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Table 1 sample analysis results / % 
Table 2 Effect of calcination temperature on whiteness
Table 3 Effect of calcination time on whiteness
2.1.3 Formulation of the heating system
Table 4 Heating system
Table 5 Effect of whiteness of chlorinating agent
In the test, it was found that the amount of 3% to 5% of the chlorinating agent (close to the molar ratio of the chlorinating agent to the reaction of iron and titanium oxide) is better, and the hardness of the product is increased significantly, so that the whiteness is lowered.
references
Liu Wei Zhang Jun Chen Wei
(Shandong Institute of Geological Science, Jinan 250013, China)
CLC number: TD952.5 Document code: A Article ID: 1671-9492 (2004) 03-0034-02
Since coal-based kaolin associated with the coal, kaolin crystals present in the gap of fixed carbon, it presents an off-white or gray-black; otherwise affect the whiteness of kaolin include iron, titanium and other coloring minerals, they are generated after the high-temperature calcination oxide Will make the raw material yellow or brick red. Therefore, by removing carbon and iron, titanium, and the like by a process such as calcination or impurity removal, the whiteness of the product can be improved.
Paper-based paint-grade calcined kaolin, with high grades and high added value, is the product that can best exert the potential value of high-quality coal-based kaolin in China and is in line with the international market. We conducted a whitening process study on the properties of a high-quality coal kaolin in Shandong Province. The whiteness of the product produced was over 93%, which fully met the requirements of whiteness of paper-based coating grade calcined kaolin.
1. Quality and sample treatment of coal-based kaolin
1.1 The quality of coal-based kaolin
The kaolinite is mainly composed of kaolinite. The main chemical analysis indexes are: SiO 2 , Al 2 O 3 , TFe 2 O 3 , TiO 2 , LOI (loss on ignition), and K 2 O and Na 2 . O, CaO, MgO, etc. High-quality coal-based kaolin, kaolinite with high content and flakes, low content of iron, titanium and other impurities, generally required to be converted to SiO 2 without LOI, the total amount of Al 2 O 3 is 90% to 95%, SiO 2 / Al 2 O 3 ≈ 2 (molar mass ratio), TFe 2 O 3 + TiO 2 <1, TFe 2 O 3 <0.4% to 0.5%. In this study, the coal-based kaolin is a high-quality coal-based kaolin. The chemical analysis index and whiteness analysis are shown in Table 1. The total amount of SiO 2 and Al 2 O 3 when converted without LOI is 97.1%. In addition, although the total content of iron and titanium is less than 1%, the titanium content is high, so the whitening test pays special attention to titanium. Remove.
1.2 sample processing
The particle size of the raw material has a great influence on the process of calcination decarburization and iron removal and titanium. The particle size is coarse, the carbon content inside the particle is not easy to play during calcination, so that the constant temperature is long and the whiteness of the calcined product is low; when the particle size is fine, the specific surface area is large, the carbon is volatile, the constant temperature is short, and the reaction is removed when removing iron and titanium. More fully, making the product whiter. The raw material was pulverized to about 1250 mesh, and tested to be d 95.5 = 10 μm, d 35.2 = 2 μm, maximum particle diameter 13.83 μm, median diameter d 50 = 2.87 μm, specific surface area 29379 cm 2 /g, and the particle size distribution of the raw material is shown in FIG. 1 .
ingredient
SiO 2
Al 2 O 3
Fe 2 O 3
TiO 2
LOI
SiO 2 /Al 2 O 3
BaiDu
content
42.99
38.04
0.17
0.74
16.52
1.92
24.5
Figure 1 raw material particle size distribution
2, whitening process research
2.1 calcination decarburization
The calcination decarburization was first carried out using an SRJX-high temperature electric furnace. At this stage, the final calcination temperature and the constant temperature time were tested, and a heating system was established according to the combustion characteristics of the coal.
2.1.1 Final temperature test
Determining the final temperature is the first problem to be solved in the calcination process. The calcination test temperature is from 600 to 1100 ° C, the temperature is from 3 to 5 ° C / min, and the final temperature is about 1 h. It is found that the effect is best when it is close to 1000 ° C. The particles are more than 1000 ° C. began to harden a surface (generated high hardness mullite and quartz side), so brightness decreases. The test results are shown in Table 2. [next]
Temperature / °C
600
700
800
900
1000
1100
BaiDu/%
50.4
64.7
80.3
87.9
89.4
88.7
2.1.2 Calcination time test
The raw material is calcined at a final temperature of 800 ° C, the heating rate is 3 to 5 ° C / min, and finally four constant temperature times are taken. As a result (see Table 3), it is shown that only by maintaining a calcination time, the decarburization can be thorough, and the product can be compared. High whiteness. For the particle size of the raw materials used in this test, the final constant temperature should not be lower than 2h. If the particle size is too thick or too fine, the final constant temperature should be adjusted appropriately.
