Yin Hongfeng He Tingshu Ren Wei Xie Jianhong

School of Materials Science and Engineering, Xi'an University of Architecture and Technology

Abstract The annual discharge of ore dressing tailings in China has reached 600 million tons, but its resource utilization rate is only about 7%. The nature of tailings is very similar to the requirements of building materials. Therefore, the use of tailings to produce building materials is the reduction of pollution until The most effective way to achieve zero emissions. Thesis Meishan iron ore tailings were studied preparation unburned and burned brick has important guiding significance and practical value.
Key words solid waste, tailings, brick making

China's ore reserves and production are very large, but because the grade of ore is generally low, especially the iron ore with the largest amount of mining, more than 95% are poor ore, which needs to be processed before entering the blast furnace, so a large amount of iron is produced. Mine tailings. China's iron ore tailings have the characteristics of large quantity, small particle size, various types and complex nature. At present, China's iron ore tailings stockpiling of billions of tons, accounting for nearly one-third of the total metal mine tailings dumps. The large amount of tailings discarded, occupying a large amount of land, polluting the environment, wasting a lot of valuable resources, and spending a lot of funds for the construction of tailings ponds. Therefore, it is very important to make full use of this resource for the development and application of tailings.
The principle of comprehensive utilization of tailings should be based on the ability to consume tailings in large quantities, with more thorough utilization, wide product sales, low energy consumption and simple production process. According to the physical and chemical properties of iron ore tailings, the use of iron ore tailings to manufacture various building bricks is an effective way to make extensive use of tailings.
1 Physical and chemical properties of Meishan iron ore tailings The physical and chemical properties of Meishan iron ore tailings are shown in Tables 1 to 4.

Table 1 Chemical composition of tailings samples ( % )
sample
FeO
Fe 2 O 3
SiO 2
Al 2 O 3
CaO
MgO
TiO 2
K 2 O
Na 2 O
S
P
C
Burnout
Re-election
7.58
13.32
34.12
11.20
9.94
2.40
0.38
1.75
0.16
0.978
0.457
3.37
15.65
Reducing phosphorus ore
13.77
18.81
22.18
3.24
12.76
2.89
0.17
0.49
0.15
0.964
1.34
4.85
17.81
Integrated mine
12.08
15.60
25.89
6.90
12.46
3.76
0.25
1.02
0.15
0.962
0.957
4.34
17.12
Table 2 Mineral composition of tailings samples ( % )
sample
Siderite
Hematite
magnetite
Pyrite
Carbonate
apatite
Shi Ying
Diopside
Chlorite
clay
other
Re-election
14.0
7.0
3.4
1.7
11.3
2.5
16.5
7.4
17.1
15.5
3.6
Phosphate rock
27.6
16.6
0.2
1.8
10.2
7.3
16.0
4.0
10.4
3.1
2.8
Integrated mine
22.8
12.4
1.4
1.8
10.6
5.2
16.2
5.1
12.8
8.8
2.9
Table 3 Physical properties of tailings samples
Sample
Specific gravity (g/cm 3 )
Bulk density (g/cm 3 )
Specific surface area (m 2 /g)
Re-election
2.87
1.21
15.81
Phosphate rock
3.13
1.27
7.07
Integrated mine
3.01
1.17
10.44
Table 4 Particle size composition of tailings samples ( % )
Sample
>0.1mm
0.075~0.1mm
<0.075mm
Re-election
7.36
5.53
87.11
Phosphate rock
29.71
3.22
67.07
Integrated mine
21.88
3.67
74.45
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It is seen from the data above, the Meishan tailings high iron content, the sum of silicon oxide and aluminum oxide as compared with other low tailings, while containing high calcium oxide and magnesium oxide. Such a characteristic determines that the tailings are used to prepare steamed bricks with low silica content, and the calcined bricks are prepared because the firing temperature of the building bricks is relatively close to the decomposition temperature of carbonate (iron dolomite and calcite ) in the tailings. For this reason, there may be an effect of calcium oxide and magnesium oxide on the resistance of the fired brick to lime burst. In addition, the tailings have a higher density than the general construction clay , and the finer tailings have a finer grain size. Because the tailings contain a certain amount of clay, they have good plasticity and bonding. With these advantages and disadvantages, we carried out research on steaming and brick making and firing bricks.
2 Brick making results and analysis
2.2.1 Preparation and Experimental Results of
Unburned Bricks The preparation process of unfired bricks is as follows:
Tailings → refining ingredients (pulverized coal tailings + ash + cement) → kneading (powder + water + + superplasticizer elicitor) → compression molding → natural curing at room temperature 24 hours of steam curing deg.] C → 80 → 8 hours Finished product → inspection.
The experimental results are shown in Table 5.

