AU2016210678A1 - A process for the production of thorium phosphate from thorium oxalate and recovery of oxalic acid - Google Patents

Abstract

Ti: A process for the production of thorium phosphate A process for producing insoluble thorium phosphastes from thorium oxalate comprising the steps of (i) rpulping the thorium oxaae pmcipitate in water and reacting the slurry at about 60-7C with an alkali phosphate compound to precipitate as thorium phosphate and sodium oxalate (ii) separating such thorium phosphate precipitate by filtration (iii) crystaIizing the sodium oxalate fiom filtrate (iv) outing the sodium oxalate thus formed with sulphuric acid to convert the oxalate to oxalic acid and sodium sulphate (vi) crystallizing the oxalic acid first by cooling and sodium sulphate in the next sep by evporaion and then lg the Oxalic acid in step (i) as well as the moher liquor o. sodiumsulphate crystalisation poess in step (iv).

Description

TITLE: A process for the production of thorium phosphate. FIELD OF INVENTION:

The present invention relates to a process for the production of thorium phosphate and to the recovery of oxalic acid. BACKGROUND OF THE INVENTION:

It is known to this art that certain industries, in particular those which are based on the hydro-metallurgical treatments of ores like Monazite or uranothioranite with either sulphuric acid Or caustic soda, can produce^ various natural thorium salts, such as,: geocrally, the chlorides nitrates which are highly soluble in water.

Of late various inventors have found out the solution of producing various thorium compounds which is as insoluble and as non-leachabie as possible, namely, into a form nihich is completely inert, in particular to the environment. Not only the effluent generated by the insolubilization operation would thus be freed of the undesirable thorium values and could then optionally be enhanced in value, but, additionally, the recovery of the thorium would then be carried out in a directly stomble form and m a reliable arid economic manner.

It will be appreciated that processes for the preparation of compounds of the thorium phosphate type are known to this art. Thus, it is known that such compounds can be obtained by direct reaction between, on the one hand, a solution of a soluble thorium salt (nitrate, chloride) and. on the other, ari alkali metal phosphate or phosphoric add (see. especially. Paul Pascal, Nouveau Traite de Chimie Minerale (New Treatise on Organic Chemistry], Volume IX, page 1132 et seq (1963)). However, in all cases, gels are produced which are extremely difficult, indeed impossible, to filter. Consequently, such synthetic routes cannot be used on a truly industrial scale^

Thierry delloye et all .vide US patent no US5403565A, placed an industrial scale treatment of soluble thorium compounds to convert same into a thorium phosphate that is both insoluble and non-leachable, with a view to controlling polluting problems related to discharges and/or storage of thorium products and other radioactive materials. The process mainly consists of producing an innocuous water-insoluble thorium phosphates, notably orthorhombic thorium phosphates, by (0 reacting such water-soluble thorium compounds, e.g., the nitrates andfor chlorides, with a base, for example aqueous ammonia, in an aqueous reaction medium, to precipitate a thorium hydroxide (ii) next reacting the precipitate thus formed with a phosphating compound, e.g., phosphoric acid or a soluble phosphate salt, also in an aqueous reaction medium, to precipitate a thorium phosphate and then (iii) separating such thorium phosphate precipitate.

Given that the complete insolubilization of the thorium constituted a necessary precondition to attain storage which is both economic and which has, on a long term basis, no noxious or harmful impact on the environment, the present inventors then considered insoluble compounds of the thorium phosphate type. Indeed, these compounds have been shown to be the thorium salts which have the weakest solubilities, Consequently, to succeed In perfectly controlling, on an industrial scale the Λ ^ synthesis of thorium phosphates from soluble thorium compounds it would be required -to simultaneously provide (i) effluents which have been freed of this species, and thus potentially added in value, (ii) for the storage of thorium in As most insoluble, and thereby most inert, form and. finally, optionally, (Hi) for the use of the phosphates thus prepared as a Coating and/or protective material for storing other radioactive wastes.

