FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(section 10 and rule 13)
1. Title of the invention
SELECTIVE SEPARATION OF PHOSPHATE MINERALS FROM OTHER MINERALS, USING AMINOTRIS (METHYLENEPHOSPHONIC ACID) , AND DDETHYLENETRIAM1NEPENTAKIS (METHYLENEPHOSPHONIC ACID) AS DEPRESSANTS
I Applicants)
(a) Name: Tata consultancy Services Ltd.
(b) Nationality: An Indian Company.
(c) Address: Air India Building, 11a floor Nariman
Point Mumbai 400 021.
3. Preamble to the Description
The following specification particularly describes the invention and the


manner in which it is to be performed.



FIELD OF THE INVENTION
This invention relates to separation of phosphate minerals from other minerals, particularly from dolomite containing ores.
BACKGROUND OF THE INVENTION
Phosphate ore is used to manufacture phosphoric acid and other commercial products required by fertilizer producers. The vast majority of phosphate ore must be beneficiated prior to its usage so as to separate the phosphate bearing minerals from other gangue minerals such as silicates and carbonates. Froth flotation is one of the most commonly used techniques to achieve this. The process is based on making the desired mineral surface hydrophobic while maintaining the surfaces of other minerals hydrophilic. The technique has been practiced by phosphate industry since 1950's. Some of the commonly used methods are as follows :-
1. Direct Flotation
The phosphate minerals are floated directly using fatty acid collector and appropriate depressants for suppressing gangue minerals.
2. Reverse Flotation
Carbonate minerals are floated in slightly acidic conditions with fatty acid collector while phosphates are depressed using phosphoric acid.

3. Double Stage Flotation
In the first stage, phosphates and carbonates are floated using fatty acid collector at alkaline pH, rejecting silicates in the tail. Hie float from stage I is subjected to second stage flotation wherein carbonates are floated in acidic pH using fatty acid while keeping the phosphates depressed with phosphoric acid.
Some of these processes have certain problems and limitations.
The direct flotation process is applicable to only siliceous phosphate deposits since the selective reagents are currently available to float apatite efficiently from its associated silicate gangue.
The reverse flotation process is not suitable for high silica containing carbonate-phosphate ores since one cannot obtain marketable grade even after flotation of carbonate constituents. One needs to have another stage of flotation to remove silicate gangue.
The double stage flotation process requires addition of large dosages of reagents such as sulphuric /phosphoric/hydrofluoric acids to depress apatite and to maintain a low pH of less than 5, throughout flotation. At higher pITs it is not possible to depress apatite efficiently. Several cleaning stages are needed to obtain the product of desired quality.





Thus, designing or developing more selective collectors or depressants for separation of phosphates (apatite) from carbonates (dolomite) is necessary.
This task however has remained challenging due to very similar behavior of dolomite and apatite minerals during flotation process. Both these minerals have common cation Ca+2 and similarly sized anions PO4 ~3 and CO3'2, which makes it even more difficult to apply conventional chelation chemistry for designing selective reagents.
Currently several deposits of dolomite rock phosphate in the world are unexploited for want of a viable beneficiation process for obtaining the rock phosphate product of desired quality. While beneficiation of siliceous phosphate ores using froth flotation is commercially established and successful, upgradation of dolomite phosphate ores remains without a satisfactory solution.
PRIOR ART
The prior art shows efforts of several research groups all around the world searching for selective reagents including several types of phosphonic acids which can accomplish satisfactory separation of fluoroapatite (calcium fluoroapatite) from dolomite.

The U.S. patent No. 4,287,053 by Lehr et al discloses a phosphate ore beneficiation process using hydroxyethylidene diphosphomc acid (melhylhydroxy diphosphonate) as a depressant for beneficiating phosphate ores containing alkaline earth metal carbonate mineral impurities. The said process involves fatty acid/fuel oil as collector.
The U.S. patent No. 4,317,715 by Hintikka et al discloses a process for
selective froth flotation of phosphate and carbonate minerals from finely divided phosphate-carbonate-silicate ores or concentrates. This method uses SO2 or CO2 to inactivate the collector agent coatings on surfaces of carbonate minerals and from flotation of slurry in order to obtain separate recovery of a phosphate concentrate and carbonate concentrate.
The U.S. patent No.4,358,368 by Hellsten et al discloses a process
for the froth flotation of calcium phosphate containing minerals and flotation reagents for such a process. This process uses an amphoteric chemical reagent (having both cationic quaternary amine and anionic carboxylate/sulphonate groups) as a collector.
The U.S. patent No. 4,364,824 by Snow et al discloses a process





