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Oolitic red, brown iron ore is now recognized as the most difficult election of iron ore. With the gradual reduction of available iron ore resources in China, the study of high-efficiency beneficiation technology for scorpion red and limonite ore has highlighted importance and urgency. The ore reserves of an iron ore in Sichuan are large, and the ore contains about 38% iron. The iron minerals are mainly in the form of scorpion red and limonite. The harmful impurities have a phosphorus content of 0.654%, which is a high-phosphorus-like red brown iron ore. Phosphorus minerals are intertwined with iron minerals, and the size of the inlay is extremely fine. Kunming University of Science and Technology passed a large number of experiments, using the reduction roasting-weak magnetic separation-reverse flotation process for the ore, and obtained a good selection index.
First, the nature of the ore
The iron minerals in the test samples are mainly hematite and limonite, with a small amount of magnetite; the gangue minerals are mainly calcite , chlorite, quartz, etc., and contain apatite. The spectral analysis, chemical multi-element analysis and iron phase analysis of the samples are shown in Tables 1 to 3.
Table 1 Spectral analysis results of samples %
element
Ag
Al
B
Ba
Be
Bi
content
0.0001
1
<0.001
0.04
<0.001
<0.001
element
Ca
Cd
Co
Cr
Cu
Fe
content
1
<0.001
0.004
0.003
0.008
>10
element
Ga
Ge
Mg
Mn
Mo
Ni
content
0.002
<0.001
0.5
0.2
0.004
0.01
element
P
Pb
Sb
Si
Sn
Ti
content
0.3
0.006
<0.01
>10
0.003
0.03
element
V
W
Zn
In
Ta
Nb
content
0.01
<0.003
0.02
<0.01
<0.005
<0.01
Table 2 Sample chemical multi-element analysis results %
element
Fe
S
P
SiO 2
Al 2 O 3
CaO
As
content
38.30
0.028
0.654
15.87
5.16
1.60
<0.0001
Table 3 Sample iron phase analysis results %
Iron phase
magnetite
Red limonite
Iron carbonate
Iron silicate
Iron sulfide
total
Iron content
4.07
30.22
1.02
2.69
0.13
38.13
Iron distribution rate
10.67
79.26
2.68
7.05
0.34
100.00
It can be seen from the iron phase analysis that the iron in the ore sample mainly exists in the form of red limonite, and the distribution rate of iron in the red brown iron ore is 79.26%.
Process mineralogical studies have shown that hematite is produced in the form of aggregates with a fine particle size per unit size, generally below 0.004 mm. The brown (needle) iron ore is mainly distributed in the form of cement between the granules, and the magnetite is also embedded in the granules with more chlorite. Some of the chlorite and the scaly hematite are in a dip-like distribution, and a part of the concentric layer and the hematite circle form the granule. There are two types of quartz, one is produced in the form of debris, distributed between the granules, often wrapped in limonite, hematite; the other is the epigenetic quartz, often in the form of veins, each Suture contact. Apatite is the main form of harmful elemental phosphorus in ore. It is mainly granular, and it is distributed in the form of granules in the cement of hematite and limonite and the core of hematite granules. The particle size is generally between 0.005 and 0.2. Mm.
Second, the test plan
A large number of exploratory experiments were carried out on the test ore samples, such as strong magnetic separation, direct flotation, strong magnetic separation desliming-positive flotation, strong magnetic separation desliming-reverse flotation, etc., but due to the nature of the ore, the selection The effect is not good, and the phosphorus content in the concentrate cannot be reduced to less than 0.3%. To this end, it was decided to treat the ore by reduction roasting-weak magnetic separation-reverse flotation process, that is, firstly reduce the red iron iron ore to magnetite by reduction roasting, and then select the iron essence with higher iron content by weak magnetic separation. Mine, and finally use reverse flotation to reduce the phosphorus in the concentrate to less than 0.3%.
Third, reduction roasting test
(1) Calcination temperature test
The coke with a particle size of -1 mm and a dosage of 5% is used as a reducing agent, and the ore which has been broken up to -3 mm is reduced and calcined at 900, 950, 1000, 1050 ° C for 15 min, and then ground to -300 mesh to account for 95% at 71.62. Weak magnetic separation was performed under kA/m magnetic field strength, and the results are shown in Fig. 1.
Figure 1 Calcination temperature test results
■—iron grade; ◆—iron recovery rate
It can be seen from Fig. 1 that when the calcination temperature is too low, the reduction is insufficient, the grade and recovery rate of the iron concentrate are low, and the calcination temperature is too high, which causes over-reduction, which also affects the grade and recovery rate of the iron concentrate. When the calcination temperature is 1000 ° C, the grade and recovery rate of iron concentrates are the highest. Therefore, the calcination temperature was determined to be 1000 °C.
(2) Reducing agent dosage test
The raw ore crushed to -3 mm is separately added with coke having a particle size of -1 mm, and the amount is 3%, 5%, 8%, and 10%, and calcined at 1000 ° C for 15 min, and then ground to -300 mesh to account for 95% at 71.62. Weak magnetic separation was performed under kA/m magnetic field strength, and the results are shown in Fig. 2.