Vladimir Brandel, Nicolas Dacheux, Michel Genet, Catherine Lindecker el al vide US patent no US5953678 A ,1999 described Thorium phosphates, method for preparing same, and use thereof for storing radioactive materials,

The Process for the preparation of thorium phosphate of formula Th.sub.4 P,sub.6 O.sub.23 comprising the steps of reacting a foorium compound in the solid state and a phosphating agent selected from the group consisting of ammonium dlhydrogenorthophosphate and boron phosphate BPO.suM, at a temperature of 165°C to 210”C and at least one heat treatment of the product obtained by the reaction of the thorium compound and the phosphating agent, at a temperature of 850°C to 1300°C phosphaiing agent being such that the atomic th/P ratio is 1/4 to 2/3.

Vladimir Brandel. Nicolas Dacheux, Michel Genet et al vide US Patent number: 7195745,in 2007 relates to a process for the preparation of a product based on a phosphate of at least one element M(IV), for example of thorium and/or of actinide(!V)(&)y This process comprises the fQltowing stages: a) mixing a solution of thorium(IV) and/or of at least one achnide(IV) with a phosphoric add solution in amounts such that the molar ratio PO 4: M(1V) is from 1.4 to 2, b) heating the mixture of the solutions in a closed container at a temperature of SO to 250* C^'tn order to precipitate a product comprising a phosphate of at least one element M chosen from thoriumflV) and actinide(lV)s having a P/M molar ratio of 1J5. and c) separating the precipitated product from the solution. The precipitate can be converted to phosphate/diphosphate of thorium and of actinide(s). The process also applies to the separation of uranyl ions from other cations.

United States Patent Office 3,351.436 PatentedNov. 7,1967 3,351,436 preparation of thorium pyrophosphate James F. Server, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Filed Dec. 28, 1964, Ser. No. 421,5876 Claims

The method of preparing thorium pyrophosphate which comprises mixing stoichiometric quantities of methyl alcohol solution of thorium nitrate and phosphoric acid, and recovering the resulting thorium pyrophosphate precipitate and firing the precipitate at a temperature of about 1100°C and for about. 2 hrs to form crystalline thorium pyrophosphate.

Ktvat I the et al vide US Patent US 5171887 A, 1992 developed a process for the preparation of oxalate by dissolving the erode sodium oxalate in an aqueous solution to form a solution of sodium oxalate; separating insolubles from the solution; passing the solution through an ion exchange column to convert sodium oxalate, the ion exchange column having a bed of cation exchange resin of the acidic tjpe, the solution as it passes over the bed of resin exchanging sodium ions of thesodium oxalate with hydrogen ions of the resin to proditce sodium hydrogen oxalate acid, oxalic acid or mixtures thereof depending upon the strength of acidity of the resin, the exchanged sodium ions and the Al metal ions remaining on the bed of resin; and recovering the sodium hydrogen oxalate, oxalic acid or mixtures thereof as the effluent solution from the ion exchange column.

Joseph Zaher, Bryan FritzEer, Scott Hutchison et al US 20070066847 A1,2007 developed A process for the manufacture of oxalic acid dihydrate in which ah aqueous solution of sodium oxalate is contacted with hydrochloric acid and the resulting mixture then cooled to precipitate oxalic acid, folowed by optional recovery and recycling of the sodium oxalate and hydrochloric add Into the reaction chamber. A process comprising the steps of: a) contacting an aqueous solution of hydrochloric add with sodium oxalate in a reaction zone at a temperature between about 35* C. and about 140* C. to form a mixture, wherein the molar ratio of the water to the sodium oxalate Is between 20 to 1 and 350 to 1, and the molar ratio of the hydrochloric acid to the sodium oxalate is greater than 3 to 1 and less than 45 to 1; b) cooling the mixture to a temperature between about -10“ C. and.about 25* C^to form precipitated oxalic add dehydrate ih a slurry, c) separating the precipitated oxalic add dehydrate from the slurry, thereby leaving a first residual solution;

