Bentonite for pellets and sodium modification process thereof

Abstract

The invention discloses bentonite for pellets and a sodium modification process thereof, and belongs to the technical field of iron ore pellets. The sodium modification process comprises the following steps: adding sodium hexametaphosphate into a calcium bentonite ore pulp solution, fully dispersing to realize primary sodium modification treatment of the calcium bentonite, and reacting PO4 < 3-> with calcium ions in the bentonite in the primary sodium modification treatment process to form [CaPO4] <->, so that the surfaces of bentonite particles are negatively charged; continuously adding sodium carbonate into the bentonite ore pulp solution subjected to primary sodium treatment, and fully mixing and dispersing to realize secondary sodium treatment of the calcium bentonite; sodium pyrophosphate continues to be added into the bentonite ore pulp solution subjected to secondary sodium treatment, pyrophosphate ions and calcium ions form stable complex precipitates through sufficient mixing and dispersing, and third-stage sodium treatment of bentonite is further achieved. By adopting the sodium modification process disclosed by the invention, the sodium modification effect can be effectively ensured, the upgrading and modifying time of the bentonite can be shortened, and the upgrading and modifying efficiency can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of bentonite preparation for pelletizing, and more specifically relates to bentonite for pelletizing and a sodiumization process thereof. Background Art

[0002] Bentonite is the most important inorganic binder for pellets, and its main component is montmorillonite. Montmorillonite is a 2:1 type layered silicate composed of two layers of silicon-oxygen tetrahedral sheets with a layer of aluminum (magnesium) oxygen octahedral sheets in the middle. Due to its loose interlayer structure, water molecules or other organic molecules can enter the interlayer, making it have unique properties such as water absorption and expansion, high dispersibility, and adsorption. Generally speaking, bentonite can absorb 8-15 times of its own volume of water, and its volume can expand several times or even dozens of times. It can be dispersed into a gel and suspension state in a water medium. These unique properties create conditions for bentonite to be used as a pellet binder.

[0003] Domestic bentonite generally has many impurities and poor quality, and most of them are calcium-based bentonite. The proportion of pellet ore used in production is as high as 3%, which can easily lead to a serious reduction in the iron grade of the pellets. On this basis, researchers focus on improving the properties of bentonite itself, using physical purification, chemical purification, sodium modification, organic modification and other methods to improve the quality of bentonite, and have carried out extensive research. Among them, the sodium modification of calcium-based bentonite is to convert calcium-based bentonite into sodium-based bentonite by using a sodium agent, but the existing sodium modification process of bentonite has the problems of long quality modification time, low efficiency, or unclear effect. Therefore, it is of great significance to further improve the efficiency and effect of sodium modification of bentonite.

[0004] After searching, the Chinese patent application No. 2017103634981 discloses a sodium bentonite and a preparation method thereof, wherein the sodium bentonite is prepared from the following raw materials in parts by weight: 90-98 parts of calcium-based bentonite, 1-10 parts of sodium salt, 1-3 parts of viscosity enhancer, 0.5-2 parts of synergist, and 0.01-1 parts of lubricant. The application adopts a preparation method of acidification followed by compounding to avoid chemical reactions between sulfuric acid and other components. At the same time, the absorbency, stability, and lubricity of the acidified bentonite are greatly improved, but the overall preparation process is relatively complicated. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems of low efficiency or unclear effect of the existing sodium modification process of bentonite raw soil, and provide a pelletizing bentonite and its sodium modification process. The sodium modification process of the present invention can not only effectively ensure the sodium modification effect, but also reduce the quality modification time of bentonite and improve the quality modification efficiency.

[0006] In order to achieve the above object, the technical solution provided by the present invention is:

[0007] The present invention provides a sodiumization process of bentonite for pelletizing, comprising:

[0008] First, sodium hexametaphosphate is added to the calcium-based bentonite slurry solution, and the calcium-based bentonite is fully dispersed to achieve the primary sodium treatment. During the primary sodium treatment, PO4 3- Reacts with calcium ions in bentonite to form [CaPO4] - , so that the surface of bentonite particles is negatively charged;

[0009] Further adding sodium carbonate to the bentonite slurry solution after the primary sodium treatment, and fully mixing and dispersing the solution to achieve the secondary sodium treatment of the calcium-based bentonite;

[0010] Sodium pyrophosphate is further added to the bentonite slurry solution after the secondary sodium treatment. After sufficient mixing and dispersion, the pyrophosphate ions and calcium ions form a stable complex precipitate, thereby further realizing the tertiary sodium treatment of the bentonite.

