Method for preparing low-activity magnesium oxide based on roller kiln electric calcination

Abstract

The invention relates to the technical field of magnesium oxide preparation, and particularly discloses a method for preparing low-activity magnesium oxide based on roller kiln electric calcination. The method comprises the following steps: putting a magnesium hydroxide raw material into a sagger of a roller kiln, controlling the advancing speed of the sagger to be 1.4-4.5 m / h, and sequentially passing through a preheating area, a calcining area and a slow cooling area to obtain low-activity magnesium oxide, the filling amount of the saggar is 3 kg / saggar to 3.5 kg / saggar; the temperature of the preheating area is 290 DEG C to 710 DEG C, the temperature of the calcining area is 740 DEG C to 860 DEG C, and the temperature of the slow cooling area is 760 DEG C to 590 DEG C. According to the invention, the low-activity magnesium oxide with narrow activity fluctuation range and high purity is prepared by accurately controlling the propelling speed of the electric heating roller kiln, the sagger filling amount, the regional temperature control and other parameters, the stability of low-activity indexes is obviously improved, and the qualified rate of finished products is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium oxide preparation, and in particular to a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. Background Art

[0002] Existing low-activity magnesium oxide is generally produced by calcining in rotary kilns or gas-fired kilns. During the production process, large temperature fluctuations and uneven heat transfer occur, resulting in a large fluctuation range in the activity value of the magnesium oxide, generally 30mg / L to 80mg / L, making it difficult to accurately control the activity index. In addition, gas impurities will penetrate into the product, affecting the cleanliness of the magnesium oxide. The impurity content of magnesium oxide is generally above 0.5%. In addition, the thermal efficiency of gas-fired kilns is low (usually ≤50%), and the energy consumption per unit weight of product is as high as 800m3. 3 / t~1000m 3 / t; fuel combustion also produces SO2, NO x and dust, which pollutes the environment and increases the cost of waste gas treatment, such as the operating cost of online maintenance, and there is also the risk of environmental emissions not meeting standards.

[0003] To address these issues, electric calcining kilns emerged. Their clean heating process prevents impurities from fuel combustion from contaminating the raw materials, produces no waste gas emissions, and is environmentally friendly. However, there are currently no reports on the use of electric calcination to produce low-activity magnesium oxide. Applicants have discovered that using electric calcining kilns to produce low-activity magnesium oxide is difficult to achieve in a finished product that meets the activity requirements, with a defective rate as high as 30% to 40%. Summary of the Invention

[0004] In response to the above problems, the present invention provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. By precisely controlling parameters such as the propulsion speed of the electric heating roller kiln, the filling amount of the sagger and the regional temperature control, low-activity magnesium oxide with a narrow activity fluctuation range and high purity is produced, which significantly improves the stability of the low-activity index and greatly increases the first-time finished product qualification rate.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is: The present invention provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln, comprising the following steps: The magnesium hydroxide raw material is loaded into the sagger of the roller kiln, and the advancing speed of the sagger is controlled to be 1.4m / h~4.5m / h. It passes through the preheating zone, calcination zone and slow cooling zone in sequence to obtain low-activity magnesium oxide; The filling amount of the sagger is 3kg / sagger to 3.5kg / sagger; the temperature of the preheating zone is 290℃~710℃, the temperature of the calcining zone is 740℃~860℃, and the temperature of the slow cooling zone is 760℃~590℃.

[0006] Compared to existing technologies, the present invention provides a method for preparing low-activity magnesium oxide using electric calcination in a roller kiln. By controlling the sagger loading, uniform heat transfer can be ensured, meeting the low activity requirement of the finished magnesium oxide (i.e., low-activity magnesium oxide). Controlling the sagger advancement speed improves calcination efficiency while controlling the activity value. Controlling the zone temperature further controls the stability of the activity index while ensuring that the magnesium oxide activity is not lost, narrowing the fluctuation range of the activity index of the low-activity magnesium oxide. The preheating zone removes residual moisture and carbon dioxide from the magnesium hydroxide raw material, the calcination zone controls the grain growth rate of the resulting magnesium oxide, and the slow cooling zone effectively suppresses activity rebound.