Indian Rare Earths Limited. Udyogamandat RED was operating a plant for processing 4000 MTPA of Monazite. The Caustic process involves,treating the ground monazite sand (-325 mesh), with 50 % caustic at a temperature of 140-16Q°C for 9 h, treating the digested mass with water to convert phosphate values to trisodhim phosphate and U, Th and Rare earths to their hydroxides, separating the Hydroxides and TSP by decantation. The.TSP solution is crystallized, centrifuged and dried to get TSP crystals. Selective leaching of the hydroxides with dilute HCI at pH 3 to soluble rare earths as rare earth chlorides and Uranium and thorium as hydroxides which js known as thorium concentrate or thorium hydroxide cake. Redissolution of the Uranium and thorium as hydroxides by HCI to corresponding chlorides with a free acidity of 1.5 to 2.0 N. Extracting the uranium values from aqueous chloride solution by liquid liquid extraction with a tertiary amine (Alamine 336), The raffinate containing Thorium and some rare earths are separated by two routes. (1>Thorium extracted with PC88A and purified ,lhan converted to thorium oxalate. Problem ; titanium values also extracted which is ·> difficult to strip and hence hydroflouric acids was used to ship which is a highly hazardous chemical. (2) selective precipitation with stoichoimetric quantity of oxalic acid to thorium oxalate without converting the rare earths* Problem: thorium is contaminated with litOe rare earths. However presently The thorium chloride solution (raffinate) from Uranium extraction section is collected and a part of this solution is transferred to Thorium Nitrate section for production of thorium nitrate and the balance solution is treated with oxalic acid to precipitate thorium oxalate. The thorium oxalate is filtered, neutralized and transferred in slurry form and disposed in the underground RCC trenches»

Draw backs of the prior art: t. Direct precipitation of thorium phosphate as reported in some of the prior arts from their chloride and nitrate salt solutions with phosphoric acid or phosphate salts result in a gel foritiatiori in case of high concentration of thorium where as low concentration result in very fine nano particle which is difficult to filter with slow filtration rate. 2. Formation of precipitate with phosphoric acid requires ammonia or ammonium hydroxide or any alkali as neutralising agent adding cost to the processing. 3. Some of the prior art reported a thorium phosphate as thorium phosphate diphosphate requires physical mixing of salts of thorium compound and phosphoric add and direct pyrolysis of the mixture. 4. Some of the prior art the salts of thorium first converted to thorium hydroxide with ammonia and than treated with a phosphating agent where specific parameters are to be maintained to regulate the particle size of thorium phosphate. 5. Treatment of effluent generated during the conversion is high as reported in some of the earlier works and were not addressed property. 6. Thorium oxalate at present reported as a storing material in India requires proper neutralisation as the oxalates has been prepared from the chloride .nitrate or sulphated acidic solutions. - 7 . In case of Prolonged storing of thorium as oxalate, a lot of Oxalic acid is blocked and the thorium content as Th02 in cake varies from 30 % in wet cake where as 45-50 % in dry cake. 8* Apart from several conventional method of producing oxalic acid , only few articles have shown the method of producing oxalic acid from sodium oxalate with hydrochloric acid at 20 to 450 fold that stoichiometric requires for the conversion to oxalic acid and lot of heat energy is required for crystallization as lot of water input is supplied from hydrochloric acid,; OBJECTS OF THE INVENTION:

An object of the present invention is lo propose a process for the production of thorium phosphate. ;

Anotherobject of tile present invention is to propose a process for the recovery af oxalic acid.

Further object of theprescnt invention is to propose aprocess in which thepartide size of precipitate can be controlled.

Yet another object of this invention is to propose a process where radioactivity in (each solution is aimost 10 time less than ttorium oxalate carried Under similar conditions.

Still furtherobject ofthls invention is to propose a process where the vaJuableby-product oxalic acid is recovered and ean be reused.