[0011] Aiming at the technical problems that the existing sodium modification process of raw bentonite is either low in efficiency or not obvious in sodium modification effect, the present invention optimizes the sodium modification process of bentonite. On the one hand, sodium hexametaphosphate, sodium carbonate and sodium pyrophosphate are used in combination, and on the other hand, the adding timing of the three substances is optimized, so that not only the sodium modification effect of bentonite can be effectively improved to meet the quality requirements of first-grade bentonite, but also the sodium modification effect of bentonite can be prevented from being greatly affected on the iron grade of the pellets when it is added to the pellets as an adhesive; at the same time, the recovery rate of montmorillonite can be effectively guaranteed, and the sodium modification efficiency can be significantly improved. Moreover, the overall process operation is simple and easy to be industrially promoted and applied.

[0012] Specifically, sodium carbonate is usually added as a sodiumizing agent for bentonite in the prior art, but when sodium carbonate is used as a sodiumizing agent alone, if the addition amount of sodium carbonate is low, the yield of montmorillonite is low, and the residue needs to be purified twice; if the addition amount of sodium carbonate is high, the water absorption rate of bentonite will be reduced, and the requirements of the national first-level bentonite standard cannot be met. Based on the above situation, the present invention can further improve the sodiumization quality and quality of bentonite by the composite addition of sodium hexametaphosphate, especially further improve the expansion index and water absorption rate of bentonite, but the addition of sodium hexametaphosphate will affect the yield of montmorillonite in bentonite. Therefore, the present invention further compositely adds sodium pyrophosphate, so that the yield of montmorillonite in bentonite can be effectively improved, and the sodium modification effect of bentonite, the quality and taste of the obtained bentonite, and the yield of montmorillonite in bentonite can be effectively guaranteed by the composite effect between the three.

[0013] It should be noted that the order of adding the three substances in this application is crucial to ensure the sodiumization effect. First, sodium hexametaphosphate is added to the solution as a dispersant to generate Na + and PO4 3- , forming [CaPO4] with calcium ions in bentonite - , so that the surface of bentonite particles is negatively charged. According to the principle of like charges repel each other, the bentonite particles repel each other, which increases the dispersibility between the particles (but the amount of sodium hexametaphosphate added cannot be too much, otherwise Ca2PO4 precipitation will be formed, affecting the sodiumization effect).

[0014] After the surface of bentonite particles is negatively charged, sodium carbonate is added, and sodium carbonate enters the solution to form Na + and CO3 2- The surface of bentonite particles is negatively charged, attracting Na + Formation of NaCaPO4, NaCaPO4 and CO3 2- A replacement reaction occurs to form CaCO3 precipitation. [NaPO4] is left on the surface of bentonite. 2- , further attracting Na + The formation of Na3PO4 further enhances the Na-chemical effect.

[0015] However, sodium carbonate will also form Na + and HCO 3- , which weakens the solidification effect on calcium ions, causing the calcium ions to leave the bentonite but still exist in the solution. Therefore, the present invention adds sodium pyrophosphate after adding sodium carbonate. After sodium pyrophosphate enters the solution, pyrophosphate is formed. The pyrophosphate ion has a strong complexing effect, so it can also form a stable complex precipitate with calcium ions.

[0016] Furthermore, the addition amount of sodium hexametaphosphate, sodium carbonate and sodium pyrophosphate accounts for 1.5% to 2.5%, 1.0% to 2.0% and 1.5% to 2.0% of the dry mass of calcium-based bentonite, respectively. The addition amount of the three substances has an important influence on simultaneously ensuring the quality of sodium-treated bentonite and the yield of montmorillonite. If the addition amount is too small, it will lead to insufficient sodium treatment or a low yield of montmorillonite. If the addition amount is too high, it will worsen the quality of sodium-treated bentonite. + With Ca 2+ The exchange reaction between them may reduce the yield of montmorillonite.

[0017] Specifically, with the increase of sodium carbonate dosage, various indicators of bentonite show a phenomenon of first increasing and then decreasing. When the sodium carbonate dosage is 1.5%, various indicators are optimal, but the yield of montmorillonite is relatively low. Therefore, the preferred addition amount of sodium carbonate is 2.0%. When the sodium carbonate dosage is 2.5%, the solution is viscous and cannot be precipitated. With the composite addition of sodium hexametaphosphate dosage and the increase of its content, various indicators of bentonite show a phenomenon of first increasing and then decreasing as a whole, especially the expansion index and water absorption rate of bentonite have a significant improvement. When the sodium hexametaphosphate dosage is 2.0%, the effect is optimal, while the yield of montmorillonite shows a phenomenon of first decreasing and then increasing. At this time, with the increase of the composite addition of sodium pyrophosphate and the increase of the added amount, the water absorption rate and swelling index of the obtained bentonite slowly increased, while its blue absorption, montmorillonite content and montmorillonite yield increased first and then decreased, reaching the highest when the added amount was 1.5% sodium pyrophosphate. After analysis, this may be due to the fact that the addition of a higher concentration of sodium pyrophosphate has a certain degree of quality improvement and sodium effect, which indirectly causes an increase in the yield by increasing the montmorillonite content; while an excessively high concentration of sodium pyrophosphate weakens the quality improvement and sodium effect, and leads to a rapid decrease in the yield as the quality of the yield decreases.

