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Mineral Processing, Applications of Flocculation, Dewatering, Thickening
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179
5 CHAPTER 5 SELECTIVE FLOCCULATION OF DILBAND IRON
RE 5.1 INTRODUCTION
In chapter 4 quite extensive work was conducted to stabilize the Dilband iron ore
slurry which is the prerequisite of selective flocculation. The dispersion parameters
were optimized on the basis of sediment wt% within a settling interval of 2.5 min.
Since the type of dispersant on the basis of sediment wt% could not be optimized in
the dispersion tests, therefore it was resolved that optimal dispersant will be worked
out on the basis of the selective adsorption of flocculant. Literature pertaining to
selective flocculation, in third chapter, indicated that: type of flocculant and their
respective doses, flocculant addition method, flocculant mixing speed, flocculant
mixing time, type of dispersant and their doses, slurry pH and floc washing are the
main flocculation operating parameters. Therefore in the present chapter effect of the
above operating parameters on the selective flocculation of Dilband iron ore is
described.
5.2 PREPARATION OF FEED SAMPLE
The sample used for selective flocculation was wet grinded in ball mill to achieve
100% 40µm with and without the aid of pH modifier and dispersant. As received and
preenriched material with gravity separation (handsachse) was used as a feed material
for grinding. Initial set of flocculation tests were conducted on the the material used in
dispersion tests whose preparation is discussed in section 4.2.
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CHAPTER 5 SELECTIVE FLOCCULATION OF DILBAND IRON ORE
180
5.3 PREPARATION OF STARCH SOLUTION
Corn starch was dissolved in distilled water according to the method described by
Arol (1984) and Weissenborn(Weissenborn, 1993). The 0.5g of corn starch was
diluted in the 100 ml distilled water and heated up to 130oC in autoclave at 30psi and
left for 30 min. Thereafter cooling the solution and shaking manually was further
diluted so as to have 1000 ppm stock solution. The starch solution was discarded after
24hours.
5.4 PREPARATION OF POLYACRYLAMIDE (PAA) FLOCCULANT SOLUTION
The polyacrylamide solutions of Magnafloc 155, and 156 were prepared in
accordance with the procedure used by Jones (1988). 0.5gram of PAA pre-wetted
with 0.5gram of ethanol was dissolved in distilled water. The mixture gently swirled
by hand for one minute. More water was added and mixture gently swirled by hand
for a further minute. This was repeated until sufficient water was added to produce
0.5% (w/w% ) solution of flocculant. The flocculant solution was left on magnetic
stirrer for 9 hours. The stock solution was further diluted to have a 1000 ppm
concentration and conditioned for one hour prior to use. The PAA magnafloc 1597
and 1696 were also used in present study. Since these flocculants were in solution
form so no special method was used. The PAA solutions were discarded after one
week.
5.5 SELECTIVE FLOCCULATION TEST
The selective flocculation procedure was constant except some modifications in
flocculation addition and floc washing. The general selective flocculation procedure
used is given below.
181
5.5.1 Dispersion
The Dilband iron ore sample of <40 µm was dispersed in distilled water by
maintaining the optimized dispersion parameters in the beaker of 500 ml.
5.5.2 Flocculant Addition
Generally following three methods of flocculant addition were used.
The slurry was immediately transferred to the 250 ml cylinder where volume and
pH adjusted, and shacked 10 times by inverting the cylinder. Thereafter required
doses of the flocculant added in three intervals. After each addition the flocculant
mixed by inverting the cylinder 5 times.
Just after dispersing the slurry the flocculant added within the beaker by keeping
the stirrer speed low up to 300 rpm. In this case the flocculant was further mixed
for 1 min. Thereafter slurry transferred immediately into cylinder and inverted
three times before leaving for 2.5 min settling interval.
The flocculant was added during sonicating the slurry ultrasonically. In this case
the slurry in beaker placed over a sonicator and flocculant added and conditioned
for 1 min. After that slurry transferred to cylinder and shaked for three times by
inverting cylinder.
5.5.3 Floc Washing
Washing involved filling the cylinder containing flocs with distilled water, inverting
the cylinder five times and allowing 2.5 minutes for floc settling prior to supernatant
siphoning. This was repeated three times. The procedures used in floc washing are
shown in Figure 5.1.
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5.5.4 Performance Assessment
The one sediment and two supernatants samples collected from each test were dried at
100oC and weighed. The crude performance assessment was made by measuring the
density of samples and computing the % hematite from density-hematite relation.
Samples with significant improvement in density were analyzed on XRF.
Figure 5.1: Selective flocculation test procedures used in Dilband iron ore.
183
5.6 RESULTS
The effect of dispersants, flocculants, solid concentration, slurry pH, and method of
flocculant addition were evaluated. The results along the test parameters are briefed in
the following sections.
5.6.1 Survey of Effective Dispersant and Its Dose
Initial attempts were made to survey the effective dispersant and its dose, since in the
dispersion tests this parameter could not assessed significantly. Therefore standard
test conditions for initial set of selective flocculation tests used, as ascertained from
the literature survey and preliminary dispersion tests were as follows.
Sample <40µm Dilband iron ore Water Distilled
Dispersants
Type % Dose w.r.to stecheometric amount of Ca+2 Cations in ore
EDTA 10, 30, 60, 100, 150, 300 SS 15, 30, 60, 80, 150 STPP 15, 30, 60, 80, 150, 230, 450 SHMP 15, 30, 40, 60, 80
Stirring Speed 2000 rpm Settling Time 2.5 min Stirring Time 5 min Slurry Ph 10.5
Solid Concentration 10% (w/v) Flocculant Dose
10 ppm
Flocculant Corn Starch Floc washing 3 times
The result of selective flocculation tests at different doses of EDTA, SS, STPP and
SHMP are shown in Figure 5.2 to Figure 5.9. It is very clear from the results that non
of the dispersant could be effective to improve the % grade in any of the test product
(i.e. sediment, supernatant one and supernatant two) significantly. The selectivity line;
the line of average grade of feed ore, indicates the improvement in the grade of the
test products. Hardly 5% increase in grade (calculated) with less than 10% recovery
184
could have been achieved either in sediment or in some cases in supernatant one. The
marginal improvement of first supernatant grade was noticed when 90% material
flocculated within 2.5 min, while improvement in sediment took place when almost
material remained suspended. This trend of minor improvement in the % grade of
either first supernatant or sediment found in all the four dispersants.
50
55
60
65
70
75
10 60 110 160 210 260
% Dose of EDTA
% G
rade
Sediment
Superantant 1
Superantant 2
Selectivity line
Figure 5.2: Effect of EDTA Doses on % grade of Dilband iron ore at 10mg/l corn starch and 10.5 pH .
0
5
10
15
20
25
30
35
40
45
50
10 60 110 160 210 260
% Dose of EDTA
% R
ecov
ery
Sediment
Superantant 1
Superantant 2
Figure 5.3: Effect of EDTA Doses on % recovery of Dilband iron ore at 10mg/l corn starch and 10.5 pH .
185
50
52
54
56
58
60
62
64
66
15 45 75 105 135% Dose of SS
% G
rade
Sediment
Superantant 1
Superantant 2
Selectivity line
Figure 5.4: Effect of SS doses on % grade of Dilband iron at 10mg/l corn starch and 10.5 pH
0
10
20
30
40
50
60
15 45 75 105 135
% Dose of SS
% R
ecov
ery
Sediment
Superantant 1
Superantant 2
Figure 5.5: Effect of SS doses on % recovery of Dilband iron ore at 10mg/l corn starch and 10.5 pH
186
50
52
54
56
58
60
62
64
66
15 65 115 165 215 265 315 365 415
% Dose of STPP
% G
rade
Sediment
Superantant 1
Superantant 2
Selectivity line
Figure 5.6: Effect of STPP Doses on % grade of Dilband iron ore at 10mg/l corn starch and 10.5 pH .
0
10
20
30
40
50
60
15 65 115 165 215 265 315 365 415
% Dose of STPP
% R
ecov
ery
Sediment
Superantant 1
Superantant 2
Figure 5.7: Effect of STPP doses on % recovery of Dilband iron ore at 10mg/l corn starch and10.5 pH .
187
50
52
54
56
58
60
62
64
15 35 55 75
% Dose of SHMP
% G
rade
Sediment
Superantant 1
Superantant 2
Selectivity line
Figure 5.8: Effect of SHMP doses on % grade of Dilband iron ore at 10mg/l corn starch and 10.5 pH .
0
10
20
30
40
50
60
70
15 35 55 75% Dose of SHMP
% R
ecov
ery
Sediment
Superantant 1
Superantant 2
Figure 5.9: Effect of SHMP doses on % recovery of Dilband iron ore at 10mg/l corn starch and 10.5 pH .
The flocculation efficiency of starch noticed to decrease with increase of% dose of
the dispersants except STPP. From the results of present set of the test work, again
selection of optimal dispersant remained unresolved. Therefore 300% EDTA (i.e
4.8kg EDTA/ton of ore), 150% SS (i.e. 2.4kg SS/ton of ore), 150% STPP (i.e. 2.4kg
STPP/ton of ore) and 80% SHMP (i.e. 1.28kg SHMP /ton of ore ) were arbitrary
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selected for further test work. The XRF analysis of these samples is shown in
Table 5.1.
