Flotation agent solution properties

First, flotation agent classification commonly used flotation agent in addition to inorganic acids, alkalis, salts, mainly surfactants. Surfactants play a dual role in flotation: adsorption at the solid/liquid interface, making the surface of a particular mineral hydrophobic (as a collector ) or making a particular surface hydrophilic (inhibiting or flocculation); They exert an influence on the foam-mineral attachment power. The latter type of surfactant is customarily referred to as a foaming agent.
Since flotation surfactants are generally transferred to the interface by aqueous phase, the main applications in flotation are those agents which are more or less soluble in water. In some cases, insoluble hydrocarbons or other oils must be used, in order to allow them to reach the interface in a relatively short period of time, these liquids are dispersed into an emulsion in the aqueous phase by means of a soluble surfactant.
Flotation agents are mainly classified into surfactants and polymers.
(1) Surfactants Surfactants such as fluorine are mainly used as surfactants and hydrocarbon surfactants. They are used as collectors, foaming agents, inhibitors, flocculants and emulsifiers for coal and minerals. Agents, etc.
The sulfur representative surfactant is the main flotation agent of sulfide ore, and its polar group contains at least one sulfur atom which is not bonded to oxygen. Usually from the parent compound by the oxygen-containing thioxo derived from, such as mercaptans, thiocarbonates (xanthate, etc.), thio phosphate and the like. In addition, there are a wide variety of thio acids (RCOSH), thioamides (RCS•NH2). The non-polar groups of the sulfur representative surfactant are primarily short chain hydrocarbon groups: various combinations of ethyl to hexyl, phenol, cyclohexyl and alkyl-aryl groups. Xanthate, black medicine and DOW's Z-200 are the most commonly used thio compounds in flotation.
Most common characteristics thio compound is: have a very high chemical activity of the acid, an oxidizing agent and the metal ion, when various metal ions and substrate interaction, hydrophobic thio compound - hydrophilic properties change dramatically. Thus, although many insoluble metal salts of xanthate or dithiophosphoric acid have strong dipole moments, the short chain homologs of these salts are hydrophobic.
Non-sulfur representative surfactants are mainly various types of surfactants. For example, sulfonate/sulfate type, carboxylate type, phosphate type and amine salt and quaternary ammonium salt type, etc., can be used for flotation of various minerals. Table 1 shows typical flotation agents for research and application in the 1990s.