[0018] Therefore, it is further preferred that the addition amounts of sodium hexametaphosphate, sodium carbonate and sodium pyrophosphate account for 2.0%, 2.0% and 1.5% of the dry basis mass of calcium-based bentonite respectively. At this time, the overall mass of the sodium-treated bentonite and the yield of montmorillonite can be effectively coordinated.

[0019] Furthermore, the liquid-to-solid ratio (mass ratio) of the calcium-based bentonite slurry solution is (3-5): 1, and the solution temperature is 20-30°C. As the liquid-to-solid ratio of the calcium-based bentonite slurry solution increases, the bentonite particles are dispersed more evenly in the water, and the full contact between the sodium agent and the particles destroys the card house structure, releasing the impurities relying on the structure. According to the characteristics of the high density of sand and gravel impurities, the impurities are precipitated by free sedimentation or centrifugal force, thereby increasing the montmorillonite content in the upper suspension. Although continuing to increase the liquid-to-solid ratio of the slurry is beneficial to the purification of bentonite, the degree of improvement is small, which not only increases the difficulty of dehydration, but also increases the cost of investment in the process, resulting in a large waste of water.

[0020] Furthermore, between two adjacent sodium treatments, the bentonite slurry solution is filtered using a 0.4-0.6 mm square sieve.

[0021] Furthermore, the method further comprises: performing solid-liquid separation on the mixed solution after the three-stage sodium treatment to obtain sodium bentonite.

[0022] As one of the implementation methods, the primary, secondary and tertiary sodium treatments are all carried out under electromagnetic stirring conditions, first electromagnetic stirring for 20 to 40 minutes, and then settling for 25 to 35 minutes.

[0023] As another preferred implementation, the primary, secondary and tertiary sodium treatments are all subjected to vibration dispersion of the mixed solution under the action of reciprocating centrifugal force, first rotating counterclockwise for 40 to 60 seconds, then rotating clockwise for 40 to 60 seconds, the centrifugal speed is 500 to 800 rpm, and the centrifugal vibration time of the primary sodium treatment is 2.5 to 3.5 minutes, the centrifugal vibration time of the secondary sodium treatment is 3.5 to 4.5 minutes, and the centrifugal vibration time of the tertiary sodium treatment is 3.5 to 4.5 minutes. By vibrating and dispersing the mixed solution under the action of centrifugal force, it is not only convenient to fully sodiumize the bentonite, but also possible to directly realize the stratification of the sodiumized bentonite and impurities without the need for sedimentation treatment, thereby further improving the sodiumization efficiency and greatly shortening the sodiumization time.

[0024] Furthermore, after the three-stage sodium treatment, the mixed solution is subjected to rotational centrifugation separation in the same direction at a centrifugal speed of 3000-4000 rpm.

[0025] The present invention also provides bentonite for pelletizing, which is sodium-treated bentonite obtained by any of the above-mentioned sodium-treatment processes.

[0026] Preferably, the montmorillonite content of the bentonite is 75% to 85%, and the blue absorption capacity is 33 to 38 g / 100 g. -1 , expansion index is 75~85ml·g -1 , water absorption rate is 460~600%·(2h) -1 .

[0027] In summary, the technical solution provided by the present invention can achieve the following beneficial effects compared with the prior art:

[0028] (1) The present invention performs sodium treatment on bentonite by combining three substances, and optimizes the adding order of the three substances to perform multi-stage sodium treatment, thereby effectively improving the sodium treatment effect on bentonite and improving the quality and grade of bentonite, while also effectively ensuring the yield of montmorillonite in bentonite. The process is simple to operate, has high sodium treatment efficiency, and greatly shortens the sodium treatment time.

