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Preparation and properties of tungsten tailings bioceramics
Bioceramics, also known as high-efficiency film-coated lightweight bioceramics, have chemical properties, abrasion resistance, impact resistance, corrosion resistance, high temperature resistance, large specific surface area, strong interception ability, and no release of toxic and harmful substances to water bodies. Features, is the ideal filter material for modern water treatment processes.
At present, there are many reports on the preparation of bioceramics from shale , clay , etc. The preparation of bioceramics from tungsten tail sand has not been reported in China. In this experiment, the preparation of bioceramics was carried out using the tailings of the tailings reservoir of the Dayu Xia Tungsten Mine in Jiangxi Province.
First, test materials and equipment
The tailings raw material for preparing bioceramics is fresh tailings from the tailings pool of the Dayuxiatang tungsten mine in Jiangxi Province. The main chemical components are shown in Table 1.
Table 1 Main chemical components of tungsten tailings
ingredient
SiO 2
Al 2 O 3
CaO
K 2 O
Na 2 O
Fe 2 O 3
other
content
79.6
8.5
0.11
1.43
1.02
1.75
6.31
Other auxiliary materials as concentrated hydrochloric acid, slag, pulverized coal ash, clay, pore-forming material (wood or foam), a binder (modified starch), a white acrylic resin type paints, xylene and the like solvents.
The main equipment used in the test includes AE200 electronic analytical balance, ball mill , granulator, electrothermal constant temperature drying oven, muffle furnace, ASAP specific surface area and porosity analyzer, XRF-1700X fluorescence analyzer, LTDX-650 scanning electron microscope.
Second, the preparation of bioceramics
(1) Preparation process
The bioceramic preparation process is shown in Figure 1.
Figure 1 Bioceramic preparation process
The tailings were modified with a 20% hydrochloric acid solution to have a large number of pores. The modified tailings are mixed with slag, fly ash and clay in a certain ratio and uniformly stirred, and a small amount of pore-forming material and binder are added to prepare spherical ceramsite raw materials on the granulator. The ceramsite raw material is placed in an electric heating constant temperature oven at 120 ° C for 1 h, then transferred to a muffle furnace, gradually heated to 500 ° C in 1 h, constant temperature for 10 min, and then the temperature is adjusted to 800 ~ 1200 ° C for 30 min, baked Cool naturally to room temperature. After the calcined product is placed in a ball mill to polish the surface by self-grinding, the acrylate-based white paint diluted with xylene is sprayed with a spray gun, and after drying at room temperature, the final bioceramic product is obtained.
In the test, the volume ratio of slag to fly ash is fixed at 1:1, the ratio of (slag + fly ash) to clay is fixed at 3:1, and (slag + fly ash + clay) is defined as auxiliary material. Effect of the starting material and ratio of the test materials investigated tailings volume ratio of the main tailings V / V of ceramic materials properties.
When spraying acrylate type white paint, the air compressor pressure is 0.2-0.5MPa, the spray gun atomization angle is 30°~50°, the spray gun mouth is away from the ceramsite distance is 15~50cm, the normal temperature drying time is 0.5~1.5h, the coating is dry. The film thickness is 20 to 30 μm.
(II) Effect of raw material ratio on physical properties of ceramsite
The volume ratio of tailings to excipients was changed to V tailings /V excipients , and calcination was carried out at a temperature of 1100 ° C. The physical properties of the obtained bioceramic products are shown in Table 2.
Table 2 Physical properties of bioceramics under different raw material ratios
Sample number
V tail sand / V accessories
Particle density / (g / cm 3 )
Bulk density / (g/cm 3 )
Specific surface area / (m 2 /g)
Acid solution /%
Alkali soluble rate /%
Barrel strength / MPa
1
2
3
4
1.50
1.25
1.00
0.75
3.60
1.67
1.61
1.59
2.30
1.00
1.10
0.97
3.1
10.5
9.7
11.5
0.26
0.22
0.17
0.17
0.47
0.43
0.33
0.31
5.1
8.9
8.1
9.1
It can be seen from Table 2 that when the amount of tungsten tailings is large, the prepared bioceramics have a small compressive strength, and the particle density and bulk density are large. This is because the smelting properties of the tungsten tailings are poor, and when the amount is large, the grains are microscopically The compactness of the structure is affected; as the amount of tungsten tail sand decreases, the proportion of fly ash increases, the degree of crystallization of the fired bioceramics is high, the structure compactness is improved, the surface is smooth, the pores are uniform, and the cylinder pressure is high. The specific surface area increases and the bulk density decreases.