When used as a flocculant, in general, the larger the molecular weight, the longer the molecular chain, the stronger the bridging effect, and the better the effect. However, the molecular weight is too large, not only the dissolution is difficult, the molecular motion is sluggish, and the adsorbed solid particles are too far apart, are not easy to aggregate, and the flocculation effect is deteriorated. Generally, the relative molecular mass is 105~107, and the actual use concentration is generally 0.05%~0.2%. Studies have shown that at the same molecular weight, linear PAM has better flocculation effect than branched type, while in the same linear PAM, when the degree of hydrolysis is about 30%, there is an appropriate amount of -COO- between the groups. The electrostatic repulsion increases, the molecular chain is straightened, which is beneficial to bridging, and the flocculation effect is better. Although the molecular weight excessive flocculant not only has the disadvantage of low solubility, but also has a high viscosity, the movement in the solution is slow, affecting the flocculation. effect. On the other hand, the molecular weight is large, the molecular chain is long, and the bridging effect is large. Therefore, in order to improve the performance of the flocculant, it is necessary to develop a macromolecular flocculant having a large molecular weight and a low solution viscosity. It has been reported that an acrylamide monomer and a surfactant having a small HLB value are converted into an oil-in-water type by water-in-oil polymerization, and a molecular weight, a low viscosity, and a solubility property can be obtained. Good macromolecular flocculant.
When used as an inhibitor or a dispersant, the molecular weight should be smaller. After adsorption on the mineral surface, because the molecular chain is not too long, it is not enough to cause bridging, and multiple hydrophilic groups make the mineral surface hydrophilic, inhibited or dispersed, and the branched macromolecular agent tends to be more linear than the linear one. it is good.
Second, the balance in the flotation agent solution
The balance of the flotation agent in the solution includes the acid-base balance of the flotation agent in the solution, the dissociation equilibrium, the association equilibrium, the adsorption equilibrium at each interface, the hydrolysis hydration balance of the inorganic ions, and the polymer flotation agent in the solution. The balance in the middle.
Through the acid-base balance calculation, the pH value of the flotation agent solution can be known to facilitate pH adjustment and control. From the dissociation equilibrium of the flotation agent, the relationship between the pKa value of the flotation agent and the flotation behavior, and the active component of the flotation agent floating under different conditions can be known. From the association equilibrium, the semi-micelle adsorption, the role of the ion-molecular complex in the floatation, the hydrophilic-hydrophobic balance of the flotation agent, and the like can be discussed.
(1) Acid-base balance of flotation agent For ionic flotation, the pH of the medium changes due to hydrolysis or dissociation reaction in aqueous solution, which affects the effect of the agent on the suspended minerals and between the agents. interaction. Therefore, it is important to know in advance how a certain concentration of a certain agent changes the pH of the medium, and it is very important for the adjustment and control of the pH adjustment of the slurry and the interaction of the agent in the research and production. The pH values ​​of simple monobasic acid, base and salt solutions can be calculated from the dissociation equilibrium, and various graphical methods are used for the pH values ​​of the polyacid, alkali and salt flotation reagent solutions. There are mainly ф-pH diagram method (planogram method for distribution coefficient of flotation agent ф with pH value) and logarithm of concentration diagram, ie lgc-pH diagram method (graphic method of concentration c of each component as a function of pH). [next]
The xanthate is hydrolyzed in water to form xanthogen HX, which is then dissociated into X- and H+. In the study of the mechanism of action of xanthate, molecular adsorption and ion adsorption hypotheses have been proposed. According to the molecular adsorption hypothesis, HX is an effective mode of action, as can be seen from Figure 1, the pH of the flotation liquid should be pH < Pka, as shown in Figure 2, curve 2, sphalerite flotation. When the pH of the flotation liquid is less than 4, the xanthate is mainly present in the form of HX, and the flotation effect of the sphalerite is preferably 2 to 4 at pH. However, Figure 1 does not explain why the zinc blende does not float after pH < 1, although the xanthate is 100% HX. According to the ion adsorption hypothesis, the pH of the flotation liquid should be pH>pKa, as shown in curve 1 in Fig. 2. When the pH is greater than 4, the flotation effect of galena is best, and the xanthate is mainly in the form of X-form; When the pH is greater than 11, the galena floatability decreases, which may be due to the competitive adsorption of OH-.
When the original concentration of xanthate is limited, the role of the agent should be discussed. It is necessary to consider not only the dissociation, but also whether the absolute concentration reaches the effective range. Usually, the concentration of xanthate required for sulphide ore is more than 10 ^-5 mol/L. If X- is an effective component, it is required to:

Lgc _T -lg(K _a +[H ⁺ ])+lgK _a >10 ^-5

If HX is used as an active component, it is required to:

Lgc _T -pH-lg(K _a +[H ⁺ ])>10 ^-5

Fig.1 Logarithmic plot of concentration of each component of xanthate solution (xanthine concentration 1.0 × 10 ^-3 mol/L)


Figure 2 Relationship between flotation recovery and pH of lead-zinc sulfide ore 1 - galena, 1.0 × 10 ^-5 mol/L EX (yellow)
2— Sphalerite, 2.5 × 10 ^-4 mol/L EX (Wen Huang) [next]