Still another object of this invention is to propose a process where a cheaper reagent such as Trisodium phosphate is used. BRIEF DESCRIPTION OF THE INVENTION:

According to thii: invention there is provided a process for producing insoluble tborium phosphates from thorium oxalate comprising the steps of (i) repulping the thorium oxalate precipitate in water and reacting die slurry at about 60-70°C with an alkali phosphate compound to precipitate as thorium phosphate and sodium oxalate (ii) separating such tborium phosphate precipitate by Shratkm (iii) crystallizing the sodium oxalate from filtrate 0v) treating the sodium oxalate thus formed with sulphuric acid to convert the oxalate to oxalic acid and sodium sulphate (vi) crystallizing the oxalic acid first by cooling and sodium sulphate in the next step by evaporation said Own recycling die oxalic acid in step (i) as well as the mother liquor of sodium sulphate aystalisatipn process in step (tv).

The process flow sheet isgiven in the accompanying figure L

Fig-1: shows thc prOCcssing of thorium phosphate from thorium oxalate.

Fig. 2: shows XRD pattern of thorium phosphates of present work and some of the earlier •work. DETAILED DESCRIPTION OF THE INVENTION; *

The present invention relates to an industrial scale of producing insoluble thorium phosphate from thorium oxalate» with a view to controlling polluting problems related to discharges and/or storage of thorium products and other radioactive materials. The process is also riming at recovering the oxalate values as oxalic acid, recycling the waste water and disposing low effluent and zero solid waste to the environment A major object of tb* present invention is. (be provisiooof an economically industrial process for the conversion of thorium oxalate to fhoritnn phosphate with recovery of oxalate values for reuse to avoid or ameliorate foe above disadvantages and drawbacks to date diancteririhg the state of this art.

During foe processing of Monazite (specially Indian monazite) by either caustic route or by sulphuric acid route large quantities of thorium values are recovered. As the use of thorium is restricted to iihclear application and a very rinril quantity is being used for gasmettle applications, so most of the thorium values are stored as oxalates in specialty designed trenches to prevent any radioactive spillage.

Similarly a huge quantity of trisodium phosphate dodecahydrate crystal are being generated during the processing of mona2ite by caustic route. Due to low marketability .trisodium phosphate also not regarded as a valuable byproduct.

Of iate various inventors have found out the solution of producing various thorium compounds which is as insoluble and as nOn*ieachable as possible, namely, into a form which is completely inert, in particular to the environment.

Among them Thorium phosphate in different forms like Th&(P04)4 and thorium phosphate diphasphate (Ttu ΡβΟ») are found to be most stable.

The present work involves the conversion of thorium oxalate to thorium phosphate by utilizing the trisbdium phosphate dodecahydrate and subsequently recovering the oxalate values as oxalic acid for reuse.

The process involves a) Repulping of thorium oxalate precipitates with water or a recycled liquor; The thorium oxide content in oxalate cakes varies from 30-40 % as Th02. The thorium oxalates are precipitated foam the corresponding nitrates or chlorides or sulphate by oxalic acid from an acidic solution. The precipitate is little slow in filtration , hence to reduce cycle time and extra unit operation the cake is settled and pumped to trenches where the water slowly escapes from the cake. b) Trisodium phosphate is dissolved in wateitrecyded liquor) and filtered to separate the insoluble contents. The insoluble contains .Uranium, thorium, rare earths jand other cationic species; About 0^2-0.4 % insoluble's are reported in TSP crystal. It is observed that the stoichiometric requirement of P for the conversion to either of the phosphates are Th3(P04)4 and thorium phosphate diphasphate ( Th* ΡβΟκ) are found to be almost same .Hence 1()-20 excess over the stoichiometric requirement of TSP in terms of P was taken. c) The TSP solution is added to thorium oxalate slurry with continuous stirring while maintaining a temperature of 60 - 70°C for 2 to 3 h. The ph is maintained at 7 - 9. The pH is generally automatically maintained. However H is observed that the reaction is partially taking place in cold condition. d) The thorium phosphate precipitate is filtered and washed 3 to 4 times by hot water to remove sodium oxalate solution from thorium phosphate. Washing of thorium phosphate is essential to remove sodium from thorium phosphate; e) The sodium oxalate concentration in the fittatre is maintained at approx 35 gpl,. caustic lye was added to increase the common ion and cooled to crystallise sodium oxalate crystal. The filtrate is recycled to repulp the thorium oxalate cake and TSP dissolution as well. f) Sulphuric add is added to the sodium oxalate crystals to convert to sodium sulphate and oxalic acid value. However a 3 fold or more sulphuric add is required for complete conversion other wise a large portion of oxalate is remained as sodium oxalate: A saturated condition of oxalic add is maintained with requisite dilution and sulphuric acid value’ ; ' g) The oxalic acid concentration is maintained at approx 140 gpl and coded at about 20°C to crystallize oxalic acid crystal. The recovery of oxalic acid is above 90%.