[0007] The present invention controls the calcining conditions of the electric heating roller kiln, and the filling amount (filling density) of the sagger and the advancing speed have a synergistic regulating effect. Low-speed advancing can extend the residence time of the material, so that the activity of the obtained magnesium oxide product is reduced to within the target range.

[0008] Preferably, the content of magnesium hydroxide in the magnesium hydroxide raw material is ≥65% (more preferably 65% ​​to 68%).

[0009] Preferably, the particle size of the magnesium hydroxide raw material is 80 mesh to 120 mesh.

[0010] Preferably, the material of the sagger includes at least one of corundum or mullite.

[0011] Corundum or mullite has high high temperature resistance (1300°C~1500°C). The present invention has found through a large number of experiments that the use of saggers made of corundum or mullite can effectively control the content of heavy metals in low-activity magnesium oxide and improve the purity of low-activity magnesium oxide.

[0012] Preferably, the size of the sagger is (320-340) mm×(320-340) mm×(140-160) mm.

[0013] Preferably, the saggers are fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers in the upper and lower layers.

[0014] Traditional electric calcining roller kilns generally use a single sagger for feeding. The present invention uses a double-layer, four-row feeding method to heat eight saggers simultaneously, which not only improves work efficiency and increases output (0.55t / shift to 0.6t / shift), but also improves the quality of the low-activity magnesium oxide product.

[0015] Preferably, the time for passing through the preheating zone is 150 min to 180 min, and the advancement speed of the sagger is 3.3 m / h to 4.5 m / h.

[0016] Preferably, the time taken to pass through the calcining zone is 500-600 min, and the pushing speed of the saggar is 1.4-2 m / h.

[0017] Preferably, the time taken to pass through the slow cooling zone is 105-130 min, and the pushing speed of the saggar is 3.3-4.5 m / h.

[0018] Preferably, the roller kiln comprises 22 temperature zones, i.e. 1st temperature zone-22nd temperature zone, which are arranged in a straight line in sequence; the preheating zone is composed of the 1st temperature zone-7th temperature zone, the calcining zone is composed of the 8th temperature zone-17th temperature zone, and the slow cooling zone is composed of the 18th temperature zone-22nd temperature zone.

[0019] Further preferably, in the 22 temperature zones of the roller kiln, the temperature of the 1st temperature zone is 295-305℃, the temperature of the 2nd temperature zone is 395-405℃, the temperature of the 3rd temperature zone is 495-505℃, the temperature of the 4th temperature zone is 545-555℃, the temperature of the 5th temperature zone is 595-605℃, the temperature of the 6th temperature zone is 645-655℃, the temperature of the 7th temperature zone is 695-705℃, the temperature of the 8th temperature zone is 745-755℃, the temperature of the 9th temperature zone is 745-755℃, the temperature of the 10th temperature zone is 795-805℃, the temperature of the 11th temperature zone is 845-855℃, the temperature of the 12th temperature zone is 845-855℃, the temperature of the 13th temperature zone is 845-855℃, the temperature of the 14th temperature zone is 845-855℃, the temperature of the 15th temperature zone is 845-855℃, the temperature of the 16th temperature zone is 845-855℃, the temperature of the 17th temperature zone is 845-855℃, the temperature of the 18th temperature zone is 745-755℃, the temperature of the 19th temperature zone is 695-705℃, the temperature of the 20th temperature zone is 695-705℃, the temperature of the 21st temperature zone is 595-605℃, and the temperature of the 22nd temperature zone is 595-605℃.

[0020] Further preferably, the length of each temperature zone is 1.4-1.6 m.

[0021] In the present application, the temperature of each temperature zone can be controlled individually, and the temperature control of a temperature zone of a specific length is more accurate. By controlling the temperature range of the 22 temperature zones of the roller kiln, the activity range of the low-activity magnesium oxide can be further ensured to be narrow and more stable.

[0022] Preferably, after passing through the slow cooling zone, the following steps are further included: stepwise cooling to 140-160℃, then using air suction cooling to reduce the temperature of the material to below 60℃, to obtain the low-activity magnesium oxide.