(III) Effect of calcination temperature on physical properties of ceramsite
According to the raw material ratio of the sample 3 in Table 2, calcination was carried out at different temperatures, and the physical properties of the obtained bioceramic product are shown in Table 3.
Table 3 Physical properties of bioceramics at different calcination temperatures
Calcination temperature
/°C
Particle density / (g / cm 3 )
Bulk density / (g/cm 3 )
Specific surface area / (m 2 /g)
Acid solution /%
Alkali soluble rate /%
Barrel strength / MPa
800
900
1000
1100
1200
2.30
1.80
1.60
1.57
1.52
1.30
1.30
1.01
0.91
0.93
7.5
9.2
10.5
12.5
12.8
0.25
0.21
0.19
0.18
0.17
0.45
0.41
0.32
0.22
0.23
6.7
7.8
8.8
8.9
9.1
It can be seen from Table 3 that as the calcination temperature increases, the bulk density of bioceramics decreases gradually, the compressive strength increases gradually, and the specific surface area gradually increases. When the temperature reaches 1100 °C, the indexes tend to be stable. Therefore, the calcination temperature is about 1100 ° C or so.
(4) XRD analysis of ceramsite samples
The prepared ceramsite filter material is spherical particles with uniform particle size, reddish brown appearance, microporous surface, and interlaced internal network, which has strong adsorption. The ceramsite samples 1 and 3 in Table 2 were tested with a D/Max-3B X-ray powder diffractometer at 25 ° C and 50% relative humidity (Ni filter, tube voltage 30 kV, tube current 30 mA, The scanning speed was 2°/min), and the directional X-ray diffraction pattern was obtained as shown in Fig. 2.
Figure 2 XRD pattern of the sample
It can be seen from Fig. 2 that the amorphous scatter characteristics of the bioceramic samples are very weak, the diffraction characteristics of the ceramsite crystals are prominent, and the main crystalline phase is CaSiO 3 , indicating that the crystallization degree of the product is high under the test conditions. hardness.
(5) SEM analysis of ceramsite samples
3 is a SEM photograph of Sample 1 and Sample 3 in Table 2. It can be seen that the sample is more crystallized, which is consistent with the XRD analysis results; the crystal is mainly in the form of granular aggregates, the overall structure is uniform and the microstructure is relatively dense. According to the fracture theory, the densification of the grain microstructure can create favorable basic conditions for the improvement of mechanical properties. Therefore, theoretically, the prepared bioceramics have good mechanical properties, ie, have high compressive strength and Flexural strength.
Figure 3 SEM photo of the sample
Third, the bioceramic film test
The film test used ceramsite products with V tailings /V accessories = 1.00 and calcination temperature of 1100 °C; the test device consisted of high water tank, biological ceramsite fluidized bed and flow meter, as shown in Figure 4. The fluidized bed is made of plexiglass with a diameter of 30cm and a packing height of 200cm. The lower end 40cm ceramsite has a particle size of 16-20mm, the middle 60cm ceramsite has a particle size of 10-15mm, and the upper end 100cm ceramsite has a particle size of 6-10mm.
Figure 4 Bioceramic film hanging test device
The experiment used the sewage discharge in the school cafeteria to listen to domestic sewage as the treatment object, the hydraulic retention time was 5h, and the water temperature was 20-23 °C. The COD cr of the influent water during the filming period was 817 mg/L, and the COD cr decline rate was only about 17% in 6 days, 80% in 15d, and 93% in 20d. The data measured after several consecutive days were stable. It shows that the hanging film of the ceramsite has been basically completed, and the fluidized bed enters a stable operation stage.
The film test shows that the surface of the bioceramic product can be used for biofilm growth, and the specific surface area affects the amount of biofilm; the pores on the surface of the ceramsite are beneficial to the adhesion and fixation of microorganisms, and at the same time, the attached microorganisms are played. Shield protection from shearing and scouring of water.
During the test, the ceramsite products with no white paint on the surface were compared with the ceramsite products with white paint on the surface. The results showed that under the same conditions, the ceramsite coated with white paint on the surface was slightly faster. Flushing is also easier, and the acid resistance, alkali resistance, and wear resistance of the ceramsite are increased, and the breaking rate is reduced.
Fourth, the conclusion
(1) Using tungsten tailings from the large ridge tungsten mine as raw materials, supplemented by slag, fly ash and clay, roasting method can produce high strength, large porosity and specific surface area, good chemical and physical stability. Bioceramics.
(2) The film test shows that the prepared tungsten tail sand bioceramic film has good performance, strong microbial adhesion, fast attachment speed and easy backwashing.
(3) The surface coating of white paint can improve the performance of bioceramics.