FIELD OF INVENTION:
This invention relates to a process for removing phosphorus from low
grade iron ore.
The present invention is related generally to leaching of phosphorus from
low grade/reject iron ore and more precisely to novel process of leaching
phosphorus from iron bearing minerals by caustic solution with
regeneration of chemicals using atmospheric gas. The process has three
stages i.e. extraction, filtration cum washing and regeneration of caustic
solution and the final left over is used as value added product or
otherwise further processing
BACKGROUND OF THE INVENTION:
Phosphate, which is one of the essential constituent of iron bearing
materials and it, is deleterious in the manufacture of iron and steel. The
invention is related to removal of phosphorus from iron bearing materials
like ore/concentration/reject/slime. Phosphorus is of the main harmful
constituent to ferrous metallurgy and it adversely affects the quality of
iron and steel products. The removal of phosphorus from iron bearing
materials involves smelting process, physical separation and chemical
leaching. Chemical leaching is relatively simple process as it can directly
treat the sinter fines without strict requirements for the particles size.
Problems with the Prior Art
1. The present patent is specific to high temperature roasting with
possibility of substantial of loss iron content.

2. Phosphorus leaching by various mineral acids is high cost
oriented.
3. Both of the methodology like alkali roasting and acid leaching is
silent about the regeneration of chemical used therein.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a process for removing
phosphorus from low grade iron ore;
Another object of this invention is to propose a process for regeneration
of chemicals;
Still another object of this invention is to propose a process for
phosphorus leaching which is cost effective;
Further, object of this invention is to propose a process for removal of
phosphorus, which is very simple.
SUMMARY OF THE INVENTION:
According to this invention there is provided a process for removing
phosphorus from low grade iron ore comprising:
extracting phosphorus from the iron ore by the addition of sodium
hydroxide at 80 to 95°C;
subjecting the soluble phosphorus salt to the step of washing and
followed by Alteration;
regenerating sodium hydroxide by reacting the sodium phosphorus salt
with a salt at a temperature range of 80 to 90°C for 60 to 90 minutes.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure la & lb is the block diagram illustrating the flow chart of the
extraction with regeneration step of the present invention;
Figure 2 is the leaching kinetics of phosphorus at different temperature;
DETAILED DESCRIPTION OF THE INVENTION:
Controlling factors
a. Surface area
Surface are also depends upon the quality of mixing that place
inside the reaction vessel. The process generally comprises sizing
of ore, below 25-micron size ore. The surface are area increases,
agitator is used which creates a more vigorous mixing with slurry.
b. Slurry ratio & Temperature
As described in the experiments and shown in the figure below
This relates to tap density when a fixed quantity of phosphorus
powder is trapped in a closed measuring cylinder till the volume of
the powder remains constant and does not decrease with further
tapings.
c. Regeneration
Regeneration of the solution is the conversion of sodium salt to
sodium hydroxide by the use of calcium hydroxide
Soluble sodium salt + Ca (OH)2 CaCO3 + 2NaOH

The generated sodium hydroxide is used for the digestion of iron ore.
Calcium hydroxide can be either purchased from market or the calcium
carbonate can be heated at around 850°C for converting it to calcium
oxide which when comes in contract with water become as calcium
hydroxide. This depends on the market value of each product and costs
involved for either processing or purchasing. All the studies carried out
for regeneration have yielded around 85% conversion to sodium
hydroxide
The generation was carried out in different temperature from 30°C to
95°C and it was found that around 85°C to 90°C, taking 45 minutes to
complete the reaction. Calcium salt produced in this process has purity
of around 97-98% and can be sold in the market.
Following the out comes of experiments;
1. Phosphorus can be selectively removed from iron ore by leaching
with sodium hydroxide. A properly leached ore contains
phosphorus at a level of 0.02%. The iron loss from the ore can be
limited to less than 0.2%.
2. The leached ore has to be washed in a counter current loop
operation in order to reduce the alkalinity of residue
The results show that phosphorus present in apatite, goethite,
limonite and kaolinite can removed by alkali leaching, but those
occurring in iron phase could not. Hydrofluoric acid is most
effective among the all kind of inorganic and organic acids.
Similarly, sodium hydroxide is the most efficient leaching reagent
between the all alkali and alkaline earth hydroxide. Main

advantage of this process are i) ease leaching of phosphorus matter
in the main process stream, ii) 85-90% recovery of ore, iii)
improved iron value of leached ore,
Now here an attempt has taken to make the process techno-
economic by recycling of alkali. Effective or optimize process of acid
and alkali recovery helps us to established the process feasibility.
In current experimental approach, we have designed the
experiment such a way it minimize the loss of alkali.
The phosphorus removal methodology developed by us in slurry
extraction is a novel process where chemical used are regenerated in a
closed operation.
Successful studies for extraction of phosphorus are on laboratory scale.
Further studies are needed to carry out for suitable to bench scale
resulted from laboratory study.
Reject or slime of iron ore has phosphorus content of around 0.18% to
0.13%. This phosphorus can be leached out economically by proposed
process, which needs the requirements of the various industries.
The process consists of three steep namely;
1. Extraction
2. Filtration cum washing
3. Regeneration