Table 5.1: XRF analysis of samples selectively flocculated at 30 ppm corn Starch and optimal dispersant doses.
Dispersant Density (g/cc)
XRF Analysis Tape % Dose Al2O3 SiO2 P2O5 CaO Fe2O3 EDTA 300 3.70 6.28 19.58 1.07 7.47 62.50 SS 150 3.68 6.43 20.45 1.09 7.32 61.51 STPP 150 3.65 6.29 20.20 1.10 8.55 60.74 SHMP 80 3.67 6.44 20.52 1.15 8.81 60.17
5.6.2 Survey of Optimal Corn Starch Dose
Following set of the test parameters were used to study the effect of corn starch dose
on selective flocculation of Dilband iron.
Sample <40µm Dilband iron ore
Water Distilled
Dispersants
Type % Dose w.r.to
stecheometric amount of Ca+2 Cations in ore
EDTA 300
SS 150
STPP 150
Stirring Speed 2000 rpm Flocculant Corn Starch
Stirring Time 5 min Slurry pH 10.5
Solid Concentration 10% (w/v) Settling Time
2.5 min
Floc Washing 3 Times
The results shown in Figure 5.10 to Figure 5.15 indicate that percent grade of each
product of test still remained poor at all starch doses. With increase in starch dose
increase in percent recovery at the cost of percent decrease in grade resulted. The
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grade and recovery of sediment and first supernatant remained reciprocal in all
dispersants. Percent grade of first supernatant increased with decrease in percent
grade of sediment. Similarly vise versa case remained for their respective percent
recoveries. The XRF analysis of the samples with lowest percent recovery and
approximately ≤ 40% recovery is given in Table 5.2.
50
52
54
56
58
60
62
64
66
68
70
0 10 20 30 40 50 60 70
Starch (ppm)
% G
rade
Sed
Sus 1
Sus 2
Figure 5.10: Effect of corn starch dose on % grade of Dilband iron ore at 300% EDTA and 10.5 pH .
190
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
Starch (ppm)
% R
ecov
ery
Sed
Sus 1
Sus 2
Figure 5.11: Effect of corn starch dose on % recover of Dilband iron ore at 300% EDTA and 10.5 pH .
50
55
60
65
70
75
0 10 20 30 40 50 60 70 80
Starch (ppm)
% G
rade
Sed
Sus 1
Sus 2
Figure 5.12: Effect of corn starch dose on % grade of Dilband iron ore at 150% SS and 10.5 pH .
191
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80
Starch(ppm)
% R
ecov
ery
Sed
Sus 1
Sus 2
Figure 5.13: Effect of corn starch dose on % recovery of Dilband iron ore at 150% SS and 10.5 pH .
50
55
60
65
70
75
0 5 10 15 20 25 30 35 40
Starch (ppm)
% G
rade
Sed
Sus 1
Sus 2
Figure 5.14: Effect of corn Starch dose on % grade of Dilband iron ore at 150% STPP and 10.5 pH .
192
0
10
20
30
40
50
60
0 5 10 15 20 25 30 35 40
Starch (ppm)
% R
ecov
ery
Sed
Sus 1
Sus 2
Figure 5.15: Effect of corn starch dose on % recovery of Dilband iron ore at 150% STPP and 10.5 pH .
Table 5.2: XRF analysis of samples selectively flocculated at different
doses of starch and optimal doses of dispersants.
Disp
Starch ( ppm)
Density (g/cc)
% R XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
300% DTA 20 3.76 14.7 6.464 19.92 1.24 6.785 62.48
30 3.58 43.2 6.838 22.41 1.442 6.642 59.70
150% SS 20 3.75 8.879 6.61 21.55 1.45 7.993 62.48
50 3.65 33.31 6.577 21.08 1.47 8.42 59.04
150% STPP
1 3.71 12.77 6.65 20.40 1.22 8.01 60.55
15 3.58 44.36 6.53 20.43 1.23 8.96 59.77
5.6.3 Survey of Optimal Flocculant
To find out most effective flocculant for Dilband iron ore the different grades of PAA
were tried. PAA flocculant grades and the test parameters used are given below.
193
Sample <40µm Dilband iron ore
Water Distilled
Dispersants
Type % Dose w.r.to stecheometric
amount of Ca+2 Cations in ore
EDTA 300
SS 150
Stirring Speed 2000 rpm
Stirring Time 5 min
Solid Concentration 10% (w/v)
PAA Flocculants Magnafloc 155, 156, 1597, and 1697
Flocculant Dose 1 ppm of Magnafloc 155 and 156
0.5 ppm of Magnafloc 1597 and 1697
Slurry pH 10.5
Settling Time 2.5 min
Floc Washing 3 Times
Results of the tests are shown in Figure 5.16 to Figure 5.19. Results indicate that
PAA also not behaved as selective flocculant for Dilband iron ore. In all the
194
magnafloc grades the grade of sediment remained equivalent to the feed ore. On the
basis of marginal increase in percent grade of first supernatant with poor percent
recovery magnafloc 155 and magnafloc 156 noted to be a better flocculant than
magnafloc 1597 and magnafloc 1697. The XRF analysis of the samples using EDTA
is given in Table 5.3.
50
52
54
56
58
60
62
64
66
68
70
Magnafloc155 Magnafloc 156 Magnafloc1597 Magnafloc1697
PAA Grades
% G
rade
Sed
Sus 1
Sus 2
Figure 5.16: Effect of PAA floculants on % grade of dilband iron ore at 300% EDTA and 10.5 pH .
195
0102030405060708090
Magnafloc155 Magnafloc 156 Magnafloc1597 Magnafloc1697
PAA Grades
% R
ecov
ery
Sed
Sus 1
Sus 2
Figure 5.17: Effect of PAA floculants on % recover Dilband iron ore at 300% EDTA
50
55
60
65
70
75
Magnafloc155 Magnafloc 156 Magnafloc1597 Magnafloc1697
PAA Grades
% G
rade
Sed
Sus 1
Sus 2
Figure 5.18: Effect of PAA floculants on % grade of Dilband iron ore at 150% SS and 10.5 pH .
0102030405060708090
Magnafloc155 Magnafloc 156 Magnafloc1597 Magnafloc1697
PAA Grades
% R
ecov
ery
Sed
Sus 1
Sus 2
Figure 5.19: Effect of PAA floculants on % recovery of Dilband iron ore at 150% SS and 10.5 pH .
196
Table 5.3: XRF analysis of samples selectively flocculated with PAA magnafloc at optimal doses of EDTA
Magna Dose Density (g/cc)
% R XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
155 1 3.57 77.72 6.515 20.64 1.21 8.76 59.77
156 1 3.57 34.96 6.485 20.73 1.23 9.24 59.51
1597 0.5 3.56 58.71 6.40 20.34 1.23 9.01 59.83
1596 0.5 3.57 51.31 6.785 20.03 1.21 8.41 60.47
5.6.4 Effect of pH
To evaluate the effect of pH on percent grade of Dilbnad iron ore, the selective
flocculation tests using the different doses of corn starch was studied. Test parameters
used are as under.
Sample <40µm Dilband iron ore
Water Distilled
Dispersant 150%
SS
Stirring Speed 2000 rpm
Stirring Time 5 min
Solid Concentration 10% (w/v)
Flocculant Corn Starch
Flocculant Dose ( ppm) 5, 10, 15, 20, 25, 30
197
Slurry pH 10.5 and 11.5
Settling Time 2.5 min
Floc Washing 3 Times
The results shown in Figure 5.20 indicate that with pH increase to 11.5 the selectivity
of the corn starch for the Dilband iron ore could not be improved except the marginal
charges. Starch almost behaved similarly in both pH values. The XRF analysis of the
samples is given in Table 5.4.
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30Corn Starch Dose (ppm)
% a
ge
% Grade of Sed at10.5pH
% Grade of Sed at11.5pH
% Recovery in Sed at10.5pH
% Recovery in Sed at11.5pH
Selectivity Line
Figure 5.20: Effect of pH and starch doses on % grade and %recovery of Dilband iron ore at 150% SS.
Table 5.4:XRF analysis of samples selectively flocculated with 10 and 20 ppm corn starch at optimal doses of SS.
Starch ( ppm) pH Density
(g/cc) % R
XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
10 10.5 3.73 11.2 6.80 21.22 1.28 4.91 62.98
11.5 3.77 8.401 6.71 21.12 1.31 5.24 62.77
20 10.5 3.7 26.34 7.22 23.59 1.53 5.13 62.70
11.5 3.73 15.15 6.53 19.96 1.19 6.22 63.37
198
5.6.5 Effect of Solid Concentration.
The effect of solid concentration on selective role of corn starch for Dilband iron ore
was studied. For this two more solid concentrations viz 5% and 7% were tried. The
results shown in Figure 5.21 indicate that with decreasing the solid concentration
marginal decrease in wt% of the material flocculated had taken place. XRF analysis (
Table 5.5) did not show any change in the percent grade.
