FIELD OF THE INVENTION
The present invention relates to an integrated process for iron ore slime leaching.
BACKGROUND OF INVENTION
Indian hematite ores are typically rich in iron but contain unusually high alumina (as
high as 7%). Iron ore slimes which have high alumina content and particle size of below
150μm are normally discarded as waste during the mining and processing stages of iron
ore. These wastes are generally stored at the tailing dams. It is estimated that nearly
18% - 25% of tailing are generated during processing of the iron ore. Although the major
compositions of iron ore slime are hematite, quartz, alumina, mica and kaolin, iron ore
slime is still discarded primarily due to its particle size and chemical composition which
are not suitable as feed for the blast furnaces. High alumina containing slime produces
slag with high alumina content, which is highly viscous and requires substantial
quantity of flux. It generates relatively larger slag volume which results in an increase
in coke consumption and a decrease in blast furnace productivity. Several
beneficiation methods such as gravity separation, flotation, magnetic separation, and
flocculation, are known in the art for processing alumina rich iron ore fines and slimes.
But due to the poor liberation characteristics, the recovery through these known
processes is very less for example 50%, when compared to that obtained through
chemical beneficiation techniques. But the yield is limited to 50% irrespective of the
method. This is due to the poor liberation behavior of the ore.

Chemical leaching involves mixing of contaminated soil with a chemical solution to
transfer metals from a solid matrix into a leaching solution. The cleaned soil and the
leaching solution are first separated and then different solution processing methods are
used to regenerate the leachant and recover a useful metal or salt. In
the hydrometallurgical industry, leaching has a variety of commercial applications
including chromium, nickel, copper, zinc, lead, cadmium, tin, cobalt, vanadium, titanium,
molybdenum, gold, silver, palladium, and platinum beneficiation. Chemical leaching
technology can be adopted to iron ore slimes to generate iron rich and less alumina
(<2%) containing product.
Although the fines can be sintered to larger particle, the alumina to silica ratio which is
normally more than one, pose a serious problem during sintering process and
subsequent smelting in blast furnace. The alumina content in the slime needs to be
reduced in order for it to be used as the feed for blast furnace. One of the most
immediate technological challenges that the industry is facing is to deal with the
problem of processing alumina rich iron ore fines and slimes. High alumina slag
which is highly viscous requires larger quantity of flux and relatively larger slag
volumes resulting in an increase in coke consumption and a decrease in blast
furnace productivity. According to one estimate, a decrease in alumina content in the
sinter from 3.1 to 2.5% will improve the RDI by at least six points, lower blast furnace
coke rate by 14 kg per tonne of hot metal and increase its productivity by about 30%
under.

Removal of materials by dissolving them away from solids is called leaching. The theory
and practice of leaching are well-developed because for many years leaching has been
used to separate metals from their ores. The combination of chemical leaching and
leachant regeneration is known as hydrometallurgical processing, and typically includes
one or more of the following four steps: Dissolution of the desired metal, purification
and/or concentration of the metal, recovery of the metal or a metal salt, and regeneration
and reuse or treatment and disposal of the leaching solution.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an integrated process for iron ore
slime leaching, which utilizes a chemical leaching method.
Another object of the invention is to propose an integrated process for iron ore slime
leaching, which uses concentrated hydrochloric acid.
A further objection of the invention is to propose an integrated process for iron ore slime
leaching, in which the iron ore slime is chemically leached with concentrated
hydrochloric acid.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process to recover Fe values with low alumina and silica
content from high alumina iron ore slimes using chemical leaching method. According to
the invention, the slime sample is leached with concentrated Hydrochloric acid (35.5%
w/w). The un-dissolved solid matter separated contains high alumina and silica fractions.
The iron rich solids are precipitated by addition of calcium oxide (CaO) at a pH value of
4-4.5. At pH 4-4.5, iron rich material are precipitated and at pH greater than 4.5, alumina

starts precipitating. Regeneration of hydrochloric acid is carried out using sulphuric acid
(H2SO4) and it produces calcium sulphate (CaSO4). The acidification is carried out till pH
1 to recover all chlorides, the precipitate is separated and the acid is re-used for the
leaching process. 95.4% of iron values are recovered using this process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Flow sheet for the process of leaching of iron ore slime followed by
regeneration of spent acid
Figure 2: Material balance for slime leaching process
DETAIL DESCRIPTION OF THE INVENTION
Iron ore slime samples collected from washeries and dried. The samples were analyzed
for their composition. Iron is a basic inorganic component and can be dissolved in acids
and hence, hydrochloric acid was used for the leaching process. 80 grams of slime
sample is mixed with concentrated hydrochloric acid (35.5% w/w) in stoichiometric
proportions. The un-dissolved solid matter was separated using filtration technique and
analyzed for the chemical constituents present inside. The iron rich solids were
precipitated by addition of calcium oxide (CaO) at a pH value of 4-4.5. The reactions
during leaching and precipitation stages are mentioned below. The major portion of
alumina is left in the leaching solid residue and the alumina in the leachant will be in the
liquid phase at the prevailing pH condition.

