The fine particles in the beneficiation process are derived from the mud of the ore. Due to the primary and secondary causes, the production of the slime is actually unavoidable. The so-called primary slime is the argillaceous mineral naturally formed by the ore deposit due to geological mineralization; the secondary slime, that is, the slime produced by the mineral raw material during the processing, such as the fine grinding process of the ore, is not conducive to the conventional physical sorting process. Ultrafine particles.
A large number of experiments and production data analysis showed that the lower limit of the optimal particle size range of foam flotation is 3~7μm, the general easy-floating sulfide ore is lower, 3~5μm; the oxidized ore is higher, 5~7μm; below 0.1μm It belongs to the colloidal dispersion, which is called fine particles between 5~7μm and 0.1μm. Fine particles have two major characteristics: first, the mass is small, and second, it is larger than the surface. These characteristics cause a series of changes in its physicochemical behavior in the medium, resulting in deterioration of fine particle flotation. The physicochemical characteristics of the fine particles and the influence on the flotation are shown in Fig. 1.
In order to overcome the series of micro-particles that cause deterioration of flotation and improve particle flotation, the ore dressers have studied a series of special-effect processes for fine-grain flotation. According to the principle of particle flotation kinetics, increasing the flotation particle size can greatly increase the flotation speed. Selective agglomeration of the particles increases the particle size of the particles. There are two ways to selectively agglomerate mineral particles: one is selective flocculation flotation with polymer surfactants, and the other is hydrophobic agglomeration. There are many particle sorting processes based on hydrophobic agglomeration, such as emulsion flotation, carrier flotation, pellet flotation, and two-liquid separation.
The premise of fine particle flotation is to selectively hydrophobize the surface of the target ore. Therefore, it is important to study the specific agents and optimal conditions for hydrophobization on the surface of fine particles.
Fig.1 Effect of physical and chemical characteristics of fine particles on flotation
1. Selective flocculating agent
Selective flocculation refers to the selective flocculation of a certain component from a stably dispersed suspension by a flocculant, and is separated from other components still in a dispersed state, thereby achieving the purpose of sorting. The process generally comprises: 1 slurry dispersion; 2 flocculant selective adsorption and formation of flocs; 3 flocculation adjustment. The purpose is to form a floc that meets the requirements of the subsequent separation process and to minimize inclusions in the floc; 4 to separate the flocs from the suspension. Among them, slurry dispersion is a prerequisite for the process. The selective adsorption of flocculant and the formation of flocs are the main body and key of the process. The adjustment of the floc and the separation from the suspension are also guaranteed to proceed smoothly and obtain good results. Process factors that cannot be ignored by the sorting indicator.
Non-selective mutual coagulation between pulps is an important obstacle to the selective flocculation of fine particles. To overcome this obstacle, the slurry must be pre-selected for dispersion treatment. In practice, the dispersing agent is added to disperse the slurry. Common dispersants are polyvinylidene sodium phosphate, sodium silicate, sodium hydroxide, sodium carbonate and the like, some of the inhibitors such as tannins, lignosulfonates, humic acid and sodium polyacrylate, in Under certain conditions, there are also obvious dispersion effects. The choice of dispersant depends on the specific conditions of the ore type, mineral composition, dispersed objects, water quality, type of flocculant selected, and source of the agent. In addition to the chemical dispersion method, physical methods such as strong mechanical agitation and ultrasonic dispersion can also be used, the latter being more effective and widely used under laboratory conditions, but industrialized due to severe constraints on energy consumption and dispersion conditions. There are still some difficulties in application.