0
10
20
30
40
50
60
70
300%EDTA 150%SS 150%STPP
Dispersants
Wt%
10% Solids
7% Solids
5% Solids
Figure 5.21: Effect of% solid on % recovery of Dilband iron ore at 30 ppm corn starch and 10.5 pH .
Table 5.5: XRF analysis of samples selectively flocculated with 50 ppm corn starch at optimal doses of EDTA.
% Solid pH Density (g/cc)
% R XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
5
10.5
3.62 59.00 6.26 19.82 1.10 8.47 61.61
7 3.65 61.81 6.59 20.39 1.26 6.75 62.05
10 3.68 63.20 6.60 20.51 1.29 7.12 61.57
199
5.6.6 Effect of Method of Flocculant Addition.
General three methods of flocculant addition given below were studied in present
work.
Flocculant addition into cylinder.
Flocculant addition during stirring the slurry at 300 rpm and 600 rpm
Flocculant addition during sonicating the slurry into beaker.
No significant effect on % grade or selectivity of the starch resulted. However
addition of starch at 600 rpm indicated marginal increase in wt% of material settled
(flocculated). This shows that proper mixing of flocculant could happen at 600 rpm.
The XRF analysis of the flocculated samples is given in Table 5.6.
Table 5.6: XRF analysis of samples selectively flocculated at different starch addition methods, 20 ppm starch, and 300% EDTA.
Starch Added @
Density (g/cc)
% R XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
Cylinder 3.76 14.7 6.46 19.92 1.24 6.78 62.48
300 rpm 3.73 16.9 6.75 21.46 1.43 8.01 62.53
600 rpm 3.75 17.5 7.03 19.27 1.20 6.69 62.87
Sonication 3.69 15.25 6.36 19.73 1.08 7.97 62.28
5.6.7 Effect of Sample Preparation Method
To avoid the ambiguity of slime adherence effect known as smearing effect during the
grinding the material grinded with addition of 150% SS and maintaining the 10.5 pH
value in distilled water. The flocculation tests on this material using 30 ppm corn
starch at 10.5 pH were repeated. The result showed that with change in material
preparation method Dilband iron ore could not selectively flocculated.
200
5.7 DISCUSSION
In order to flocculate Dilband iron ore selectively all the major process parameters
were studied. The results indicated that all the flocculation parameters failed to
separate the gangue minerals from ore selectively. The poor selective flocculation
results raised many questions to be answered. Like:
Are the dispersants not working effectively to disperse the gangue minerals?
Is the slurry pH not appropriate?
Is the method of starch addition not adequate?
Is the feed sample severely slime coated during the grinding?
Is the starch not playing its selective role for Dilbnad iron ore?
Is the material not liberated?
Possible answeres concerning these questions and role played by flocculation
parameters in Dilband iron ore slurry are discussed below.
5.7.1 Effect of Dispersants
The general role of the dispersants outlined in the literature is to improve the
selectivity of the flocculant for mineral of interest via complexing with the polyvalent
metal cations like Ca+2, Mg+2, and Fe+3 and increasing the zeta potential of the gangue
minerals(Arol, 1984; Baris Beklioglu; Mathur, et al., 2000; Weissenborn, 1993). In
present study all the well known dispersants EDTA, SS, SHMP, and STPP at different
doses were tried to enhance the selectivity of the corn starch for the hematite present
in the Dilband iron ore along with the quartz, kaolin, fluorapatite and clinochlore
gangue minerals keeping in view the polyvalent metal cation concentration. The
201
results indicated that with increase of the dispersant dose except STPP the significant
decrease in % recovery with marginal increase in % grade resulted. The increase in
zeta potential with increase dispersant concentration is the basic cause of loss of%
recovery. Therefore at higher concentration of dispersants it would become difficult
for starch molecules to adsorb on to the mineral surface. The flocculant
conformational changes from extended to flattened can also be attributed with
increase in % dose of dispersants due to increase in zeta potential.
The effect of dispersant% doses on % grade, based on density, indicated that with
increasing the dispersant dose a marginal improvement in the grade took place. This
indicated that dispersants are not working effectively in dispersing the gangue
minerals. The XRF analysis of the samples with somewhat better density
improvement, shown in Table 5.1, further confirmed that non of the dispersant could
have been able to disperse the quartz and fluorapatite minerals efficiently. The
improper selection of dispersants or their respective dose one can speculate behind
poor selectivity of flocculant. But the results in hand dose not attest this conjecture,
since the prime role of the dispersants in increasing the zeta potential of the system is
played effectively as is witnessed from the significant changes in percent recovery.
Therefore non selective flocculation at different doses of dispersants can also be
attributed with poor selectivity of corn starch, poor liberation of ore or both. Since
selectivity of corn starch for hematite in a system containing gangue mineral chiefly
quartz is widely acknowledged in the literature(Khalil and Aly, 2002; Montes-
Sotomayor, et al., 1998; Pavlovic and Brandao, 2003; Peres and Correa, 1996;
Ravishankar, et al., 1995; Subramanian and Natarajan, 1991; Weissenborn, 1996;
Yong, 1985), therefore attributing failure of grade improvement with poor selectivity
202
of corn starch would be surmise at this stage. Whereas improper corn starch dose, not
suitable pH value, poor mixing of the starch, or inconveniency in adsorbing to the
hematite surface due to presence of gangue particles surrounding the hematite are the
possible causes to be answered before attesting the poor liberation of Dilband iron
ore.
5.7.2 Effect of Corn Starch Dose
In previous section poor selectivity of corn starch for Dilband iron ore was inferred
might due to be in effective starch dose. With increasing the dispersant doses it was
seen that starch at 10 ppm dose was not able to destabilize the material, while at low
dispersant doses the slurry was flocculating without selectivity. Therefore keeping the
higher dispersant doses constant and starch doses as variable the flocculation tests
were attempted. Results indicated that although the percent recovery increase with
increasing the starch doses but without encouragable improvement in the percent
grade. No significant improvement in the selectivity of starch suggested that corn
starch dose can not be attributed the cause of poor selectivity.
5.7.3 Effect of Slurry pH
Slurry pH is well recognized to play significant role in altering the selective role of
the flocculants (Drzymala and Fuerstenau, 1981; Hogg, et al., 1993; Khan, 1985;
Mathur, et al., 2000; Paananen, 1980). Keeping in view the governing role of slurry
pH, the selective flocculation tests for Dilband iron ore were tried on 10.5 pH and
11.5 pH , where starch selectivity for hematite in comparioson with quartz is widely
recognized in the literature(Arol, 1984; Colombo, 1986; Gururaj, et al., 1983; Jones,
1988; Kafali, et al., 1988; Mathur, et al., 2000; Paananen, 1980; Ravishankar, et al.,
1995; Weissenborn, 1993). Since Dilband iron is composed of two main gangue
203
minerals namely quartz and fluorapatite, therefore etiology of poor selectivity of
starch at these pH values is discussed individually.
Generally the selectivity of starch for hematite in a system like Dilband iron ore
containing quartz, the chief gangue mineral, is supposed due to significant difference
in their respective point of zero charge and thereby zeta potential values at 10.5 pH .
Literature pertaining to electro kinetic properties of quartz indicate that point of zero
charge of quartz normally exist <2pH. Therefore at 10.5 pH to 11.5 pH values the
zeta potential of quartz is too negative comparatively to hematite having point of zero
charge at about 8.5 pH. According to the investigations of Arol (1984) the zeta
potential value of quartz ranges in between -80 to -120mv at 11pH, while that of
hematite is hardly increase up to -69mv at 11pH. Therefore at 10.5 pH or 11.5 pH
values the adsorption of starch onto quartz is supposed to be too difficult
comparatively to hematite. The poor selectivity of starch for hematite in comparison
with quartz in Dilband iron ore, therefore, can not be attributed with the pH values of
the slurry used.
Similar to quartz poor selectivity of starch for hematite in comparison with
flourapatite present in the Dilbnad iron ore can also be understand considering their
respective point of zero charge and resulting zeta potential at the 10.5 pH and 11.5
pH . Literature pertaining to point of zero charge of the flourapatite indicated that
difference in point of zero charges of fluoraptite and hematite is not too high, since
the point of zero charge of fluorapatite is reported at 6-7pH value(Barros, et al., 2008;
Ofori, et al., 1985; Simukanga and Lombe, 1995). Investigations of J. Ofori and
Somasundaran(Ofori, et al., 1985) indicated that zeta potential of apatite at 10.5 pH is
-20mv. If it is right to concieve the same zeta potenial values of apatite for fluoraptite
204
present in the Dilbnad iron ore or at least not too different than hematite, then poor
selectivity of starch for hematite can easily be answered.
5.7.4 Effect of Method of Floculant Addition
Upon realizing the problem of poor selectivity of starch for Dilband iron ore, poor
flocculant mixing and inconveniency of starch molecule adsorption on the hematite
surface in the cylindrical tests were also attributed. To look into this issue the starch
addition during stirring the slurry and sonicating ultrasonically was made. Results of
these tests did not differ in terms of the improvement in the selectivity. Before
adding the starch in stirring or sonication conditions it was thought that during
addition of starch in cylinders might be particles of the quartz or fluorapatite are so
closed that starch is not finding way to reach to hematite surface. Therefore addition
of starch during stirring or sonication would help to disperse the gangue particles
from the vicinity of hematite and thus selectivity may improve. This conjecture
remained invalid and the selectivity remained poor as was in cylinder.
