineral. A certain activation energy is required to move from one adsorption center to another, and there is no need for activation energy. Generally, chemical adsorption produces a monomolecular surface compound on the surface of the mineral, changing the properties of the mineral surface. 4. Adsorption double logarithmic map The chemical adsorption double logarithmic map of flotation agent interacting with minerals (p Mn+ -pH map) was proposed by Swedish scholar Du Rietz on the basis of Bjerrum map. The calculation basis is based on The size of the solubility product reflects the ability of the agent to act. The ordinate is the drug ions react with the metal ions generated a mineral precipitate the desired metal ion concentration negative logarithm pMe n +, the abscissa is the pH, which reflects the effect of various drugs relative to the mineral and metal ions acting size The upper pH limit is as in Example 1. This pM n+ -pH double logarithmic plot can also be generalized to the pM n+ -pc double logarithmic plot, whereby the concentration required for the flotation of a particular mineral by the collector can be determined, as in Example 2. Fig. 3 is drawn from the equations (1) and (2), and the horizontal line below indicates that the concentration of the metal ion required to form the diced yellow drug is small and is easy to function. The intersection of the horizontal line and the oblique line indicates the upper limit of the mineral flotation pH of the metal ion. It can be seen that the order of the action of the butyl xanthate and these ions is: Cu 2+ >Pb 2+ >Fe 2+ ～Zn 2+ pZn 2+ =pL SZnX2 -2pc Carbon number n 2 3 4 5 6 7 8 At pH=3.5, the concentration of Zn 2+ ions dissolved by ZnS is pZn 2+ = 4.3~5.2 (different differences depending on the solubility data). In Figure 4, the two horizontal lines are drawn. The shaded part between the two intersections is the concentration range of the xanthate required for flotation of sphalerite at pH=3.5, from 10-2 mol of the xanthate. /L drops to about 5 × 10-5mol/L of xanthate. Compared with the concentration required for the rapid recovery of the sphalerite flotation recovery, the corresponding concentration is calculated, which shows a good correspondence with the experimental results. 2. Electrostatic adsorption Electrostatic adsorption is the main form of some ionic surfactants and the surface of charged particles. It is believed that ionic polymers are generally adsorbed on the surface of ore particles having opposite charge signs. For example, the adsorption of polyvinylpyridine on the surface of negatively charged quartz and the adsorption of polystyrene sulfonate on the positively charged hematite particles under natural pH conditions. Table 1 Cetyl polyoxyethylene ether C16 (EO) n adsorption molecular area Adsorption of the polymer on the surface of the ore particles results in changes in the surface properties of the ore particles, such as surface electrical properties, solvation properties, rheological properties of the interfacial layer, and wettability. Lapped flange is the same to loose flange norms of DIN2641 DIN2642 EN1092-1/02 PN6 PN10 PN16 steel of S235JR P235GH P245GH P250GH and ISO9624 PN10 PN16 steel lapped flanges, lapped flange or loose flange is similar to Plate Flange but difference for the flange center hole, loose or lapped flange have a bevel of 45 or other degree in the center hole of flanges. Lapped loose Flange Pn10, lapped loose flange pn16, din2642 loose flanges, en1092-1 type 02 lapped flanges, iso9624 lapped flanges Jinan Hyupshin Flanges Co., Ltd , https://www.iflange.com
The adsorption of surfactant at the mineral/solution interface is only physical adsorption and chemical adsorption. If no electron migration occurs during the adsorption process, the process is regarded as physical adsorption. This process is reversible. , non-selective; if electron migration occurs during adsorption, it is chemisorbed, irreversible and highly selective. It is extremely useful to study the adsorption system by infrared spectroscopy to identify whether electron migration occurs during the adsorption process. If the component of the study is physical adsorption, the spectrum of the adsorbent-adsorbent system is simply a superposition of the respective spectra of the adsorbent and the adsorbate, and no new adsorbent bands appear. However, for the chemisorbed component, a certain change spectrum can be obtained (compared with the combination of the map representing the adsorbent plus the adsorbate map), and a certain shift of the new band and other bands of the adsorbate can be observed.