[0023] Further preferably, the step cooling rate is ≤10°C / min (more preferably 6°C / min to 10°C / min).

[0024] The present invention can further suppress the rebound of the activity of the magnesium oxide product by controlling the rate of step cooling, while avoiding lattice defects caused by high-temperature sudden cooling, thereby improving the structural stability of the finished product.

[0025] Preferably, the iodine absorption value of the low-activity magnesium oxide is 50 mg / L to 60 mg / L.

[0026] The present invention has the following beneficial effects: Compared with fuel calcination, the present invention adopts an electric heating roller kiln. Electric energy is used for heating without combustion exhaust gas, and the impurity content of the product can be reduced to below 0.1%, which is clean and pollution-free. Electric calcination has no exhaust gas emissions, no need for online detection, and no environmental risks. The electric heat conversion efficiency is ≥90%, and the unit energy consumption can be reduced to 700kWh / t~900kWh / t, optimizing energy consumption.

[0027] By controlling the sagger's propulsion speed, loading volume, and the roller kiln's temperature curve, this invention stabilizes the activity index of the finished magnesium oxide. The iodine absorption value of the low-activity magnesium oxide is 50mg / L to 60mg / L, resolving the issues of slow reaction and precipitation during application. By designing and adjusting the roller kiln's 22 temperature zones, the temperature curve is more stable and uniform during operation, enabling precise temperature control within ±2°C, significantly improving the stability of the low-activity index. Furthermore, compared to low-activity magnesium oxide produced by traditional rotary kilns or gas-fired kilns (with a finished product qualification rate of 60% to 74%), the defective rate of the finished magnesium oxide produced by this invention's electric calcination in a roller kiln is reduced by over 26%, achieving a finished product qualification rate of over 98.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of an electric heating roller kiln in an embodiment of the present invention; In the figure, 100 represents the inlet air chamber, 200 represents the preheating zone, 300 represents the calcining zone, 400 represents the slow cooling zone, 500 represents the cooling zone, 600 represents the outlet air chamber, 700 represents the heating rod, 800 represents the roller, 900 represents the glue discharge chimney, and 1000 represents the sealing gate. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] In the embodiments of the present invention, deionized water is used. Water without manufacturer indication is commercially available.

[0031] In the present invention, the method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln is completed in an electric heating roller kiln. The structural schematic diagram of the electric heating roller kiln is shown in FIG. Figure 1 As shown, the electric roller kiln includes an inlet plenum 100, a preheating zone 200, a calcining zone 300, a slow cooling zone 400, a cooling zone 500, and an outlet plenum 600, which are connected in sequence. Heating rods 700 are located on the upper and lower inner surfaces of the preheating zone 200 and the calcining zone 300, and a roller table 800 runs through the inlet plenum 100, the preheating zone 200, the calcining zone 300, the slow cooling zone 400, the cooling zone 500, and the outlet plenum 600. The total length of the electric roller kiln is 50 meters.

[0032] Air chambers are located at the front and rear ends of the kiln body, namely the inlet chamber 100 and the outlet chamber 600. These chambers are divided into multiple independent sealed displacement spaces by sealed gates 1000. Each cavity contains independent air intake, exhaust, and transmission systems. When the sagger enters one of these sealed displacement spaces for air exchange, the air atmosphere in the other cavities is not affected, ensuring the required firing atmosphere. When the amount of binder being discharged is high, regular exhaust can be achieved through a valve below the drainage funnel.

[0033] The furnace is divided into a preheating zone 200, a calcining zone 300, and a slow cooling zone 400. The furnace is sealed externally to ensure the required firing atmosphere. The furnace ceiling features a cordierite boron plate structure supported by silicon carbide and covered with 1260 blanket. The sides and bottom utilize a composite insulation structure of lightweight bricks and lightweight insulation board. The use of lightweight insulation materials, with low heat capacity and rapid temperature rise and fall, allows for sensitive temperature control and significant energy savings. The preheating zone 200 includes zones 1 through 7, the calcining zone 300 includes zones 8 through 17, and the slow cooling zone 400 includes zones 18 through 22.