5.7.5 Effect of Solid Concentration
In tracing the root cause of poor selectivity solid concentration were also altered with
these hopes that might be solid concentration give the solution of problem. Results of
different solid concentration indicated that issue of the poor selectivity remained as it
is. However the marginal increase in wt% of material flocculated at higher
concentration suggest that flocculating efficiency of starch at higher solid is
increased to some extent. This increasing trend in flocculating efficiency with
increasing solid content can be attributed to the decrease in inter particle distance due
to which increase in particle particle collision rate had facilitated starch molecules to
205
adsorb effectively. Dominancy of particle-particle collision over the rate of flocculant
adsorption is known a key parameter in bridging floculation. Weissenborn (1993) and
Khan (1985) had the similar findings with increasing the solid concentration.
5.7.6 Sample Preparation Method
Literature pertaining to selective flocculation of iron ores indicate that major reasons
for loss in selectivity in mixed minerals and natural ore systems are the slime coating,
may be generated during grinding, and presence of even trace levels of surface active
impurities(Arol, 1984; Mathur, et al., 2000). In other words material grinding is the
detrimental to the success of selective flocculation which governs the smearing effect
of the valuable mineral and the production of the polyvalent metal ions. In order to
mitigate the possible smearing effect of quartz and fluorapatite on hematite surface
causing during the grinding stage, the material grinded in presence of sodium silicate
at 10.5 pH in distilled water was also used in the present work. The results indicated
that problem of poor selectivity of starch remained unsolved. Poor grade of the
flocculated material even in the material grinded in presence of sodium silicate and
10.5 pH value suggested that smearing effect can not be regarded the cause of the
poor selectivity of corn starch in Dilband iron ore system.
5.7.7 Effect of PAA
Although the poor selectivity of PAA for iron ore bearing minerals in comparison
with starch is widely accepted(Ravishankar, et al., 1995; Subramanian and Natarajan,
1991; Weissenborn, 1993), even though a trial of PAA flocculants was made with this
speculation that might be the coarser hematite particles are present in the system and
starch is not capable to capture them. This conjecture was based on the findings of
206
Behl et al, that with increasing particle size, one needs higher molecular weight
polymers to achieve high flocculation efficiency (Mathur, et al., 2000). The second
impulse of using the PAA was the poor flocculation of hematite particles with starch
in Barsua Indian iron, which meant that it could not always be true for starch to be the
only flocculant for iron ores(Gururaj, et al., 1983; Ravishankar, et al., 1995). Based on
these assumptions four grades of PAA magnafloc 155, magnafloc156, magnafloc
1597 and magnafloc 1697 were tried in flocculating the Dilband iron ore. Test results
indicated that particle capturing tendency of all these flocculants was quite more than
starch, whereas grade of the flocculated material remained equivalent to the feed
grade and poor than starch. This poor performance relative starch confirmed the
superiority of starch for flocculating the iron ore more effectively than PAA.
5.7.8 Conclusion
In previous section possible speculations behind the poor selective flocculation of
Dilband iron ore were discussed. Each operating parameter critically observed and
finally the two major root cause were supposed to be responsible of poor performance
of selective flocculation. These are:
The Dilband iron ore is not completely liberated, specially quartz is so heavily
intergrown into the grains of hematite that all the selective flocculation parameters
failed to separate it.
The fluorapatite, if it is liberated, might have the equivalent zeta potential to the
zeta potential of hematite at operating pH and dispersants doses. Therefore starch
could not preferably adsorbed onto hematite.
207
The speculation about the poor liberation and relative evidences are discussed in
section 5.7, while to prove the second speculation a selective flocculation tests on
synthetic system conducted. The flocculation of fluorapatite with corn starch at 10.5
and 11.5 pH in absence of catios conducted. It is noted that fluorapatite flocculated
likely to hematite with approximately same settling rates. The literature pertaining to
flotation provides convincing evidences of apatite depression with starch(Filho, et al.,
2000; Guimarães, et al., 2005; Pearse, 2005). Structural compatibility between end
groups of apatite and starch has been attributed the cause of preferential adsorption of
starch onto apatite relative to calcite. Therefore, flocculation of fluorapatite with corn
starch in synthetic system provides sufficient evidence to substantiate the floccultion
of fluorapatite present in Dilband iron ore, if liberated, during the selective
flocculation attempts.
5.8 EVIDENCE OF POOR LIBERATION OF DILBAND IRON ORE
The evidence from experimental results pertaining to poor liberation of the Dilband
iron ore are as under.
5.8.1 Selective Flocculation Tests
The evidences of the poor liberation of Dilband iron ore were noted through out the
flocculation test work from the increasing trend of the density value of the first
supernatant sample with increase in wt% of flocculated material. Quite substantial
increase in the density value of the first supernatant was observed as and when more
than 80% material was flocculating. The XRF analysis of one of the first supernatant
samples collected from the selective flocculation test using magnafloc 155 and 300%
EDTA was conducted. The XRF result of the first supernatant and sedimented
208
(flocculated) material with approximately equal wt% and density is given in
Table 5.7. Substantial increase in hematite and decrease in quartz content in 1st
superantant sample comparatively to sediment (flocculated) sample shown in
Table 5.7 provides sufficient evidence about the poor liberation of Dilband iron ore.
The significant increase in hematite content in the supernatant suggest that
sufficiently un liberated material was used into the flocculation test.
5.8.2 Sub Sieve Size Classes
The mesh of liberation of Dilband iron ore anticipated in previous work was based the
elemental, density, and magnetic susceptibilities along with stereomicroscopic and
SEM images analysis of different size classes. From all these results it was
conjectured that mesh of liberation might exist below 15µm. Therefore selective
flocculation tests were conducted on the material containing 85% <15µm material.
Poor performance of the selective flocculation tests attributed to poor liberation of ore
once again enforced to think about the exact mesh of liberation of Dilband iron ore.
Therefore to confirm and ascertain this hypothesis the sub sieve size classes by
velocity classier and beaker decantation method were collected using the stokes law.
The size classes along with density and XRF analysis are given in Table 5.8.
Table 5.7: XRF analysis of sediment (flocculated) and 1st supernatant sample
Sample % R Density (g/cc)
XRF Analysis
Al2O3 SiO2 P2O5 CaO Fe2O3
1st Sup 10.35 3.77 6.673 16.35 1.20 5.25 67.33
Sediment 15.15 3.73 6.53 19.96 1.19 6.22 63.37
209
Results of sub sieve size classes very clearly show that hematite in Dilband iron ore is
so heavily intergrown with gangue minerals that only the material under 1.8µm could
be regarded as liberated. This shows that size fractions of Dilband iron ore used in
selective flocculation was not feasible to be flocculated selectively. The microscopic
examination of 40/20µm polished sample under reflecting light microscope strongly
supported the speculation regarding the fine intergrown of gangue minerals. The
intergrown of gangue mineral is very apparent in pictorial view of 40/20µm sample,
shown in Plate 5.1, examined in inverted light microscope. The SEM observation of
these samples will further confirm the liberation status below 5µm.
Literature pertaining to selective flocculation of natural iron ores indicate that
unflocculated material or supernatant is normally the material containing the higher
content of impurities comparatively the flocculated material(Colombo, 1986; Das,
1998; Goodman, 1981; Iwasaki and Iwao, 1981; Kafali, et al., 1988; P.
Samasundaran, 2000; Paananen, 1980; Weissenborn, 1993). Whereas in Dilband iron
ore the case remained vise versa throughout all the selective flocculation tests. In all
the flocculation tests the low grade or not sufficiently liberated reported to the
flocculated product while the better grade or sufficiently liberated reported to
supernatant or unflocculated product. The question arises that why this happened and
why starch and PAA could not flocculated the sufficiently liberated class of the
Dilband iron ore? From the XRF analysis of sub sieve size classes the answer of these
questions can easily be given. The answer is very simple and logical that efficiency of
any flocculent is not only mineral dependent but also particle size dependent. Behl et
al (1993b, C) demonstrating the significance of particle size in selective flocculation
210
observed that with increasing particle size, one needs higher molecular weight
polymers to achieve high flocculation efficiency (Mathur, et al., 2000).
Table 5.8: Density and XRF analysis of sub sieve size classes collected form 100% <40 µm Dilband iron ore.
Plate 5.1: Polished section ogf 40/20µm particles (1000x). Bright reflecting is hematite and dark is gangue minerals.