1. Physical adsorption Physical adsorption mainly occurs through electrostatic force (ion adsorption) and van der Waals force (molecular adsorption). When ion adsorption occurs in the Stetn layer, it is characteristic adsorption, which causes the potential to change; when it occurs in the diffusion layer, it is the diffusion layer, which is represented by the compressed electric double layer; when it occurs in the electric double layer, it is double Adsorption in the electric layer. When the molecular adsorption is adsorbed by a non-polar group and a non-polar surface, it is called hydrophobic adsorption, which is a weak molecule adsorption, which is an intermolecular dispersion force adsorption; when the molecule is adsorbed by a polar group and a polar surface, it is a dipole. Molecular adsorption is a strong molecular adsorption; when the molecule is adsorbed by hydrogen bonds, it is a strong molecular adsorption, which has the property of transition to chemical adsorption, such as the adsorption of particles by neutral polyacrylamide.
There are generally four types of ionic surfactants adsorbed on the surface of the ore particles: 1 electrostatic adsorption; 2 characteristic adsorption; 3 chemical adsorption; 4 hydrophobic adsorption. The first three adsorptions occur on the charged polar surface and the latter adsorption occurs on the hydrophobic (non-polar) surface.
When the concentration is very low, the adsorption of the alkylsulfonate ion, the alkyl sulfate ion and the amine ion on the surface of the oxidized mineral belongs to electrostatic adsorption. Such as cetyl trimethylammonium bromide bromide (CTAB) in phosphate minerals and suction surfaces are calcite, since negatively charged active site is far less than the calcite surface charged phosphate minerals, so closely spaced adsorbed monomolecular layer Adsorption and desorption experiments have shown that this adsorption has good reversibility. As the concentration increases, the adsorption of the ionic surfactant on the oppositely charged surface changes from electrostatic ion exchange adsorption to hemi-micelle adsorption and double-layer adsorption, at which point the solid surface changes from hydrophobic to hydrophilic.
The adsorption of polyether nonionic surfactants on the surface of non-polar minerals is a typical example of the interaction of intermolecular dispersion forces. It can be seen from Fig. 1 that the adsorption isotherm of nonylphenol ethoxylate (NPE n ) on a non-polar surface must be Langmuir type, that is, single molecule adsorption, and the polyether molecule is mainly adsorbed by a hydrocarbon chain to absorb hydrogen. The ethylene chain is directed toward water and the amount of adsorption decreases as the hydrophilic chain grows. In addition, the temperature also affects the adsorption amount of the nonionic surfactant, and the temperature rise advantageously increases the adsorption amount. 
Figure 1 Adsorption isotherm of nonylphenol polyoxyethylene ether (NPEn) on a non-polar surface
Examples of the surface active agent chemically adsorbed on the surface of the ore particles adsorbed film has been widely demonstrated infrared absorption spectrum, such as fluorite - sodium oleate, hematite - sodium oleate, copper oxide - sodium oleate, hematite - Carboxylic acid and the like. Oleic acid is considered an anionic ion exchange adsorption, RCOO fluorite surface adsorption - F substituted on a surface - associated with the Ca 2+, calcium soap produced oil; hydroxamic acids hematite iron oxide The main research method for chemical adsorption of chelate surfactants on the surface is infrared spectroscopy. Someone has questioned this, and the Lord cannot rule out the changes that may occur during the preparation of the spectral samples. In addition, the physicochemical state of the surfactant in the solution may be an important factor affecting the adsorption under certain conditions.
3. Surface micelles Many studies have shown that the concentration of long-chain surfactants is higher than that of watt-hours. It is adsorbed on the mineral surface in a single ion state. When the concentration is high, the adsorbed surfactant ionic hydrocarbon chains are hydrophobic. However, the concentration at this time is still lower than the critical micelle concentration (cmc) in the solution. Instead of forming micelles, it is called forming a half micelle, and in flotation, it is called half micelle adsorption.
As early as the 1950s, Gaudin and Fuerstenau proposed a semi-micelle theory based on the results of adsorption of ions on quartz surface, and pointed out that when the adsorption concentration of surfactant ions reaches cmc, a two-dimensional semi-adhesive is formed on the surface of the particles. The further increase in concentration can also lead to the appearance of a second monolayer on the surface (double layer adsorption). However, at this time, the polar group faces the solution, and the surface of the ore particles is converted from hydrophobic to hydrophilic.
