FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION METHOD FOR PROCESSING LOW-QUALITY ROCK PHOSPHATES
APPLICANTS
Aditya Birla Science and Technology Company Private Limited
of address Plot No. 1 & 1-A/1, MIDC Taloja, Taluka Panvel, Dist. Raigad- 410208, Navi Mumbai,
Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is
to be performed

FIELD OF THE INVENTION
[001] The present invention relates to method for producing phosphoric acid, and more particularly relates to methods for processing low grade phosphate rock into phosphoric acid and calcium phosphate.
DESCRIPTION OF THE BACKGROUND ART
[002] Phosphoric acid is produced through two methods: (a) dry method and (b) wet process. The former is an energy intensive process wherein the phosphorous ore is reacted with coke and silica at high temperature to generate phosphorous pentoxide (P2O5), followed by conversion to phosphoric acid by bubbling P2O5 in pure water.
[003] Some well-known wet methods involve attack of phosphate rock with acids, principally sulphuric acid, but also nitric, perchloric or hydrochloric acids. A hydrochloric attack of the phosphate rock is known in the art. These methods have the drawback that they generally use, for the attack, a concentrated solution of HCl which may be 20% or even 30% by weight. Also, in wet-process phosphate ore is reacted with mineral acids such as sulphuric acid, or nitric acid, or hydrochloric acid to release the phosphorous as lean phosphoric acid along with huge impurities, followed by a series of separation, purification and concentration steps to produce specific grade of phosphoric acid.
[004] Thus rock to be used has to be of good quality, that is to say, amongst others, that it must have a high P2O5 content, and fine grinding of the rock is usually required, which increases the cost.
[005] It has also been known to apply a different method of producing phosphoric acid, as described in US 2005/0238558 and in U.S. Pat. No. 7,361,323, which comprises a neutralization step.

[006] Patent No. US 6,989,136 B2 recites phosphoric acid production by etching of rock phosphate with aqueous solution of phosphoric acid (20-35% P2O5) to generate soluble monobasic calcium phosphate (MCP), followed by conversion of MCP into phosphoric acid (H3PO4) and calcium chloride by action of HCl. A further separation of the H3PO4 from the calcium chloride by solvent extraction process and concentrating lean H3PO4 was claimed.
[007] US 7,361,323B2 recites method of producing phosphoric acid from rock phosphates digested with dilute hydrochloric acid (<10%). The resultant liquor was neutralised with calcium base or its mixture (carbonate, oxide, hydroxide) leading to the formation of calcium phosphate intermediate. It highlights that preferred low HCl concentration is intended to minimise the in-situ formation of corrosive HF & fluorosilicic acid. The change in the digestion acid concentration will, therefore, change the composition of the dissolution liquor. It is to be noted that the relative lower acid concentration would imply (a) higher volume of the acid, (b) higher liquid wastewater generation and (c) More unextracted P2O5 will end up into the solid sludge.
[008] U.S. Pat. No. 3,304,157 & US3311450 uses HCl for rock digestion (concentrated HCl (>30%)) followed by solid-liquid separation of the undigested matter through clarification and filtration. The green acid liquor, comprising of phosphoric acid and metal chlorides, is then fed to the extensive liquid-liquid extraction (LLE) system to preferentially extract phosphoric acid from the soluble metal impurities. The acid is concentrated by steam stripping to further remove the fluoride & volatile impurities thereby generating technical/food grade phosphoric acid. The grade of phosphoric acid depends on the processing parameters, specifications of the rock. As the LLE systems are extremely sensitive to the composition of the DL and therefore the rock