Whether the selective flocculation separation process can completely separate useful minerals and gangue minerals is the key to finding effective selective flocculants and dispersants. The advantage of this process is that the process is simple and complete separation; the disadvantage is that it is easily affected by dissolved ions in water and is difficult to control. Therefore, the search for effective auxiliary agents to reduce the interference of dissolved ions in water on flocs will be an important research field for the industrialization of selective flocculation separation process. [next]
(I) Selective flocculant The selective flocculant is different from ordinary flocculant in that it must not only have flocculation, but also must be selective, otherwise it is impossible to sort a certain mineral from a stable suspension. The selectivity of the flocculant is the key to selective flocculation. There are many types of polymer surfactants which have flocculation properties, but they are not used in industrialization due to selectivity and cost limitation. Polyacrylamides, starches and derivatives have been put into practical use. Different ores require different flocculants. Even if the same ore is used, the composition of impurities is different. If the same flocculant is still used, the corresponding dispersant and regulator should be changed accordingly to improve the flocculant. Selective. Commonly used as selective flocculants are polyacrylamide and its hydrolyzate and modified materials, polyoxyethylene, polyacrylates, polyvinylpyridinium salts and various polypolyamines, and starches and derivatives, carboxy Natural polymer surfactants such as methyl cellulose, sodium humate, gelatin, protein and tannin are shown in Tables 9-6. In the past, natural flocculants were limited by the influence of raw material sources and yields. With the emphasis on the environment and toxicology, selective flocculants derived from natural renewable raw materials will surely receive attention.
Currently, selective flocculation separation semi-industrial test results have been many laboratory, industrial applications has been part of that covering iron ore sorting, copper ore, coal, potash, tin ore, aluminum silicate, phosphate manganese ore and the like, in table 1 for a variety of selective flocculation mixing mineral separation process.
Mineral mixture | Flocculant | Auxiliary agent | Separation method | |
Flocculated | Distracted | |||
Hematite | quartz | Starch, talcum powder, sodium humate | NaOH, Na 2 SiO 3 , (NaPO 3 ) 6 | (1) |
Hematite | Silicate, aluminosilicate | Strong hydrolyzed polyacrylamide | NaF or NaCl, (NaPO 3 ) 6 | (1) |
Silicate | Hematite | Weakly hydrolyzed polyxanthene amide | NaF or NaCl, (NaPO 3 ) 6 | (1) |
TiO 2 impurity | Kaolin | Polyacrylamide | Na 2 SiO 3 NaCl, (NaPO 3 ) 6 | (1) |
Phosphate mineral | Quartz, clay | Anionic starch | NaOH | (1) |
Pyrite | quartz | Polyacrylamide (polypropylene) | (1) | |
Sphalerite | quartz | Polyacrylamide (polypropylene) | (1) | |
Sphalerite | quartz | Polyacrylamide (polypropylene) | (1) | |
Magnesium oxide, carbonate | Gangue stone | Polyacrylamide aluminum sulfate | (polypropylene eye) | (1) |
Talc , iron ore | Fine-grained pyrite | Polyethylene oxide | Foaming agent | (2) |
Gangue stone | Chrome ore | Carboxymethyl cellulose | NaOH Na 2 SiO 3 | (3) |
Galena | quartz | Hydrolyzed polyacrylamide | (4) | |
Galena | Calcite | Weakly hydrolyzed polyacrylamide | (NaOH Na 2 SiO 3 ) 6 | (4) |
Calcite | quartz | Hydrolyzed polyacrylamide | ||
Calcite | Rutile | Strong hydrolyzed polyacrylamide | (NaPO 3 ) 6 | (4) |
Bauxite | quartz | Strong hydrolyzed polyacrylamide | (NaPO 3 ) 6 | (4) |
coal | shale | Polyacrylamide | (NaPO 3 ) 6 +Ca 2+ | (4) |
Barite | Fluorite , quartz | corn starch | Na 2 SiO 3 | (4) |
Chrysocolla | quartz | Cellulose yellow drug | NaOH, Na 2 S, NaCl | (4) |
Chrysocolla | quartz | Nonionic polyacrylamide | (NaPO 3 ) 6 , NaCl | (4) |
Copper oxide, copper sulfide | Dolomite, calcite, quartz | Polyacrylamide-diethyl hydroxydiethyl ether | (NaPO 3 ) 6 , NaCl | (4) |
Titanium ore | Feldspar | Hydrolyzed polyacrylamide | NaF | (4) |
Limonite | Quartz, clay | Hydrolyzed polyacrylamide | NaOH, (NaPO 3 ) 6 | (4) |
锡石 | quartz | Hydrolyzed polyacrylamide | CuSO 4 , Pb(NO 3 ) 2 | (4) |
(2) After selective flocculation, the flocculated useless gangue mineral is floated by flotation, and then the useful minerals in a dispersed state, such as flocculating clay, are separated by flotation, and the clay is flocculated and floated by flotation, and then Perform potassium salt flotation;
(3) flocculation gangue, and then flotation of useful minerals, such as chromite at pH = 11.5, flocculation of gangue with carboxymethyl cellulose, oleic acid floating chromite;
(4) For coarse and fine particle classification, coarse particle flotation, and fine particle selective flocculation before flotation.
