beneficiation studies of Iron ore slime from Karnataka, India through dispersion and selective flocculation in presence of surfactants and polymers with a view to ...
NEHA KUMARI, A. VIDYADHAR, J. KONAR and R.P. BHAGAT
Proceedings of the XI International Seminar on Mineral Processing Technology (MPT-2010) Editors: R. Singh, A. Das, P.K. Banerjee, K.K. Bhattacharyya and N.G. Goswami © NML Jamshedpur, pp. 564–571
BENEFICIATION OF IRON ORE SLIMES FROM KARNATAKA THROUGH DISPERSION AND SELECTIVE FLOCCULATION Neha Kumari, A. Vidyadhar, J. Konar and R.P. Bhagat Mineral Processing Division, National Metallurgical Laboratory, Jamshedpur - 831 007, CSIR, India 1 Analytical Chemistry Division, National Metallurgical Laboratory, Jamshedpur - 831 007, CSIR, India
ABSTRACT During the wet processing of iron ores, substantial amount of fine particles/slimes is generated in downstream which need to be recovered effectively for their usage and beneficiation. The present paper describes the beneficiation studies of Iron ore slime from Karnataka, India through dispersion and selective flocculation in presence of surfactants and polymers with a view to produce pellet grade fines. The slime sample had a feed grade of 63.84% total Fe, 2.64% Silica and 3.98% alumina. Detailed characterization data indicated that 76 Wt% of the sample was below 49 micron size. XRD analysis indicates that the sample constituted hematite and goethite as in major phase whereas magnetite, kalonite and silica in minor phase. The zeta-potential data indicates that the iep is about 5.1. The dispersion studies of the fine iron ore particles were carried out with sodium hexa meta phosphate (SHMP), tetra sodium pyrophosphate (STPP) and Dispersant N6, a low molecular weight anionic poly-acrylamide polymer. The effect of process parameters pulp density, types of reagents and their dosage on the separation index following dispersion was studied. The selective flocculation studies were carried out on fully dispersed slime sample using modified starch and polyethylene oxide as selective flocculant. The results show that about 95% recovery could be achieved through the separation following dispersion with the enhancement of Fe grade from 1.5 wt. % to 2 wt. %. Keywords: Iron ore slime, Beneficiation, Zeta-potential, Dispersion, Flocculation.
INTRODUCTION Indian iron ores contain fine-grained clay minerals that present considerable difficulties in beneficiation and lowering of aluminium content in the blast furnace feed. Attempts to wash Indian iron ores for the purpose of removal of alumina–through selective dispersion and settling– have met with only limited success.[1,2] The process of dispersion utilizes the differences in surface chemical properties of various particles in the mixed suspension, it is based on the preferential adsorption of a selective dispersant on the on the particular minerals to be dispersed, leaving the remainder of the particles in suspension which is settled under gravity. Earlier studies has been carried out in the presence of inorganic dispersants, like sodium silicate and sodium hexametaphosphate, SHMP.[3,4] In separation system involving clays, SHMP was found to be a better dispersant than sodium silicate due to its higher adsorption that leads to a higher surface charge. Attia & Deason[5] proposed the use of polymeric dispersant such as PEO in enhancing separation 564
BENEFICIATION OF IRON ORE SLIMES FROM KARNATAKA THROUGH DISPERSION…
selectivity in systems. Certain low molecular weight polymeric dispersants adsorb at the interface and prevent coagulation due to entropic and mixing interaction.[6] Bhagat et al. have observed that low molecular additives help in improving grinding efficiency, also the separability of certain types of minerals by reducing hetero-coagulation.[7,8] Selective flocculation is one of the most promising techniques for separation fine/ ultra-fine minerals. Pradip and co-workers[9–11] have systematically investigated the possibility of achieving selective separation amongst hematitealumina-kaolinite-montmorillonite minerals, the mineral constituents representative of indian iron ore slimes. The beneficial effect of a more selective flocculant like starch mercaptan was observed with synthetic dispersants as well.[12] The objective of the present investigation is to study the dispersion and flocculation behavior of Iron ore slimes from Karnataka with a view to produce pellet grade fines. The effect of process parameters pulp density, types of reagents and their dosage on the separation index following dispersion was studied and discussed in the experimental results. EXPERIMENTAL Materials Pure hematite and quartz minerals were hand-picked from the mines of Barajamda sector, Jharkhand. These minerals constituted 67.6% Fe and 94% SiO2 respectively. Iron ore slimes from M/s Mineral Sales Private Limited, Karnataka was used for the present study. The sub-sieve analysis of the sample indicated that 96 wt% fraction was below 100 micron size and 76 wt % was below 49 micron size. The chemical analysis of the slime is shown in Table 1 and size wise chemical analysis is shown in Table 2. Table 1: Chemical composition (in wt. %) of MSPL iron ore slimes Fe (T)
SiO2
Al2O3
CaO
MgO
LOI
63.84
2.64
3.98
0.14
0.08
2.86
Table 2: Size wise chemical analysis (in wt. %) of MSPL iron ore slimes sample Size in µ
Wt.%
Fe
SiO2
Al2O3
LOI
+149
1.82
51.26
17.88
8.90
3.85
+105
1.51
63.39
4.90
2.24
1.37
+74
3.53
63.98
5.11
2.15
1.47
+63
6.46
66.01
1.71
1.25
1.32
+49
11.10
66.16
1.64
1.82
1.67
+42
3.33
66.34
1.55
1.71
1.71
–42
72.25
64.11
2.67
4.56
2.71
Head Cal.