fed into the system impacts the process parameters, maintainenece & production. Thus, this process selectively works for few rock phosphates in the existing condition.
[009] Most of the phosphoric acid plants use sulphuric acid for digestion and there has been extensive modifications and upgradations made on this process till date. A substantial problem faced by the prior art in processing low-grade phosphate rock for the production of phosphoric acid and other products is the relative substantial proportion of slimes, sand and other impurities contained in the phosphate rock. Typically processing a rock with high impurities such as Al, Fe and soluble Si would be difficult and one has to compromise the production or the quality of the phosphoric acid.
[010] To overcome the above problem, in U.S. Pat. No. 3,150,957 grade phosphate rock is acidulated with phosphoric acid and the impurites are decanted from the reaction mixture to provide a high grade phosphate rock.
[011] U.S. Pat. No. 3,919,395 describes an extraction process for the recovery of phosphorus compounds from both high and low grade phosphate ores, especially apatite-containing ores, using room temperature extraction of coarsely ground ore with dilute mineral acids in order to remove dissolved R2O3 (where R is metals such as Fe, Al, Cr) impurities from the ore to upgrade the ore.
[012] Known process treat phosphate rock in order to remove impurities by the use of weak acid ~10% HCl, hence generated larger volumes of solid & liquid waste and loss of useful products.
[013] The inventors of present application have now found that is possible to process low quality phosphate rocks, by a wet process, to obtain high quality phosphoric acid.
OBJECT OF THE INVENTION
[014] An object of the invention is to process low grade phosphate rocks for preparation of phosphoric acid and other useful products.

SUMMARY OF THE INVENTION
[015] In as aspect, the invention provides a process for treating low grade phosphate rock comprising:
a) reacting phosphate rock with a solution of hydrochloric acid to form a slurry comprising an aqueous phase and a solid phase;
b) filtering slurry of step (a) to separate said aqueous phase and said solid phase;

(c) performing a first neutralization of said aqueous phase of step (b) by addition of a calcium compound;
(d) filtering the neutralized aqueous solution from step (c) to obtain a filtrate and a waste cake.
(e) evaporating filtrate of step (d) to increase concentration of filtrate to desired
level.
[016] In an aspect, waste cake generated in step (d) is washed with acidified water containing dilute inorganic acid, such as hydrochloric acid, sulphuric acid, nitric acid, as suitable, to recover P2O5.
[017] In an aspect, optionally, filtrate from step (d) is subjected to a second neutralization by addition of a calcium compound, followed by separating solid and aqueous phase from neutralized solution and a subsequent re-dissolution of the solid, formed from second neutralization with concentrated hydrochloric acid.
BRIEF DESCRIPTION OF THE DRAWINGS
[018] The foregoing summary, as well as the following detailed description of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, there are shown in the drawings embodiments which are presently preferred and considered illustrative. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein. In the drawings:

[019] Figure 1 is a block diagram representing steps of process according to the invention
for processing low grade phosphate rock. [020] Figure 2 is X-ray diffraction profile of calphos cake obtained in present invention
showing pure crystalline Brushite phase.
DESCRIPTION OF THE INVENTION
[021] In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.
[022] As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.
[023] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention

[024] As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e. to mean including but not limited to.
[025] While the present invention is susceptible of embodiment in various forms, there is hereinafter described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.
[026] The installation illustrated in FIG. 1 shows the scheme of process proposed in present application. The blocks highlighted in gray are the new steps integrated to the known process for processing low grade phosphate rock.
[027] In as aspect, as shown in figure 1, the invention provides a process for treating low grade phosphate rock comprising.
a) reacting phosphate rock with a solution of hydrochloric acid to form a slurry
comprising an aqueous phase and a solid phase;
b) filtering slurry of step (a) to separate said aqueous phase and said solid phase;
(c) performing a first neutralization of said aqueous phase of step (b) by addition of a
calcium compound;
(d) filtering the neutralized aqueous solution from step (c) to obtain a filtrate and a
waste cake.
(e) evaporating filtrate of step (d) to increase concentration of filtrate. to desired level.
[028] Step (a) of the process, illustrated in FIG. 1, consists of reacting phosphate rock with HCl. For instance, phosphate rock with a P2O5 content greater than 30% P2O5 is introduced into a reactor 1 together with an aqueous solution of HCl (~20-35% w/w). A residue of impurities is obtained in the form of a solid cake after liquid-solid