The filtrate contains sodium sulphate is evaporated and concentrated to recover the sodium sulphate crystal. h) Hie mother liquor of sodium sulphate solution is recycled back along with some sulphuric acid to maintain the sulphuric acid content and provide the necessary dilution for converting sodium oxalate to oxalic acid. 0 The thorium phosphate is dried and calcined for furtherstoringpurpose. j) The oxalic acid generated is reused for further precipitation. EXAMPLES:

The objects of the invention its advantages and means for attaining the same are disclosed here under in greater details with reference to non-limiting embodiments of die same, The examples are by w*y of illustration only and in no way restrict the scope of the invention.

Example'1 100 g of Thorium oxalate (wet cake) is repulped in 300 ml of water to prepare a slurry. The composition of feed thorium oxalate is as fotows

ThOj= 30 %, 59 g of trisodium phosphate is dissolved in 300 ml water and filtered to separate the insoluble contents» The insoluble contains , Uranium, thoriunvrare earths and other cationic species.

The TSP solution is added to thorium oxalate sluny with continuous stirring in a 2I borosit glass beaker while maintaining a temperature of 60 - 70°C tor 3 h. The pH is maintained at 7-9.

The thorium phosphate precipitate is filtered a Buchner tunnel and washed with 200 ml( 50 ml four times) of hot water maintained at 60-70 °C to remove sodium oxalate solution from thorium phosphate. Washing of thorium phosphate is essential to remove excess sodium from thorium phosphate.

Qty of wet cake thorium phosphate * 67.9 g

Qty of dry cake thorium phosphate * 44.0 g (dried at 110°C)

The sodium oxalate concentration is 34s5 gpt, sodium hydroxide flakes are added and cooled to crystallise sodium oxalate crystal.

Qty of sodium oxalate crystal * 35.0 g (28.5 g as sodium oxalate)

Recovery of sodium oxalate » 93.7 %

Volume of filtrate obtained^ 800 mi

Example-2 100 g of Thorium oxalate (wet cake) is repulped in 300 ml of filtrate (of the 800 ml filtrate obtained in erample-1) to prepare a slurry. The composition of feed thorium oxalate is as follows

ThOr^jO%, 59.4 g of trisodium phosphate is dissolved in 300 ml of filtrate (of the 800 ml filtrate obtained in example-1) and filtered to separate the insoluble contents. The insoluble contains, Uranium, thorium, rare earths and other cationic species.

The TSP solution is added to thorium oxalate slurry with continuous stirring in a 21 borosil glass beaker while maintaining a temperature of 60 - 70°C for 3h. The pH is maintained at 7-9.

The thorium phosphate precipitate is filtered a Buchner funnel and washed with 200 ml( 50 mi four times) of hot water maintained at 80-70 °C to remove sodium oxalate solution front thorium phosphate. Washing of thorium phosphate is essential to remove exoess sodium from thorium phosphate,:

Qty of wet cake thorium phosphate = 68.0 g

Qty of diy cake thorium phosphate =44 20 g (dried at 110°C>

The sodium oxalate concentration is 34.7 gpl, sodium hydroxide flakes are added and cooled to crystallise sodium oxalate crystal.

Qty of sodium oxalate crystal = 35,2 g( 28.5 g as sodium oxalate) -

Recovery of sodium oxalate = 93.75 %

Volume of filtrate obtained- 805 mi Ρ <ample*3 < Ο Ο kg of Thorium oxalate(wet cake) is repulped in 301 of deionised water to prepare a ilurry. The composition of feed thorium oxalate is as follows oo

ThOa- 30 % . T—i

<N vo 6 kg of trisodium phosphate is dissolved in 30 I water and filtered to separate the r—i ^ ' ^ insoluble contents. The ihsotuble contains VUranium, thorium, rare earths and other cationic species.

