AU2016210678B9 - 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 Aprocessforproducing insoluble thorium phosphastesfrom thorium oxalate comprising the steps of (i)rpulping the thorium oxae pmcipitae in water and reacting the slurry at about 60-7C with an alkaliphosphate copound to precipitate as thorium pophae and sodium oxalate (ii) separating such thorium phosphate precipitate by filtration (iii) cryst4izing-the sodium xalate fiom filtrate (iv) outing the sodium oxalate thus formed with sulphuric acid to convert the oxalate to oxalic acid and sodium sulphae (vi) crystaliing the oxalic acid first by cooling and sodium sulphate in the next sp by evporaion and thenwlig the xalic cid in step (i) as well as themher liquor o. sodiumsulphate crystalisation process step(iv).

Description

TITLE:

A processfor theproduction of thorium phosphate.

FIELD OF INVENTION:

The presentinvention relates to a process for the production of thoium phosphateand to

the rovery ofoxalic acid.

BACKGROUND OF THE INVENTION:

It is khown to this artdi certain industries, in particular those which are based on the

hydro-metallurical agents of ores lke Monazite or uraathinite with either

sulphuric acid or caustic soda can produce, various natural thodurn salts, such as

generally the chlorides or nitrates which are highly soluble in water.

Of late various inventors have found out the solution of prodcirg various thorium

compounds which.s as insoluble and as non-lescbable as possible, namely, into a form

whichis completely inert, in particular to the environment. Not only the effluent

generated by the insolubilization operationwould thus be freed of the undesirable

thoriun values and could then optinally be enhanced in value, but, additionally, the

recoveryof thethorium would then be carried out in a directly storable form and in a

reliable and economic manner.

it wil 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, an alkali metal phosphate or phosphoric acid

(see. especially. Paul Pascal, Nouveau Traie de Chime Minerale [New Treatise on

Organic Chemistry Volume IX, page 1132 et seq (1963)), However, in all cases, gels

are produced which are extremely difficult, eed impossible, to fiter. Consequently such syntheticoutes cannot be used on a truly industrial scale

Thierry delloye et all videe 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 dischargesand/or storage of thorium products another radioactive materials. The

process mainly consists of producing anInnocuous water-Insoluble thorium phosphates,

notably orthorhombic thorium phosphatesby (1) reacting such water-soluble thorium

compounds,e g, the nitrates and/or chlordes, 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, toprecipitate 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 an 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 theweakest

sotubilities. Consequently, to succeed In perfectly controlling, on an industrial scale the synthesis of thorium phosphates from soluble thorium compounds it would be required to simultaneously provide () efluents which have been freed of this species, and thus potential addedin vale, (ii) for the storage of thorium in itsm insolubland thereby most inert, form and. finally, optionally, (Ii) for the use of the phosphates thus prepared as acoating ancYor protecivm Meaterialor storgotherradiocivewastes.

Vladimir Brandel, Nicolas Dacheux, Michel Genet, Catherine Lindecker et a video US patentnoUS5536-8A1999 describedThorum phosphates, method for preparing same. and use thereof for storing radioactive mterais

The Process for the preparation of thorum phosphate of formula Th.sub.4 Pisub.8 Q.gub23 comprising the steps of reacting a thoumt compoundinthesoid state and a phosphaling agent sealed from the group consisting of ammonium dhydrbortophosphate and boren phospheaBPOsub4, 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 8500 C to 1300°C phosphaing 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 actinideV)(s)This process comprises the foblowing stages: a) mixingasolutionof

thorium(IV) and/orof at least one actinide(IV) with a phosphoric acid solution in amounts such that the molar ratio PO 4: M(iV) is from 1A to 2,b) heatinghe mixture of the solutions in a closed container at a temperature of 50 to 250° C,.in order to precipitate a product comprising a phosphate of at least one element M chosen from thorium(IV) and actinde(V)s having a P/M molar ratio of 15, 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 ons from othercations.