Established in 1974, the Tierden concentrator in the United States uses tapioca starch as a flocculant to treat ore as a refractory fine-grained non-magnetic iron-bearing rock. Its main iron minerals are hematite and imaginary hematite, gangue minerals. Mainly quartz, vermiculite and other silicate minerals, the average embedding grain size of iron minerals is 10~25μm, and the original ore grinding to less than 25μm (500 mesh) reaches 85%, in order to achieve full dissociation. After selective flocculation treatment, 15%~30% of the slime can be removed from the ore, and the loss of iron is only 5%. The annual processing of iron ore containing 36% of ore is 10 million tons, and it can produce 4 million tons of pellets containing 65% iron. The ore dressing flow chart is shown in Figure 2. In 1979, it expanded to an annual processing capacity of 21 million tons of raw ore, with an annual output of 8.1 million tons of pellets.
The key to the success of using tapioca starch as flocculant is to effectively adjust the surface electrical properties of minerals, and create favorable conditions for the dispersion of pulp and the selective adsorption of starch on the surface of iron minerals. Using sodium hydroxide, sodium silicate and sodium tripolyphosphate to adjust the pH of the slurry to 11, all minerals in the iron oxide shale slurry are highly negatively charged and dispersed, quartz (or vermiculite) silicate and iron oxide, etc. The electrical points are about Ph=2, 5, and 7, respectively. When the slurry Ph = 11, in the absence of Ca 2+ , the quartz surface has a very negative zeta potential (-120 mV), and the potential of the iron oxide is also close to -60 mV. The high electronegativity of the quartz surface promotes its high dispersion and prevents the starch from interacting with the quartz, thereby increasing the selectivity of the process, as shown in Figure 3.
Figure 2 Flow chart of the US Tilden Concentrator
Figure 3 Electrical properties of minerals in a typical taconite suspension [next]
In order to enhance the dispersion, the dispersant is added to the mill, and then a small amount of caustic tapioca starch is added to the thickener to effectively floculate the iron oxide. Selective adsorption of starch on iron oxide minerals simultaneously plays a role in selective flocculation and inhibition, which creates favorable conditions for further removal of silicate gangue minerals from flocs by reverse flotation.
Since the adsorption of starch on iron oxide minerals is irreversible, the flocculation desiliconization flotation can directly use the cationic amine collector to float the gangue minerals. If the anion collector is used for flotation, calcium ions are needed. Activated quartz. These two schemes can obtain similar indicators. Due to the simple process of the previous scheme, the Tierden ore is treated with cationic reverse flotation quartz to improve the quality of iron concentrate. The dosage of the agent is: sodium hydroxide 1kg/t, sodium tripolyphosphate 0.136kg/t, sodium silicate 0.408kg/t, caustic tapioca starch 0.136kg/t, coke dextrin 0.272kg/t, cationic collector 0.09kg/t. The mine also successfully treated tailings with lime and polyacrylamide as flocculants, allowing 95% of the return water to be used, reducing the cost of drug consumption and reducing environmental pollution.
In recent years, the Tierden concentrator in the United States has used water glass and/or sodium tripolyphosphate as dispersant, tapioca starch as flocculant, and anionic collector (saponified tar oil fatty acid Acintol FA- under Ph>11 conditions. 2) Activate quartz with calcium chloride to carry out anion reverse flotation of an oxidized iron strontium ore containing a large amount of calcite silicate and apatite under conditions of Ph11.5~12 (at this time, interference by calcium ions) It is not advisable to use cationic reverse flotation).
Different from the Tilden process, the selective flocculation of iron ore in the Jayton deposit in Canada is based on the de-slurry process. It uses two-stage selective four-stage selective flocculation-de-sludge and uses corn starch as a flocculant to directly obtain iron. 65% concentrate. The ore ore mainly contains hematite, followed by magnetite. The hematite has a size of 5~30μm and the magnetite is coarse. It is 20~200μm. The gangue minerals are mainly quartz, silicate and chloride. Typical results of semi-industrial tests are shown in Table 2.