100.00
64.28
2.85
3.91
2.43
Table 2 indicates that gangue mineral constituents were considerably high in +150 micron size. That is, hematite was more finely disseminated and concentrated in finer (–150 micron) size fractions. Besides, the Fe assay in the sub-sieve fraction increased with decreasing the size of the ore sample. 565
NEHA KUMARI, A. VIDYADHAR, J. KONAR and R.P. BHAGAT
Sink and float studies Sink and float study of the different size fractions of the sample was carried out using bromoform (sp. gr. 2.89) and the results was shown in Table 3. From these results it is apparent that good liberation occurs below 105 micron size as regards separation of SiO2, whereas in case of Al2O3 separation liberation occurs below 74 micron. Table 3: Sink and float analysis of the iron ore slimes sample Fe (wt.%)
SiO2 (wt.%)
Al2O3 (wt.%)
72.57
63.67
2.62
4.39
27.43
15.73
47.18
20.82
50.52
14.84
20.82 2.15
Size in µ
Product
Wt. %
+ 149
Sink Float
Head Calc. + 105
100.0 Sink
88.67
66.36
2.15
Float
11.33
19.15
36.62
11.5
61.01
6.05
11.50
Head Calc. + 74
100.0 Sink
92.97
67.19
0.75
1.12
Float
7.03
21.49
52.82
15.78
63.98
4.41
15.78
Head Calc. + 63
100.0 Sink
96.04
67.86
0.23
1.21
Float
3.97
18.75
37.54
12.22
65.92
1.71
12.22
Head Calc.
100.0
The grade of Fe in the sink product increases with the finer fraction (Table 3). Also, the yield of sink had the lowest value at +149 micron size fraction. The yield increased significantly at +74 micron size fraction and lower one. Reagents The dispersants sodium hexa meta phosphate (SHMP) and Tetra sodium pyro phosphate (STTP) were procured from Central Drug House, Mumbai. Dispersant N6, a low molecular weight polyacrylamide was supplied by SNF Floeger. The selective flocculants starch was obtained from Qualigense Fine Chemicals, Mumbai. Zeta-potential Measurements The Zeta-potentials were measured using Zeta Probe (Colloidal Dynamics, USA). The mineral suspension was prepared in 10–3 KNO3 electrolyte solutions, conditioned for 15 minutes at room temperature (28°C). The solid content of the suspension was maintained at 2 wt%. The pH of the slurry was varied using acid/alkali (0.2 M HCl / 0.2 M NaOH) solutions prepared from analyticalgrade reagents.