Figure 2 Reductant dosage test results
■—iron grade; ◆—iron recovery rate
It can be seen from Fig. 2 that the amount of reducing agent coke is preferably 5%, and the magnetic separation index of the calcined ore is the best.
(C) firing time test
The raw ore crushed to -3 mm is added with coke having a particle size of -1 mm and a dosage of 5%, and calcined at 1000 ° C for 5, 7.5, 10, 12.5, 15 min, respectively, and then ground to -300 mesh to account for 95% at 71.62 kA. Weak magnetic separation was performed at /m magnetic field strength, and the results are shown in Fig. 3.
Figure 3 Roasting time test results
■—iron grade; ◆—iron recovery rate
It can be seen from Fig. 3 that the calcination effect is best when the calcination time is 15 min, and the iron grade and recovery rate of the magnetic separation concentrate are the highest, so the calcination time is determined to be 15 min.
(4) Reducing agent particle size test
The amount of raw ore to be crushed to -3mm is 5%, the coke with particle size is +3mm, -3+2mm, -2+1mm, -1mm, and is calcined at 1000 °C for 15min, then milled to -300 mesh, 95%, at 71.62kA Weak magnetic separation was performed at /m magnetic field strength, and the results are shown in Table 4.
Table 4 Reductant particle size test results
Reducing agent particle size / mm
product
Yield/%
Iron grade /%
Iron recovery rate /%
+3
Concentrate
Tailings
Raw ore
47.45
52.55
100.00
56.37
21.66
38.13
70.15
29.85
100.00
-3+2
Concentrate
Tailings
Raw ore
47.55
52.45
100.00
57.83
20.27
38.13
72.12
27.88
100.00
-2+1
Concentrate
Tailings
Raw ore
48.01
51.99
100.00
58.93
18.92
38.13
74.19
25.81
100.00
-1
Concentrate
Tailings
Raw ore
48.36
51.64
100.00
60.85
16.85
38.13
77.18
22.82
100.00
It can be seen from Table 4 that in the case where the temperature and time of the magnetization roasting and the amount of the reducing agent are the same, the finer the particle size of the reducing agent coke, the better the magnetic separation effect of the calcined ore. This is because the fine particle reducing agent has a large surface area and is in sufficient contact with the mineral, so that the reduction reaction is relatively complete. However, if the reducing agent particle size is too fine, the processing cost will be increased industrially. Therefore, it was confirmed that the reducing agent coke had a particle size of -1 mm.
(5) Analysis of the phase of roasting iron ore
The iron phase analysis was carried out on the calcined ore obtained under the above-mentioned suitable reduction calcination conditions, and the results are shown in Table 5.
Table 5 Analysis results of calcined iron phase
Iron phase
magnetite
Red limonite
Iron carbonate
Iron silicate
Iron sulfide
total
Iron content
33.90
4.71
0.38
2.76
0.11
41.86
Iron distribution rate
80.99
11.25
0.91
6.59
0.26
100.00
It can be seen from Table 5 that the raw ore is crushed to -3 mm, the coke with a dosage of 5% and a particle size of -1 mm is added, and calcination at 1000 ° C for 15 min can increase the distribution rate of magnetic iron in the ore from 10.67% to 80.99%. The restoration effect is ideal.
Fourth, weak magnetic separation test
(1) Magnetic field strength test
The coke with a dosage of 5% and a particle size of -1 mm was added to the raw ore crushed to -3 mm, calcined at 1000 ° C for 15 min, and then ground to -300 mesh to account for 95%, respectively at 55.70, 71.62, 111.41, 143.24 kA/m magnetic field. Weak magnetic separation was performed under the intensity, and the results are shown in Table 6.
Table 6 Weak magnetic separation magnetic field strength test results
Magnetic field strength / (kA / m)
product
Yield/%
Iron grade /%
Iron recovery rate /%
55.70
Concentrate
Tailings
Raw ore
30.93
69.07
100.00
61.51
27.66
38.13
49.89
50.11
100.00
71.62
Concentrate
Tailings
Raw ore
48.36
51.64
100.00
60.85
16.85
38.13
77.18
22.82
100.00
111.41
Concentrate
Tailings
Raw ore
51.86
48.14
100.00
59.03
15.61
38.13
80.29
19.71
100.00
143.24
Concentrate
Tailings
Raw ore
53.64
46.36
100.00
57.79
15.38
38.13
81.30
18.70
100.00
It can be seen from Table 6 that the weak magnetic separation magnetic field strength should be 71.62 kA/m. When the magnetic field strength is too high, the concentrate iron grade is less than 60%. When the magnetic field strength is too low, the concentrate iron recovery rate is less than 50%.