Acid Leaching:
Fe2O3 + HCI → FeCI3 +3 H2O
Al2O3 + 6HCI → 2AICI3 + 3 H2O
Precipitation at pH= 4.3:
2FeCI3 + 3CaO → Fe2O3 + 3CaCI2
The precipitated solids were separated using gravity separation technique and washed
with water to remove chlorides. At pH 4-4.5, iron rich material gets precipitate and at a
pH of greater than 4.5, alumina start precipitating. Hence, the precipitation is limited to
pH 4.5. The next stage is to recover the hydrochloric acid from the calcium chloride
solution. Calcium chloride readily reacts with sulphuric acid (H2SO4) and forms calcium
sulphate (CaSO4). The acidification is carried out till pH of 1 to recover all the chlorides
based on the following reaction. The calcium sulphate is separated and the acid is re-
used during the leaching process. The compositions of the chemical constituents in
various streams is mentioned below in Table-1.
Acid Recycle (Acidification):
CaCI2 + H2SO4 → CaSO4 + 2HCI

The precipitation at different pH conditions is mentioned in Table-2. From Table-2, it is
very clearly observed that, alumina precipitation is more at pH greater than 4.5 and is
more than 2%, which is not acceptable as blast furnace feed material.
The precipitation of calcium sulphate can be observed from the chemical constituents
chart shown in Table-3. It is clear that, 66.7% of the calcium containing product is
precipitated. The overall flow sheet of the process is shown in Fig. 1. The overall
material balance sheet is shown in Fig. 2 and it has been calculated a recovery of 95.4%
of iron values has been achieved.

Methodology followed for slime leaching process
80 grams of slime sample is mixed with concentrated hydrochloric acid (35.5% w/w) in
stoichiometric proportions. The un-dissolved solid matter is separated using filtration
technique and was analyzed for it's chemical constituents. The iron rich solids are
precipitated by addition of calcium oxide (CaO) at a pH value of 4-4.5. The major portion
of alumina is left in the leaching residue and the leached alumina in liquid phase at
particular pH condition.

The precipitated solids are separated using gravity separation technique and washed
with water to remove chlorides. At pH 4-4.5, iron rich material gets precipitated and at a
pH of greater than 4.5, alumina start precipitating. Hence the precipitation is limited to
pH of 4.5. The next stage is to recover the hydrochloric acid from calcium chloride
solution. Calcium chloride readily reacts with sulphuric acid (H2SO4) and forms calcium
sulphate (CaSO4). The acidification carried out till pH 1 to recover all chlorides based on
the following reaction. The calcium sulphate is separated and the acid is re used for
leaching process. The overall material flow diagram was shown in Fig. 1.

We Claim:
1. An integrated process to treat iron ore slimes using chemical leaching method,
the process comprising the steps of:
leaching of high alumina iron ore slime to recover iron values using
hydrochloric acid leaving alumina and silica rich material in the solid;
- precipitation of the recovered iron rich solid at a pH of 4-4.5 using
quick lime (CaO); and
regeneration of hydrochloric acid by addition of sulphuric acid to the
spent solution.
2. A process as claimed in claim 1, wherein leaching of the slime is carried-out
using hydrochloric acid at 50°C temperature which separates 99.4% Fe (T) from
the slime.
3. A process as claimed in claim 1, wherein said iron rich solid precipitates at a pH
of 4-4.5, the solid containing 67% Fe (Total) and less than 2% alumina.
4. A process as claimed in claim 1, wherein the spent hydrochloric acid is
regenerated back by precipitating 66.7% calcium based compound in sulphuric
acid.

5. A process as claimed in claim 4, wherein the calcium based compound is
calcium sulphate.

ABSTRACT

The invention relates to an integrated process to treat iron ore slimes using chemical
leaching method, the process comprising the steps of leaching of high alumina iron ore
slime to recover iron values using hydrochloric acid leaving alumina and silica rich
material in the solid; precipitation of the recovered iron rich solid at a pH of 4-4.5 using
quick lime (CaO); and regeneration of hydrochloric acid by addition of sulphuric acid to
the spent solution.