separation. The filtrate is a solution is called a green acid liquor (DL-1) comprising
phosphoric acid and metal chlorides having highly acidic pH. [029] In an embodiment, the concentration of hydrochloric acid used in the process present
invention is in the range of ~20-35% w/w, so that loss of the P2O5 is minimum in the
solid waste and the volume of the green acid liquor is minimal. [030] Rock phosphate contains fluorapatite [Ca10(PO4)6F2] as major phase along with calcite
(CaCO3), dolomite (CaCO3MgCO3), silicates and quartz (SiO2). The reaction with
HCl are as follows:
Ca10(PO4)6F2 + 20HCl → 10CaCl 2 + 6H3PO4 + 2HF CaCO3 + HCl → CaCl 2 + 2H2O + CO2 (gas) CaCO3MgCO3 + 4HCl → CaCl2 + MgCl2 + 2H2O + 2CO2 (gas) HF + SiO2 or silicates → H2SiF6 + H2O Fe, Al salts + HCl → FeCl3, AlCl3 [031] The metal chlorides, fluorosilicic acid, unreacted HF, excess HCl and H3PO4 remains
in the liquid phase as DL-1. The green colour of the acid liquor (DL-1) is attributed to
the presence of chloride salts of Fe, Cr. The quartz and unreacted apatitic-phosphate
& dolomitic phases comprises of the acid insoluble portion. [032] Step (b) of the process is where the solid and liquid phase of green acid liquor is
separated in a clarifier by clarification and filtration. In an embodiment, the
clarification is performed by addition of flocculating agents in the clarifier. [033] Step (c) of the process, as illustrated in Fig 1, consist of performing a first
neutralization of said aqueous phase of step (b) by addition of a calcium compound.
The pH may be increased, for instance, between 0.5-1.0. The calcium compound is
selected from a group consisting of calcium hydroxide, calcium oxide, preferably
calcium hydroxide. The neutralization of aqueous solution of step (b) mainly proceeds

with the reaction between the neutralizing agent and HF, HCl, H2SiF6, FeCl3, AlCl3, H3PO4 (present in the DL-1) to not only reduce the silicon & fluoride contents from the solution as poorly soluble CaSiF6 but it also acts a pH moderator to enable co-precipitation of the Al, Fe impurities with calcium-fluoro/chloro/hydroxy-phosphates or mixed calcium phosphates (CaHPO4+CaHPO4-2H2O). At this step it is necessary to allow some phosphate formation to trap most of the impurities in solid state.
[034] In an embodiment, water is optionally added while performing the first neutralization step. In another embodiment, the first neutralization is carried out at a temperature in the range of 20°C to 40°C while stirring the aqueos phase.
[035] Step (d) of the process as illustrated in Fig 1, consist of separation of solid-liquid phase obtained in step (c) by filtering the neutralized aqueous solution from step (c). The filtration is performed by vacuum filtration using stable filter media. The liquid phase separated in step (4) shows >80% removal of Fe & Al and efficiency of P2O5 recovery is ~75-83%.
[036] Step (e) of the process is evaporation of filtrate from step (d) to increase the concentration of filtrate to desired level. In an embodiment, evaporation is performed under vacum at a remperature of 60 to 80oC.
[037] In another embodiment, as shown in figure 1, the present invention provides a process for treating low grade phosphate rock comprising:
(a) reacting phosphate rock with a solution of hydrochloric acid to form a slurry comprising an aqueous phase and a solid phase;
(b) filtering slurry of step (a) to separate said aqueous phase and said solid phase;
(c) performing a first neutralization of said aqueous phase of step (b) by addition of a calcium compound;

(d) filtering the neutralized aqueous solution from step (c) to obtain a filtrate and a waste cake.
(e) optionally washing waste cake generated in step (d) with 1-10% acidic water to recover P2O5.
(f) optionally, performing a second neutralization of filtrate from step (d) by addition of a calcium compound, preferably oxide, hydroxide of calcium;
(g) and separating solid and aqueous phase from solution of step (f).
[038] The waste cakes from step (d) is leached/washed with dilute acid, preferably dilute
hydrochloric acid to recover a portion of the P2O5. The recovered P2O5 stream may be
recycled. [039] The process of second neutralization of filtrate from step (d) results in increase of pH
in the range of pH 7-12, so as to generate phosphate rich salts of calcium as solid
phase and the impurities remain in the liquid phase. [040] The second neutralization is carried out at a temperature in the range of 20°C to 40°C
while stirring the aqueous phase at a speed in the range of 200-350 rpm. [041] In an embodiment, the residence time of first and second neutralization is in the range
of 30-120 minutes. The first and second neutralization is carried out by slow addition
of calcium compound thereby minimising the impact of froth-formation, if any,
during the neutralisation process. [042] The separation of solid and aqueous phase of step (g) is carried out by sedimentation
and filtration operations known in the art. The solid phase separated, identified as
calphos cake residue is the enriched calcium phosphate with low impurity. [043] In an embodiment, the liquid phase separated from step is recycled partly in the
process of neutralization to reduce the overall intake of calcium compound in the
process.