[0029] (2) XRD and infrared spectroscopy analysis of the sodium-modified soil obtained by the sodium-modification process of the present invention revealed that the sodium-modified soil had stronger stretching vibration absorption characteristic peaks of free -OH and COO- stretching vibration than the original soil, and the internal hydrophilic groups also increased significantly; elements such as SiO2 and CaO were further reduced, and Na +The increase in the content of impurities further proves the reduction of impurities and the increase of the degree of sodium. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The Fourier transform infrared analysis spectra of the modified soil and the original soil obtained in Example 1;

[0031] Figure 2 The XRD patterns of the modified soil and the original soil obtained in Example 1;

[0032] Figure 3 Schematic diagram of the structure of the sodiumization device in the embodiment of the present invention.

[0033] Explanation of reference numerals: 1. support table; 2. fixed disk; 3. rotating disk; 401. first sodium-reducing agent liquid tank; 402. second sodium-reducing agent liquid tank; 403. third sodium-reducing agent liquid tank; 5. first delivery tube; 6. second delivery tube; 7. fixed tube; 8. centrifuge tube; 801. opening; 9. articulated ball; 10. rotating rod; 11. supernatant container; 1101. outflow hole. DETAILED DESCRIPTION

[0034] In order to further understand the content of the present invention, the present invention is now described in detail in conjunction with specific embodiments.

[0035] Example 1

[0036] This embodiment provides a sodiumization process of bentonite for pelletizing, comprising:

[0037] The original soil was crushed and mixed with water in a ratio of 1:4 to obtain a calcium-based bentonite slurry solution with a solution temperature of 20°C;

[0038] First, sodium hexametaphosphate is injected into the calcium-based bentonite slurry solution. The amount of sodium hexametaphosphate added accounts for 2.0% of the dry mass of the calcium-based bentonite. The mixed solution is fully shaken and dispersed under the action of reciprocating centrifugal force to achieve the primary sodium treatment of the calcium-based bentonite. Specifically, the mixed solution is first centrifuged counterclockwise for 1 minute, then clockwise for 1 minute, alternating in sequence. The centrifugal speed is 650 rpm, and the total treatment time is 3 minutes. During the primary sodium treatment process, sodium hexametaphosphate generates Na + and PO4 3- ,PO4 3- Reacts with calcium ions in bentonite to form [CaPO4] - , so that the surface of bentonite particles is negatively charged; but according to the principle of like charges repel each other, the bentonite particles repel each other, thereby increasing the dispersibility between the particles, but the amount of sodium hexametaphosphate added cannot be too much, otherwise Ca2PO4 precipitation will form.

[0039] Then, sodium carbonate is added to the bentonite slurry solution after the primary sodium treatment. The amount of sodium carbonate added accounts for 2.0% of the dry mass of the calcium-based bentonite. The mixed solution is fully shaken and dispersed under the action of reciprocating centrifugal force to achieve the secondary sodium treatment of the calcium-based bentonite. During the secondary sodium treatment, the mixed solution is first centrifuged counterclockwise for 1 minute, then clockwise for 1 minute, alternating in sequence, the centrifugal speed is 650 rpm, and the total treatment time is 4 minutes. After sodium carbonate enters the solution, it will form Na + and CO3 2- Since the surface of bentonite particles is negatively charged, it will attract Na + Forming NaCaPO4. NaCaPO4 and CO3 2- A replacement reaction occurs to form CaCO3 precipitation. [NaPO4] is left on the surface of bentonite. 2- , further attracting Na + Na3PO4 is formed, which further enhances the Na-ization effect.

[0040] Then, sodium pyrophosphate is added to the bentonite slurry solution after the secondary sodium treatment to carry out the tertiary sodium treatment of the bentonite, and the amount of sodium pyrophosphate added accounts for 1.5% of the dry basis weight of the calcium-based bentonite. During the tertiary sodium treatment, the mixed solution is first centrifuged counterclockwise for 1 minute, then centrifuged clockwise for 1 minute, alternately, the centrifugal speed is 650 rpm, and the total treatment time is 4 minutes.

[0041] Since sodium carbonate will also form Na + and HCO3 - , resulting in a weakened solidification effect on calcium ions, causing calcium ions to leave bentonite but still exist in the solution. Sodium pyrophosphate enters the solution to form pyrophosphate ions. Pyrophosphate ions have a strong complexing effect and can form a stable complex precipitate with calcium ions, thereby helping to avoid the addition of sodium carbonate to form HCO3 - This leads to a weakening of the calcium ion curing effect.

[0042] After the three-stage sodium treatment, the mixed solution is continued to be subjected to high-speed rotating centrifugal motion in the same direction at a centrifugal speed of 3000 rpm. Under the high-speed centrifugal force, the precipitate is concentrated at the bottom, which is conducive to the separation of the supernatant.