[0034] Cooling zone 500 is divided into air-cooled and water-cooled components based on the cooling medium (specific configuration depends on the equipment). Silicon carbide rods or finned tubes are arranged at the top and bottom of the air-cooled components as air ducts, connected to the exhaust fan ducts at the rear. The exhaust fan directs external cooling air to displace the air in the ducts as a cooling method. The cooling rate can be controlled by controlling the air displacement flow rate through the fan frequency. Spiral flat tubes or finned tubes are arranged at the top and bottom of the water-cooled components as water channels. Circulating water absorbs heat from the cavity, reducing the internal temperature.

[0035] The main drive system of the roller furnace (including roller 800) adopts segmented helical gear independent transmission. The reduction motor drives the main shaft to operate. The main shaft is equipped with helical gears to form several pairs of helical gear transmissions. The roller rods are connected to the output ends of each pair of gears through sleeve-type universal joints, thereby driving the roller rods to operate.

[0036] In order to better illustrate the present application, further examples are provided below by way of examples.

[0037] Example 1 The present example provides a method for preparing low-activity magnesium oxide based on roller kiln electric calcination, comprising the following steps: 100 mesh magnesium hydroxide raw material (magnesium hydroxide content of 67%) is loaded into the corundum material of the roller kiln, and sequentially passes through the inlet gas chamber 100, the preheating zone 200, the calcination zone 300, the slow cooling zone 400, the cooling zone 500 and the outlet gas chamber 600, the total firing cycle is 15.5h, the energy consumption is 680kWh / t, and low-activity magnesium oxide is obtained.

[0038] The loading amount of the sagger is 3.5kg / sagger, and the size of the sagger is 330mmx330mmx150mm; the sagger is fed in a double-layer four-column manner, and four columns of saggars are placed side by side along the feeding direction, and the upper and lower two layers of saggars are fed at the same time.

[0039] The preheating zone 200 is composed of 1-7 temperature zones, the temperature is 300-700℃, the average pushing speed of the sagger is 3.71m / h, and the total time is 170min. The calcination zone 300 is composed of 8-17 temperature zones, the temperature is 750-850℃, the average pushing speed of the sagger is 1.64m / h, and the total time is 550min. The slow cooling zone 400 is composed of 18-22 temperature zones, the temperature is 750-600℃, the average pushing speed of the sagger is 3.75m / h, and the total time is 120min. In 1-22 temperature zones, the length of each temperature zone is 1.5m, and the specific temperature of each temperature zone is shown in Table 1.

[0040] Table 1: Operating temperature setting of each temperature zone in Example 1

[0041] In the cooling zone 500, the material is stepwise cooled to 150℃ at a rate of 8℃ / min, and then air suction cooling is used to reduce the temperature of the material to below 60℃.

[0042] Example 2 The present example provides a method for preparing low-activity magnesium oxide based on roller kiln electric calcination, comprising the following steps: 120 mesh magnesium hydroxide raw material (magnesium hydroxide content of 66%) is loaded into the sagger of the roller kiln, and sequentially passes through the inlet gas chamber 100, the preheating zone 200, the calcination zone 300, the slow cooling zone 400, the cooling zone 500 and the outlet gas chamber 600, and low-activity magnesium oxide is obtained.

[0043] The filling capacity of the sagger is 3.3kg / sagger, and the size of the sagger is 330mm×330mm×150mm; the sagger is fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers above and below, and a total of 8 saggers are fed simultaneously.

[0044] The preheating zone 200 consists of zones 1 to 7, with temperatures ranging from 295°C to 695°C, an average sagger advancement speed of 3.50 m / h, and a total duration of 180 min. The calcining zone 300 consists of zones 8 to 17, with temperatures ranging from 745°C to 848°C, an average sagger advancement speed of 1.5 m / h, and a total duration of 600 min. The slow cooling zone 400 consists of zones 18 to 22, with temperatures ranging from 745°C to 595°C, an average sagger advancement speed of 3.46 m / h, and a total duration of 130 min. Each zone in zones 1 to 22 is 1.5 m long, and the specific temperatures of each zone are shown in Table 2.

