Kaolin widely used in the ceramic industry, paper industry, rubber and plastics, building materials industry, chemical industry, paint industry, and many other sectors. Depending on the application, there are different requirements for the whiteness of kaolin . For example, in the paper industry, the whiteness of coated grade kaolin is >83%. In the ceramic industry, the production of high-grade ceramics requires Fe2O3 < 0.15 %. In kaolin processing, the application of traditional beneficiation processes (conventional re-election, magnetic separation, flotation) does not remove the impurity iron from the finely divided and superfine kaolin powders to the standard content. Therefore, the ore dressing workers have taken a different approach and sought non-traditional The new method of removing iron from kaolin greatly reduces the content of impurity iron in kaolin, and realizes the deep processing and economic value of kaolin . The following describes the removal of Gaoling
There are several ways to increase the whiteness of iron in the soil.
1) Adsorption flotation method Adding carrier limestone powder to the slurry of finely divided kaolin (fineness - 43μm, containing Fe2O3 0.172%), limestone powder as adsorbent, adsorbing Fe2O3 from the slurry solution onto the limestone powder carrier, the carrier can be Relying on its own hydrophobicity, the hydrophobicity caused by the reliable collector adheres to the bubbles, and the iron-containing carrier foam product and the in-tank product containing the kaolin concentrate are obtained, thereby separating Fe2O3 from the kaolin. The equipment used for adsorption flotation is a conventional mechanical agitation flotation machine. The collector used is tal oil and ammonium sulfate.
For inhibiting kaolin, pH adjusted with sodium carbonate, sodium silicate ore slurry as a dispersing agent. Since the carrier adsorption is a plurality of action actions such as adsorption, absorption, mixed crystal, entrapment, coagulation, etc., the pH of the medium and the addition of the carrier are
Time, place, etc. have a great influence on adsorption flotation. The process flow is shown in Figure 1. Fe2O3 in kaolin can be reduced from 0.172% to less than 0.15% by adsorption flotation .
2) The two-liquid flotation kaolin slurry transferred into an aqueous solution of a certain concentration, was added to the desired pH value was adjusted to pH-adjusting agent, added after stirring for a certain time catching collector, a predetermined time after the mashing continued, followed by addition of an organic after the solution was sufficiently stirred and then a suitable time, allowed to separate layers, separated, the organic phase to obtain the product (including Fe2O3) product and an aqueous phase (containing kaolin). This apparatus is similar to the method by extraction separation means. The process flow is shown in Figure 2.
Effect of stirring speed on a two-liquid separation flotation index is large, the dispersion was stirred sufficiently insufficient strength against the organic phase, so that the chance of iron droplets colliding contact with an organic mineral decrease; however, too strong stirring easily formed intermediate phase ( milky turbid liquid), so that the sorting effect is deteriorated, suitable agitation intensity is necessary. This method of eliminating iron good results, especially when the solution is added an additive in addition to iron better effect can - recoveries removal rate of 2 μm Fe2O3 kaolin and kaolin product concentrate to achieve the desired results. At the same time, this method can also recycle the organic solution , and the recycling effect is very good.
3) The basic reaction of solid sodium dithionite in addition to iron and sodium dithionite to remove iron is as follows:
Fe2O3 + Na2S2O4 + 2H2SO4 W2NaHSO3 + 2FeSO4 + H2O
This reaction reduces the ferric iron to soluble ferrous iron and removes iron by filtration . The reaction is a reversible reaction, the process requires immediate filtration washed to eliminate, to prevent oxidation of divalent iron into Fe2O3 in the air, which brings great difficulty to industrial production, it is difficult to achieve the desired iron indicators. However, with the addition of Na2S2O4 process an appropriate amount of iron chelating agent, the chelating agent to chelate functional groups with Fe2 + to form a stable chelate, a chelating agent and a water-soluble chelate functional group which promotes hydrophilicity, and therefore stable generation Water-soluble chelate, the iron-containing chelate
After the bleaching of the kaolin, the filtrate is removed, thereby achieving the purpose of removing iron. The solid agent Na2S2O4 is combined with the additive chelate to remove iron. The whiteness of the product is stable and the quality is reliable. The bleaching product does not need to be washed, and the pollution to the surrounding environment is reduced. But solid Na2S2O4 price Geang expensive, and in case of the presence of aerobic tide, easily decomposed and oxidized and reduced efficacy, so they have to be very careful in the transport and storage sectors.