(2) Association of balanced non-sulfurized ore collectors, such as long-chain fatty acid salts, long-chain fatty amine salts and sulfonates, because of the long hydrophobic hydrocarbon chain and strong interchain interaction, which can occur Hydrophobic association; if a hydrophilic group contains a hydrogen atom, hydrogen bonding can also occur. Therefore, this type of agent is in a single molecule or ion state at a low concentration, and at a certain concentration, a dimer, an ion-molecular association (low association) is formed; at a higher concentration, a half micelle is formed. Or micelles (highly associated). Secondly, due to the limited solubility of the hydrophobic chain water, the influence of the dissolution equilibrium on the dissociation equilibrium should also be considered. Flotation can be based on different flotation activities of different structural associations. By controlling the medium conditions, the components with high flotation activity are dominant, which is beneficial to improve the flotation process, such as the surface tension of oleate and dodecylamine solution. The lowest pH corresponds to the maximum pH at which the ion-molecular association is formed, which is obtained from the logarithmic plot of the concentration of the corresponding flotation agent solution dissociation-association equilibrium, indicating that among the various components, The surface activity of this component is the largest, and flotation studies have also shown that the formation of molecular-ion associations also has an important impact on the flotation process. Thus, the concentration of the agent and the pH of the flotation solution can be controlled to achieve better flotation.
3. The relationship between the physical and chemical properties of flotation agents and flotation (1)
The type of flotation agent is related to its flotation of minerals. For example, sulphide ore is commonly used as a surface active agent, oxidized ore is usually a surfactant such as a carboxylate or a sulfonate, a silicate mineral is usually an amine collector, and a non-polar mineral is a hydrocarbon collector. .
(2) Relative molecular mass Common low molecular weight surfactant, mainly as a collector and a foaming agent, its relative molecular mass has little relationship with flotation performance. However, for large molecular weight (>10 ³ ) polymers, such as sodium polyacrylate, its flotation performance is closely related to the relative molecular mass. When used as an inhibitor, the relative molecular mass is small; as a dispersant, generally relative molecules The mass is about 10 ⁴ ; as a flocculant, the relative molecular mass is 10 ⁵ ~ 10 ⁶ .
(III) Molecular structure
The molecular structure of the flotation agent needs to have a certain size of hydrophilic and hydrophobic groups, the geometric size and the ratio of affinity and hydrophobicity will affect the flotation performance of the flotation agent. For collectors, when used in sulfide ore, the hydrophilic group (or pro-mineral group) often contains divalent sulfur groups such as -SH and -S; if used in non-sulfide ore, it is generally It is an oxygen- and nitrogen-containing group such as -OH, -NH ₂ and -O, -COOH, -SO ₃ H, and the like. For foaming agents, inhibitors, dispersants, etc., the hydrophilic groups are commonly known as -COOH, -OH and -SO ₃ H.
The size of the drug molecule is closely related to the selectivity of the mineral. The highly selective sulfide ore collector has a large cross-sectional area (6.2 to 12 nm). In the same type of collector, it is usually better to have a larger molecular cross-sectional area. For example, compared with the ester of xanthate, the width of the ester is larger than that of xanthate, and the selectivity of the ester is also higher. When they flotonate sphalerite-pyrite and chalcopyrite-pyrite, if the ratio of recovery of the minerals of the gamma is indicative of the selectivity of flotation, then:
: isopropyl isopropyl xanthate > propyl xylenate > isopropyl black drug > butyl xanthate acrylate > butyl xanthate;
: isopropyl isopropyl xanthate > propylene butyl xanthate > propylene butyl xanthate > propylene butyl xanthate > butyl xanthate;
This order is also roughly the order of geometric size (molecular cross-sectional area).
Similarly, the poorly selective oxidized ore collector has a smaller molecular cross-sectional area.
1. Collector 1 is used for non-ferrous metal sulfide ore. The group electronegativity (X _g ) is small, the molecular weight of the non-polar group (or the number of carbon atoms n) does not need to be large, the structure of the polar group -C-B-A, and the number of A atoms (bonded atoms) It is sulfur, B atom can be an atom with high electronegativity, such as oxygen and nitrogen, C is an atom with a small electronegativity, such as carbon or phosphorus, and the diameter of the polar group dg can be large;
2 for non-metallic oxidized ore. X _{g is} larger, n is larger, cmc and HLB are smaller, -C is more oxygen atoms in C-B-A; B is carbon, phosphorus, arsenic, sulfur, etc., C is nitrogen, sulfur, oxygen, etc., d _g Smaller
3 for black, rare metal non-sulfur ore. X _{g is} medium, n is medium, cmc and HLB are small, and A is an atom such as oxygen or nitrogen;
Reducing Xg maintains selectivity when the capture is enhanced; increasing n reduces the selectivity when the capture is enhanced.
2. Inhibitors The polar group is required to be the same as the collector, but the more the number (ratio) of polar groups, the better, and it is distributed throughout the molecule;
The 2n value is generally small, or the ratio of _Xg /n is large.
3. Foaming agent When 1Xg is large, the solubility and polarity are good; [next]
2 is better when there is a certain double bond, but the 叁 key is not good;
3 has a certain branch is better.
(4) Critical micelle concentration
The critical micelle concentration cmc is a measure of the amount of surface activity of the surfactant and is therefore important for flotation. Factors affecting cmc also affect the flotation properties of the flotation agent.
Many studies have shown that the concentration of surfactants is not very large, and when there are no other additives, the micelles are mostly spherical. At concentrations > 10 cmc, the micelles are non-spherical and generally rod-shaped. However, surfactant molecules adsorbed on the mineral surface cannot form micelles as in solution, but form two-dimensional half micelles. This is called semi-micelle adsorption in flotation studies and is important for the flotation process, see Figure 3.
The smaller the cmc, the greater the hydrophobicity of the agent, indicating that the proportion of non-polar groups in the surfactant molecule is larger, revealing that it is likely to act as a collector, and the trapping property is stronger; the cmc is larger, indicating the hydrophilicity in the drug molecule. Strong, polar base ratio is large, can not be a collector, but may be used as a foaming agent; if the cmc value is large, the agent dissolves and disperses well in water, and may be used as an inhibitor.