Table 5 Effect of Cement Content on the Strength of Unburned Bricks
Numbering
Fly ash addition amount (%)
Cement addition amount (%)
Compressive strength (MPa)
colour
M1
10
3
3.1
Light red
M2
10
6
7.4
Light red
M3
10
10
10.2
Light red

It can be seen from the above table that when the cement content reaches 10%, the compressive strength can reach the strength requirement of the MU10 building brick.
2.2.2 Preparation and experimental results of fired bricks
The effects of batch composition, molding pressure and firing temperature on the properties of the fired products were investigated. The composition of the ingredients is shown in Table 6. The experimental results are shown in Tables 7 and 8.
It can be seen from the above results that when the tailings utilization rate is above 80%, the strength of the finished product can be obtained to meet the strength requirement of the building brick in the above MU10. However, the bulk density, porosity and water absorption of the finished product of the tailings are higher than that of ordinary building clay sintered bricks. As the firing temperature increases, the compressive strength of the finished product increases. At 1150 ° C, the finished product with higher strength than MU30 strength can be obtained. At 1100 ° C, the finished product with higher strength than MU25 strength can be obtained. At 1000 ° C, the finished product with higher strength than MU15 strength can be obtained. The purpose of adjusting the strength of the finished product can be achieved by adjusting the firing temperature and the molding pressure, and simultaneously adjusting the firing temperature and the molding pressure have a greater influence on the strength of the finished product, as shown in Table 8.

Table 6 Composition of fired bricks ( % )
Numbering
Tailings
Sticky soil
S1
100
0
S2
95
5
S3
80
20
Table 7 Effect of ingredient composition and firing temperature on properties of fired products
Numbering
Firing temperature (°C)
Bulk density (g/cm 3 )
Porosity (%)
Water absorption rate (%)
Compressive strength (MPa)
colour
S11
1000
1.92
44.6
21.3
16.4
red
S21
1000
1.94
44.3
20.2
17.8
red
S31
1000
1.90
43.9
19.9
19.1
red
S12
1100
1.96
44.3
21.4
28.0
Light red
S22
1100
1.96
39.8
22.1
26.4
Light red
S32
1100
1.94
38.7
19.4
29.8
Light red
S13
1150
2.01
39.4
19.6
42.1
Brown red
S23
1150
1.99
38.9
19.5
44.5
Brown red
S33
1150
1.95
36.7
19.2
26.5
Brown red
Note: The molding pressure is 61.4 MPa. [next]
Table 8 Effect of molding pressure on the properties of finished products
Numbering
Firing temperature (°C)
Molding pressure (MPa)
Bulk density (g/cm 3 )
Water absorption rate (%)
Compressive strength (MPa)
colour
S22
1100
32.3
1.90
22.1
15.8
Light red
S32
1100
32.3
1.84
21.1
18.1
Light red
S24
1100
61.4
1.96
21.4
26.4
Light red
S34
1100
61.4
1.94
19.4
29.8
Light red
S23
1150
61.4
1.99
19.5
44.5
Brown red
S33
1150
61.4
1.95
19.2
26.5
Brown red

The strength of the S3 group of finished products with the firing temperature is different from the other two groups. The strength of the other two groups increases with the increase of the firing temperature; while the S3 has a lower strength when the firing temperature is 1150 °C, which is due to the decrease. At this temperature, there is a long crack in the finished product, which affects the compressive strength. The cause of cracking needs further study.
Because Meishan is located in Jiangsu Province, it is a non-severe weathered area. At the same time, because the average temperature in the area is high, the minimum temperature is rarely lower than minus 10 degrees. For this reason, the freezing test can be omitted.
Since the raw material contains high calcite and iron dolomite, decomposition has occurred at a temperature lower than the firing temperature, and free calcium oxide and magnesium oxide may have an effect on the lime burst resistance of the finished product. For this purpose, the finished product was subjected to X-ray diffraction analysis, and the results are shown in Fig. 1 and Fig. 2. It can be seen from the figure that there is no calcite and iron dolomite at 1000 ° C, indicating that decomposition has occurred, and no periclase is found. Magnesium oxide and calcium oxide react with silicon oxide to form diopside. The product was fired at 1000 ° C for two weeks, and the sample did not change. Therefore, whether it is from the phase composition or the immersion experiment, it indicates that the fired product has good resistance to lime bursting.

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Figure 1 Meishan iron ore tailings diffraction pattern

Figure 2 Diffraction pattern of 1000 ° C fired product

3 Conclusion
The preparation of unburned bricks and fired bricks was studied by using Meishan iron ore tailings. The effects of batch composition, molding pressure and firing temperature on product properties were studied. The conclusions are as follows: (1) Using tailings by means of steaming Obtained bricks with strength that meet the strength index of MU10; (2) The utilization rate of the tailings of the fired products is greater than 80%; (3) The firing temperature, molding pressure and composition can be adjusted to obtain the firing index of the sintered brick series. (4) 1000~1150 °C with the change of firing temperature, the color of the finished product has vermilion to reddish to brownish red; (5) due to the formation of diopside during firing, calcium oxide and magnesium oxide will not The anti-lime bursting properties of the fired product adversely affect. (6) The bulk density, porosity, and water absorption of the fired product are higher than those of the clay sintered brick.

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