United States Patent Ofilce 3,351,436 Patented Nov. 7, 1967 3,351,436 preparation of thoriumpyrophosphate James F. Server, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Filed Dec. 28, 1964, Ser. No. 421,587 6 Claims

The method of preparingthorium pyrophosphate which comprises mixing stoichiometric quantities of methyl alcohol solution of thorium nitrate and phosphoric acid, and recovering the resulting thorium pyrophosphat precipiateand firing theprecipitueat a tenperure of about 10 C and for about 2 hrs to form crystalline thorium

pyrophosphatc.

Kwati the e1 al video US Patent US 5171887 A,1992 developed aProcess for theprpaMion ofOxalate by dissolving the cnde sodium oxa in anaqueous soltOnO0formambito iodium oxalate; separating insoluble.(fromtie solution; paying the solutiontdha oexcanecolmntconvtsodiumoxalate,theionexchange column having abed of ca"onexchaerinoftheaidiecthe lution asit passes over the bed of rei, exhmg sodiM nOf the sodiumuoxalatewV~ihydrogenionsof the resin topoduce "odmnhydrogen oxalate acd.oxalic acid OrmUixturesherefdepndingquon the strength of acidity of the resin, the exchanged sodium ions and the Almetal 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 Fritzler, Scott Hutchison et al US 2007006847 A1,2007 developed A process for the manufacture of oxalic acid dihydrate in whichan aqueous solution of sodium oxalate is contacted with hydrochloric acid and the resulting mixture

then coold to precipitate-oxalic acidic followed by optonal recovery and recycling of the sodium oxalate and hydrochloric acid Into the reaction chamber. A process comprising

the step of a) contacting an aqueous solution of hydrochori acid with sodium oxalate

in a reaction zone at a temperature between about 3W C. and about 140' C. to form a

mixture, wherein the molar ratio ofthe 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 toI 1and less than 45 to 1; b) cooling the mixture to a temperature

between about -10° C. and.about 25°C, to form preipitated xalic acid dehydrate in a

slurry c) separating the precipitated oxalic acid dehydrate from the slry,thereby

having af stresidualsolution;

Indian Rare Earths Limited. UdyogamandalRED was operaing a plant for prce g

4000 MTPA of Monazte The Caustic process involvestreating the ground monazite

sand (-325 mesh), wth 50 % caustic at a temperature o140160"Cfor9htreakng

thedigestedmasswithwater t onvert phosphatevalues to trisodIumphsate and U, Th and Rare earths to theirhydroxides. separating the Hydroxides and TSP by decantation The SP solution is crystallized, centrifuged and dried to get TSP crystals.

Selectie 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 is known as thorium concentrate or thorium hydroxide cake. Redissoluon 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 frorn 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

,than converted to thorium oxalate. Problem titanium values also extracted which is

difficult to srp and hence hydroflouric acids was used to strip which is a highly

hazardous chemical. (2) selective precipitation with stoichoinetric quantity of oxalic

acid to thorium oxalate without converting the rare earths, Problem: thorium is

contaminated with little rare earths. However presently The thorium chloride sokition

(raffinqte) from Uraniumextractionsection is collected and a part of this solution Is

transferred to Thorium Nitrate section forproduction 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:

1.Direct precipitatio ofthorium phosphate as reported in some of thepriorartsfrom or phosphate saltsresult in their chloride and nitrate salt solutions with phosphoric acid

a ge foiiationin case of highconcentration ofthoriumwhereaslowconcentration toFilter with slow filtration rate,, resultinveryfinenanoarticlewhich is difficult

vry prtcleWa rentin inao

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 ofsalts of thorium compound and phosphoric acid and direct pyrolysis of the mixture.