Figure 3: Micelleization of surfactants in solution and on mineral surfaces

The range of the amount of flotation agent can also be estimated using the cmc value. If the concentration of HMC which starts flotation and formation of half micelles is regarded as the lower limit of the amount of collector required for flotation.
On the other hand, at the time of flotation, when the dose exceeds a certain limit, the flotation recovery rate can be lowered, and even the flotation does not occur. The concentration of the drug at this time is called "critical inhibition concentration" and is represented by CDC. According to research, CDC also has a certain relationship with cmc, CDC is about 4 times that of cmc. After the amount of collector is large, the recovery rate of mineral flotation decreases, and it is considered that this is because the precipitate of insoluble salts formed by the collector and metal ions can be dissolved in the micelle. When the concentration of the collector is large, if CDC is reached, a lot of micelles are formed in the solution, so that the collector adsorbed on the surface of the mineral and the precipitate of the metal salt thereof are dissolved in the micelle, and the surface of the mineral is restored to hydrophilicity. Lost buoyancy. Therefore, 4 cmc can be approximately used as the upper limit of the amount of the collector.
When the surfactant flotation agent is adsorbed on the mineral surface, the addition of polar organic substances such as alcohol will reduce the electrostatic repulsion between the surfactant ions, so that the surfactant molecules can easily reach the HMC on the mineral surface and the semi-micelle adsorption occurs. Large flotation effect. For the ionic surfactant solution, when an inorganic salt having the same ion is added thereto, such as adding NaCl to the RSO ₄ Na solution, the surface activity of the solution will increase and the cmc will decrease. This may suggest that when using ionic surfactant flotation, the addition of a certain concentration of inorganic ions will facilitate the action of the agent and reduce the amount of the agent.
(V) the surface tension of the flotation in a solid - liquid - gas interface of the three-phase sub-process mineral material. Therefore, the interfacial tension is important for the flotation process. The most intuitive sign of mineral floatability is its wettability, minerals that are easily wetted by water, hydrophilic and difficult to float; minerals that are not easily wetted by water, hydrophobic and easy to float. The flotation agent is adsorbed at the liquid/gas interface and the liquid/liquid interface to study the effect of interfacial tension on the flotation, and the "γ-flotation" separation mineral can be realized. For the mineral-floating agent solution system, if the surface tension of the flotation agent solution is greater than the γ _{c of the} mineral (the critical surface tension of the solid, the surface tension of the homologous liquid and its contact angle θ on the same solid are cos θ-γ _{In the L} diagram, the obtained straight line is extended to cos θ=1, and the corresponding surface tension is the critical surface tension of the solid.) The mineral is not wetted, floated, and floated; otherwise, the mineral is wetted, so it cannot be floated. . Thus, depending on the relationship between the surface tension of the flotation agent and the critical surface tension of the mineral, or artificially adjusting the surface tension of the flotation agent solution, the mineral can be separated by flotation. For two minerals γc1 and γ _c2 with different wettability critical surface tensions, under the condition of γ _c1 <γ _LG γ _c2 , mineral 2 will be wetted by the solution, while mineral 1 will float up to achieve separation.
(6) HLB value The HLB value is an indicator for characterizing the hydrophilic and lipophilicity of the surfactant. The difference in HLB will directly affect the flotation properties of the flotation agent. In the three major classes of collectors, foaming agents and conditioners, the ratio of molecular polar groups to non-polar groups is different. Thus, the HLB value can be used to determine the possible use of the flotation agent or to estimate the ratio of polar and non-polar groups in the drug molecule. [next]
The role of the collector is to make the mineral surface hydrophobic, so the proportion of non-polar groups is larger, and the HLB value is smaller; the inhibitor is to make the mineral surface hydrophilic, the proportion of polar groups is larger, and the HLB value is larger; The foaming agent is mainly adsorbed at the liquid/air interface, and the HLB value is intermediate, and the polar group is mainly a group such as -OH, -O-, etc. which does not have a synergistic effect with the mineral. The HLB values ​​of the acid formulas of the three types of flotation reagents are shown in Table 3.

