Abstract:
Dilband iron ore deposits, discovered in 1997 by Geological Survey of Pakistan
(GSP) in Kalat Division Balochistan, Pakistan, is of significant importance from
socio-economical point of view among the rest indigenous iron ore deposits
discovered so far in Pakistan. Because of its relatively low iron content, high gangue
minerals specially quartz and more importantly high phosphorous ( i.e. steel polutant)
content,
it requires an adequate concentration method, in order to meet the
requirements of Pakistan SteelMills ore specification (i.e. 57-60% Fe (min.), 8.5%
SiO 2 (max.), 0.5% Al 2 O 3 (max.), 0.1% P (max.), and 0.05% S. This work, therefore,
is aimed to up-grade Dilband iron ore through an adequate physical concentration
methods. This calls for detailed mineralogical, petrological, elemental, and intergrown
investigations as these studies are widely recognized to be the mandatory steps in the
selection of an appropriate concentration method and play significant role in
developing the cost effective process flow sheets.
For mineralogical, petrographic, and elemental analysis XRD, thin section and SEM
attached with EDS, and Atomic Absorption Spectrometer and XRF techniques were
used. Mineralogical study revealed that Dilband iron ore is mainly composed of
46.27% hematite, 17.41% quartz 14.47% calcite, 9.24% chlinochlore, 10.5%
kaolinite, and 1.75%
fluorapatite minerals. Three types of iron stones namely
hematite-ooides, hematite-peloids, and hematite biosparite were identified from
petrographic study. Elemental analysis of different size fractions ranging from 600
xivμm down to 38 μm indicated that Dilband iron ore contains average of 40.18% Fe,
18.34% SiO 2 , 5.32% Ca, and 2.262% Al. Whereas, average analysis of different size
fractions on XRF indicated 44.3% Fe, 20.4% SiO 2 , 8.8% CaO, 6.35% Al 2 O 3 , 1.3%
P 2 O 5 , and 0.065% SO 2 . From the mineralogical, X-ray mapping with EDS, and
elemental analysis data finely dissemination of impurities specially quartz, and
fluorapatite in hematite phase was conceived, suggesting that Dilband iron ore is not
amenable to upgrade with conventional physical techniques.
For assessing the mesh of liberation the physico-chemical attributes of different size
fractions along with the examination of coarser to ultra fine particles under reflected
microscope, polarized
microscope, stereomicroscope and scanning electron
microscope attached with EDS at different accelerating voltages and magnifications
was conducted. The results of density, magnetic susceptibility, and elemental analysis
revealed that mesh of liberation of Dilband iron ore exists below 15 μm particle size.
The image analysis of particles and x-ray mapping results confirmed that gangue
minerals are so finely disseminated that complete liberation of hematite phase is
seldom to achieve even below 10 μm. Particularly quartz (SiO 2 ) phase is so finely
disseminated within the matrix of hematite that even in the particles of 2 to 5 μm the
100% hematite phase was not observed. Interlocking of quartz and calcite within the
80% hematite enriched particles was observed in the most of the particles finer than
15 μm. Acid treatment tests of the ore using hydrofluoric acid and hydrochloric acid
further confirmed that exact mesh of liberation exist below 2μm.
Based on these studies selective flocculation process was envisaged to be the adequate
process for beneficiation of Dilband iron ore. For this, determination of energy
required for comminuting to probable mesh of liberation, zetapotential measurement,
xvcontent of polyvalent metal ions, slurry stablization and finally the selective
flocculation was performed. Besides this ore enrichment by means of density and
magnetic separation prior to subsequent selective flocculation tests were also
attempted.
Work index of two size classes of Dilband iron ore was calculated from grindability
tests. Based on grindability test results the work index value calculated for 3800μm
80% passing was 11.85 kwh/t and that for 5200μm 80% passing was 9.3 kwh/ton.
Ball mill grinding test indicated that dry grinding in open circuit is not efficient and
consumes energy of 88.48kwh/t of ore for grinding 1000/40μm to 80% <40μm size.
In dispersion tests effect of particle size, solid concentration, pH, dispersants and their
doses, stirring speed, and sonication, has been extensively studied. The point of zero
charge (PZC) of Dilband iron ore system was determined by using the Zetaphormeter
III (CAD E400), and found at 4.25 in acid range. The dispersion results confirmed the
significant role of particle size in the slurry stabilization and the optimal conditions
for <38 μm Dilband iron ore slurry were found at 10% solid concentration, 10.5 pH ,
2000 rpm stirring speed and 5min stirring time. The optimization of dispersant and its
dose found quite difficult due to marginal change in sediment wt% , however on the
basis of elemental analysis and sediment wt% 6.4k g/ton (i.e. 400% of stacheometric
amount of Ca +2 cation present in Dilband iron ore) of EDTA was recommended.
Selective flocculation tests of Dilband iron ore slurry using corn starch, potato starch
and polyacrylamide (PAA) flocculants were conducted. The selective flocculation
results carried out on Dilbnad iron ore suggest that either the selective flocculation
process is not the adequate beneficiating technique to upgrade the ore upto the
xvirequirements of the Pakistan SteelMills or it achieves nearly half of the beneficiation
results expected. Applying flotation to selectively flocculated ore do not upgrade it
further due to high intergrowth status of impurities.
Pre enrichment attempts were also made to check magnetic susceptibility attribute. It
was found to give some better results in separating less intergrwon from highly
intergrwon particles of -500 and +315μm size fraction. Results indicated that 60%
removal of P 2 O 5 and 30% of SiO 2 is possible with density followed by magnetic
separation. Substential decrease in silica and phosphorous content in less intergronwn
part suggest that a process flow sheet based on magnetic susceptibility attribute would
be a suitable route to some exent for Dilband iron ore.