[0043] The Fourier infrared analysis spectra and XRD spectra of the modified sodium soil and the original soil in this example are as follows: Figure 1 , Figure 2 As shown, combined Figure 1 It can be seen that the high frequency area of ​​the original soil is at 3442cm -1The broad absorption band at 1636 cm is attributed to the stretching vibration of HOH bonds of water molecules between montmorillonite layers. -1 Bending vibration at 1035cm -1 The absorption band at is attributed to the asymmetric stretching vibration of Si-O-Si and stronger absorption. After purification and sodiumization in Example 1, new peaks begin to appear, and the original peak intensity is also strengthened, indicating that the degree of sodiumization is relatively high and the effect is sufficient. Compared with the original soil, the sodium-treated soil has stronger free-OH stretching vibration absorption characteristic peaks and -COOH stretching vibration peaks, and the internal hydrophilic groups increase.

[0044] Combination Figure 2 The interlayer spacing of the original montmorillonite is reduced from d(001)=1.5297nm to d(001)=1.2508nm in this embodiment, indicating that the sodiumization effect is sufficient, the impurity peak is reduced, and the synchronous purification sodiumization effect is obvious.

[0045] Specifically, the sodium-making device for bentonite used in this embodiment is as follows: Figure 3 As shown, it includes a support platform 1, a rotating disk 3 and a sodiumizing agent liquid warehouse, wherein a fixed disk 2 is fixedly arranged on the support platform 1, the rotating disk 3 is horizontally rotated and installed below the fixed disk 2, and a plurality of centrifuge tubes 8 uniformly spaced and distributed are arranged at the bottom of the rotating disk 3 around its circumferential direction. The sodiumizing agent liquid warehouse includes a first sodiumizing agent liquid warehouse 401, a second sodiumizing agent liquid warehouse 402 and a third sodiumizing agent liquid warehouse 403, and the three liquid warehouses are respectively filled with sodium hexametaphosphate solution, sodium carbonate solution and sodium pyrophosphate solution, and their mass concentrations are 8-10%, 10-12% and 3-5%, respectively. Three different sodiumizing agents are sequentially injected into the centrifuge tube 8 through the three liquid warehouses for sodiumization treatment, and the injection amount of the sodiumizing agent can be controlled by a flow valve or a gas metering valve. After mixing, the rotating disk 3 is driven to rotate, so that the plurality of centrifuge tubes 8 can be driven to be in a centrifugal state, which is convenient for fully oscillating and dispersing the mixed solution, realizing the centrifugal separation of the bentonite supernatant and impurities, without the need for sedimentation separation and other operations, greatly improving the sodiumization effect, and the overall operation is simple.

[0046] Furthermore, a fixed tube 7 is provided at the bottom of the rotating disk 3, and the top of the centrifuge tube 8 is rotatably connected to the fixed tube 7 through a hinge ball 9, and the bottom of the hinge ball 9 is fixedly installed at the mouth of the centrifuge tube, and its size matches the diameter of the centrifuge tube to ensure the sealing of the mouth of the centrifuge tube and prevent the mixed liquid from overflowing during the centrifugal rotation. Among them, the hinge ball 9 and the centrifuge tube 8 can be threadedly connected, or other fixed connection methods can be used. However, when the rotating disk 3 is stationary, each centrifuge tube is in a vertical state, and when the rotating disk 3 rotates, each centrifuge tube is in an inclined state under the action of centrifugal force. Specifically, in this embodiment, the liquid outlets of the three liquid bins are all connected with a first delivery pipe 5, and the rotating disk 3 and the fixed tube 7 are respectively provided with second delivery pipes 6 corresponding to a plurality of centrifuge tubes 8, the first delivery pipe 5 is connected to the second delivery pipe 6, and the hinge ball 9 is processed with a delivery channel for the second delivery pipe 6 to pass through, and the aperture of the delivery channel is larger than the outer diameter of the second delivery pipe 6.

[0047] It should also be noted that the rotation drive structure of the rotating disk 3 in the present embodiment is not limited, as long as it can drive the centrifuge tube to rotate relative to the fixed disk 2. For example, the rotating disk 3 can be directly driven to rotate by a motor-gear mechanism, or a rotating rod 10 can be set at the bottom center of the rotating disk 3, and the rotating rod 10 can be driven to rotate by a motor, thereby driving the rotating disk 3 to rotate together.