4) Electrochemical synthesis of sodium dithionite iron removal method to electrolyze sulfite aqueous solution under weakly acidic conditions to form dithionite ions on the cathode of the electrolytic cell :
2HSO3 - + 2H+ + 2e = S2O2 - 4 + H2O
The dithionite ion has a strong reducing effect and can make ferric iron
Reduction to divalent Fe2 + : Fe2O3 + S2O4 2 - + 4H+ = 2Fe2 + + 2HSO3 - + H2O
Thereby converted into Fe2O3 solid hydrated Fe2 + ions into the solution, to achieve the purpose of separation and kaolin. This method can reduce the iron ore content of 1.115% (mainly Fe2O3) containing iron to 0.137% of iron . The new ecological S2O4 2 - produced in situ by this electrolysis method is more effective than the bleaching effect of solid Na2S2O4, without the use of expensive solid Na2S2O4, and the cost of medicine is low. Further, throughout the reaction process, the hydrogen ion sulfite press HSO3 - electrolysis S2O4 2 - Bleaching HSO3 - in a cyclic manner, comprising HSO3 - filtrate treated can be reused, reducing the hydrogen addition salts of sulfite amount, but also reduce the sulfur emissions of waste water pollution. But this method of electrolysis equipment once
5) High Gradient Magnetic selective flocculation of iron in the kaolin slurry method flocculant added into the pulp, fine mineral particles by polymer flocculant effect, connected in series to each other into a loose floc group, a single product iron flocculation content reduced from Fe2O3 1.118% 0.169%, then flocculation of the product through the HGMS separation to give a final product containing Fe2O3 down to 0.149%. For a single high-gradient magnetic separation, the primary separation product contains 0.161% Fe2O3, and the Fe2O3 after the second separation is 0.152%, which does not meet the requirements of high-quality kaolin product Fe2O3 < 0.15 %. The selective flocculation and high gradient magnetic separation combined with iron removal can reduce the Fe2O3 content of the product to less than 0.15 %. This method can greatly improve the quality of refractory kaolin with low quality and high iron content , and find a new way for the raw material source of high-grade porcelain . However, the high-gradient magnetic separation equipment of this method has a higher one-time investment.
6) the magnetic separation of magnetic seed finely divided coal-based kaolin (fineness - stirring with a stirrer of 20 m) of the pulp into the adjustable speed. Quantitative dissolved as a dispersant is added (e.g., sodium pyrophosphate), adjust the pulp concentration of 40% to 50%. Adding pH adjusting agent, the pH is adjusted to 515--710, stirred for 10 min, stirring until a uniform, pre-dispersion was added to adjust the magnetic seed good (- 6μm or micro-fine magnetite - 1μm artificial ferrite particles), the magnetic iron species selective, titanium minerals aggregated particles, improve the magnetic properties of these purposes weakly magnetic minerals. The key is the magnetic seed reunion good micro-fine adjust the pH of the pulp suspension, so that it is interposed between the magnetic object and the kinds of minerals or the isoelectric point of the isoelectric point mineral purposes, in which case the magnetic object species and electrically charged mineral surfaces The opposite is true, which is conducive to mutual cohesion. After 3 minutes of high-intensity adjustment , the magnetic separation (field strength 114-115 T) in a 4 × 10 type high gradient magnetic separator is given. magnetic
The slurry flow rate and magnetic separation concentration (10% - 15%) are adjusted at the time of selection, so that the dynamic residence time of the slurry in the magnetic medium is 30-60 s. After the pulp is completely passed, the pulsating water is washed, and the magnetic product is washed after demagnetization. . The process flow is shown in Figure 3. The magnetic separation process can make the ore containing 1.138% Fe2O3 and 0.197% TiO2 coal kaolin. The removal rates of iron and titanium are 52.12% and 49.15%, respectively.