Note: The ratio method, HLB = [∑ (organic) / ∑ (inorganic)] × k, k is a constant, about 10; addition method, HLB = HL (HLB) i • wi, wi is mixed surface activity The mass fraction of i in the agent.
If you want to get a certain use of the drug, what kind of ratio is used for the polar structure and the non-polarity in the molecule, or what kind of agent can be obtained after processing a specific pharmaceutical raw material? Problems often encountered in the development of pharmaceuticals.
When preparing an agent for a given polar group, for example, to manufacture an alkylphosphonic acid for a collector, it is known by calculation that the drug has a certain degree of trapping property, and the HLB is required to be less than about 4, and the non-polarity is at this time. The base must be at least singapore. It can be seen that if a strong collector is to be prepared at this time, it is necessary to use a surfactant having a hydrocarbon chain length greater than octyl or more (7) Hydrophobic association energy.
The magnitude of the hydrophobic association energy Ñ„ value is important for the interaction of the collector with the mineral, such as the adsorption of the semi-micelle, the ratio of the hydrophilic-hydrophobic groups in the collector molecule. For the same type of surfactant, there are differences in the Ñ„ values ​​obtained during different associations. The hydrophobic association energy of the hydrocarbon chain is closely related to the surface activity of the flotation agent and other surfactants, and it varies with the number of carbon atoms in the normal homologue. Studies have shown that each mole-CH ₂ —The energy (Ñ„) is 1254~4180J; for the flotation agent, the Ñ„ value is 1672~3344J. According to the total surface energy nÑ„ value of the non-polar group (nφ indicates hydrophobic capacity, n is CH ₂ number, Ñ„ value is generally 0.6~1.0) and the electronegativity difference ΔX can be determined by the following formula: The hydrophilic/hydrophobic index i:

i=∑△X ² -∑nÑ„

It goes without saying that the value of i can be used as a criterion for classification and estimation of the size of the ore dressing agent; the collector has a strong hydrophobic ability for i hours; the inhibitory i is strong when it is large; when the value of i is constant, it can be determined. The quantitative relationship of non-polar groups is helpful in designing the structure of the agent. For the collector, if it is adsorbed to the mineral to produce sufficient hydrophobicity to achieve flotation, the non-polar group overcomes the hydrophilicity of the mineral in addition to the hydrophilicity of the polar group. If the hydrophilicity of the mineral is measured by ΔX ² M of its constituents (X ² M is the square of the electronegativity difference of the mineral component AB (X _A —X _B ) ² , the non-polar group in the collector molecule The requirement is nφ=â–³X ² R+â–³X ² M (where ΔX ² R is the polarity characteristic of the valence bond (X _g -X _M ) ² when the agent is bonded to the mineral component. If Ñ„=1; The non-polar relationship calculated by the agent in various applications is consistent with the actual situation of the drug.

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