[0048] Furthermore, the side wall of each centrifuge tube 8 is located in the middle and upper part of the centrifuge tube central axis. The side is processed with an opening 801 for the supernatant to flow out and can be opened or closed. Therefore, after sufficient centrifugation, the opening 801 is opened to facilitate the supernatant to flow out and separate from the lower sedimentation impurities. More preferably, the aperture of the opening 801 is 1-2mm, and its height from the bottom of the centrifuge tube 8 is 80-85% of the overall height of the centrifuge tube 8. In this embodiment, a supernatant container 11 is also provided below the centrifuge tube 8 to receive the sodium-treated and separated bentonite supernatant. In order to facilitate the removal of the supernatant in the supernatant container 11, a spiral lifting foot is provided at the bottom of one end of the supernatant container 11, and an outflow hole 1101 is processed at one end of the bottom of the supernatant container 11 away from the foot.

[0049] Comparative Example 1

[0050] This comparative example provides a sodium treatment process for bentonite for pelletizing, and its operation is basically the same as that of Example 1, with the main difference being that only 2.0% of sodium carbonate is added for sodium treatment in this comparative example.

[0051] Comparative Example 2

[0052] This comparative example provides a sodium treatment process for bentonite for pelletizing, and its operation is basically the same as that of Example 1, with the main difference being that only 2.0% of sodium hexametaphosphate is added for sodium treatment in this comparative example.

[0053] Comparative Example 3

[0054] This comparative example provides a sodium treatment process for bentonite for pelletizing, and its operation is basically the same as that of Example 1, with the main difference being that only 1.5% of sodium pyrophosphate is added for sodium treatment in this comparative example.

[0055] Comparative Example 4

[0056] This comparative example provides a sodium treatment process for bentonite for pelletizing, and its operation is basically the same as that of Example 1, with the main difference being that in this comparative example, 2.0% sodium hexametaphosphate and 2.0% sodium carbonate are added step by step in sequence to perform a two-stage sodium treatment.

[0057] Comparative Example 5

[0058] This comparative example provides a sodium treatment process for bentonite for pelletizing, and its operation is basically the same as that of Example 1, except that in this comparative example, 2.0% sodium carbonate and 1.5% sodium pyrophosphate are added step by step in sequence to perform a two-stage sodium treatment.

[0059] Comparative Example 6

[0060] This comparative example provides a sodiumization process for bentonite for pelletizing. The main difference between this comparative example and Example 1 is that in this comparative example, sodium carbonate, sodium pyrophosphate and sodium hexametaphosphate are added together into the calcium-based bentonite raw soil slurry solution for centrifugal rotation sedimentation dispersion treatment.

[0061] Comparative Example 7

[0062] This comparative example provides a sodiumization process for bentonite for pelletizing. The main difference between this comparative example and Example 1 is that in this comparative example, sodium pyrophosphate is first added for primary sodiumization, then sodium carbonate is added for secondary sodiumization, and finally sodium hexametaphosphate is added for tertiary sodiumization.

[0063] The quality indexes and yields of the modified bentonite obtained in Example 1 and Comparative Examples 1-7 are shown in Table 1 and Table 2, respectively. Combining the data in the table, it can be seen that only by adding sodium carbonate, sodium pyrophosphate and sodium hexametaphosphate in combination and performing multi-stage sodium treatment in a certain order can the quality and yield of the sodium-treated bentonite be effectively guaranteed.

[0064] Table 1 Quality indicators of the sodium soil obtained in Example 1 and Comparative Examples 1-7

[0065]

[0066]

[0067] Table 2 The yield of montmorillonite in Example 1 and Comparative Examples 1-7

[0068]

[0069] Example 2

[0070] The sodiumization process of bentonite for pelletizing of this embodiment comprises:

[0071] The original soil was crushed and mixed with water in a ratio of 1:3 to obtain a calcium-based bentonite slurry solution with a solution temperature of 25°C;

[0072] First, sodium hexametaphosphate is injected into the calcium-based bentonite slurry solution, and the addition amount of sodium hexametaphosphate accounts for 1.5% of the dry basis mass of the calcium-based bentonite. Under the action of reciprocating centrifugal force, the mixed solution is fully shaken and dispersed to achieve the primary sodium treatment of the calcium-based bentonite. Specifically, the mixed solution is first centrifuged counterclockwise for 40 seconds, and then clockwise for 40 seconds, alternating in sequence. The centrifugal speed is 500 rpm, and the total treatment time is 4 minutes.

[0073] Then, sodium carbonate is continuously added to the bentonite slurry solution after the primary sodium treatment, and the amount of sodium carbonate added accounts for 1.5% of the dry basis weight of the calcium-based bentonite. The mixed solution is fully shaken and dispersed under the action of reciprocating centrifugal force to achieve the secondary sodium treatment of the calcium-based bentonite. Specifically, during the secondary sodium treatment, the mixed solution is first centrifuged counterclockwise for 50 seconds, and then clockwise for 50 seconds, alternating in sequence, the centrifugal speed is 500 revolutions / min, and the total treatment time is 200 seconds.