As shown in Fig. 2, the anionic surfactant dodecane has three stages in the adsorption process of sodium sulfonate on the surface of the positively charged corundum : the first stage is electrostatic adsorption mainly based on electrostatic adsorption, and the concentration increases. Due to the hydrocarbon chain association of surfactants, half micelles are formed, which leads to a rapid increase in the adsorption density on the surface of the mineral. The potential has undergone a positive value reduction to electrical neutralization, a change in number, and an increase in negative values. At the stage, characteristic adsorption occurs. When the concentration of sodium dodecyl sulfate is further increased, a half micelle and a micelle state are formed, and the electrostatic repulsion between the negative ions of the surfactant is increased, so that the adsorption density is increased, but the rate of increase of the negative potential is greatly reduced. SLOW. [next]
When the mutual attraction between the surfactant hydrocarbon chains cannot overcome the repulsive force between the charged ionic groups (such as the hydrocarbon chain is too short or the surfactant has two or more ionic groups with the same charge and the ionic strength in the aqueous solution) In the very low case, the structure of the half micelle cannot be formed, so the adsorption of the second stage is no longer present. At this time, since the first stage can still carry out ion exchange and ion pair adsorption to the surface electrical property is zero, the adsorption isotherm is Langmuir type, that is, it is steep at the beginning and tends to be flat at the late stage of adsorption. If the ionic strength of the aqueous solution is high, the adsorption in the first and third stages is weak, the slope is similar, and the adsorption isotherm is close to a straight line.
Figure 2 Schematic diagram of surfactant adsorption and adsorption isotherms and corresponding ζ units
Example 1 Determination of preferential flotation conditions in the separation of polymetallic sulphide ore. Take the butyl xanthate (KBX) as a collector, and its effect is as follows:
Figure 3 Ding Huang and Cu 2+ Pb 2+ Zn 2+
Double logarithmic graph of Fe 2+ action [next]
The above results can be said to be the basis of the high alkali process medication. Some mineral processing plants, e.g. Fankou, high-alkali process, successful flotation separation of Pb-Zn and Zn-Fe. First adjust the pH to 12, sphalerite, pyrite is suppressed, galena is floated, and ZnSO 4 is added to prevent the activation of ZnS by pb 2+ . Then, at high pH, ​​the flotation sphalerite is activated by CuSO 4 , and the pyrite is still suppressed, thereby achieving selective separation of pb, Zn, Fe sulfide ore.
Example 2 Determination of xanthate concentration during sphalerite flotation Figure 4 depicts the relationship between the required metal ion concentration and the concentration of the reagent ion (pZn 2+ -pc) when different chain length xanthate is combined with sphalerite. The equilibrium relationships and constants used are as follows:
pL SZnX2 8.3 9.5 10.43 11.8 12.9 13.9 15.8
Thus, each oblique line in Fig. 4 is obtained.
Figure 4 Effect of xanthate concentration and chain length on flotation of sphalerite
(2) Enhancement of adsorption
Numerous studies have shown that as long as a surfactant is adsorbed at the solid/liquid interface, any other additives, whether surfactant or non-polar oil, tend to co-adsorb at the pre-treated solid/liquid interface. Adsorption has been a common phenomenon. The degree of co-adsorption depends on the nature of the bonding between the two components and the nature of the solid adsorbent groups.
1. Non-polar oil Non-polar oil has been used in the fine particle sorting process. It can be added directly or after emulsification. Because of its hydrophobicity, it is used in combination with surfactants to enhance the adsorption of surfactants at the solid/liquid interface. The non-polar oil molecules are associated with the non-polar hydrocarbon chain of the collector adsorbed on the surface of the inorganic mineral, which increases the hydrophobicity of the mineral surface. When the amount of non-polar oil is large, it adsorbs and spreads on the surface of the hydrophobized ore, forming an "oil bridge", which increases the hydrophobic cohesion of the fine-grained minerals, and increases the ratio of fine-grained minerals at the oil/water interface. It is easier to enrich and enter the oil phase at the gas/water interface. According to different oil dosages, various hydrophobic agglomeration sorting processes have been developed, such as emulsification flotation, oil agglomeration sorting, and two-liquid separation. After the ore particles are slurried with an aqueous surfactant solution (collector), a non-polar oil is added and then pulverized, and the mixture is stirred under vigorous stirring to form an emulsion, which then enters the separator and undergoes emulsification flotation (liquid/liquid interface extraction). Process). In this system, the effect of the collector and the mineral surface is generally unaffected by the hydrocarbon oil, which may increase the hydrophobic capacity of the collector's non-polar groups. Oleic acid oil and coal, heavy mineral oil, and sodium lauryl sulfate emulsifier prepared emulsion has successfully sorting a particle size of 10μm wolframite.