[0045] Table 2 Operating temperature settings for each temperature zone in Example 2

[0046] In the cooling zone 500, the material is cooled stepwise to 140°C at a rate of 10°C / min, and then suction cooling is used to reduce the material temperature to below 60°C.

[0047] Example 3 This embodiment provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln, comprising the following steps: The 80-mesh magnesium hydroxide raw material (containing 68% magnesium hydroxide) is loaded into a corundum-mullite sagger of a roller kiln and sequentially passes through an inlet air chamber 100, a preheating zone 200, a calcining zone 300, a slow cooling zone 400, a cooling zone 500 and an outlet air chamber 600 to obtain low-activity magnesium oxide.

[0048] The filling capacity of the sagger is 3kg / sagger, and the size of the sagger is 340mm×340mm×140mm; the sagger is fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers above and below, and a total of 8 saggers are fed simultaneously.

[0049] The preheating zone 200 consists of zones 1 to 7, with temperatures ranging from 305°C to 705°C, an average sagger advancement speed of 4.20 m / h, and a total duration of 150 min. The calcining zone 300 consists of zones 8 to 17, with temperatures ranging from 755°C to 855°C, an average sagger advancement speed of 1.8 m / h, and a total duration of 500 min. The slow cooling zone 400 consists of zones 18 to 22, with temperatures ranging from 755°C to 605°C, an average sagger advancement speed of 3.28 m / h, and a total duration of 105 min. Each zone in zones 1 to 22 is 1.5 m long, and the specific temperatures of each zone are shown in Table 3.

[0050] Table 3 Operating temperature settings for each temperature zone in Example 3

[0051] In the cooling zone 500, the material is cooled stepwise to 150°C at a rate of 8°C / min, and then suction cooling is used to reduce the material temperature to below 60°C.

[0052] Example 4 This embodiment provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln, comprising the following steps: The 120-mesh magnesium hydroxide raw material (containing 65% magnesium hydroxide) is loaded into the mullite sagger of the roller kiln and sequentially passes through the inlet air chamber 100, the preheating zone 200, the calcining zone 300, the slow cooling zone 400, the cooling zone 500 and the outlet air chamber 600 to obtain low-activity magnesium oxide.

[0053] The filling capacity of the sagger is 3.2kg / sagger, and the size of the sagger is 320mm×320mm×160mm; the sagger is fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers above and below, and a total of 8 saggers are fed simultaneously.

[0054] The preheating zone 200 consists of zones 1 to 7, with temperatures ranging from 295°C to 705°C, an average sagger advancement speed of 3.94 m / h, and a total duration of 160 min. The calcining zone 300 consists of zones 8 to 17, with temperatures ranging from 745°C to 855°C, an average sagger advancement speed of 1.64 m / h, and a total duration of 550 min. The slow cooling zone 400 consists of zones 18 to 22, with temperatures ranging from 755°C to 595°C, an average sagger advancement speed of 4.09 m / h, and a total duration of 110 min. Each zone in zones 1 to 22 is 1.5 m long, and the specific temperatures of each zone are shown in Table 4.

[0055] Table 4 Operating temperature settings for each temperature zone in Example 4

[0056] In the cooling zone 500, the material is cooled stepwise to 160°C at a rate of 9°C / min, and then suction cooling is used to reduce the material temperature to below 60°C.

[0057] Example 5 This embodiment provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln, which is similar to Example 1, except that: the roller kiln includes 19 temperature zones, namely temperature zones 1 to 19, which are arranged in a straight line; the preheating zone consists of temperature zones 1 to 6, the calcining zone consists of temperature zones 7 to 15, and the slow cooling zone consists of temperature zones 16 to 19. The average advancement speed of the preheating zone, calcining zone and slow cooling zone is slightly slowed down. Specifically, the following steps are included: The 100-mesh magnesium hydroxide raw material (containing 67% magnesium hydroxide) was loaded into a corundum sagger in a roller kiln and sequentially passed through an inlet air chamber 100, a preheating zone 200, a calcining zone 300, a slow cooling zone 400, a cooling zone 500, and an outlet air chamber 600. The total firing cycle was 15.5 hours, and the energy consumption was 680 kWh / t, thereby obtaining low-activity magnesium oxide.