A. Extraction:
Extraction refers to digestion of phosphorus present in ore to form
sodium phosphate. The required quantity of sodium hydroxide is
dissolved in water and iron ore material is added after the temperature of
the caustic solution reaches greater than 90°C. Extraction studies ware
carried at various temperatures with various slurry ratios in order to
optimize the same. The extraction temperature of around 95°C with 1: 15
slurry ratio was decided as the optimum because of the higher
phosphorus leach out as can be seen in the Table 1. The extraction is
carried at this temperature and slurry ratio for a period of 120 minutes,
which is optimum reaction time, established by the experimental results
and further increase in time of extraction hardly leach the value
obtained, which is evident from experimental results given in the tables
and figure.
Hence, the optimum time for extraction is 120 minutes at around 95°C
with 1.15 slurry ratio at reaction speed 800-900rpm.
The process generally comprises sizing of ore, below 25-micron size ore.
Thereafter, the solution is removed and the leached ore washed with
water.
As in case of most leaching operations, the particle size directly affects
leaching time and one may vary the particle size by, for example,
crushing and screening.

This process may be carried out in a batch or continuous way.
Conventional equipment and procedure may be used in both the case. In
continuous process, multiple stage extraction procedure can be used
whereby pregnant liquor is recycled through leaching stages to maximize
utilization of leaching reagent.
The present invention is combined of phosphorus removal with high iron
recovery and also increase the iron grade of the dephosphurized product
thereby making these low grade reject more valuable and usable in iron
production. Therefore, the practice of the invention would be worth
nothing for conserving the iron ore resources through the world.
The leach reactor was made of tersion with loading capacity of 1 kg ore
Two modes of the operations were used.
1. Circulating operation: In such a test, the leach solution was
continuously recycled., at a constant reaction speed, through
tapping until the apatite and iron phase in ore was dissolved to
minimum level. The bulk solution was sampled at a certain time
interval.
2. Single-phase operation: The fresh leach solution was added after
single operation by Alteration

B. Filter cum washing:
In the filtration process, the soluble sodium phosphate goes out from
residue. This is crucial step to remove the sodium of required
specification by varying counter current washing to ensure the residue
free from sodium.
Extraction:
1. NaOH + Coal Na3PO3 or Na3PO4 + Insoluble residue
Filtration cum washing
2. Na3PO3 or Na3PO4 + Insoluble residue + H2O Insoluble residue + Na3PO3
or Na3PO4
Regeneration:
3. Na3PO3 or Na3PO4 + Flue gas Soluble sodium salt + P205 +Na3PO3
4. CaO + H2O Ca(OH)2
5. Soluble sodium salt + Ca (OH)2 CaC03 + 2NaOH
The two main requirements for regeneration produced are;
1. Surface area
2. Slurry ratio (Tap density)
3. Temperature
4. Sparging

WE CLAIM:
1. A process for removing phosphorus from low grade iron ore
comprising:
extracting phosphorus from the iron ore by the addition of sodium
hydroxide at 80 to 95°C;
subjecting the soluble phosphorus salt to the step of washing and
followed by Alteration;
regenerating sodium hydroxide by reacting the sodium phosphorus
salt with a salt at a temperature range of 80 to 90°C for 60 to 90
minutes.
2. The process as claimed in claim 1, wherein the step of extraction is
preferred by preparing a slurry of sodium hydroxide dissolved in
water with ratio from 1:5 to 1:20 and the iron ore material is added
at a temperature greater than 90°C at a reaction speed of 800 to
900 rpm and for a period of 120 minutes to form sodium phophate.
3. The process as claimed in claim 1, wherein the step of Alteration
and regeneration are carried out for a period of 1 hour and 30
minutes respectively.
4. The process as claimed in claim 1, wherein the step of regeneration
the salt used in selected from calcium oxide and calcium
hydroxide.
5. The process as claimed in claim 1, wherein the particle size of iron
ore is below 25 micron.

6. The process as claimed in claim 1, wherein the concentration of
sodium hydroxide 25% by weight.
7. The process as claimed in claim 1, wherein the 85% of sodium
hydroxide is regenerated.
8. The process as claimed in claim 1, wherein the 85% yield of ore
having iron value of 67-68%.

A process for removing phosphorus from low grade iron ore comprising:
extracting phosphorus from the iron ore by the addition of sodium
hydroxide at 80 to 95°C; subjecting the soluble phosphorus salt to the
step of washing and followed by Alteration; regenerating sodium
hydroxide by reacting the sodium phosphorus salt with a salt at a
temperature range of 80 to 90°C for 60 to 90 minutes.