This observation suggest that any flocculent with particular molecular weight would
not be suitable for all particle size classes. Lower the particle size, flocculent with
Velocity Classes and Relative Grade
Particle size ( µm) Wt% Density
(g/cc) SiO2 P2O5 Fe2O3 CaO Al2O3
5 7.72 3.98 17.89 1.30 63.42 7.96 6.59 15 61.62 3.53 19.60 1.34 55.02 8.05 6.01 20 15.83 3.67 21.29 1.37 58.70 8.59 6.62
>20 14.84 3.79 20.55 1.25 60.68 7.31 6.68
Beaker Decantation Size Classes and Relative Grade1.8 22.09 3.87 17.41 1.23 67.77 3.79 7.28 5 31.44 3.64 21.39 1.80 59.94 7.10 6.79 10 16.4 3.56 21.44 1.09 62.19 6.01 6.40 15 8.26 3.54 24.55 1.36 56.10 8.29 6.52 20 7.59 3.62 21.91 1.27 59.60 7.95 6.38
>20 14.17 3.70 --- --- --- --- ---
211
lower molecular weight would be needed. In other words for selective and effective
flocculation one has to select the flocculent of optimal molecular weight.
Weissenborn (1993; 1996) has also correlated the selectivity of starch with respective
particle size of hematite and kaolin. According to findings of Weissenborn (1996)
starch selectively flocculated hematite comparatively to kaolin because hematite was
coarser (>2µm) than the kaolin particles (<2µm). Based on the literature findings the
ineffective and unselective role played by starch and PAA in Dilband iron ore can be
attributed to wide difference in particle size of sufficiently liberated and un liberated
particles. The sufficiently liberated material is available in so ultrafine particles that
for starch or PAA molecules the capturing of these particles may not be possible. Poor
flocculating efficiency of ultrafine hematite particles <2µm in synthetic system with
starch is observed by B. Gururaj et al (1983). Based on particle size of hematite
relative to gangue minerals that have been examined on the stereo microscope
preferential adsorption of starch on gangue minerals comparatively to hematite can be
anticipated.
Secondly the dispersants doses used in selective flocculation tests were optimized on
the basis of sediment wt% and flocculation efficiency of averagely coarser particles.
Therefore over dispersion of ultrafine particles can be inferred at the optimized
dispersant doses. Thus over dispersion of ultrafine particles would have jeopardized
the selectivity in flocculation tests. Adverse effect of SS dispersant on flocculating
efficiency of <2µm particles in Indian iron ore is reported in literature(Gururaj, et al.,
1983).
212
5.8.3 Acid Treatments
Along XRF analysis and density measurements of the products of the selective
flocculation tests and different size classes obtained either by sieving (wet or dry) or
velocity and beaker decantation methods the stereo microscope was also used to
identify and discriminate the minerals. Under the examination of all the samples the
identification of liberated quartz (if exist), calcite and fluorapatite remained
controversial, due to similarities in their lustre. Therefore to discriminate decisively
between the quartz, calcite and fluorapatite under the stereo microscope, it was
decided to give the acid treatment to a particular size class that can be easily
examined. For this 60/40µm size class was selected and the following acid treatments
were given.
Hydrofluoric (Hf) treatment
HCl (diluted 1:2 ratio) treatment.
Hydrofluoric followed by HCl treatment or vice versa.
The idea behind Hf treatment was just to remove the quartz, since Hf only reacts with
quartz. Whereas treatment with diluted HCl was given only to remove the calcite. The
samples after diluting with particular acid was left into the dryer set at 60oC just to
heat the samples near to dry. After that residue filtered and acetone washed. The acid
treated samples then observed under the stereo microscope. The microscopic plates of
feed, Hf treated, HCl treated, and Hf followed by HCl are shown in Plate 5.2 to 5.7.
Image shown in Plate 5.2 indicate that a sample without acid treatment contains
majority of grey particles, often regarded to be hematite rich particles, comparatively
to gangue particles with transparent, translucent and opaque lustre. Sample treated
213
with Hf shown in Plate 5.3 indicate that sample is left only with the gangue minerals,
whereas all the grey particles vanished. The particles with opaque lustre are either
gangue or hematite particles covered with SiF4 compound since the sample were not
heated at higher temperatures where SiF4 compound formed due to the addition of Hf
could evaporate. On the other hand sample treated with diluted HCl shown in Plate
5.4 indicates the enrichment in the grey particles (hematite). While sample treated
with Hf followed by HCl (diluted) or HCl (diluted) followed by Hf shown in Plate 5.5
and Plate 5.6 respectively did not bring the significant difference in the content of
opaque or translucent particles. However marginal difference in the content of grey
particles between the samples treated with Hf followed by HCl and HCl followed by
Hf observed. Sample treated with Hf followed by HCl shown little bit higher content
of grey particles comparatively the sample treated with HCl followed by Hf. This
might be due to difference in exposure of the grey particles. Grey particles treated
with HCL first may have higher exposure for Hf than the sample directly reacted with
Hf. This exposure difference can be conceived by comparing the images of feed
sample (Plate 5.2) with HCl treated (Plate 5.4). The higher content of opaque lustre
particles in the samples treated with Hf followed by HCl or vice versa may be the
hematite particles coated with SiF4.
From the microscopic examination of samples only Hf treated (Plate 5.3) and Hf
followed by HCl (Plate 5.5) or vice versa it was surprisingly noted that:
Hematite grain in any significant size that can be observed under the stereo
microscope was seldom to find.
Liberated hematite grains, if are present then they, are spherical in shape.
214
These strange results indicate that hematite do not exist in any significant grain size at
least, otherwise it is impossible for hematite to be dissolved within these acids. If not
then at least liberated hematite grain is not in sufficient quantity to be observed
significantly.
To confirm the hypothesis of hematite existence in ultrafine particles except the
spherical particles the samples were heated to 900oC to remove the coating of SiF4
compound. Thereafter samples re examined under stereo microscope and their density
and XRF analysis was conducted.
The XRF analysis and density of acid treated samples shown in Table 5.9 witness that
hematite do not digested in the given acid treatments.
215
Plate 5.2: 60/40µm material used in acid treatments.
Plate 5.3: 60/40µm material after HF treatment.
Plate 5.4:60/40µm material after HCl (Diluted) treatment.
Plate 5.5: 60/40µm material after Hf treatment followed by HCl (Diluted).
Plate 5.6: 60/40µm material after HCl (diluted) treatment followed by Hf.
Table 5.9: XRF analysis and density of acid treated samples Sample ID Density SiO2 P2O5 CaO Fe2O3 Al2O3
60/40 µm_Feed Material 3.95 19.68 0.84 6.783 63.52 5.380
60/40 µm_Diluted Hf(1:2) 3.98 13.18 0.63 12.628 62.08 5.600
60/40 µm_Diluted HCl(1:2) 3.94 22.78 0.27 0.551 68.89 5.014
60/40 µm_Concentrated Hf 4.31 5.45 0.45 20.256 58.67 5.999
60/40 µm_Diluted HCl (1:2)_ Hf 4.91 6.77 0.08 10.18 84.39 3.458
60/40 µm_Concentrated HCl 2.44 84.09 0.08 0.254 6.63 4.454
216
The microscopic examination of HCl followed by Hf and only Hf samples after
heating at 900oC confirmed that all the opaque lustre was due to presence of SiF4
compound and quite significant hematite particles/ grains only in the HCl followed by
Hf treated sample become visible. Three postulations can be made in this regard:
Hematite is present in significant grain size and was not visible due to SiF4
coatings.
Colloidal hematite particles are cemented together at 900oC.
Significant particles are of kaolin, poor digestion of kaolin in Hf and diluted HCl
can be substantiate from XRF analysis, on which hematite is coated.
To elucidate the mystery of hematite existence either in colloidal or significant
particle size this sample was further treated with concentrated HCl with this
conjecture that kaolin, if it is present, would not dissolve in it. The microscopic
examination of the residue indicated that all the hematite wiped out in filtrate with
HCl and only significant kaolin particles observed.
Therefore based on stereo microscopic examination the existence of hematite near to
colloidal particles can be substantiated. If this is right then it would be not wrong to
postulate that hematite is just coated on to gangue minerals specially on quartz in
Dilband iron ore. To confirm this, particles of 60/40µm size fractions were diluted
with concentrated HCl and left for 45 min at 80oC with this objective that if hematite
is present in the significant grain size and quartz is disseminated into hematite grain
then quartz should disintegrate into fine particles when digestion of hematite will
takes place likewise in case of concentrated Hf, if not then it would be right to
perceive that hematite is present in colloidal size and all the particles with grey lustre
217
are the quartz particles just coated with hematite. The microscopic examination of
residue (84% SiO2) apparently attested the postulation of hematite coating onto
quartz particles, since size of all the particles was approximately equal to feed
material (Plate 5.7).
Plate 5.7: 60/40µm material after HCl (Concentrated) treatment.
In the light of microscopic examination of acid treated samples it can be envisage that
any attempt to separate the quartz would left the hematite in colloidal size. Therefore
it would be conceived with quite confidence that hematite can not be separated from
quartz at least by any physical means.