[044] The calphos cake from step (g) has a P2O5 content in the range of ~37-41%, moisture content in the range of ~4-6% moisture, and calcium oxide in the range of ~35-42%. In an embodiment, the calphos cake is reacted with hydrochloric acid having a concentration in the range of 20-35% to obtain a second green acid liquor (DL-2). The Fe, Al, Si contents of DL-2 are less than that in the green acid liquor (DL-1). The acid liquor (DL-2) is fed to the LLE batteries for further processing as per the existing method.
[045] It has been shown that very good results have been obtained. This will be illustrated in the following example which is not limitative. The following examples, though not restricted to single type, may be used to understand the efficacy of the proposed process.
WORKING EXAMPLES EXAMPLE 1
[046] In one example of the embodiment, the rock phosphate (identified as Rock T1) with the specification range as in Table 1 was used to generate the green acid liquor.

Quality parameters Specification range of Rock T1 Analysis of Rock T1
Moisture, % 2-3 2-3
P2O5 dry basis % 35.2-36.7 35.2-36.7
Insoluble SiO2% 3-4 3-4
Soluble SiO2% 0.5-1.5 0.5-1.5
Ca% 35-37 35-37
Aluminium as Al2O3% 1.0-1.2 1.0-1.2
Iron as Fe2O3% 1.5-1.7 1.5-1.7
Fluoride as F% 3.9-4.2 3.9-4.2
Table 1
[047] The green acid liquor (Green acid-T1) was generated by dissolving 1 Kg of rock with 2.5Kg of 25-26% HCl, followed by separation of the undissolved insolubles by filtration. Quality of the Green acid-T1 is given in Table 2. No heat was provided as the reaction is exothermic in nature.

Quality parameters Green acid-Tl
Density (g/mL) 1.305
P2O5 (g/L) 129
Ca(g/L) 129.8
Free acid as HCI(g./L) 20.5
Si as SiO2(g/L) 2.57
Aluminium as AI2O3 (g/L) 1.55
Iron as Fe2O3 (g/L) 1.66
Table 2
[048] To 100 g of Green acid-T1, 22 mL of distilled water was added followed by slow addition of ~6.0 g of calcium hydroxide till pH of the solution is reaches to ~0.8. The stirring was maintained at 250 rpm and temperature was ~27±2 °C (no heat was provided).
[049] White precipitation is observed in the solution at step 2. To separate the solid-liquid phases the contents were subjected to filtration & simultaneous washing using ~16 g distilled water. ~5.4 g of the vacuum-dried residue (Phos-T20-0 pH 0.8, dried at 27±2 °C) was obtained. ~139.1 g of the filtrate having density of ~1.22g/mL was also collected. The efficiency of P2O5 recovery at this stage is ~82% for single stage washing and filtration.
[050] To 100.8g of the filtrate of step 3 about 4.2g of solid calcium hydroxide is added slowly till pH is increased to 11. Considerable amount of white precipitate is seen as this stage. The stirring was continued for ~30 min at 250 rpm speed. Thereafter the contents were filtered, washed with ~60.7g water and the white cake of calcium phosphate is collected. At this stage, ~13.5 g of vacuum-dried cake (Phos-T20-0.8 pH 11) and ~152.3g of waste filtrate (density ~1.074g/mL) were obtained.
[051] The waste filtrate and the Phos-T20-0.8 pH 11, generated in step 4, contains ~3.2g/L and 40.6% P2O5, respectively. The efficiency of P2O5 recovery at this stage is ~92.4% for single stage washing and filtration.

[052] The efficiency of removal of impurities Fe, Al and Si (expressed as Fe2O3, Al2O3 & SiO2 respectively) by applying the steps 2-5, has been found to be ~95.3%, 94.6% and 74.5% as shown in Table 3. About 24.3g of Phos-T20-0.8 pH 11 is generated per 100 mL of the DL-T1 in this case.