2. Inorganic electrolytes increase the ionic strength of the solution due to electrical keratin, compressively diffuse the electric double layer, reduce the surface charge of the particles; in addition, reduce the dissociation degree of the ionic surfactant, thus strengthening the ionic surfactant in the same charge Adsorption on the surface of solid particles reduces adsorption on the surface of oppositely charged solid particles.
When the surface of the solid particles is electrically neutral, the addition of the inorganic electrolyte promotes the decrease in the dissociation degree of the ionic surfactant and also increases the adsorption of the ionic surfactant at the solid/liquid interface because it reduces the same charge surfactant ion. The mutual repulsive force makes the adsorption layer structure denser.
3. When the composite surfactant cation and anionic surfactant are mixed, there is a strong interaction between the two, including the electrostatic interaction of the isotropic ions and the hydrophobic interaction of the hydrocarbon chain, thus increasing their surface adsorption and mixing the surface. The adsorption of the active agent on the solid/high-elastic interface is superior to the adsorption of any single surfactant, and has a significant synergistic effect. However, it is important to remember that the two ions are equimolar and cause precipitation. If a small amount of cationic surfactant is added to the anionic surfactant aqueous solution, the amount of adsorption can be significantly increased, and the addition of a small amount of the carboxylate to the cationic surfactant also promotes adsorption.
Studies have shown that the mixed system of cation, anionic hydrocarbon and fluorocarbon chain surfactant also has a comprehensive synergistic effect, and its maximum adsorption amount is larger than that of single surfactant, and it is also larger than the general carbon cation and yttrium mixed system. many.
When one of the two different surfactants is adsorbed on the solid/elastic interface, the addition of the second surfactant (which should not be adsorbed to the solid/liquid interface under normal conditions when present alone in the solution) will This second surfactant will be co-adsorbed in large amounts. Surfactants such as those used as foaming offerings are clearly adsorbed onto solids that have been covered by the collector.
Second, the adsorption of polymer at the interface (a) adsorption type
Polymer adsorption mainly relies on the action of polar groups (-O-, -COOH, -CONH 2 and other functional groups) on the structural unit to act on the surface of the ore particles, from the surface flocculation, Dispersion or inhibition properties have an impact. There are three main types of adsorption: electrostatic interaction, hydrogen bonding and covalent bonding. For different ore-polymer surfactants, the types of adsorption that play a major role are not the same.
1. Hydrogen bond adsorption Hydrogen bond adsorption is the main way of adsorption of nonionic surfactants such as polyacrylamide, starch and dextrin on the mineral surface. For example, polyacrylamide-CONH 2 can form hydrogen bonds with the corresponding elements on the surface of the ore particles by using -NH 2 and -C-O. As shown in Figure 5, the adsorption free energy is about -24kJ, which is similar to the hydrogen bond energy, indicating that it is adsorbed on the mineral surface by hydrogen bonding. Further, hydrolyzed polyacrylamide is mainly hydrogen-bonded on the surface of TiO 2 .
Figure 5 Adsorption of polyacrylamide on hydroxyapatite (•) and fluoroapatite ( ° ) [next]
However, a large number of experimental results indicate that adsorption may occur even when the ionic polymer is the same as the surface of the ore. For example, polystyrene sulfonate and polyacrylic acid can be adsorbed on the negatively charged hematite particles. This indicates that in some cases, the electrostatic bond does not dominate the adsorption of the ionic polymer, and hydrogen bonding or a stronger covalent bond may become a major factor.