7) High-temperature roasting method The fixed carbon content in coal-series kaolin is generally about 2%. Carbon is present in the kaolinite crystal gap, so that the kaolinite in the coal-based kaolin is grayish-black or gray-white. This kaolin is often removed by high-temperature oxidation roasting. Charcoal to increase the whiteness of kaolin. However, Fe-containing minerals in kaolin, such as pyrite (FeS), siderite (FeCO3) and limonite (Fe2O3·3H2O), are converted to Fe2O3 when calcined at high temperatures , causing the material to become yellow or brick. Red, therefore, it is necessary to take measures such as iron and titanium before or during roasting to increase the whiteness of the product to over 90%. Using high temperature chlorination roasting method, while in addition to carbon, can be removed object iron, titanium coloration factor, kaolin achieve whitening. Chlorination temperature calcined kaolin, kaolin participation in C, the conversion of the iron-titanium oxide of a low melting point of FeCl3 highly volatile (boiling point 315 deg.] C) and of TiCl4 (boiling point 136 deg.] C), the conversion of carbon CO, CO2, Thereby, C, Fe, Ti are separated from the kaolin. Its chemical reaction formula is as follows:
2MeO + C + 2Cl2 = 2MeCl2 + CO2
MeO + C + Cl2 = MeCl2 + CO
Under the same conditions, is calculated by thermodynamics, the free enthalpy ΔG ° according to the size of the reaction arrangement, the order of the various oxides like ability to react with chlorine: K2O> Na2O> CaO> MgO > Fe2O3> TiO2> Al2O3> SiO2. Obviously, those arranged MeO Al2O3 before, during acceleration carbothermic chlorination, by controlling temperature and atmosphere, can be converted into the gaseous chlorides are removed, and the SiO2 and Al2O3 have to retain, kaolin Fe and Ti in addition to achieve The purpose of impurities. Chlorination high temperature roasting process, the temperature is preferably 800 ~ 900 °C,
Suitable starting materials a particle size of 325 mesh - 400 mesh, the amount of chlorine is usually about 3% by weight of kaolin, calcined dynamic than static roasting, baking fluidization technology best, possible to obtain high-quality high brightness kaolin.
8) chemical synthesis of the nascent liquid dithionite bleaching related kaolin whitening methods reported in spite of many, but the vast majority of manufacturers still can not escape from dithionite (commonly known as hydrosulfite) reduction method. As mentioned above, the insurance powder is expensive, and it is easy to decompose and oxidize in the case of moisture, thereby reducing the efficacy. Therefore, it is a meaningful thing to find an effective bleaching agent that is far cheaper than the insurance powder to replace the expensive insurance powder . I produce new chemical liquid by dithionite salt is a method for bleaching kaolin: NaHSO3 solution was added to the kaolin slurry to adjust the slurry to a certain number with H2SO4 pH values, introducing a slurry containing the zinc metal particles In the reactor, after the reaction reaches a certain time, the effluent slurry is added to the Na2CO3 solution, the pH of the slurry is adjusted to neutrality, and then filtered, and the obtained filter cake is a bleaching product. The bleaching principle of this chemical method is as follows: In an acidic medium, the following main chemical reactions occur in the slurry in the slurry :
NaHSO3 + H2SO4 = Na2SO4 + 2H2SO3
H2SO3 = SO2 + H2O
2NaHSO3 + SO2 + Zn = Na2S2O4 + ZnSO3 + H2O
ZnSO3 + H2SO4 = ZnSO4 + H2SO3
H2SO3 = SO2 + H2O
Zn + 2H2SO3 = ZnS2O4 + H2O
The nascent liquid dithionite (Na2S2O4 and ZnS2O4) produced by the reaction has strong reducibility, and they react with the solid iron oxide in the kaolin slurry as follows:
Fe2O3 + Na2S2O4 + 2H2SO4 = 2NaHSO3 + 2FeSO4 + H2O
Fe2O3 + ZnS2O4 + 2H2SO4 = Zn ( HSO3 ) 2 + 2FeSO4 + H2O
The FeSO4 formed by the reaction is dissolved in water and removed in a subsequent filtration operation , thereby whitening the kaolin. This method allows whiteness kaolin increased from 72% to 83% on the (in the case of the bleaching reaction at room temperature), the total cost of the solid bleaching agent sodium dithionite significant decline (same index lower phase ratio), than only 1 / 3 ~ 1 / 2 of the insurance powder method. This method is expensive equipment need for a high price, less one-time investment, and the process is simple, easy operation. At the same time, in the bleaching and reduction process, NaHSO3 and Zn (HSO3) 2 are continuously formed, which are added as regeneration agents to the formation reaction of Na2S2O4 and ZnS2O4. The test proves that rational recycling of the reaction solution can reduce the amount of NaHSO3. further reduce the cost of reagents. Since GENESIS kaolin and around the different types, there are large differences in the type of colored impurities, the number and occurrence status kaolin contained, it is necessary from a practical method of selecting in addition to iron kaolin, through experiments, selection The best solution and process conditions.
Source: Separation Circle
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