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Dispersion Studies In the dispersion studies the suspension of fine iron ore particles was destabilized to effect the separation by density difference of hematite and gangue constituents. 400 ml suspension of –45 micron iron ore particles at the desired level of pulp density was taken into a 500 ml graduated beaker. To this measured volume of dispersant was added. The suspension was stirred for 5 min at high shear followed by 1 min. at low shear. Thereafter, the particles were allowed to settle for 5 minutes under gravity. The suspension, thereafter, was separated as upper part (300 ml) and lower part (100 ml). These samples were dried and analyzed chemically. Flocculation Studies In the selective flocculation studies, 400 ml of –45 micron iron ore particles was taken into a 500 ml graduated beaker and conditioned for 5 min. using the dispersant at neutral pH. Thereafter, selective flocculant was added and the suspension was conditioned for 5 min. while slow stirring. The suspension was fractionated into lower part and upper part. The particles were dried and analyzed for its chemical constituents. RESULTS AND DISCUSSION X-ray diffraction Studies X- ray diffraction of the sample shows that the sample constituted hematite as the major mineral phase. Other minor phases that could be identified in the sample are: Goethite, Kaolinite, Magnetite, and Quartz. The XRD analysis of the MSPL iron ore slimes is shown Fig. 1. XRD 1
d=2.6942
4000
d=2.51169
d=1.48459 d=1.59787
d=1.45210
d=1.69304
d=1.83899
d=2.28651
d=2.37392
d=2.96816
d=3.56355
d=3.33134
d=4.81935
1000
d=2.20219
d=3.67028
2000
d=7.10529
Lin (Counts)
3000
0 13
20
30
40
50
60
70
80
2-Theta - Scale
Fig. 1: X-ray powder diffraction spectrum of MSPL Iron ore slimes sample. Zeta-potential Measurements The zeta-potential of iron ore sample as a function of pH is depicted in Fig. 2. The results indicate that the iso-electric point (iep) is at about 5.1. The surface became positive until about pH 5.1, and above which the surface is negatively charged. 567
NEHA KUMARI, A. VIDYADHAR, J. KONAR and R.P. BHAGAT
15
Zeta Potential (mV)
10
5
0
-5
-1 0
2
3
4
5
6
7
8
pH
Fig. 2: Zeta-potential of MSPL iron ore slimes as a function of pH. Dispersion studies The beneficiation studies of iron ore slimes sample was carried out using dispersion and selective flocculation techniques. The separation parameters are defined as follows. Yield (%): The ratio of amount of concentrate following dispersion and settling of Particles for 5 min. to the total iron ore samples treated and expressed as percentage. Grade (%): The weight % of Fe in the concentrate. Table 4: Results on dispersion of iron ore slimes with SHMP Exp. 1 2 3 4
Product
PD
Wt. %
Fe%
Dis. Fe%
Rec. Fe %
2
7.21
41.94
3.024
4.774
Lower Part
2
92.79
65.0
Upper part
3
6.48
41.27
Lower Part
3
93.52
65.26
61.03
Upper part
4
4.97
39.32
1.95
Lower Part
4
95.03
64.36
61.16
96.90
Upper part
7
4.64
45.19
2.10
3.28
Lower Part
7
95.36
64.86
61.85
96.72
Upper part
60.31 2.676
95.22 4.201 95.79 3.096
The effect of pulp density, types and dosage of dispersant on the separation parameters was studied. Tables 4, 5 and 6 shows the results of separation of iron ore fines (–45 micron size) at 2%, 3%, 4% and 7% pulp density using organic and inorganic dispersants SHMP, N6 and STPP simultaneously at neutral pH. The dispersant dosage is maintained at 25 × 10–4 g per g of solid. 568
BENEFICIATION OF IRON ORE SLIMES FROM KARNATAKA THROUGH DISPERSION…
From these results it is apparent that about 95% recovery in Fe could be achieved through the separation following dispersion while grade of Fe improved from 1.5 to 2% in absolute basis. A marginal change in the separation was observed when the dispersant type was varied. This was because the separation was not so effective at neutral pH and a major portion of the product reported to the lower part of the suspension. The same was applicable when the pulp density was varied within the range of 2% to 7%. These observations indicate that further experiments could be necessary with varying pH. Table 5: Results on dispersion of iron ore slimes with N6 Exp. 1 2 3 4
Product
PD%
Wt. %
Fe%
Dis. Fe%
Rec. Fe %
Upper part
2
7.45
45.22
3.37
5.32
Lower Part
2
92.55
64.85
60.01
94.68
Upper part
3
5.26
42.03
2.21
3.49
Lower Part
3
94.74
64.49
61.10
96.51
Upper part
4
7.37
43.29
3.19
Lower Part
4
92.62
65.82
60.96
95.02
Upper part
7
6.24
43.15
2.69
4.18
Lower Part
7
93.76
65.79
61.68
95.82
4.978
Table 6: Results on dispersion of iron ore slimes with STPP Exp. 1 2 3 4
Product
PD%
Wt. %
Fe%
Dis. Fe%
Rec. Fe %
Upper part
2
5.79
42.57
2.464
Lower Part
2
94.21
65.61
61.81
96.16
Upper part
3
6.55
42.18
2.76
4.26
Lower Part
3
93.45
66.43
62.08
95.74
Upper part
4
6.43
42.04
2.70
4.19
Lower Part
4
93.57
65.94
61.70
95.80
Upper part
7
6.24
40.27
2.51
3.91
Lower Part
7
93.76
65.80
61.69
96.09
3.83
Flocculation Studies The selective flocculation results using the flocculant, starch, show that the grade of Fe could be increased by 1.5 to 2%, in absolute term in the concentrate which is lower part of the suspension (Table 7). As expected, a better separation following dispersion and selective flocculation in case of mixture of synthetic minerals: hematite and quartz was achieved than that in case of actual ore slimes (Table 8). The selective flocculation technique is reported respond better when the in case of synthetic mixture rather than in case of actual ore system because of surface defects and liberation in the later case. The selective flocculation experiment to retrieve addition Fe value from the upper part of the suspension had limited success. 569
NEHA KUMARI, A. VIDYADHAR, J. KONAR and R.P. BHAGAT
Table 7: Selective flocculation results of MSPL iron ore slimes using starch Exp.
