The processing of Uranium Ore from  Jaduguda,  Bhatin and

Narwapahar and Uranium concentrates from Surda, Rakha and

Mosaboni copper  concentrator  plant  tailings to produce mangesium Di-uranate commonly known as  yellow cake invol-ves different stages and needs to be analysed for its U308 content. The methods used for  the analysis depends on the uranium content in the sample

Pandey, V M

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ANALYSIS OF URANIUMIN THE URANIUM ORES OF INDIAV. M. PANDEY'The processing of Uranium Ore from Jaduguda, Bhatin andNarwapahar and Uranium concentrates from Surda, Rakha andMosaboni copper concentrator plant tailings to produce mangesium1)i-uranate commonly known as yellow cake involves different stagesand needs to be analysed for its U308 content. The methods used forthe analysis depends on the uranium content in the sample. Themethods generally used are :(i) Radiometric Assay and Chemical Assay for feed samplei.e. upto grinding section(ii) Colorimetric Method(iii) Fluorimetric for ion exchange barren and tailings(iv) By titrimetric method with K2Cr2O7 for final producti.e. yellow cake(v) Emission spectrometry for all types of samplesThe brief description of different methods adopted are as follows:(i) Radiometric Method : Generally Beta and Gamma counters areused for radiometric assay of the sample. The counting methods aregenerally used for the quick determination of the sample where ap-proximate assessment is required. But before using the countingmethod it should be ensured that the ore samples are in radiometricequilibrium otherwise this method of analysis will be of little use. Thismethod cannot be used for accoutability purposes.'Superintendent-Control, Research & Development, Urantum Corporation of India Ltd.,Jaduguda Mines, Singhblwm, BiharXI-1Beta Activity Measurement : Beta activity of the sample is meas-ured byGeiger Muller Counter. The Geiger counting Tube consists ofessentially two electrodes one usually a fine wire and the other con-centric metal cylinder of about an inch diameter. The space betweentwo electrodes is filled with a suitable gaseous mixture (usually Ar-gon and ethyl alcohol) at a few cros. pressure and a potential ofabout 1000 V is applied across the electrodes. The voltage and thegas pressure are so adjusted that in the absence of ions in the gasno discharge take place. A Beta particle passing through the tube andproducing one or more ion pairs initiates a cascade of ionisation. Acomparatively large surge of current results. The electronic quench-ing circuit to which the tube is attached is designed so that after avery short period of current flow about (10-4 to 10.5 seconds) thecurrent is interrupted and the tube is re-charged to enable it todetect another particle. The pulse is amplified and sealed down bya scaling circuit to allow high counting rates to be handled bymechanical recorder.Gama-Activity Measurement : Since Gamma rays are not chargedparticles, they are not detectable directly by ordinary counting devices.Instead electrons ejected from matter by the passage of highlypenetrating gamma rays can cause ionisation, which is then detected.The ordinary Geiger tube may be used to detect gamma - radiationin the presence of beta activity if a suitable absorber, such as metalplate, is interposed between the tube and the sample to filter out beta- particles. The intensity of gamma radiation is slightly diminished,and the electrons ejected from the absorber and tube walls arecounted, the value given being proportional to gamma activity.Ionisation chambers, particularly when filled with gas under pressure,are also used for determining gamma-activity.N.B: Most experiments with radio active indicators involve thecomparison of a control sample with an unknown.XI-22. Colorimetric Method(a) Determination of Uranium in samples Free from interferingElements with Peroxide in Alkaline MediumRegents : (i) Standard U,,08 solution 1 mg/ml(ii) Sodium hydroxide 50% solution (w/v)(iii) Hydrogen peroxide 20% solution (v/v)Take suitable standard in the range of 1-2 mg/ml and samplesolution for determination and blank. Add 5 ml of 50% NaOH andmix well. Add 1 ml of 20% H2O2 and make up the volume of solu-tion to 50 ml with distilled water and keep for 15 minutes and filterthrough double No.40 filter paper. Measure the optical density of thesample solution thus prepared against standard and blank solutionprepared in a similar manner. Measure optical density at 380 mµ Ina spectrophotometer.Extraction of Uranium as Nitrate with TBP followed by Colori-metric Determination with Peroxide in Alkaline Medium : Thismethod is