The TSP solution is added to thorium oxalate sluriy with continuous stirring at 60 rpm in a jacketed glass line reactor heated with thermic fluid heater while maintaining a temperature of 60 - 70°C for 3 h. The pH is maintained at 7-9.

The thorium phosphate precipitate is filtered a notch funnel and washed with 20 iitre( 51 four times) of hot water maintained at 60-70 °C. to remove sodium oxalate solution from thorium phosphate. Washing of thorium phosphate is essential to remove excess soaiumrffpmjh^^

Qty of wet cake thorium phosphate «= 6.9 kg

The wet cake is dried in a batch drier.

Qty of dry cake thorium phosphate * 4.45 kg (dried at 1 tO°C)

The sodium oxalate concentration is 34.5 gpt . sodium hydroxide flakes are .added and cooled to crystallise sodium oxalate Crystal.

Qty of sodium oxalate crystal = 3,6 kg (231 kg as sodium oxalate)

Recovery of sodium oxalate - 93,66 %

Volume of filtrate obtained^ 80 litre Examples

The thorium phosphate as obtained from example 3 is dried and calcined at different temperatures and the parameters like surface area, density, bufc density and xrd patterns are mentioned in tabie>1.

Tebie-fj ;·'·"'

The XRO patterns of some of the prior art along with present work thorium phosphate calcined at 900°C are given in figure 1.

Example-5

The feed thorium oxalate was produced at Monazite plant of Indian rare earths limited, al Aluwa. kerala and was kept in trenches for storing purpose at OSCOM, Indian rare earths limited situated in Orissa.

The Mterability studies of Thorium oxalate taken as feed material vs Thorium phosphate prepared by the present route are given in tabled Surface Area of Buchner funnel 46 cm2 Filter cloth used= Polyester doth

Quantity equivalent of Thorium oxide taken for each experiments 60 g Vacuum in blank (with arid without cloth) « 57 mm of Hg

Tabte-2

Example-6 120 ml of sulphuric acid( 98 % sulphuric acid) is added with stirring to 128 g of sodium oxalatef from example 3) in a borosii glass beaker to convert to sodium sulphate and oxalic acid value. Total volume is maintained at 470 ml with water. The temperature is maintained at 80°C for 30 min.

The oxalic acid concentration is found to be 141 gpl and cooled to 20°C in a tee bath to crystallise oxalic add crystal. The crystals are filtered in a buchner funnel,

Qty of oxalic add generated: 89 g

The recovery is 95 %.

Volume of filtrate s 445 ml

Composition of oxalic add: H^Ov 2H20=992 %r S0«=0.$ %

The filtrate contains sodium sulphate is evaporated and concentrated to recover the sodium sulphate crystal.

Qty of sodium sulphate qystal = 150 g

Volume of mother liquor generated- 130 ml (The mother liquor of sodium sulphate solution is recycled back in next batch to maintain the sulphuric add content and provide the necessary dilution for converting sodium oxalate to oxalic acid) *

Analysis of mother liquor, free sulphuric acid = 1100 gpi Example-7 40 ml of sulphuric add( 98 % sulphuric acid) is added along with 130 ml of mother liquor generated at the end of example-6 with stirring to 128 g of sodium oxalatef from example 3) in aborosil glass beaker to convert to sodium sulphate and oxalic add value. Total volume is maintained at 470 ml with water. The temperature is maintained at80°C for 30 min.

The oxalic acid concentration is found to be 141 gpt and cooled to 2tf*C In a Ice bath to crystallise oxalic add crystal. The crystals are filtered in a buchner furmel.

Qty of oxalic add generated: 89 g

The recovery is 95 %. J

Volume of filtrate s 445 mi

Composition of oxalic add: H2CaO,. ?H20^ 99.1 % S04=0^7 %

The filtrate contains sodium sulphate is evaporated and concentrated to recover the sodium sulphate crystal.