Table 2 Typical results of the semi-industrial test of the Gelton Iron Mine
product name | Yield/% | Fe content /% | Fe distribution rate /% | Pharmacy conditions / (kg / t) |
Concentrate floc Tailings mud Feed mine | 34.1 65.9 100.0 | 65.0 11.4 27.7 | 74.6 26.4 100.0 | Corn starch 0.272 Sodium silicate 0.557 Lime 2.179 Soda 1.770 pH 9.5 |
Studies by Sresty et al. have shown that it is also possible to flocculate hematite from a hematite-quartz mixture with polystyrene sulfonate. Studies have shown that sulfonated polyenamide and natural starch respectively flocculate iron oxide ore, in terms of selectivity, the former is slightly worse than the latter, but the flocculation ability is strong, the dosage of the agent is small, which is one-tenth of the latter. . Sulfonated polyacrylamide is used in the flocculation-de-sludge-flotation test of Donganshan Iron Mine. Compared with the whole flotation without de-mudging, it can increase the concentrate grade by 0.27% and increase the recovery rate by 3.92%. In the strong magnetic-flocculation-strong magnetic current test of the mine, the sulfonated polyacrylamide flocculant can selectively flocculate the fine-grained iron minerals that are difficult to recover by magnetic separation. When the ore and concentrate grades are similar, The iron concentrate recovery rate increased by 8.17%.
Changsha Research Institute of Mining and Metallurgy uses humic acid as a selective flocculant to improve the grade of iron concentrate in the magnetic weight process of Jidong Mine from below 55% to 62%~65%, and the recovery rate is from 70%. Increase it to around 72%. The institute recently studied the SP404 flocculant mixed with the dispersant SPC-08 to study the selective flocculation de-sludge-reverse flotation process of the Guanmenshan fine-grained iron ore. The results show that when the ore grade is 32.74%, the grade is 65.33. %, an iron concentrate with a recovery rate of 87.78%.
2. Selective flocculation of copper ore in the non-ferrous metal sulfide ore, has studied the selective flocculation of galena, sphalerite and pyrite, but the current research and more mature is still the sulfide of copper ore. And oxides.
The effect of selective flocculation of copper minerals with general polyacrylamide is not obvious. Selective flocculation of quartz and dabbite mixtures using anionic, cationic and nonionic polyacrylamides found that only nonionic flocculants can selectively flocculate silicon with sodium hexametaphosphate as dispersant. Malachite, but when the concentration is high, the separation effect is reduced due to the mixing of quartz in the flocculation. [next]
An effective agent for selective flocculation of copper minerals is a variety of water-soluble polymers containing sulfhydryl groups or other complexes or chelating groups with heavy metal ions, such as xanthogenates synthesized from cellulose and its derivatives. The cyanite can be selectively flocculated from quartz, and it is also found that dissolved Cu 2+ may activate quartz, which makes the flocculation lose selectivity, but the addition of a small amount of sodium sulfide and sodium chloride can improve the selectivity. The former can eliminate the activation of quartz by Cu 2+ , which can increase the ionic strength and reduce the electrostatic repulsion potential of the negative charge between the cyanite and the polymeric xanthate. Others, such as hydroxypropyl cellulose, can effectively flocculate chalcopyrite from quartz, and selectively floculate chrysocolla with amylose xanthate.
Polyamide amide-glyoxal-bis-hydroxy aniline (PAMG) developed by Attia is an effective selective flocculant for copper minerals, and complex copper ore for fine particle impregnation has proven to be technically feasible. In order to ensure the quality of the concentrate, multiple stages of flocculation and dispersion are required to eliminate the mixed gangue minerals, and effective dispersing agents such as sodium hexametaphosphate and Dispex N40 mixture are also selected.
(2) Improving the selective flocculation process of the flocculant The flocculation process is similar to foam flotation, and the general principle is to improve the selectivity of the process. Therefore, which minerals are preferentially flocculated from the mixed suspension is the first consideration in the design of selective flocculation processes. In principle, the useful minerals may be preferentially flocculated, and the gangue may be preferentially flocculated, but the choice of the two methods should be based on ensuring the maximum selectivity of the process and the technical and economic rationality. In fact, both methods have been successfully applied in the industry. Generally, in order to reduce the inclusion of flocs, minerals with a large amount of minerals are often dispersed, and minerals with a small amount of flocculation are often used.