4.Some of the pior artthe salts thorim first converted to houm 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 duringthe conversions high as reported in some of

the earlierworks and werenot addressed property

6. Thorium oxatate-at present reported as a storing material in India requires proper

neutralisationas the oxatates hasbeen prepared from the chloridenitrateorsuphated

acidic solAtions.

and 7,sn M o6f.rongedsng of trium as oxalate , iot of oxalic acid is blocked

the thorium content as ThO2 in.cake varies from30%Inwetcakewhereas4550%in

dry cake.rI

8,Apartfrom several conventionalmethod of producing oxalicacid, onlyfewarticles oxalatewithhydfroOfiC have showntthe method of producing oxalic acid from sodium acid and adiat20 to 450 fold thastoichifltl requires for thecorverSioftto oxalic as lot of water input is supplied from lot of heat energyis required for crystalization

hydrochloricac.

SUMMARY OF THE INVENTION:

The present invention proposes a process for the production of thorium

phsopate.

The present invention also proposes a process for the recovery of oxalic

acid.

The present invention also relates to a process in which the particle size

of precipitate can be controlled.

The present invention further relates to a process where radioactivity in

leach solution is almost 10 time less than thorium oxalate carried under

similar conditions.

The present invention additionally relates to a process where the valuable

by-product oxalic acid is recovered and can be reused.

The present invention also relates to a process where a cheaper reagent

such as Trisodium phosphate is used.

According to this invention there is provided a process for producing

insoluble thorium phosphates from thorium oxalate comprising the steps

of (i) repulping a thorium oxalate precipitate in water to form a slurry and reacting the slurry at about 60-70C with an alkali phosphate compound to precipitate as thorium phosphate and sodium oxalate (ii) separating such thorium phosphate precipitate by filtration to obtain separated thorium phosphate and filtrate containing the sodium oxalate (ii) crystallizing the sodium oxalate from said filtrate (iv) 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 and then recycling the oxalic acid instep (i) as well as the mother liquor from the sodium sulphate crystallisation process in step (iv).

The process flow sheet is given in the accompanying figure 1.

BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Fig.1: shows the processing 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 oxalaW, with a view to controlling pollting problems related to dicharps

aidorstorageo fhoriumprodects and other radioactive materials. The process is also

aiming at recovering the oxalat values as oxalic acid, recycling the waste water and

disposing low effluentand zero solid waste to e Avironment.

A major object of the present inversion isbe provision of economically industrial process

for the conversion of thorium oxalate to thorium phosphate with recovery ofoxalate values

for reuse to avoidor amelorate the above disadvantages and drawbacks to date

characterizing the state of this at

Duringtheprocessing of Monazite (speciallIndian monazite) by either caustic route or by

sulphuric acid route large quantities of thorium values arerecovered. As the use ofthorium is

restricted to nuclear application and a very small quantity is being used for gs mentle

applications so mostof the thorium values are stared as oxalates in specially desired

trenches to preventany radioactive spillage. -

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

Of late various inventors have found out the solution of producing various thorium compounds which is as insoluble and as non-leachable as possible, namely, into a form whcis completely inert in particular to the environment

Among them Thorium phosphate in different forms like T(PO4)4 and thorium phosphate diphasphate( Th4 PeO) are ond to be most stable.

The present wjrk involves the conversion of thoriumroxalate to thorum phosphate by utilizing the Irisodium phosphate dodecahydrate and subsequently recovering the oxalate values asoxalic acid for reuse.

The process involves

a) Repulping of-thoriumoxalate precIpitateswitwater or a recycledcpior.The thorium

oxide content in oxalate cakes varies from 30- 40 %as Th2O. The thorium oxalates are precipitated from the corresponding nitratesr chlodes or sulphate by oxalic acid from

an acidic solution. The precipitate is littleslow in filtration, hence to reduce cycle time

and extra un operation the cake is seWedad pumped to trenches where the water

slowly escapes from the cake.

b) Trisodium phosphate is dissolved in water(recycled liquor) and fittered to separate

the insoluble contents. The insoluble contains.Uranium, thorium, rare earthsand other

cationi spedes About O2-.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 Th 3 (PO4)4 and thorium phosphate diphasphate (Th 4 P60) are found to be almost same .Hence 1020 excess over the stoichionericrequirement 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 -70C for 2 to 3 h The ph is maintained at 7 - 9. The pH is generally automatically maintained. Howeverit 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 ISessential-toremove sodiurn from thorium phosphate

e) the sodium oxalate concenlration in thefitatre is maintained at approx 35gpl

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.