Impurity profile DL-T1 (g
in 100 mL
DL) Phos-T20-0.8 pH 11 (%) Phos-T20-0.8 pH 11 (g in 100 mL DL-T1) Efficiency of
impurity Removal
at new stage (%)
Fe2O3 0.166 0.032 0.08 95.3
Al2O3 0.155 0.034 0.08 94.6
SiO2 0.257 0.269 0.065 74.5
Table 3
EXAMPLE 2
[053] In another embodiment, DL-1-T2, having different composition (due to the
heterogenous nature of the rock phosphate) than the DL-1-T1 but prepared at similar
conditions as in example 1 was used. [054] 400g of DL-1-T2 was stirred with slurry of calcium hydroxide in both the stages and
quantity of water used for the washing operation (per g of DL used) in filtration at
stage 2 was reduced as compared to example 1 as in Table 4.

Step 1: pH ~0.8-1.0
Input Stage 1 Green acid liquor (DL-T2) (g) 400

Water 100

Calcium hydroxide (Anhydrous basis) (g) 25.8

Water for washing residue (g) 53
Output-Stage 1 Wet Calphos-9R-Res-1 (g) 53.4

Weight of Calphos-9R-Filt.-1 (g) 525.3

Volume of Calphos-9R-Filt.-1 (mL) 434
Step 2: pH ~10-12
Input Stage 2 Weight of Calphos-9R-Filt.-1 (g) 500.7

Calcium hydroxide (Anhydrous basis) (g) 21.3

Water for washing residue (g) 59
Output Stage 2 Weight of wet residue Calphos-9R-Res-2 (g) 152.2

Weight of Calphos-9R-Filt.-2 (g) 429.2

Volume of Calphos-9R-Filt.-1 (mL) 390
Table 4

[055] The composition of the feed DL (DL-1-T2) and the residues at the 2 stages have been analysed to evaluate the efficiency of the stages for each component pertaining to the claimed stages. The data is provided in Table 5. Table 5 shows that the Calphos-9R-Res-2 (%) has significant as compared to the Rock phosphate T1.
[056] It is observed that at stage 1 maxiumum removal of Fe, Si, Al is achieved. Thus, stage 2 will be optional, yet useful, to concentrate the phosphate content and thereafter generating lower volumes for further processing; typically, if processing a acid mixture (filtrate at stage 1) having lower concentration of P2O5 or higher volume in the liquid-liquid extraction of phosphoric acid, as per the existing IMI process, is difficult or will incur more organic solvent consumption.

Rock-T1 (%) DL-1-T2 (g/L) Calphos-9R-Res-1 (%) Calphos-9R-Res-2 (%) Efficiency -Stage 1 (%) Efficiency -Stage 2 (%) Overall
Efficiency
(%)
Moisture 2.3 -- 47.8 58.6 --
P2O5 35.6 (dry basis) 120 33 (dry basis) 38.5 (dry basis) 75 (recovery) 98 (recovery) 73 (recovery)
Insoluble 3.9 -- <0.5 0.6 -- -- --
Ca 37.0 110 25.7 30.1 -- -- --
Fe 0.8 1.16 1.05 0.04 93 0.0 92
Al 0.9 0.925 0.92 0.04 90 1.8 90
Si 0.4 1.2 0.53 0.25 46 0.4 46
Table 5
EXAMPLE 3:
[057] The wet cake generated at stage 1, having P2O5 ~17.2% (As Is basis), was contacted with ~45 mL of 1% HCl solution for about 2-5 minutes and filtered. About 62 g of transparent colourless filtrate, having 66 g/L of P2O5 was obtained. About 43% of the P2O5 could be recovered by adopting the HCl washing step.
EXAMPLE 4:
[058] To demonstrate the process without using the second neutrailisation, green acid liquor (DL-1-P; Table 6) from phosphoric acid plant, using a specific grade of rock, was adopted. To ~400 g of the DL-P, 130 mL of 20% slurry of calcium hydroxide was

reacted to generate ~425 mL of filtrate (identified as Filtrate-1 in table 6) and ~44g of Residue-1. The efficiencies of P2O5 recovery & impurity removal is provided in Table 7. About ~300 mL of the filtrate-1 was concentrated by evaporation to obtain a concentrated liquor (identified as Conc.-Filt.-1, composition presented in Table 6), which can be further used in existing process as per the steps (Figure 1).