Qty of sodium sulphate crystal 3166 g

Volume of mother liquor generated2 140 ml (The mother liquor of sodium sulphate solution is recycled back in next batctr to maintain the “Sulphuric atfiTcoftlenl and provide the necessary dilution for converting sodium oxalate to oxalic acid).

Analysis of mother liquor, free sulphuric add = 1009 gpl ‘

Example-8: 25 g of thorium oxalate andC5 gi of thorium phosphate calcined at 900½ were repulped in 250 ml deionised water in different potypropylene beakers and stirred at a rpm of 60 • for 24 h. . . 1 -

The individual slurry after 24h filtered through 542 what man Alter paper. The filtrate was analysed for thorium content and gross alpha andj beta activity and are given in table -3.

Table-3

♦

Claims (12)

1. WE CLAIM:

   1. A process for producing insoluble thorium phosphates from thorium oxalate comprising the steps of (i) repulping the thorium oxalate precipitate in water and reacting the slurry at about 60-70°C with an alkali phosphate compound to precipitate as thorium phosphate and sodium oxalate (ii) separating such thorium phosphate precipitate by filtration (iti) crystallizing the sodium oxalate from filtrate (iy) treating the sodium oxalate thus fbnncd with sulphuric acid to convert the oxalate to «relic acid and sodium sulphate (vi) crystallizing the oxalic acid first by cooling and sodium sulphate in the next step by evaporation and Iheti recycling the oxalic acid in step, ^(i) as well as the mother Ikfuoi’of sodium sulphate ctystalisation process in stepQv).
2. 2. The process as claimed in claim I, wherein said alkali phosphate compound comprises of an alkali metal phosphate, tn sodium phosphate dodecahydraie generated in the process of monazite digestion with caustic soda.
3. 3. The process as daimedm claim i, comprising washing step (ii) thorium phosphate precipitate with hot water and maintained at temperature 60-70*0.
4. 4. The process as claimed in claim 1, comprising drying the step (ii) precipitate at 110°C for 2-5 h and subsequently calcining the dried thorium phosphate precipitate at 800-900*0.
5. 5. The process as claimed in claim 1, wherein said sodium oxalate filtrate alter separation of thorium phosphate is healed and/or treated with caustic soda and cooled to 20*0 to crystallize the sodium oxalate crystal.
6. 6. The process as claimed in claim 5, wherein the sodium oxalate crystals are separated by filtration.
7. 7. The process as claimed in claim 6, wherein the filtrate generated after the separation of sodium oxalate is recycled far puling the thorium oxalate and making trisodlum phosphate solution.
8. 8. The process as claimed in claim 1 and ¢, therein said sodium crystal is treated with 5 to 4 times the Stokhionieinc requirement of sufehuric acid to convert sodium oxalate to oxalic acid and sodium sulphate.
9. 9. The process as claimed in claim I and 6, wherein said sodium oxalate crystal (as crystalised) is treated with 98% sulphuric acid to convert sodium oxalate to oxalic acid and sodium sulphate and dilution is to be done with deionised water so as to achieve a concentration of about 140 grams per litre of oxalic add.
10. 10. The process as claimed in claim 1 and 9, wherein said oxalic acid and sodium sulphate solution is cooled to 20?C to crystallize the oxalic acid crystal from sodium sulphate solution and the said oxalic acid crystals ate separated by filtration. It. The process as claimed in claim 10, wherein said sodium sulphate filtrate alter separation of oxalic acid crystals » evaporated till crystallization point to crystallize : the sodium sulphate crystal and the sodium sulphate crystals are separated by filtration.
11. 12.The process as claimed in claim ί and II, wherein said sodium sulphate mother liquor afier separation of sodium sulphate crystals is recycled at step no 8 and/or 9.
12. 13. Th. ptoccaa as claimed Ib claim 1, whemii, the said thorium phosphate i, havfog ft. ^i"™^^“^''.«‘aaP,zj%eN,lnd248ls0lll<||XijRt[e earths.