3. Chemical adsorption of some polymers with higher chemically active functional groups, such as hydrolyzed polyacrylamide containing -COOH, cellulose xanthogen containing -C(-S)-, etc., through its highly reactive functional groups and minerals The surface is chemically bonded and adsorption occurs. Sulfonated anionic active group such as polyacrylamide and the surface of the tin ions and a chemical bond cassiterite, polyacrylamide with a hydroxamic acid group is partially hydrolyzed with a titanium ore form a covalent bond, coordinate bond and hydrogen bond. Due to the strong chemical bond force and good selectivity, the development of such polymer flotation agents is promising. The introduction of chemically active functional groups in polymer flotation agents is an important way to improve the selectivity of their action.
4. Hydrophobic adsorption The hydrophobic portion (hydrocarbon chain) in the polymer segment may be adsorbed onto the non-polar solid surface by hydrophobic interaction. For example, carbon black which has been surface-purified (deoxygenated or hetero-cationic) has a surface which acts on polystyrene sulfonic acid by hydrophobic action to adsorb it. Rubio has experimentally proved that after the surface of the chrysocolla or malachite is hydrophobized with Na 2 S or potassium pentyl xanthate, the polyoxyethylene can act on it to flocculate the ore without hydrophobization. Then no flocculation occurs.
(2) Adsorption state
Since there are many sites in the molecular chain of the polymer flotation agent adsorbed on the surface of the mineral or solution, and the molecular chain is long, the unadsorbed part is curled or looped into the solution, as shown in Fig. 6, it cannot form a tightly oriented arrangement. Adsorption layer. The data in Table 1 indicates that hexadecyl polyoxyethylene ether is adsorbed on the surface of the solution, and each molecule occupies a larger area than the cross-sectional area of ​​the alkyl chain (22 mm 2 ), that is, it is not closely aligned on the surface of the solution. . Macromolecules such as polyenamides often have an adsorption fraction of only 1% on the mineral surface. The polymer surfactant molecules adsorbed on the surface of the mineral have various configurations, such as ring type, tail type, horizontal type, etc., and the configuration is mainly based on the position of the hydrophilic group in the molecule.
Figure 6 Schematic diagram of the adsorption of the surfactant on the mineral surface
For nonionic polymers, it is generally inferred that it does not have a significant effect on the surface electrical properties of the ore particles. A lot of experimental data also proves this. For example, although tannins have a significant effect on the aggregation and dispersion of hematite, they do not change the potential of the ore. However, in fact, the adsorption of non-ionic polymers on the surface of the ore particles often causes changes in the structure of the electric double layer. These changes include: the displacement of the characteristic adsorbed ions by the 1 chain sequence; the displacement of the partially oriented water molecules by the 2 chain sequence; The 3 chain sequence causes a change in the dielectric constant of the outer layer of the electric double layer; the adsorption of the 4 polymer causes a change in the thickness of the electric double layer.
The adsorption of the non-ionic polymer on the charged surface causes the counter ions in the solution to move outward, and even the concentration distance of the same ion adsorbed by some characteristics in the Sterm layer is also shifted outward by a δ (polymer adsorption layer thickness). That is to cause the Helmholtz face (OHP) to move outward. Even without changing the potential distribution, the thick test of the electric double layer increases δ correspondingly, which will have an effect on the intergranular interaction of the ore particles.
When the total electrolyte concentration in the solution is small, the effect of the ionic polymer on the surface properties of the ore particles is mainly manifested by the influence on the surface electrical properties, and its effect is similar to that of simple ions; when the total electrolyte concentration is increased, the properties of the ionic polymer A series of changes will occur, mainly to reduce the dissociation degree of ionic groups in the polymer, affecting the extension strength of the molecular chain, that is, the change of the morphology of the polymer, thus the chain ring and chain tail appearing in the adsorption layer; the polymer adsorption layer The rheological properties change; the steric effect of the ore interface gradually emerges, which affects the interaction of the ore particles.
Due to the presence of multiple polar groups on the polymer chain, its adsorption tends to cause an increase in the hydrophilicity of the surface of the ore. Therefore, the polymer can be regarded as a kind of surface wetting agent (for water).