Unit Composition of DL-1-P Composition of Filtrate 1 Composition of Conc. Filt-1
P2O5 g/L 113 70 129
Ca g/L 115 109 196
Fe mg/L 1227 123 221
Al mg/L 264 33 59
Si mg/L 1049 265 477
Cr mg/L 27.6 9.3 16.7
Cu mg/L 10 5.6 10.1
Table 6

Efficiency%
P2O5. recovery 83.02
Fe removal 86.56
Al removal 83.25
Si removal 66.14
Table 7
CHARACTERIZATION
[059] X-ray diffraction of the Phos-T20-0.8 pH 11 (see Figure 2) confirms the presence of well-crystalline calcium phosphate phase (Brushite, DCPD) phase. About 20g of the cake is dissolved in 25% HCl to generate 29 mL of secondary acid liquor (DL-2) with lower impurity (0.22g/L Fe2O3 & 0.23g/L of Al2O3 & 1.8 g/L of SiO2) & higher P2O5 (280 g/L) in solution than the reference acid liquor from relatively good rock phosphate (120-125g/L P2O5, 1.0-1.26g/L Fe2O3, 5.5-6.4g/L of Al2O3 & 3-3.9g/L of SiO2). Thus, the desired improvement in the DL-2 quality (higher P2O5 and lower impurities) has been achieved through this process.
ADVANTAGES

[060] The invention opens up scope of using rock with high Fe, Al, soluble Si impurities in
the existing process for preparing phosphoric acid. [061] The invention reduces the amount of Si, Fe & Al in the feed to the liquid-liquid
(LLE)system, which is expected to reduce operational issues in the primary LLE
section. [062] Reduction of Fe-content in the process of the present invention will reduce the
limitations of the metal extraction process. [063] In the process a part of the generated aqueous liquor (pH ~7-12) may also be used to
treat the acid sludge/waste of the process, thereby reducing lime and water
consumption for the ETP process.

We Claim:
1) A process for treating low grade phosphate rock comprising:
a) reacting phosphate rock with a solution of hydrochloric acid to form a slurry
comprising an aqueous phase and a solid phase;
b) filtering slurry of step (a) to separate said aqueous phase and said solid phase;
(c) performing a first neutralization of said aqueous phase of step (b) by addition of a
calcium compound;
(d) filtering the neutralized aqueous solution from step (c) to obtain a filtrate and a
waste cake.
(e) evaporating filtrate of step (d) to increase concentration of filtrate. to desired level.
2) The method as claimed in claim 1, wherein calcium compound of step (c) is calcium oxide or calcium hydroxide.
3) The method as claimed in claim 1, wherein concentration of hydrochloric acid is in the range of ~20-35% w/w.
4) The method as claimed in claim 1, wherein first neutralization is carried out at a
temperature in the range of 20oC to 40oC.
5) The method as claimed in claim 1, wherein first neutralization is carried out for a duration of 30-120 minutes.
6) The method as claimed in claim 1, wherein filtration of step (d) is carried out by vacuum filtration.
7) A process for treating low grade phosphate rock comprising:
a) reacting phosphate rock with a solution of hydrochloric acid to form a slurry
comprising an aqueous phase and a solid phase;
b) filtering slurry of step (a) to separate said aqueous phase and said solid phase;
(c) performing a first neutralization of said aqueous phase of step (b) by addition of a calcium compound;

(d) filtering the neutralized aqueous solution from step (c) to obtain a filtrate and a waste cake.
(e) optionally performing a step of second neutralization of filtrate from step (d) by addition of a calcium compound; and
(f) separating solid and aqueous phase from solution of step (e).
(g) dissolution of the solid obtained in step (f) in concentrated hydrochloric acid for
further use.
8) The method as claimed in claim 7, wherein second neutralization is carried out at ambient temperature in the range of 20oC to 40oC for a duration of 30-120 minutes.
9) The method as claimed in claim 7, wherein waste cake generated in step (d) is washed with dilute acid, preferably dilute hydrochloric acid to recover P2O5.
10) The method as claimed in claim 8, wherein calcium compound of step (e) is calcium
oxide or calcium hydroxide.