for flotation of phosphate ore containing dolomite. This process is basically a reverse flotation process which is similar to conventional methods used in India. In this process, inorganic phosphates/phosphoric acid and flurosilicic acids are used as apatite depressants. This process in addition, requires large quantities of of H2S04 for maintaining pH of the slurry at below 6.
The U.S. patent No. 4,372,843 by Lawver et al discloses a process
for beneficiating phosphate ores containing dolomite. This process is similar to the one disclosed in U.S. patent No. 4,364,824 described above.
The U.S. patent No. 4,486,301 by Hsieh et al discloses a process
of beneficiating high carbonate phosphate ore. This multi-stage flotation separation process uses hydroxyethylidene diphosphonic acid and hydrofluoric acid as modifying agents and a fatty acid as a collector. The phosphate and carbonate minerals are collected as rougher concentrate from the over flow in die first stage and in the second stage carbonate is floated separately while keeping die apatite depressed. High dosages of H2SO4 / HF are needed to keep pH in the desirable range of 5.2-4.8.

The U.S. patent No. 4,568,454 by Mehrotra et al discloses a process for
beneficiation of high carbonate phosphate rock. The process uses CO2 for conditioning the slurry followed by addition of an anionic collector to the slurry and subjecting the slurry to the from flotation which concentrates carbonate mineral impurities in float. Process employs CO2 to depress flotation of phosphate related to carbonate mineral impurities.
The U.S. patent No. 4,636,303 by Hsieh et al discloses a process
for beneficiation of dolomitic phosphate ores. This multi-stage flotation process is similar to what is disclosed in an earlier patent (U.S. patent No. 4,486,301). It was developed for the processing of a phosphate ore containing coarse weathered dolomite. The process is similar to double stage flotation. In this process, hydroxyetfaylidene diphosphonic acid is used as a depressant and fatty acid as collector for the flotation of rougher concentrates obtained in the first .stage.
The U.S. patent No. 4,648,966 by Hsieh et al, is similar to the U.S. patent No. 4,636,303 as described above.

U.S. patent No. 4,690,752 by Shaw discloses a process whereby fine phosphate ore slimes containing carbonate impurities are selectively flocculated using a nonionic polymer like polyacrylamide and subsequently floated.
U.S. patent No. 6,341,697 by Miller employs hydroxamate collectors for flotation separation of phosphate mineral from associated dolomitic gangue.
Apart from the patents, the subject has also been an area of intensive research covered in various publications from time to time.
Some recent relevant publications are:
(1) S.Zheng and KW. Smith (1997), "Dolomite depressants in the flotation of apatite and collophane from dolomite", Minerals engineering, Vol. 10, no. 5, pp. 537-545.
(2) S.M.Assis et al (1988), " A new approach for the flotation of Brazilian carbonated phosphate ores", Proceedings of the XVI international mineral processing congress, Stockholm, Sweden, Forssberg, K.S. Eric.,(Ed)., Elsevier Pub., pp. 1561-1572.

(3) H. Sis and S. Chander (2003), "Reagents used in the flotation of phosphate ores: a critical review", Minerals Engineering, 16, pp 577-585.
(4) H. Sis and S. Chander (2003), "Improving froth characteristics and flotation recovery of phosphate ores with nonionic surfactants", Minerals Engineering, 16, pp 587-595.
The continuing research reflected in the patents and publications referred here above indicate the selection of appropriate reagents for separation amongst phosphate ores.
The prior art mainly deals with various kinds of reagents, which accomplish better separation of phosphate values. Almost all the reagents reflected in the prior art are effective in acidic pH region. This requires use of acids such as sulphuric acid, phosphoric acid and hydrofluoric acid for controlling/maintaining the pH at a desired level. Hence all these processes require handling and consumption of acids on the large scale pausing problems in the plant besides adding to the cost of processing dolomitic ores as dolomitic ores consume acid at low pH's.