(2) Grinding fineness test
The coke with a dosage of 5% and a particle size of -1 mm is added to the raw ore crushed to -3 mm, and calcined at 1000 ° C for 15 min, and then ground to -200 mesh, -300 mesh, -400 mesh, -500 mesh, respectively, 95%. Weak magnetic separation was performed at a magnetic field strength of 71.62 kA/m, and the results are shown in Table 7.
Table 7 Weak magnetic separation grinding fineness test results %
Grinding fineness
product
Yield
Iron grade
Iron recovery rate
-200 mesh 95
Concentrate
Tailings
Raw ore
53.45
46.55
100.00
57.23
16.19
38.13
80.23
19.77
100.00
-300 mesh 95
Concentrate
Tailings
Raw ore
48.36
51.64
100.00
60.85
16.85
38.13
77.18
22.82
100.00
-400 mesh 95
Concentrate
Tailings
Raw ore
34.52
65.48
100.00
61.60
25.76
38.13
55.77
44.23
100.00
-500 mesh 95
Concentrate
Tailings
Raw ore
31.14
68.86
100.00
61.52
27.55
38.13
50.24
49.76
100.00
It can be seen from Table 7 that the finer the fineness of the grinding, the more complete the dissociation of the iron mineral monomer, and the higher the iron ore grade, but the fineness of the grinding is too fine, resulting in serious loss of iron during magnetic separation. According to the test results, it is determined that the appropriate grinding fineness - 300 mesh accounts for 95%.
(3) Weak magnetic separation process test
The above test shows that the calcined ore is directly ground to -300 mesh and 95% is subjected to weak magnetic separation. Although iron concentrate with iron grade above 60% can be obtained, the recovery rate of iron is low, and if iron concentrate is further The reverse recovery of phosphorus will reduce the iron recovery rate. To this end, it is decided to carry out stage grinding of the roasting ore, that is, firstly discard a part of the tailings by weak magnetic roughing under the coarser grinding fineness, and then re-grind the coarsely selected concentrate to reduce the fine grinding. Quantity, reducing the impact of mud on iron recovery. The test procedure and conditions are shown in Figure 4, and the test results are shown in Table 8.
Figure 4 Roasting - weak magnetic separation test process and conditions
Table 8 Roasting - weak magnetic separation test results %
product
Yield
grade
Recovery rate
Fe
P
Fe
P
Concentrate
Tailings
Raw ore
50.14
49.86
100.00
60.13
16.01
38.13
0.496
0.713
0.604
79.06
20.94
100.00
41.23
58.77
100.00
It can be seen from Table 8 that after the stage grinding and phase weak magnetic separation measures, the iron recovery rate is improved, and the iron grade of the concentrate is guaranteed to be above 60%, but the phosphorus content in the concentrate is 0.496%, which is not consistent. Smelting requires that phosphorus be reduced to less than 0.3% by reverse flotation.
V. Anti-flotation phosphorus reduction test
Sodium carbonate is used as a pH adjuster, starch is an inhibitor of iron minerals, PB is a collector of phosphorus minerals, and 2 # oil is a foaming agent. A coarse-paste reverse flotation is performed on a weak magnetic separation concentrate ( As shown in Figure 5), the phosphorus content in the concentrate was reduced to 0.225% (see Table 9).
Figure 5 Reverse flotation phosphorus reduction test process and conditions
Table 9 Results of reverse flotation phosphorus reduction test %
product
Yield
grade
Recovery rate
Fe
P
Fe
P
Concentrate
Tailings
Raw ore
90.81
9.19
100.00
60.92
52.34
60.13
0.225
3.178
0.496
92.00
8.00
100.00
41.13
58.87
100.00
Sixth, the whole process test results
The whole process and test conditions of the reduction roasting-weak magnetic separation-reverse flotation test are shown in Fig. 6. The final test results are shown in Table 10.
Figure 6 Reduction roasting - weak magnetic separation - reverse flotation test process and conditions
Table 10 Full Process Test Results %
product
Yield
grade
Recovery rate
Fe
P
Fe
P
Concentrate
Tailings
Raw ore
45.53
54.47
100.00
60.92
19.08
38.13
0.225
0.921
0.604
72.74
27.26
100.00
16.96
83.04
100.00
Table 10 shows that a high-phosphorus-like red-brown iron ore in Sichuan can be obtained by a reduction roasting-weak magnetic separation-reverse flotation process, and a qualified iron concentrate with an iron grade of 60.92% and a phosphorus content of 0.225% can be obtained. The iron recovery rate was 72.74%.
Seven, conclusion
(1) Iron ore in an iron ore in Sichuan is mainly in the form of braided red and limonite, with a phosphorus content of 0.604%. It belongs to high-phosphorus-like refractory iron ore. It is difficult to obtain qualified iron ore by conventional mechanical beneficiation method. mine.
(II) Through a large number of experiments, this study determined that the ore was treated by the reduction roasting-weak magnetic separation-reverse flotation process, and a better selection of 60.92% concentrate grade, 0.225% phosphorus content and 72.74% iron recovery rate was obtained. Other indicators have laid the foundation for the development and utilization of the ore.