OSulphuicacid s added tothesodiumoxalate crystals to convert to sodium sulphate and oxalicacid value However a 3 fold or moresuphuric acid is required for complete

conversion other wise a large portion of oxalate is remained as sodium oxalate A

saturated condition of oxalic acid is maintained withrequisite dilution and sulphuric acid

valoe.

g) The oxalic acid concentration is maintained at approx 140 gp and cooled at about 2C to crystallinze oxalic acid crystal. Therecoveryof oxalic acid is above 90%.

Thefiltatecotainssodiumsulphate isevaporated and centrated to recoverthesodium suphatecryst.

h)The mother liqor of sodium sulpha e solution j3 ec ycd e dbkao=gwpi

cid to maintain thesulphuricacid content and provide thenecessarydiutionfor conveng sodium oxalate to oxatic acid.

I The thorium phosphates driedand calined for funrtstorigpupose

j) The oxalic acid generated isreused forfunher precipiation.

EXAMPLES:

leobjectsofthe invention its advantagesai means forattainingthesamendisod

here under in greater details withreference to non-limiting embodiments of the The Uamps are by wOy of illustration only and in no way restrict t scope of the innto.

Example-1

100 g of Thorium oxalate (wet cake) is repuiped in 300 ml of water to prepare a slurry.

The composition offed thorium oxalate is asfolows

ThO2= 30 % ,

59 g of trisodium phosphate is dissolved in 30 0 ml water and ilered to separate the insoluble tonents, The insoluble contains, Uranium thorium, rare earths and other cationc species.

The TSP solution Is added tothorium oxalate slury with continuous stirringina 21 borosfglass beakerwhile maintaining a temperature of 60 - 7C ot 3 h. The pH is maintainedait 7-9.

The thorium phosphate precipitate is filtered a Buchner tunnel and washed with 200 ml(

ml four times)of hot water maintained at 60-70 °C to remove sodium oxalate solution

from thoriumphosphate. Washing of thonum phosphate Is essential to remove excess

sodium from thoium phosphate.

Qty of wet cake thorium phosphate 67.9 g

Oty of dry cake thoriumphosphate 44.0 g (dried atl10°C)

Thesoium oaate concentration is 345 gplsodium hydroxideflakes are added and

cooled to crysialise sodium oxate crystal.

Qf sodioxate crystal 35.0 g(28.5 g as sodium oxatate)

Recovery of sodium oxalate =93. %

Voumeqf filtrate oftied 800 mW

Example-2

fitrate 100 g of Thorium oxalate (wetcake) is repulp edin 300 ml offiltrate (of the 800 s obtained In exampe-to prepare slurry. Thcomposition of feed thorium oxalate

as:IOWS

ThO23Q.0%,

59.4g of trisodium phosphate is dissolved in 300 mloffiltrate(ofthe800mlflate Obtaineinexample-) and filtered to separate theinsolublecontents.Theinsoluble

contaisUraniumthoriumrareearths and other catonic species.

The TSP solution is added to thorium oxalate slurry worth continuous stirring in a 21 borosnglass beake'rwheMaintaining 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( mI four tines).of hot water mainlahed at60-70 to reov sodium oxalae solution from thorium phphatemashing of thorium hosphate is essential to removex.W sodium from thorium phosphate,

Qty of wel cake thorium phophate 680g

Oty of dry cake thorium hosphale 44.20 g (dried at 11000C

The sodium oxalate concentration is 34 gpl, sodium hydroxide flakes are added and cooled to crystalise sodium oxalate crystaL

Qty of sodumoXala crystal=35.2 g(28.5 g as sodium oxaae)

Recoveryof sodium oxalate =9325 %

Volume of filtrate obtained 805 ml

rI gamiple-3 30PI- odensewater to prepare a cake) is repulpedin kg of Thorium oxalate(wet is as follows iaflof feed thoriurn oxalate Tuyhe compose uto