5.8.4 Effect of Potato Starch
Selective flocculation tests on synthetic hematite-quartz in presence of polyvalent
metal ions equivalent to Dilband iron ore, described in section 5.9, revealed that
potato starch effectively disperse the quartz than any dispersant and improves the
selectivity of corn starch for hematite. Based on these findings selective flocculation
test on Dilband iron ore re-attempted. The optimal dose of SS followed by 50 ppm
potato starch, as learned from synthetic tests, was added into the slurry. Thereafter the
different doses of corn starch, 10 to 100 ppm, with step of 10 ppm added. After
218
addition of each dose slurry left for 2.5 min to observe the flocculation or
sedimentation. It is surprisingly noted that slurry could not flocculated, while the
slurry in absence of potato starch flocculated significantly just with addition of 20
ppm corn starch.
The stabilization of slurry containing 50 ppm potato starch with addition of corn
starch up to 100 ppm is the clear indication that corn starch did not find the surface to
be adsorbed. In other words all the particles or surface of particles where corn starch
has to adsorb were already covered with potato starch. Whereas preferential
adsorption of potato starch on quartz comparatively hematite is learned from synthetic
flocculation study of hematite-quartz system with supporting evidence from literature.
This means that majority of the particles present into the Dilband iron ore slurry are
intergrwon with quartz where potato starch adsorbed preferentially and left no
sufficient place or surface for corn starch to adsorb. Since adsorption of potato starch
induces the dispersion or floatability into the particles, therefore stabilization of slurry
took place.
5.8.5 Flotation Test
Failing in upgrading the Dilband iron ore effectively by selective flocculation, it was
supposed that selective flocculation may not be the only solution of the problem but
may be the first step to the up gradation like wise Tilden Mine USA(Colombo, 1986;
Paananen, 1980), where selective flocculation was first introduced at commercial
scale in 1975, Camdage Mines Turkey(D. Çuhadaroğlu; Kafali, et al., 1988), and
Wadi Sawawani Mines Saudi Arabia(Colombo, 1986). In Tilden plant the selective
flocculation has been used as the selective desliming step prior to anionic or cationc
219
silica flotation process(Iwasaki and Iwao, 1981; Paananen, 1980), since selective
flocculation is supposed to be more effective desliming process than hydro cyclone or
thickener.
Therefore an attempt to float the silica was made after desliming the Dilband iron ore
by using corn starch along with SS dispersant. In flotation test the flotigam K2C
collector, the more selective amine collector for silica(S. Montes Sotomayor, et al.,
1998), and MIBC frother were used after conditioning the deslimed slurry at 10.5 pH .
Three foam products and residue were collected from the test. The wt% of products
along with density and XRF analysis is given in Table 5.10.
Table 5.10: Density and XRF analysis of flotation test products. Feed Material Flotation
Feed wt (g) 31.09 Products Wt% Density (g/cc)
% Fe2O3
% SiO2 % P2O5 % CaO
Density (g/cc) 3.67 Foam 1 4.89 3.81 % Fe2O3 59.53 Faom 2 5417 3.60 59.04 25.34 1.08 4.27 % SiO2 20.63 Foam 3 29.53 3.74 64.27 19.46 1.34 6.04 % P2O5 1.30 Residue 11.42 3.37 51.73 11.58 2.15 28.13 % CaO 7.62
The results shown in Table 5.10 indicate that no selective separation of quartz could
be achieved even in the silica flotation test. Floating the silica resulted in the flotation
of hematite also, leaving the apatite rich calcite into the residue. Therefore high
intergrown of silica into hematite can be substantiated from unselective role of
flotigam collector. Further more sufficient high content of P2O5 into foam products
emphasise that fluorapatite is also finely disseminated into the grains of hematite.
Discouraging results of flotation test suggested that selective flocculation followed by
flotation is also ineffective route of upgradtion of Dilband iron ore due to sever
gangue intergrown property.
220
5.9 SELECTIVE FLOCCULATION OF SYNTHETIC HEMATITE-QUARTZ SYSTEM
5.9.1 Rational
Root cause of the poor selective flocculation of Dilband iron ore have been
extensively discussed in the previous sections. It is noted that almost all the operating
variables worked effectively in sense to disperse the overall ore and to flocculate
crudely. Despite having the supporting evidence from the results of test work and
literature it was realized to evaluate the operating parameters of selective flocculation
in the synthetic hematite-quartz system and to understand the behaviour of dispersants
specially in controlling the complex situation resulting due to presence of sufficiently
high amount of Ca+2 (16 ppm) with 3 ppm Fe+3 and 1 ppm Mg+2 cations. And to find
out the ways and means to selectively flocculate hematite with corn and potato starch.
Hetracoagulation, hetraflocculation, over and unselective dispersions are the main
issues of a system containing high content of polyvalent metal ions. Undesirable
metallurgical results of a system containing Ca+2, Mg+2, Fe+3 ions totalling above 100
ppm are anticipated by Green and Colombo(1985)(Weissenborn, 1993) , while Arol
(1984) experienced problems of hetracoagulation and hetraflocculation when the
concentration of calcium ions exceeds more than 10 ppm. Upon realizing the adverse
effects of polyvalent metal ions, selective flocculation tests in a synthetic system of
hematite and quartz containing 16 ppm Ca+2, 3 ppm Fe+3 and 1 ppm Mg+2 were
conducted. Work made in this regard is reported in this section.
5.9.2 Material and Methods
Pure hematite and quartz were received from the Department of Mineral Resources
and Petroleum Engineering, Montan University Leoben Austria. Hematite and quartz
221
were grinded for three hours in the the ceramic ball mill running at 11.3 rpm. The
particle distribution, analyzed on Mastersizer 2000 Ver.5.40, of the grinded hematite
and quartz is given in Table 5.11.
Calcium chloride, magnesium chloride and iron chloride salts were used to prepare
the 1000 ppm solutions of Ca+2, Mg+2, and Fe+3 respectively in distilled water. For pH
modification NaOH and HCl were used. Hydrofluoric acid was used for the
determination of quartz content in the flocculated material.
Corn starch and potato starch were used for selective flocculation tests. The corn
starch was prepared by two methods, one in autoclave as described in section 5.2, and
second by heating up to boiling temperature at normal atmospheric pressure. Corn
Starch cooked in autoclave was completely dissolved into the water, whereas corn
starch cooked at normal pressure was partially dissolved. Potato starch was
completely dissolved by adding 50 ml of 0.1M NaOH per 0.5gram at 85oC. The
potato starch solution left on magnetic stirrer to attain the required temperature within
4 to 6 min and then suddenly cooled in ice water. Thereafter solutions were diluted to
100 ppm concentration.
For conducting the dispersion and flocculation tests hematite and quartz of equal
weight (i.e. 50% by 50% ) were taken into beaker of 100 ml and the required
concentration of cations added. The suspension left on magnetic stirrer for 5 min
conditioning time followed by conditioning of dispersants and starch. The pH of
slurry was maintained at 10.5 pH value. Thereafter slurry transferred to the 100 ml
cylinder, shacked by inverting ten times, and finally left for 2.5 min interval. The
supernatant of about 80% of whole suspension siphoned. The sediment or flocculated
222
material and supernatant dried and weighed. The selectivity analysis was made by
analysis of quartz in sediment using weight loss method before and after addition of
hydrofluoric acid. The hetracoagulation/ hetraflocculation effects caused by addition
of polyvalent metal ions and the counter action by dispersants were accessed by line
of selectivity (i.e.% grade of the sediment in a system containing no cations and no
dispersants).
Table 5.11: Particle Size Distribution of Hematite and Quartz
Material Size Distribution
Size ( µm)
% Retained
Hematite
3 11 15 50 32 80 71 99,37
Quartz
3 15 10 52 25 83 315 99.9
5.9.3 Results and Discussion
Since the basic theme of studying the selective flocculation of synthetic system was
just to understand that how the things are behaving specially in high concentration of
polyvalent metal ions likely to Dilband iron ore. Therefore initially dispersion and
flocculation of hematite, quartz, and hematite-quartz in a system containing only Ca+2
cations was studied. Thereafter, work extended to a hematite quartz system containing
16 ppm Ca+2, 3 ppm Fe+3, and 1 ppm Mg+2. Therefore results pertaining to synthetic
system are divided into two parts. The brief of dispersion-flocculation tests conducted
in sysnthetic system is given in Table 5.12.
223
Table 5.12: Brief list of the dispersion-selective flocculation tests on synthetic system of hematite and quartz.