Product
PD%
Wt. %
Fe%
Dis. Fe%
1
Upper part (0.5 vol. % of 1000 ppm disp.)
2
19.82
56.80
11.26
17.62
Lower Part
2
80.18
65.63
52.62
82.38
Upper part (0.125 vol. % of 1000 ppm Disp.)
2
16.84
58.52
9.86
15.29
Lower Part
2
83.16
65.64
54.59
84.71
2
Rec. Fe %
Table 8. Selective flocculation results with mixture of synthetic minerals (6 gm Hematite +2 gm Quartz) PD%
Wt. %
Fe%
Dis. Fe%
Rec. Fe %
Upper part (0.5 ml of SHMP solution)
2
18.4
46.15
8.493
16.88
Lower Part
2
81.6
51.25
41.82
83.12
Upper part of Upper Part
2
51.2
46.03
23.56
51.06
Lower Part of Upper Part
2
48.8
46.3
22.59
48.94
Exp. 1
2 Selec. Floc. to retrieve
Product
CONCLUSIONS The dispersion and flocculation studies in relation to MSPL iron ore slimes show that about 95% recovery in Fe could be achieved and the grade of Fe improved from 1.5 to 2% in absolute basis. The process parameters namely, pulp density and dosage of the reagents following dispersion at neutral pH had marginal effect on the separation parameters. The system, synthetic mixture of hematite and quartz, responded better than the actual ore slime because of surface defects and poor liberation incase of ore system. ACKNOWLEDGEMENT The financial support from the Department of Science & Technology (DST) under Integrated Long Term Programme (ILTP) with Russian Academy of Sciences (RAS), Russia is gratefully acknowledged. REFERENCES [1] [2] [3] [4] [5]
Viswanathan, S. and Paranjpe, V.G., 1968, Trans. Ind. Inst. Met., 21(2), p. 71. Yu, A. T., 1968, Minerals Engineering, 20(11), p. 70. Attia, Y. A., 1977, International Journal of Mineral Processing, 4, p. 209. Krishnan, S. V. and Iwasaki, I., 1983, Transactions SME-AIME, 272, p. 1984. Attia, Y A. and Deason, D M., 1989, Colloids and Surfaces, 39, p. 227. 570
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[6] Tadros, Th. F, 1982, In: The effect of polymers on dispersion properties, Academic Press, P. 423. [7] Bhagat, R.P, Sil, S.K. and Srivastava , J P., 2002, Trans Inst. Mining & Metallurgy, Section C, Mineral Processing and Extractive Metallurgy, 111, p. c160. [8] Bhagat, R.P. and Pathak, P N., 1997, International Journal of Mineral Processing, 47, p. 209. [9] Pradip, 1994, Metals, Materials & Processess, 6 (3), p. 170. [10] Pradip, 1997, Proceedings, Conference on Raw Materials and Sintering, (CORAS'97), RDCIS (SAIL), Ranchi, p. 8. [11] Ravishankar, S.A., Pradip and Khosla, N.K., 1995, International Journal of Mineral Processing, 43, p. 235. [12] Pradip, 2003, In: Minerals Processing and Engineering, Misra, V.N., Yadav, G.D. and Sarveshwar Rao K. (Eds.), Indian Institute of Chemical Engineers, Kolkata, p. 42.
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