The processes thus become prohibitively expensive due to high consumption of reagents and environmentally unsafe as acidic pH's cause corrosion and handling problems from point of view of plant practice.
SUMMARY OF THE INVENTION
According to the invention, Aminotris (methyelephosphonic acid and Diethylenetriaminepentakis (melhylenephosphonic acid) are used for selective separation of phosphate minerals from other minerals.
The present invention comprises a process for separation of phosphate minerals from other minerals present in the phosphate ore. The process is particularly applicable to high dolomite containing phosphate ores.
The process consists of conditioning the aqueous pulp of the mineral mixture with the depressant at an acidic pH of 5.5 to 7.0. The aqueous pulp is furlfaer conditioned with a collector and is subjected to froth flotation. The impurities or unwanted minerals are collected in the froth phase, which are removed. The phosphate bearing minerals are retained in the flotation tailings. The molecular structures of the depressant molecules used are shown in Table 1.
The collector used is generally a fatty acid such as oleic acid.

Conventionally, phosphoric acid is used as to depress apatite during industrial beneficiation of rock phosphate such as that found in Rajasthan and elsewhere. The current industrial flotation practice consists of two main stages. In the first stage, apatite and dolomite are floated collectively, using sodium oleate as collector at alkaline pH, rejecting silica impurities in the tails. The float from stage I is conditioned with phosphoric acid at a lower pH of 5.5 to depress apatite. During the second stage flotation with sodium oleate, dolomite is collected in the float while apatite remains in tail.
To establish the effectiveness of the process with the depressant molecules referred above, a dolomitic rock phosphate ore obtained from Rajasthan State Mineral and Metals Corporation , Rajasthan has been used. The depressant

molecules were either synthesized in the laboratory , Pune or obtained from commercial sources.
The new depressants investigated in this invention are highly effective for apatite beneficiation. Significant enrichment is achieved in a single stage flotation only. Though the ore contained a high proportion of MgO (13.3%), its content in the beneficiated rock was reduced to 1.5% in a single step of rougher flotation.
The dosage of the new depressant required is only about 0.6 Kg/T, which is lower than that of a conventional depressant for apatite by an order of magnitude. The optimal conditioning pH is higher at 5.5-7.0 than the pH of 5.0 to 5.5 required for a conventional process, thereby saving the cost of acid used for maintaining pH.
Thus, the present invention not only helps in beneficiating difficult to float rock phosphate ores, but to reduce the consumption of reagents in a significant manner. This can result in reduction of processing costs and ease of handling the flotation products and recycling of the wastewater to the beneficiation circuit.

DETAILED DESCRIPTION OF THE INVENTION

A typical rock phosphate ore obtained from Rajasthan State Mines and Metals has been used in the process to detennine effectiveness of the depressant molecules.
To determine the composition of the ore X-ray diffraction method was used. The X-ray diffraction patterns of the ore revealed the presence of apatite, dolomite and quartz as the primary constituents. Further, the chemical analysis of ore established that the percentage of these constituents as: 23.8% P2O3 (10.4% P), 7.2% insolubles (SiO2) and 13.3% MgO.
/ The depressants used in this investigation were either synthesized in the laboratory, which may also be obtained from commercial sources.
Analytical grade sodium oleate (C17H33COONa, Mol. Wt. 304.45), procured from J.T. Baker, USA, was used as collector for dolomite minerals. A 1% aqueous solution was added to the pulp as per the required dosages.

Analytical grade H2SO4 was used for adjusting the pH of the pulp during flotation. This reagent was added as a 10% aqueous solution.

Flotation was conducted in a standard 2L capacity Hindustan Dorr Oliver flotation cell using 0.5 Kg of solids ground to the required size as stated earlier.
All the dosages reported are in the unit of kg/t of ore.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is the flow sheet of flotation process
Figure 2 shows comparison of phosphorous penta-oxide grades and
recoveries obtained with different depressants for flotation of rock
phosphate ore
Now the invention is described with reference to the Figures.
DETAILED DESCRIPTION OF INVENTION INCLUDING THE PREFERRED EMBODIMENTS
Flotation Procedures
The ore was reduced to -10# size in a closed circuit crushing and screening operation. The -10# ore was ground to 94% -200# in a laboratory rod mill at 60% pulp density. The aqueous pulp thus obtained was used as feed to the laboratory flotation process. The flow sheet of flotation experiment is shown in


Figure 1. The flotation pulp was first conditioned at a higher pulp density (35% solids) with the depressant for a period of 3-5 minutes. The pH during conditioning was maintained between 5.0 and 7.0, depending on the depressant used. Sodium oleate was added and the conditioning of the pulp continued for a further period of 3 minutes. The pulp density of the pulp was reduced to 25%, by addition of water. The pH of the pulp was continuously maintained at 5.0 to 1 7.0.
Flotation was conducted for 2 minutes (float 1). Dolomite was collected preferentially in the float while apatite remained in the tails. A second dosage of sodium oleate was added while maintaining the conditioning pH between 5.0 and 7.0. A second fraction of float was collected during next one minute (float 2). Speed of the stirring spindle was maintained at 1100 rpm throughout the flotation experiment The airflow during the flotation period was maintained at a steady value of 10 litre/min. This general procedure was followed for all the experiments reported in mis invention.