S. No
Minerals Cations ( ppm) Dispersants (wt% w.r.t. Ca+2)
Flocculant ( ppm)
H (wt%
)
Q (wt%
) Ca+2 Mg+2 Fe+3 SS EDTA STPP Potato
Starch Corn
Starch
1 100 0 0 to 16 0 0 0 0 0 0 0 2 100 0 0 to 16 0 0 0 0 0 40 0 3 100 0 0 to 16 0 0 0 0 0 0 40 4 0 100 0 to 16 0 0 0 0 0 0 0 5 0 100 0 to 16 0 0 0 0 0 40 0 6 0 100 0 to 16 0 0 0 0 0 0 40 7 50 50 0 to 16 0 0 0 0 0 0 0 8 50 50 0 to 16 0 0 0 0 0 40 0 9 50 50 0 to 16 0 0 0 0 0 0 40 10 50 50 16 0 0 0 -1500 0 0 0 0 11 50 50 16 0 0 0 0-200 0 0 0 12 50 50 16 0 0 0 0 0-300 0 0 13 50 50 16 1 3 0-1500 0 0 0 0 14 50 50 16 1 3 0 0-400 0 0 0 15 50 50 16 1 3 0 0 0-450 0 0 16 50 50 0 0 0 0 0 0 10-100 0 17 50 50 16 1 3 0 0 0 10-100 0 18 50 50 16 1 3 1000 0 0 10-100 0 19 50 50 16 1 3 0 400 0 10-100 0 20 50 50 16 1 3 0 450 0 10-100 0 21 50 50 0 0 0 0 0 0 0 10-100 22 50 50 16 1 3 0 0 0 0 10-100 23 50 50 16 1 3 1000 0 0 50 10-100 24 50 50 16 1 3 0 400 0 50 10-100
37. First Part
Part one includes the results of effect of corn starch, potato starch, and dispersants in
16 ppm Ca+2 cations.
a) Dispersion and Flocculation of Hematite
224
The dispersion and flocculation of hematite at 10.5 pH and varying content of Ca+2
cations in absence of dispersants with adding starches are studied. Results are shown
in figure Figure 5.22. Figure 5.22 indicate that marginal coagulation of hematite takes
place with addition of 16 ppm Ca+2 cations. The addition of 50 ppm potato starch
induced significant stabilization into the system, whereas 50 ppm corn starch
completely dissolved flocculated the slurry. On the other hand corn starch partially
dissolved could not flocculated the slurry rather seems to behave like potato starch.
With increased concentration of the Ca+2 cations the flocculating efficiency of the
starches increased.
0
20
40
60
80
100
120
0 5 10 15 20
Ca (ppm)
Sedi
men
t wt%
No Starch
50ppm Potato Starch
50ppm Partially DissolvedCorn Starch
50ppm Fully Dissolved CornStarch
Figure 5.22: Dispersion and flocculation of hematite 10.5 pH , 2.5 min settling
time
From the above set of flocculation tests the contrasting behaviour of the potato starch
comparatively to corn starch is noticed. The results indicate that potato starch did not
worked like a flocculent but rather dispersant. Similarly partially dissolved corn starch
behaved to some extent like potato starch. Literature pertaining to starches indicate
that starches are normally composed of amylose and amylopectin with varying
proportion(Khalil and Aly, 2002; Pavlovic and Brandao, 2003; Peres and Correa,
225
1996; Ravishankar, et al., 1995; Th. Aberle, 1994; Weissenborn, 1996; Yong, 1985).
Flocculating efficiency of amylose is less comparatively than amylopectin, therefore
flocculating efficiency of starches vary according to the proportion of these
ingredients. According to findings of Weissenborn (1996) amylose did not behaved
like amylopectin but rather remained silent in flocculating the hematite. Work of
Pavlovic and Brandao(2003) indicate that amylose are less efficient than amylopectin
in depressing the hematite in flotation process. Based on these literature findings the
contrasting behaviour of potato starch can be attributed to the ratio of amylose to
amylopectin. Therefore it could be possible that potato starch used contains only
amylose or higher content of amylose than amylopectin. Behaviour of partially
dissolved corn starch support this assumption, since amylopectin contained by
starches at normal pressure do not dissolves(Khalil and Aly, 2002). Therefore poor
flocculating efficiency of partially dissolved corn starch could be due to absence of
amylopectins. The dispersing behaviour of the potato starch could not be understood.
The effect of higher content of Ca+2 cations in flocculating the hematite is very clear
and can be correlated with the decrease in zeta potential of hematite. The findings of
the Arol (1984) indicate that with addition of Ca+2 cations the decrease in the zeta
potential of hematite takes place, therefore starch can effectively adsorbed on
hematite.
b) Dispersion and Flocculation of Quartz
Similar to hematite the flocculation of quartz with potato starch, partially and
completely dissolved corn starch at varying concentration of Ca+2 was studied. The
results shown in Figure 5.23 indicate that coagulation of quartz increases with
increasing the content of Ca+2 cations and becomes more significant at 16 ppm
226
concentration. Addition of potato starch decreased the coagulation and dispersed the
quartz. Significant dispersion of quartz with addition of potato starch noticed at 16
ppm Ca+2 Cations. Addition of corn starch, both partially and completely dissolved, in
absence and presence of Ca+2 indicate that both starches flocculated the quartz in
presence of 16 ppm Ca+2 cations, otherwise not. However the wt% of flocculated
quartz remained significantly low as compared to coagulated at 16 ppm Ca+2. This
shows that partially and completely dissolved corn starches also dispersed the quartz
and remained second and third in dispersing the quartz at 16 ppm Ca+2 respectively.
0
1020
30
40
5060
70
80
0 5 10 15 20
Ca (ppm)
Sedi
men
t wt%
No Starch
50ppm Potato Starch
50ppm Partially DissolvedCorn Starch
50ppm Fully Dissolved CornStarch
Figure 5.23: Dispersion and flocculation of quartz at 10.5 pH , and 4 min settling time.
Dispersing behaviour of starches at 16 ppm Ca+2 concentrations is interesting. Work
of Drzymala and Fuerstenau (1981) indicate that flocculent on quartz can only be
adsorbed at alkaline condition if the slurry contains the polyvalent metal ions. The
polyvalent metal ions work as activator for quartz specially in alkaline conditions.
Therefore stabilization of quartz with addition of starches at 10.5 pH in the present
work can be attributed to the adsorption or deadsorption effects in presence and
absence of Ca+2 cations respectively. In the absence of Ca+2 cations insignificant
stabilization/destablization effect of starches indicate that starches could not adsorbed
on quartz. Whereas significant effect of stabilization at 16 ppm Ca+2 cations indicate
227
that significant amount of starches would had been adsorbed on quartz. As for as
destabilization effect of starches is concerned, one has to think about the most
pertinent action played by the ingredients of the starch. Findings of Pavlovic and
Brandao (2003) indicate that amylose adsorbs on quartz while amylopectin do not,
secondly amylose induce the dispersion into the quartz. Due to this reason corn starch
is widely acknowledged as depressant for hematite in flotation of quartz with amine
collector. In flotation of quartz amylose part of the starch induce the floatability into
quartz while amylopectin depress the hematite. Thus dispersing action of potato starch
and corn starch on quartz can be regarded with the content of amylose present into the
starches. Higher dispersion effect of potato starch indicates the higher content of
amylose comparatively to corn starch. Due to these reasons in presence of Ca+2
cations more effectively amylose adsorbed onto the quartz and caused dispersion.
c) Dispersion and Flocculation of Hematite-quartz System
Dispersion and flocculation of a system containing equal amounts of hematite and
quartz in presence of 16 ppm Ca+2 cations without adding dispersants at 10.5 pH
studied. The wt% of material sedimented (coagulated/flocculated) at different
concentration of Ca+2 cations with or without addition of starch is shown in Figure
5.24, whereas the amount of quartz flocculated is shown in Figure 5.25. Figure 5.24
and Figure 5.25 clearly demonstrates the hetracogulation of hematite and quartz with
increasing amount of Ca+2 cations. With addition of corn starch the hetraflocculation
effect increased whereas potato starch reduced the hetraflocculation.
Hetracoagulation and hetraflocculation of hematite-quartz system in presence of Ca+2
cations is extensively reported in the literature. It is generally believed that addition of
228
polyvalent metal ions like Ca+2 reduced the zeta potential of the system therefore
quartz either coagulates with hematite or flocculates with starch. This
hetracoagulation or hetraflocculation effect of C+2 cations with addition of corn starch
is clearly shown with increasing trend of quartz in the sedimented or flocculated
material in Figure 5.24. Figure 5.24 further shows that addition of potato starch
mitigated the hetracoagulation and hetraflocculation effect induced by Ca+2 cations.
Although the alleviating effect of hetracoagulation and hetraflocculation by means of
addition of dispersants is widely studied, but literature pertaining to mitigating effect
of potato starch is not suffice. Present study reveals that with increasing the Ca+2
concentrations the stabilization of quartz is increased. This increasing trend of quartz
stabilization with increasing concentration of Ca+2 cations can be attributed with
increasing adsorption of potato starch on quartz. Since potato starch contains higher
content of amylose, whereas amylose induces the dispersion in the quartz as have
been seen in previous section. Therefore at higher content of Ca+2 cations higher
adsorption of amylose deactivated either hetraflocculated or hetracoagulated quartz.
The deactivation of quartz with addition of potato starch is quite in agreement with
the quartz floatability findings of Pavlovic and Brandao (2003) with amylose.
Furthermore amylopectin adsorbs more efficiently on hematite rather than quartz
(Pavlovic and Brandao, 2003; Weissenborn, 1996) therefore selective flocculation of
hematite with addition of potato starch would have been possible.
d) Effect of Dispersants
The effect of EDTA, SS, and STPP on alleviating the hetracoagulation of hematite-
quartz in 16 ppm Ca+2 cations at 10.5 pH were studied. The effectiveness of each
dispersant in mitigating the hetracoagulation effect is determined by percent recovery
229
of quartz in sediment. The results shown in Figure 5.26 indicate that almost all the
dispersants behaved quite equally. Effective role of EDTA, STPP, and SS in
controlling the adverse effect of Ca+2 found at 175% , 250% , and 1250% doses
respectively. Since the mechanism of dispersion induced by dispersants is extensively
discussed in section 4.8.3 therefore it is not repeated.