ThOg 30 %

1 water and fuitered to separate i issOlved30 6 9o utrisodum phosphate is thorium rareearths and other e insotubie containsae insolu wortents- The.Islbec"

catont species n

heater while mnrtaining a beTSPsolusadeatohoriumoxalatect whthe u glassrne reactoheated ternoflatuat at7-9 a v 7a0eCt fr 3 h The pH is

Teperuehosphaterecipittis ered a nutch funne andwashedwth20ite(5 The f rthe photphate preiita t emove so noxalate solution

ois essentatoremove excess toums of hPwaer maitano

#,fum Phosphiate. Wfshing sodlu0 Osphate,

6.9kg tyofwetcakethoriumphosphate

Thewet ca is dried inabatchdrier.

cityof dry:cake thoriumph ath 4A5ha 4 dia kI ty o dcaddeda. a. sOdium hyd ox de alkes cent3rtn is 34.5gp The sodiumoexalate odIum oxalatcystai

Qty of Sodium oxalate crystal= 3,6kg(2,81kgassiumoXaIasej

Recoveryof sodium Oxalate =93,66

% Voum of filtrate obtained= 80 litre

Exampi.4

Thorium phosphate as obtained'fromexanple3dn perauandtheparametrlikesurfacerea is drbed and Calcined at dfe

paers are mentioned intable-1b

nrnImewnlcondn Suface ny XRD --area an ct density XR

at 1 ho eUDie 8. athot 345 1,02 Aophu c2kkd at300° J 3 25- j

c aledned ata500°Caregi5e-07gght

im phosphase 4S - al C hCrystalhe le, t5 Cyt 2 at 900°C in .1 T m hosphate 2 cak ned at 1000C, 5 C a:

The XRD patier ofaeo he he oprorartalng W~eOf r w-ith-preenor thoriumn phosphale ca med at 900°C are g Ven in figure

Example-5

1he feed thorium oxalate was produced at MonaziteplantofIndianrareearthsimited

al Aluwa, kerala and was kept in trenches for storing purpose atOSCOM, Indian rare earths limited situated in Orissa

Theiilterabilty studies of Thorium Oxalfe taken asfeed material vs Thorium phospha prepare bthe present route are given in table-, Surface Area of Buchner funnel= 46 cm2

Filter cloth used Polyeser cloth

Ouantily equivalent of Thorium oxide taken for each experiment 60 g acuum irt-blank (titk ad without clot) z 57mm of Hg

CFCnbf reSPiigv shnyo ofcake wetcae mnea eter -fillrand cake to r-Gmnui .254j 317r ii 2. Thag.iflc*at oxalate n of Hg T;O.= 0.2 s ne and gplei passd through 0%put cot densitwl$ water don flocculants the massbecomes

phophae 8&nofT.=nil =4* Thocawt 360* 8mm 1W'ipbai is afiteraWe preciatehn Hg mas9 den pu

Example-B

120 ml of sulphuric acid( 98 % sulphuric acid) Is added with stirring to 128 g of sodium

oxalate( from example 3) in a borosil glass beaker to convert to sodium sulphate and oxalic aciA 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 ice bath to

crystaflise alicacid crystal. The crystals are filtered in a buchner funnel,

Oty ofoxalicacid generatd: 89 g

The recovery is 95

Volumeoffiltrae445ml

Composition of oxalic acid:

HAO4. 2H 2 O99.2 %.SO4=0.6 %

The fitrate contains sodium sulhate is evaporated and concentrated to recover the

sodium sulphate crystal

Qly of sodium sulphate crystal= 150 g

Volume of mother liqur generated= 130 ml (The mother liquor of sodium suphate

solution is recycled bak in next batch to maintn the sulphuric acd content and

provide he necessary dilution for converting sodium oxalate to oxalic acid)

Analysis of mother liquor, free sulphuric acid =1100 gpi

Example-7

40ml ofsulphuricaci(98%sulphuric acid) is added along with 130 ml ofmother liquor generated at the end of example-6 with stirring to 128 g of sodium oxalate( from example3)inaborosilglassbeakerto onvertto sodium sulphate andoxalic acid value. Total volume is maintained at 470 ml wil water The temperature is maintained at 80°C for 30 mi.