[0058] The filling capacity of the sagger is 3.5kg / sagger, and the size of the sagger is 330mm×330mm×150mm; the sagger is fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers above and below, and a total of 8 saggers are fed simultaneously.

[0059] The temperature in the preheating zone is 300°C to 700°C, the average sagger advance speed is 3.18 m / h, and the total elapsed time is 170 min. The temperature in the calcining zone is 750°C to 850°C, the average sagger advance speed is 1.47 m / h, and the total elapsed time is 550 min. The temperature in the slow cooling zone is 750°C to 600°C, the average sagger advance speed is 3.00 m / h, and the total elapsed time is 120 min. Each zone in zones 1 to 19 is 1.5 m long, and the specific temperatures for each zone are shown in Table 5.

[0060] Table 5 Operating temperature settings for each temperature zone in Example 5

[0061] In the cooling zone 500, the material is cooled stepwise to 150°C at a rate of 8°C / min, and then suction cooling is used to reduce the material temperature to below 60°C.

[0062] Example 6 This embodiment provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. The method is similar to that of Example 1, except that the average advancement speed of the sagger in the slow cooling zone 400 is 2.00 m / h, and the total elapsed time is 225 minutes. The remaining conditions are the same as those of Example 1 and are not further described.

[0063] Example 7 This embodiment provides a method for preparing low-activity magnesium oxide by electric calcination in a roller kiln. The method is similar to that of Example 2, except that the average advancement speed of the sagger in the calcination zone 300 is 3.75 m / h, and the total elapsed time is 240 min. The remaining conditions are the same as those of Example 2 and are not further described.

[0064] Example 8 This embodiment provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. The method is similar to that of Example 2, differing only in that, in cooling zone 500, the material is cooled in a stepwise manner at a rate of 20°C / min to 140°C, and then air is drawn to cool the material to below 60°C. The remaining conditions are the same as those of Example 2 and are not further described.

[0065] Comparative Example 1 This comparative example provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. The method is similar to Example 1, except that the filling amount of the sagger is replaced by 4 kg / sagger instead of 3.5 kg / sagger. The remaining conditions are the same as those in Example 1 and are not further described.

[0066] Comparative Example 2 This comparative example provides a method for preparing low-activity magnesium oxide by electric calcination in a roller hearth kiln. The method is similar to Example 1, differing only in that the sagger is advanced at a constant speed of 4.6 m / h, and the time spent in the preheating zone 200, calcining zone 300, and slow cooling zone 400 is adjusted accordingly. The remaining conditions are the same as those in Example 1 and are not further described.

[0067] Comparative Example 3 This comparative example provides a method for preparing low-activity magnesium oxide by electric calcination in a roller hearth kiln. The method is similar to Example 1, differing only in that the sagger is advanced at a constant speed of 1.3 m / h, and the time spent in the preheating zone 200, calcining zone 300, and slow cooling zone 400 is adjusted accordingly. The remaining conditions are the same as those in Example 1 and are not further described.

[0068] Comparative Example 4 This comparative example provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. The method is similar to Example 1, except that the temperature of calcination zone 300 is 900°C, and the temperatures of temperature zones 8 to 17 are all 900°C. The remaining conditions are the same as those in Example 1 and are not further described.

[0069] Comparative Example 5 This comparative example provides a method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln. The method is similar to Example 1, except that the temperature in the preheating zone is 300°C to 550°C, the temperature in the calcining zone is 600°C to 730°C, and the specific temperatures in temperature zones 1 to 17 are shown in Table 6. The remaining conditions are the same as in Example 1 and are not further described.

[0070] Table 6 Operating temperature settings for temperature zones 1 to 17 in comparative example 5

[0071] Verification test The activity value, purity, and finished product qualification rate of the low-activity magnesium oxide of Examples 1 to 8 and Comparative Examples 1 to 5 were tested with reference to HG / T3928-2012, and the test results are shown in Table 7. It should be noted that the finished product qualification rate in the present invention refers to the qualified rate of finished products with an activity value (iodine absorption value) of 50 mg / L to 60 mg / L.