followed in UCIL generally for all the uranium ore and so-lution samples containing uranium with interfering elements etc.Reagents:(i) T.B.P. 10% solution in distilled kerosene (v/v)(ii) Ferric nitrate - 5% solution(iii) Ammonium Nitrate saturated solution(iv) Sodium sulphate 5% solution (w/v)(v) Hydrogen Peroxide 20% solution (v/v)(vi) Sodium hydroxide 50% solution (w/v)(vii) Standard uranium solution 1 mg U3O8/mlXI-3Opening of the Ore and Extraction with TBP : 5.0 g of the ore isboiled with 50 ml (1:1) HNO3 for 3-4 hours. In some ore hydroflu-oric acid treatment is needed before addition of HNO3. Filter and washproperly. Evaporate the filtrate to dryness. Cool and add 5 ml of5% Ferric nitrate solution. Extract the uranium from the nitrate so-lution with 50 ml of 10% TBP in kerosene in a 100 ml separatingfunnel and shake well for 10 minutes. Allow the layer to separate.Rundown the lower layer and reject It. Add 10 ml of saturatedammonium nitrate solution and shake for two minutes. Allow thelayers to separate. Run down the lower layer and reject. Repeat thewashing with ammonium nitrate solution.Back Extraction of Uranium : Add 10 ml of sodium sulphatesolution and shake well for 5 to 7 minutes. Allow the layer toseparate. Run down the lower layer containing the uranium in to aclear 100 ml beaker. Repeat the back extraction with sodiumsulphate solution twice and collect the aqueous layer in the samebeaker.Extraction for blank and standard to be proceeded in thesimilar manner.Colorimetric determination should be carried with 50% NaOH andH2O2 as described earlier.Spectrophotometric Determination of Uranium in Sulphuric AcidLeach solution : Uranium is separated from contaminants bysolvent extraction from aluminium nitrate solution using ethylacetate. Colour is developed by introducing an aliquot of the extractinto an acetone pyridine solution of dibenzoyl methane. The absor-bance of the coloured solution is measured using a spectrophotome-ter at 390 mµ. This method is applicable for low concentration ofuranium. The lowest range is about l0µ g U3O8 in 10 ml of finalcoloured solution. The optimum range for the leach solutions is 0.1to 1.0 g/ l U3O8.XI -4Reagents :(i) Standard U308 solution 0.1 mg/ml(ii) Saturated aluminium nitrate 50%(iii) Ethyl acetate analar(iv) Dibenzoyi methane solution - Prepare 1% solution ofdibenzoyl methane in pure distilled acetone(v) Chromogenic Reagent : To 40 ml of the dibenzoyl methanesolution add 100 nil of analar grade pyridine, followed by800 nil of pure distilled acetone. Dilute this solution to1000 ml with distilled waterProcedure : Pipette out a suitable volume of leach liquor not exceed-ing 2 ml to contain between 0.05 nig and 0.50 mg U308 into 30 nilstoppered test-tubes. Add dilute ammonia dropwise till the precipita-tion of metal ions just begin. Add 5 ml saturated aluminium nitratesolution and mix thoroughly. Accurately pipette 10.0 ml of ethyl ace-tate into the test tube and shake for 2 minutes. Allow the phase toseparate. With a dry pipette carefully introduce 1 ml of organic phaseinto 10 ml volumetric flask. Fill the volume upto the mark with thechromogenic reagents, mix and keep aside for 15 minutes and meas-ure the absorbance. Treat blank and standard in the similar man-ner.3, Fluorimetric Determination of UraniumFluorimetric determination of uranium in solutions has been inuse right from the days of Manhattan Project in USA. It is one ofthe most sensitive wet chemical method available for this purpose. Itinvolves the separation of uranium from the sample solution byextraction with ethyl acetate in presence of saturated solution ofaluminium nitrate which acts as a salting out reagent.After extrac-tion an aliquot (0.1 nil) of the extract is pipetted into platinum dishspecially made for fluorinietric work and the solvent is evaporatedunder infrared lamp.The residue is fused with about 0.4gm of sodiumXI-5fluoride and sodium carbonate flux at a temperature of about 800°Cfor 3 minutes using muffle furnace. The melt is cooled and the fluo-resence of the resultant bead is measured using Galvanek Marrisionreflectance fluorinleter. Using a set of standards containing knownamount of uranium, a calibration graph is obtained. Minimum andmaximum range of estimation are 0.01 µg - 1 µg.Reagent :(i) Sodium carbonate - sodium fluoride flux (4:1)(ii) Ethyl acetate(iii) Standard Uranium solution 10 Vg U110" /1111Modified fluorimetric method : Periodically, the analytical methodsused in the laboratory are being reviewed with the aim of either im-proving the efficiency or reducing the cost and time of analysis. Whilereviewing the fluorimetric method