0
10
20
30
40
50
60
70
80
0 5 10 15 20
Ca (ppm)
Sedi
men
t wt%
No Starch
50ppm Potato Starch
50ppm Fully DissolvedCorn Starch
Figure 5.24: Dispersion and flocculation of hematite-quartz system at 10.5 pH , and 2.5 min settling time.
Figure 5.30: Wt% of Flocculated Quartz in Hematite-Quartz System at 10.5pH and 2.5min Settling Time.
0
5
10
15
20
25
30
0 5 10 15 20
Ca (ppm)
% Q
uart
z No StarchPotato StarchCorn Starch
Figure 5.25: Wt% of flocculated quartz in hematite-quartz system at 10.5 pH and 2.5 min settling time.
230
0
5
10
15
20
25
30
35
0 100 200 300 400Dispersants (wt% w.r.t. Ca+2)
% R
ecov
ery
of Q
uart
z in
Sed
EDTA (%) STPP (%)SS (ppm)
Figure 5.26: Effect of dispersants on % recovery of quartz in hematite-quartz system at 16 ppm Ca+2, 10.5 pH , and 2.5 min settling time.
38. Second Part
a) Effect of Ethylenediaminetetraacetateacid (EDTA)
The results of different doses of EDTA on stabilization of quartz and mitigating the
hetracoagulation effect at 16 ppm Ca+2, 3 ppm Fe+3, and 1 ppm Mg+2 in hematite-
quartz system at 10.5 pH are shown in Figure 5.26 and Figure 5.27. The effectiveness
of the dispersant is assessed on the basis of% grade and % recovery of hematite.
Figure 5.27 indicate that EDTA effectively dispersed the quartz via complexing with
cations when its dose is equivalent to 400% of the Ca+2 cations. Marginal difference
in % grade in a system containing only 16 ppm Ca+2 cations, and 16 ppm Ca+2, 3
ppm Fe+3 and 1 ppm Mg+2 suggest that Fe+3, and Mg+2 cations are not too detrimental
as Ca+2 cations. Whereas significant difference in % recovery dose not attest this
hypothesis. Significant difference in % grade of system containing and not containing
cations suggest that although EDTA had alleviated the hetracoagulation effect caused
by cations but could not removed completely.
231
b) Effect of Sodium Tripolyphosphate (STPP)
The results of different doses of STPP are shown in Figure 5.26 and Figure 5.28.
Figure 5.26 and Figure 5.28 indicate that STPP could not work effectively to restore
the dispersion of quartz and to minimize the hetracoagulation effect.
c) Effect of Sodium Silicate (SS)
The results of different doses of SS to counteract the hetracoagulation effect caused
by addition of polyvalent metal ions 16 ppm Ca+2, 3 ppm Fe+3, and 1 ppm Mg+2 in
hematite-quartz system at 10.5 pH are shown in Figure 5.26 and Figure 5.29. Figure
5.26 and Figure 5.29 indicate that SS had also effectively counteracted the adverse
effect of 16 ppm Ca+2, 3 ppm Fe+3, and 1 ppm Mg+2 cations at the cost of 1000%
dose (w.r.t. Ca+2). With increasing the SS dose in a system containing 16 ppm Ca+2,
3 ppm Fe+3, and 1 ppm Mg+2 efficiency of the dispersant decreased. This could not
be properly understood, since literature pertaining to such complex system is sufficed.
232
50
55
60
65
70
75
80
85
90
95
100
0 20 40 60 80
EDTA % Dose (w .r.t. Ca+2 Cations)
Wt %
% Grade at 16ppCa
% Grade at 16ppca, 3ppFe,1pp Mg
% Recovery at 16pp Ca
% Recovery at 16ppm Ca,3ppm Fe, 1ppm Mg
%Grade at No catios and NoDisp
Figure 5.27: Effect of EDTA on % grade and % recovery of hematite in hematite-quartz synthetic system at 10.5 pH .
50
60
70
80
90
100
110
0 20 40 60 80
STPP % Dose (w.r.t. Ca+2)
Wt %
% Grade at 16ppCa
% Grade at 16ppca, 3ppFe,1pp Mg
% Recovery at 16pp Ca
% Recovery at 16ppm Ca,3ppm Fe, 1ppm Mg
% Grade at NO Cation and NoDisp
Figure 5.28: Effect of STPP on % grade and % recovery of hematite in hematite-quartz synthetic system at 10.5 pH.
50
55
60
65
70
75
80
85
90
95
100
0 50 100 150 200 250 300
NaSiO3 % Doses (w .r.t. Ca+2)
Wt%
% Grade at 16ppCa
% Grade at 16ppca, 3ppFe,1pp Mg
% Recovery at 16pp Ca
% Recovery at 16ppm Ca,3ppm Fe, 1ppm Mg
% Grade at No Cations andDisp
Figure 5.29: Effect of SS on % grade and % recovery of hematite in hematite-quartz synthetic system at 10.5 pH.
233
d) Effect of Potato Starch
After optimizing the dispersant doses in a synthetic system of hematite-quartz
containing 16 ppm Ca+2, 3 ppm Fe+3, and 1 ppm Mg+2 cations at 10.5 pH , the effect
of different doses of potato starch were conducted. The effect of potato starch on %
grade and % recovery is shown in Figure 5.30 and Figure 5.31 respectively.
Figure 5.30 and Figure 5.31 indicate that in a system containing no cations and no
dispersant the addition of potato starch effectively dispersed the quartz and minimizes
the hetracoagulation/ hetraflocculation effect. The maximum% grade (89.5%
Hematite) with 77% recovery is achieved at 50 ppm potato starch. Whereas in a
system containing polyvalent metal ions the efficiency of potato starch in
counteracting the hetracoagulation effect is marginally reduced. Comparing the
effectiveness of potato starch with dispersant in a system containing polyvalent metal
ions it is noted that potato starch behaved quite effectively in dispersing the quartz.
Effect of EDTA, STPP, and SS in similar conditions shown in Figure 5.27, Figure
5.28, and Figure 5.29 respectively indicate that none of the dispersant crossed the line
of selectivity, whereas potato starch at 50 ppm concentration showed quite better
improvements in the % grade. This shows that potato starch is more effective than the
dispersants in a complex system containing quite high amount of polyvalent metal
ions. The addition of either optimized dose of SS or EDTA along with potato starch
further improved the results in terms of% grade. Quite significant improvement in %
recovery without loss in % grade achieved with 1000% SS and 50% potato starch.
Whereas EDTA did improved the % grade than SS but at the cost of% recovery.
STPP did not show any significant improvement in % grade but rather decreased the
effectiveness of potato starch.
234
76
78
80
82
84
86
88
90
0 20 40 60 80 100
Starch (ppm)
% G
rade
No Cation, No Dispersant
16ppm Ca, 3ppm Fe, 1ppmMg, and NoDIspersant
16ppm Ca, 3ppm Fe, 1ppmMg, and400ppmEDTA
16ppm Ca, 3ppm Fe, 1ppmMg, and56ppmSTPP
16ppm Ca, 3ppm Fe, 1ppmMg, and1500ppm SS
Selectivity Line
Figure 5.30: Effect of potato starch on % grade of hematite in hematite-quartz synthetic system at 10.5 pH.
60
65
70
75
80
85
90
95
100
0 20 40 60 80 100 120
Starch (ppm)
% R
ecov
ery
No Cation, No Dispersant
16ppm Ca, 3ppm Fe, 1ppmMg, andNo DIspersant
16ppm Ca, 3ppm Fe, 1ppmMg, and400ppmEDTA
16ppm Ca, 3ppm Fe, 1ppmMg, and56ppmSTPP
16ppm Ca, 3ppm Fe, 1ppmMg, and1500ppm SS
Figure 5.31: Effect of potato starch on % recovery of hematite in hematite-quartz synthetic system at 10.5 pH.
235
5.9.4 Conclusion
Evaluating the effect of polyvalent metal ions on dispersion and flocculation of
synthetic system and the role played by the chemical reagents like dispersants and
starches the possible conclusion are:
Ca+2 cations are too detrimental than the Mg+2 and Fe+3 cations.
Potato starch effectively dispersed the quartz and deactivate than any
dispersant in a system containing sufficiently high content of polyvalent metal
ions.
EDTA remained second in counteracting the hetrocoagulation effects caused
by presence of polyvalent metal ions. The effective dose of EDTA found to be
400% of the Ca+2 Cations present into the slurry.
SS remained third in dispersing the quartz selectively at the cost of 1000% of
the Ca+2 cations.
STPP could not work effectively.
Combined use of potato starch and dispersants selectively dispersed the
quartz.
Corn starch flocculates the bulk material in the absence of dispersants and
presence of cations.
Higher content of Ca+2 cations can be utilized in dispersing the quartz
effectively and selectively by addition of potato starch or the starch containing
sufficiently high content of amylose.