In flocculation, the interaction between the flocculant and the mineral should be maximized according to the difference in surface properties between the flocculated and dispersed minerals. The main methods are as follows:
1. Pre-adjustment of pulp The pH value and ion composition of the suspension medium are adjusted to adjust the interface properties of the ore particles (such as surface electrical properties) to facilitate selective flocculation.
Pre-adjustment of the slurry is indispensable for the selective flocculation process, especially for the use of common flocculants without special selectivity. To this end, it is often used to adjust the pH value of the slurry to give the ore particles a certain charge to facilitate the interaction of the flocculant with the ore particles. This is the purpose of pre-adding a pH adjusting agent and a dispersing agent before selective flocculation.
In addition, the flocculating activity of the flocculant, such as the degree of dissociation of the group, the state of extension of the molecular chain, and the number of charges and reactive groups on the molecular chain, depend to a large extent on the pH and ions of the aqueous medium. composition. Because selective flocculation is very sensitive to mineral surface contamination and the ionic composition of the medium, it is often difficult to make laboratory research results transition to industrialization. Studies have shown that when the pulp contains a high concentration of multivalent ions, the flocculant will be wound up or salted out, and the fine particles will be agglomerated, and the gangue minerals will be activated irregularly, which will affect the selective adsorption of the flocculant. . For example, when polyacrylic acid selectively flocculates hematite mixed with quartz, if the solution contains iron ions, the flocculation process loses selectivity due to the adsorption of polyacrylic acid by the activation of quartz by the iron ions. However, this activation can be eliminated by the addition of sodium edetate, sodium hexametaphosphate or potassium fluoride. At this time, hematite can be selectively flocculated from the quartz mixture even if iron ions are present.
2. Introducing a functional group with special selectivity into the polymer surfactant Introducing a functional group having a specific adsorption activity with a corresponding metal ion on the surface of the polymer surfactant, thereby improving the selectivity of the action of the agent on the surface of the mineral.
Has developed a number of polymeric surfactants containing sulfhydryl groups or other complexes or chelating groups with heavy metal ions, such as cellulose xanthate synthesized with cellulose or cellulose derivatives for lead, copper, Zinc sulfide ore and copper oxidized ore have good selectivity, while calcite, quartz, feldspar and kaolin have little or no flocculation. The flocculant can be used to selectively floculate the chrysocolla from the quartz and selectively floculate the galena from the calcite.
The glyoxal-bis-hydroxyaniline group is known to be a selective complexing agent for copper ions which can be incorporated into long chain water soluble polymers. If introduced into polyacrylamide, an effective flocculant polyacrylamide-glyoxal-bis-hydroxyaniline can be obtained for copper minerals.
The modified polyacrylamide (containing 69% chain amide polymer, 23% carboxyl group and 8% hydroxamic acid group) obtained by introducing a hydroxamic acid group into polyacrylamide improves the selectivity to the cassiterite effect. Selective flocculation of cassiterite from a mixture of cassiterite-containing quartz at a pH of 3.5 to 7 is effective.
Based on the principle that tannins and aminopyrines can selectively precipitate titanium from acid solutions, Rinelli uses these two agents to study the separation of rutile from rutile-quartz and rutile-hematite mixtures. The results show that tannins can be combined with titanium. A stable complex is formed, and the aminopyrazine stabilizes the flocculated rutile floc, and the mixture of the two agents can effectively flocculate the rutile from the above mixture.
3. Flocculant combined with other agents In order to improve the selectivity of the flocculant, several flocculants can be used in combination or the flocculant can be mixed with agents such as collectors, inhibitors and activators. Certain combination flocculants also work better than when used alone.
(1) Flocculant and collector compound
The combination of polymer flocculant and small molecule collector is one of the effective ways to improve flocculation selectivity. The reason is that the polymer flocculant hydrophobically associates with the non-polar group of the collector adsorbed on the mineral surface through its hydrocarbon chain, and acts as a bridge to produce hydrophobic flocculation. Such hydrophobic flocculation is selective because the mineral collector surface can be pre-hydrophobic by selecting a particular mineral collector. The use of hydrolyzed polyacrylamide and sodium oleate can enhance the selective flocculation of hematite, and the effect is better than sodium oleate or hydrolyzed polyacrylamide alone.
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