The specific experimental conditions pertaining to each depressant were selected so as to obtain the best result. The findings are illustrated in the following examples and summarized in Figure 2.
The following examples show the effectiveness of the depressant molecules used in the invention. Examples 1 and 2 show the results with existing





Example 1
The experimental procedure followed was the same as outlined in the above section. The pH was maintained in the range of 5.2 to 5.4 throughout the period of experiment by adding 5.4 kg/t of phosphoric acid, which also acted as depressant for apatite. Sodium oleate (0.6 kg/t) was added to collect dolomite in the float while apatite remained depressed. The results are summarized in Table 2.
Table 2: Rougher flotation results with rock phosphate ore using phopshoric acid as depressant

The pH was maintained between 5.2 and 5.4 by adding 3.0 kg/t of sulfuric acid. The ore was conditioned with 6.0 kg/t of phosphoric acid. Flotation was accomplished by addition of 0.6 kg/t of sodium oleate. The results are summarized in Table 3.

Table 3: Rougher flotation results with rock phosphate ore using phopshoric acid as depressant in presence of sulfuric acid

Example 3
The pH was maintained in the range of 5.5 to 6.5 by adding 3.8 kg/t of sulfuric acid. The ore was conditioned with 0.56 kg/t of depressant namely, aminotris (methylenephosphonic acid) (PA1). Dolomite was floated using 0.3 kg/t of sodium oleate while keeping apatite depressed. The results are summarized in Table 4.
Table 4; Rougher flotation results with rock phosphate ore using aminotris (methylenephosphonic acid) as depressant


Example 4
The addition of 3.0 kg/t of sulfuric acid kept the pH between of 5.5 and 6.3. diethylenetriaminepentakis (methylenephosphonic acid) (PA2) (0.6 kg/t) was added as depressant and ore was conditioned for 3 minutes before flotation. Most of die dolomite was collected in float using 0.2 kg/t of sodium oleate while apatite remained in tails. The results are summarized in Table 5.
Table 5: Rougher flotation results with rock phosphate ore using diethylenetriaminepentakis (methylenephosphonic acid) as depressant

While particular embodiments of the invention are described here ,the present invention however is not limited to any particular application or environment. Modifications and variations may occur to those skilled in the art .The description of the exemplary embodiments, is therefore, for the purpose of illustration and not limitation.

We claim:
1. A process for selective separation of phosphorous bearing minerals from other
unwanted minerals present in the phosphate mineral mixture, the process
comprising the steps of:
a) conditioning the aqueous pulp of the phosphate mineral mixture with a depressant molecule selected from the group consisting of Aminotris (methylenephosphonic acid) and Diethylenetriaminepentakis (methylenephosphonic acid), the phosphate mineral mixture being conditioned at an acidic pH of 5.5 to 7.0;
b) conditioning the aqueous pulp further in a fatty acid collector such as oleic acid and subjecting this aqueous pulp to froth flotation;
c) removing the impurities and unwanted materials collected in the froth phase of the froth flotation; and
d) recovering the phosphate bearing minerals retained in the flotation tailings.
Aminotris (methylenephosphonic acid)
2. A process as claimed in 1 where the Aminotris has the following molecular
structure


3. A process as claimed in 1 where the Diethylenetriaminepentakis has the following molecular structure

Diethylenetriaminepentakis (methylenephosphonic acid)
4. The process as claimed in 1, where the fatty acid collector is sodium oleate.
5. The process as claimed in 1, where the process of recovering the phosphate bearing minerals comprising the steps of:

a) conditioning the flotation tailings in the fatty acid collector and subjecting them to the froth flotation;
b) removing the impurities collected in the froth phase of the froth flotation; and
c) collecting the phosphate bearing minerals from the flotation tailings.