The oxalli acidconcentration is found to be 141 gpl and cooled to 20°C in aIce both to crystallise oxalic acid crystal. The crystals are filtered in abuchner funnel.

Qty of oxacacid generated: 89 g

The recovery I 95

Volume of filtrate 445 ml

Compositionof a cid -

H1C20.2H O 99.1%

804=0(7 %

The atecontainssodiumsulphae is evaporated andconcentrated to recover the sodim su lphatecystal6

Oly ofsodium sulphatecrystah 165.g

Volume of mother liquor generated= 140 ml (The mother liquor of sodium sulphate solution is

recycled back in next batch to maintain the sulphuric acid content and provide the necessary dilution

for converting sodium oxalate to oxalic acid).

Analysis of mother liquor, free sulphuric acid = 1009 gpl

Example-8:

g of thorium oxalate and 25 g of thorium phosphate calcined at 900°C were repulped in 250 ml

deionised water in different polypropylene beakers and stirred at a rpm of 60 for 24h.

The individual slurry after 24h filtered through 542 what man fitter paper. The filtrate was analysed

for thorium content and gross alpha and beta activity and are given in table -3.

Table-3

Filtrate generated from Gross alpha activity Gross beta activity

Thorium oxalate 750 520

Thorium phosphate 48 52

The reference in this specification to any prior publication (or information derived from it), or to any

matter which is known, is not, and should not be taken as an acknowledgment or admission or any

form of suggestion that that prior publication (or information derived from it) or known matter forms

part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the

word "comprise", and variations such as "comprises" and "comprising", will be understood to imply

the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any

other integer or step or group of integers or steps.

Claims (13)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A process for producing insoluble thorium phosphates from thorium oxalate comprising the steps of (i) repulping a thorium oxalate precipitate in water to form a slurry 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 to obtain separated thorium phosphate and a filtrate containing the sodium oxalate, (iii) crystallizing the sodium oxalate from said filtrate, (iv) 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, and then recycling the oxalic acid in step (i), as well as mother liquor from the sodium sulphate crystallization process in step (iv).

2. The process as claimed in claim 1, wherein said alkali phosphate compound comprises of an alkali metal phosphate, tri sodium phosphate dodecahydrate generated in the process of monazite digestion with caustic soda.

3. The process as claimed in claim 1, further comprising washing the separated thorium phosphate obtained in step (ii) with hot water, and maintaining it at a temperature 60-70°C.

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°C.

5. The process as claimed in claim 1, wherein said sodium oxalate filtrate after separation of thorium phosphate is heated and/or treated with caustic soda and cooled to 20°C to crystallize the sodium oxalate crystal.

6. The process as claimed in claim 5, wherein the sodium oxalate crystals are separated by filtration.

7. The process as claimed in claim 6, wherein the filtrate generated after the separation of sodium oxalate is recycled for pulping the thorium oxalate and making trisodium phosphate solution.

8. The process as claimed in claim 1 and 6, wherein said sodium oxalate crystal is treated with 3 to 4 times the stoichiometric requirement of sulphuric acid to convert sodium oxalate to oxalic acid and sodium sulphate.

9. The process as claimed in claim 1 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 acid.

10. The process as claimed in claim 1 or 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 are separated by filtration.

11. The process as claimed in claim 10, wherein said sodium sulphate filtrate after separation of oxalic acid crystals is evaporated till crystallization point to crystallize the sodium sulphate crystal and the sodium sulphate crystals are separated by filtration.

12. The process as claimed in claim 1 or 11, wherein said sodium sulphate mother liquor after separation of sodium sulphate crystals is recycled at step no 8 and/or 9,

13. The process as claimed in claim 1, wherein the said thorium phosphate is having the composition of 60% as Th, 11.5% as P, 2.3% as Na and 24.8 as O and 1% as rare earths.