[0074] Then, sodium pyrophosphate is added to the bentonite slurry solution after the secondary sodium treatment to carry out the tertiary sodium treatment of the bentonite, and the amount of sodium pyrophosphate added accounts for 2.0% of the dry basis mass of the calcium-based bentonite. During the tertiary sodium treatment, the mixed solution is first centrifuged counterclockwise for 50 seconds, then centrifuged clockwise for 50 seconds, alternately, the centrifugal speed is 500 rpm, and the total treatment time is 200 seconds.

[0075] After the three-stage sodium treatment, the mixed solution is continued to be subjected to high-speed rotating centrifugal motion in the same direction at a speed of 4000 rpm. Under the high-speed centrifugal force, the precipitate is concentrated at the bottom, which is conducive to the separation of the supernatant.

[0076] Example 3

[0077] The sodiumization process of bentonite for pelletizing of this embodiment comprises:

[0078] The original soil was crushed and mixed with water in a ratio of 1:5 to obtain a calcium-based bentonite slurry solution with a solution temperature of 30°C;

[0079] First, sodium hexametaphosphate is injected into the calcium-based bentonite slurry solution, and the addition amount of sodium hexametaphosphate accounts for 2.5% of the dry basis mass of the calcium-based bentonite. The mixed solution is fully shaken and dispersed under the action of reciprocating centrifugal force to achieve the primary sodium treatment of the calcium-based bentonite. Specifically, the mixed solution is first centrifuged counterclockwise for 45 seconds, and then clockwise for 45 seconds, alternating in sequence. The centrifugal speed is 800 rpm, and the total treatment time is 225 seconds.

[0080] Then, sodium carbonate is continuously added to the bentonite slurry solution after the primary sodium treatment, and the amount of sodium carbonate added accounts for 1.0% of the dry basis mass of the calcium-based bentonite. The mixed solution is fully shaken and dispersed under the action of reciprocating centrifugal force to achieve the secondary sodium treatment of the calcium-based bentonite. During the secondary sodium treatment, the mixed solution is first centrifuged counterclockwise for 55 seconds, and then clockwise for 55 seconds, alternating in sequence, the centrifugal speed is 800 revolutions / min, and the total treatment time is 220 seconds.

[0081] Then, sodium pyrophosphate is added to the bentonite slurry solution after the secondary sodium treatment to carry out the tertiary sodium treatment of the bentonite, and the amount of sodium pyrophosphate added accounts for 1.8% of the dry basis weight of the calcium-based bentonite. During the tertiary sodium treatment, the mixed solution is first centrifuged counterclockwise for 55 seconds, then centrifuged clockwise for 55 seconds, alternately, the centrifugal speed is 800 rpm, and the total treatment time is 220 seconds.

[0082] After the three-stage sodium treatment, the mixed solution is continued to be subjected to high-speed rotating centrifugal motion in the same direction at a speed of 3500 rpm. Under the high-speed centrifugal force, the precipitate is concentrated at the bottom, which is conducive to the separation of the supernatant.

[0083] The indicators and yields of the sodium bentonite obtained in Example 2 and Example 3 are shown in Table 3 below. According to the table, the swelling index, water absorption rate and yield of the sodium bentonite obtained in Example 2 and Example 3 are slightly lower than those in Example 1, but can meet the quality requirements of bentonite for pelletizing.

[0084] Table 3 Quality indexes of sodium-containing soil obtained in Examples 2 and 3 and the yield of montmorillonite

[0085]

[0086] Example 4

[0087] The sodium treatment process of bentonite for pelletizing in this embodiment is basically the same as that in Example 1, except that: in this embodiment, a 0.4-0.6 mm square sieve is used to filter the bentonite slurry solution between adjacent sodium treatments. The indexes of the modified soil obtained after the filtration treatment are lower than those in Example 1 to a certain extent, and the montmorillonite content, blue absorption, swelling index and water absorption rate are 79.25%, 35.4 g·100 g·100%, and 35.6 g·100 g·100%, respectively. -1 、77ml·g -1 、563.5%·(2h) -1 , but the yield of montmorillonite is higher, which is 92.15%.

[0088] Example 5

[0089] The sodiumization process of bentonite for pelletizing in this embodiment is basically the same as that in Example 1, except that the primary, secondary and tertiary sodiumization treatments in this embodiment are all carried out under electromagnetic stirring conditions (without centrifugal treatment), firstly electromagnetic stirring for 30 minutes, and then settling for 30 minutes. The quality of the sodiumized soil obtained after modification is close to that in Example 1, but its sodiumization efficiency is lower than that in Example 1.