Constant temperature time / min
50
100
150
200
Product whiteness /%
79.8
82.4
85.4
85.9
In the process of coal combustion, at 400-450 °C, pyrolysis produces flammable gas diffusion combustion, which is easier to complete; 500-650 °C burns on the surface of solid coke . In this stage, in addition to requiring the particles to reach a certain fineness, the oxygen supply is also provided. In order to be sufficient in time, the surface burning of coke can be sufficient, otherwise coking phenomenon is easy to occur, forming an anisotropic organic phase and carbon intermediate phase, which can only be fully burned at 1200-1400 °C, and this temperature will turn kaolin into high. Hardness of mullite and cristobalite. Therefore, the calcination decarburization has not been scientifically uniform from room temperature to the final temperature. According to the combustion characteristics of coal, we have developed a temperature regime with a constant temperature at several critical temperature points (such as 500-650 ° C). See Table 4). In addition, since the material is statically burned in the high-temperature electric furnace, in order to ensure sufficient oxygen supply and sufficient combustion, the material is subjected to several appropriate agitation during the entire calcination process to avoid formation of a mesophase.
2.2 chlorination roasting iron, titanium
People often use chemical drifting methods and other chemical methods such as hydrochloric acid, sulfuric acid and oxalic acid acid leaching to remove iron. Although these methods can remove most of the iron, they are ineffective for titanium and the process is complicated. The titanium content of the raw materials used in this test is relatively high relative to iron, so such methods are not suitable.
High-temperature chlorine-containing air converts iron and titanium oxides into low-melting point and high-volatility FeCl 3 (boiling point 315 ° C) and TiCl 4 (boiling point 136 ° C), and carbon is converted into CO and CO 2 , thereby making C, Fe and Ti are separated from kaolin. The chlorination roasting can directly pass chlorine gas, or a solid chlorinating agent can be added to cause metathesis to generate chlorine gas. In the test, a method of adding a certain amount of solid chlorinating agent in the calcination process is adopted. After the temperature is raised to 550-700 ° C (the temperature of the material itself), the solid chlorinating agent is produced in some raw materials by the catalyst components SO 2 and SiO. 2. Decomposition occurs under the action of H 2 O, and the generated Cl 2 or HCl converts the oxides of iron and titanium into FeCl 3 and TiCl 4 to achieve the purpose of whitening.
In the test, the chlorination roasting is dissolved into the calcination process at the same time, and only the temperature rising system is slightly adjusted, that is, the temperature is appropriately controlled at 700 ° C to ensure the decomposition of the solid chlorinating agent. The final temperature of calcination, the specific heating system is shown in Table 4. The comparison test results of different chlorinating agents are shown in Table 5.
Temperature / °C
Room temperature ~ 500
500
550
600
650
700
700～980
980
Constant temperature time / min
3 to 5 ° C / min
30
30
30
30
30
3 to 5 ° C / min
>120
Chlorinating agent dosage /%
0
2
3
5
10
BaiDu/%
89.8
92.8
93.3
93.6
92.4
In addition, the 4% chlorinating agent was added to the raw material to raise the temperature to 980 ° C, and the constant temperature was more than 6 min. As a result, the whiteness was difficult to reach 93%, which proved that the application of the heating system was effective.
3, the conclusion
The experimental research on the whitening process of this coal-based kaolin is simple and efficient, and the calcination system is equipped with an appropriate amount of chlorinating agent to increase the final whiteness without adding chlorinating agent and heating at a constant rate. 4%, which proves that this method is a preferred whitening method for the coal-based kaolin. The final product was tested to be 0.11% Fe 2 O 3 and 0.29% TiO 2 . On this basis, particle size classification or wet superfine pulverization can be carried out to obtain a double-type 90 (ie, whiteness ≥ 90%, fineness - 2 μm content ≥ 90%) paper-making grade calcined kaolin.
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[2] Lu Yinping Discussion Likai Qi, coal quality evaluation methods Kaolinite and Deep Process [J], Ore of China, 2002, 27 (3): 9-11.
[3] An Jiaxuan, Wang Boying, Practical Fine Chemicals Dictionary [M], Beijing: Light Industry Press, 1988, 891-893.
[4] Xu Shi, ore selectivity study [M], Beijing: Metallurgical Industry Press, 1983, 207.
THE PROCESS RESEARCH FOR RAISING WHITENESS OF CERTAIN
HIGH-QUALFTY COAL-SERIES KAOLINE
LIU Xuan,ZHANGJun,CHEN Wei
(Shandong Institute and Laboratory of Geological Science, Ji , nan 250013, China)
ABSTRACT
According to the property of certain high-quality coal-series kaoline, the process research has been done for raising whiteness of the kaoline, the flowsheet developed for raising whiteness is simple and high efficient, The whiteness of the final product is more than 95% , and therefore meet very well the demands of calcined kao-line used for making paper and dope.
KEY WORDS: coal-series kaoline; whiteness; calcining; chloridizing