[0072] Table 7 Performance test results of low-activity magnesium oxide in Examples and Comparative Examples

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing low-activity magnesium oxide based on electric calcination in a roller kiln, characterized in that: The following steps are involved: The magnesium hydroxide raw material is loaded into the sagger of the roller kiln, and the advancing speed of the sagger is controlled to be 1.4m / h~4.5m / h. It passes through the preheating zone, calcination zone and slow cooling zone in sequence to obtain low-activity magnesium oxide; The filling amount of the sagger is 3kg / sagger to 3.5kg / sagger; the temperature of the preheating zone is 290℃~710℃, the temperature of the calcining zone is 740℃~860℃, and the temperature of the slow cooling zone is 760℃~590℃.

2. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: The content of magnesium hydroxide in the magnesium hydroxide raw material is ≥65%, and the particle size of the magnesium hydroxide raw material is 80 mesh to 120 mesh.

3. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: The material of the sagger includes at least one of corundum or mullite; The size of the sagger is (320-340) mm×(320-340) mm×(140-160) mm.

4. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1 or 3, characterized in that: The saggers are fed in a double-layer four-row manner, with four rows of saggers placed side by side along the feeding direction, with two layers of saggers in the upper and lower layers.

5. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: The time of passing through the preheating zone is 150min~180min, and the advancement speed of the sagger is 3.3m / h~4.5m / h; The time of passing through the calcining zone is 500 min to 600 min, and the advancement speed of the sagger is 1.4 m / h to 2 m / h; The time spent in the slow cooling zone is 105 min to 130 min, and the advancing speed of the sagger is 3.3 m / h to 4.5 m / h.

6. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: The roller kiln includes 22 temperature zones, namely temperature zone 1 to temperature zone 22, which are arranged in a straight line; the preheating zone consists of temperature zone 1 to temperature zone 7, the calcining zone consists of temperature zone 8 to temperature zone 17, and the slow cooling zone consists of temperature zone 18 to temperature zone 22.

7. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 6, characterized in that: Among the 22 temperature zones of the roller kiln, the temperature of temperature zone 1 is 295°C~305°C, the temperature of temperature zone 2 is 395°C~405°C, the temperature of temperature zone 3 is 495°C~505°C, the temperature of temperature zone 4 is 545°C~555°C, the temperature of temperature zone 5 is 595°C~605°C, the temperature of temperature zone 6 is 645°C~655°C, the temperature of temperature zone 7 is 695°C~705°C, the temperature of temperature zone 8 is 745°C~755°C, the temperature of temperature zone 9 is 745°C~755°C, the temperature of temperature zone 10 is 795°C~805°C, and the temperature of temperature zone 11 is 845°C~855°C. ℃, the temperature of temperature zone 12 is 845℃~855℃, the temperature of temperature zone 13 is 845℃~855℃, the temperature of temperature zone 14 is 845℃~855℃, the temperature of temperature zone 15 is 845℃~855℃, the temperature of temperature zone 16 is 845℃~855℃, the temperature of temperature zone 17 is 845℃~855℃, the temperature of temperature zone 18 is 745℃~755℃, the temperature of temperature zone 19 is 695℃~705℃, the temperature of temperature zone 20 is 695℃~705℃, the temperature of temperature zone 21 is 595℃~605℃, and the temperature of temperature zone 22 is 595℃~605℃; The length of each temperature zone is 1.4m~1.6m.

8. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: After passing through the slow cooling zone, the process further includes: stepwise cooling to 140° C. to 160° C., and then adopting suction cooling to reduce the material temperature to below 60° C. to obtain low-activity magnesium oxide.

9. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 8, characterized in that: The step cooling rate is ≤10°C / min.

10. The method for preparing low-activity magnesium oxide based on roller kiln electric calcination according to claim 1, characterized in that: The iodine absorption value of the low-activity magnesium oxide is 50 mg / L to 60 mg / L.

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