[0090] Example 6

[0091] In this embodiment, the original soil is crushed and mixed with water in a ratio of 1:4, 2.0% sodium carbonate and 1.5% sodium pyrophosphate are added and stirred for 30 minutes for sodiumization, filtered with a 0.5mm square sieve, and then 2.0% sodium hexametaphosphate is added and stirred for 30 minutes for sodiumization and then settled for 30 minutes. After the upper clear liquid is dried, the montmorillonite content is 76.47%, the blue absorption is 33.8g·100g-1, the expansion index is 76ml·g-1, and the water absorption rate is 489.3%·(2h)-1. After weighing the dried sample, the yield is calculated to be 91.82%. The overall index meets the requirements of first-class bentonite, and the yield is relatively high.

Claims

1. A process for sodiumization of bentonite for pelletization, characterized in that: include: First, sodium hexametaphosphate is added to the calcium-based bentonite slurry solution, and the calcium-based bentonite is fully dispersed to achieve the primary sodium treatment. During the primary sodium treatment, PO4 3- Reacts with calcium ions in bentonite to form [CaPO4] - , so that the surface of bentonite particles is negatively charged; Further adding sodium carbonate to the bentonite slurry solution after the primary sodium treatment, and fully mixing and dispersing the solution to achieve the secondary sodium treatment of the calcium-based bentonite; Sodium pyrophosphate is further added to the bentonite slurry solution after the secondary sodium treatment. After sufficient mixing and dispersion, the pyrophosphate ions and calcium ions form a stable complex precipitate, thereby further realizing the tertiary sodium treatment of the bentonite.

2. The sodiumization process of bentonite for pelletizing according to claim 1, characterized in that: The added amounts of the sodium hexametaphosphate, sodium carbonate and sodium pyrophosphate account for 1.5% to 2.5%, 1.0% to 2.0% and 1.5% to 2.0% of the dry mass of the calcium-based bentonite respectively.

3. The sodiumization process of bentonite for pelletizing according to claim 2, characterized in that: The added amounts of the sodium hexametaphosphate, sodium carbonate and sodium pyrophosphate account for 2.0%, 2.0% and 1.5% of the dry basis mass of the calcium-based bentonite respectively.

4. The sodiumization process of bentonite for pelletizing according to any one of claims 1 to 3, characterized in that: The liquid-to-solid ratio of the calcium-based bentonite slurry solution is (3-5):1, and the solution temperature is 20-30°C.

5. The sodiumization process of bentonite for pelletizing according to any one of claims 1 to 3, characterized in that: Also includes: Between two adjacent sodium treatments, the bentonite slurry solution is filtered using a 0.4-0.6 mm square sieve; and / or The mixed solution after the three-stage sodium treatment is subjected to solid-liquid separation to obtain sodium bentonite.

6. The sodiumization process of bentonite for pelletizing according to claim 5, characterized in that: The primary, secondary and tertiary sodium treatments are all carried out under electromagnetic stirring conditions, first electromagnetic stirring for 20 to 40 minutes, and then settling for 25 to 35 minutes.

7. The sodiumization process of bentonite for pelletizing according to claim 5, characterized in that: The primary, secondary and tertiary sodium treatments all oscillate and disperse the mixed solution under the action of reciprocating centrifugal force, first rotating counterclockwise for 40 to 60 seconds and then clockwise for 40 to 60 seconds, with a centrifugal speed of 500 to 800 rpm. The centrifugal shaking time for the primary sodium treatment is 2.5 to 4 minutes, the centrifugal shaking time for the secondary sodium treatment is 3 to 4.5 minutes, and the centrifugal shaking time for the tertiary sodium treatment is 3 to 4.5 minutes.

8. The sodiumization process of bentonite for pelletizing according to claim 7, characterized in that: After the three-stage sodium treatment, the mixed solution is subjected to rotating centrifugal separation in the same direction at a centrifugal speed of 3000-4000 revolutions / min.

9. A bentonite for pelletizing, characterized in that: The bentonite is sodium bentonite obtained by being treated by the process described in any one of claims 1 to 8.

10. The bentonite for pelletizing according to claim 9, characterized in that: The bentonite has a montmorillonite content of 75% to 85% and a blue absorption capacity of 33 to 38 g / 100 g. -1 , expansion index is 75~85ml·g -1 , water absorption rate is 460~600%·(2h) -1 .

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