a fresh approach has been madeby substituting the solvent itself. While using ethyl acetate, extrac-tion is done in the nitrate medium. Since most of our samples arein sulphuric acid medium it was thought to use a solvent whichextract uranium in sulphate medium itself. Currently tetiary aminehas got wide application in uranium industry. Alamine-336 was foundvery selective extractant for quantitative extraction of uranium.The same solvent was selected for fluorimetric determination ofuranium. Other procedure is same as described in ethyl actateextraction system.Reagent:(i) 1% alaniine-336 (v/v) in benzene(ii) H2SO4 solution of 1.5 pH(iii) Sodium carbonate - sodium fluoride flux (4:1)(iv) Standard uranium solution 10 pg/ml.XI-6Uranium is extracted from the aqueous solution by 1.0 percentsolution of Alamine-336 in Benzene. An aliquot of the extract isevaporated and the residue fused with fluoride carbonate flux as usualas described above. Generally the old fluorimetric method has beenused for the samples containing low U308 i.e. generally below 0.02%but using Alamine extraction in sulphate medium even our feedsamples containing 0.04% to 0.10% U308 has been analysed and theresults have been compared with colorimetric method of analysis. Thedaily feed samples of one month have been compared and the resultsare given in Table-ITable - IComparison of Analysis of feed samples of September 1993 byFluorimetric and Colorimetric MethodSampleNo. Flttorit1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.010 0.011 0.012 0.013 0.0.,OR Sample % U 0 8netry Colorimetry No. Fluorimetry Colorimetry70 0.072 14 0.049 0.05071 0.071 15 0.059 0.05839 0.070 16 0.057 0.05874 0.076 17 0.063 0.06272 0.075 18 0.056 0.05539 0.068 19 0.057 0.05636 0.069 20 0.050 0.05334 0.064 21 0.054 0.05856 0.056 22 0.052 0.05431 0.062 23 0.046 0.04558 0.061 24 0.050 0.04758 0.061 25 0.069 0.7035 0.067XI-7Titrimetric Determination of Uranium in the final productThe determination of uranium in yellow cake and other U-richmaterials must often be carried out with a precision higher than thatobtainable by fluorimetric, spectrophotome tric or polarographic meth-ods and in such cases titrametric methods are almost invariably used.Although precipitation and complexometric titration method havebeen proposed for the determination of U (Kolthoff and Elving 1962),only redox methods are useful in practice. The most popular of themare those that use zinc or lead column for reduction of U6 to U4, fol-lowed by titration of U4 with standard K2Cr2O7. The disadvantage ofthese methods is that metallic reductants such as Zn, Pb, Bi will alsoreduce ions other than U6 and causes error in uranium determina-tion. For this reason, a preliminary separation of uranium by chro-motography, ion-exchange or solvent extrction has to be carried out.In 1964 Davies and Gray published a titrimetric method of Uwhich does not require column reductors , electronic instruments oran inert atmosphere , and is sufficiently selective to eanable uraniumto be determined without prior separation . This method involves thereduction of U6 to U4 by ferrous sulphate in concentrated H3PO4 me-diLini. The excess lac'' is then selectively oxidised by I-INO3 usingmolybdenum catalyst after addition of sulphuric acid and dilution withwater . The U4 is titrated with standard K2Cr2O7. using bariumdiphenyl amine sulphonate indicator.Reagents :(i) Sulphuric acid 1.5 M : Dissolve 150 g of sulphamic acidin one litre of cold water(ii) Phosphoric acid concentratedXI-8i(iii) Ferrous sulphate 1.0 M: Add 100 nil of conc.H2SO4 to 750nil water slowly, with stirring. Add 280 g of ferrous sulphateheptahydrate to the hot solution and stirr till dissolved. Cool,dilute to 1 litre with water and mix. Ferrous sulphate hex-ahydrate (395 g) may be substituted for ferrous sulphate.(iv) Nitric acid 4 M sulphamic Acid 0.1 M reagents: Dilute 250nil of conc. IINO,i (sp.gr. 1.42) to 930 ml. with water. Add70 nil of 1.5 M sulphamic acid and mix well.(v) Ammonium inolvbdate 1%%(vi) Sulphuric Acid - Reagent grade only(vii) Barium diplenyl amine sulphonate 0.04% - Dissolve 0.2 gof barium diphenyl amine sulphonate in 200 nil of boilingwater. Cool and dilute to 500 nil(viii) Standard K2Cr2O7. : 0.05 NProcedure :Transfer an aliquot of sample solution (less than 15 ml) containingupto 300 mg of U to a 500 ml conical flaskSample volume must not exceed 15 ml, and should contain nitrateequivalent to 0.25 - 3.0 nil of 15 M, HNO3Optimum quantity of uranium is 150 - 200 mgIf the sample is likely to contain Mo, total nitrate in sample aliquotshould not exceed the equivalent of 0.5 ml of 15 M HNO3.Add 5 nil of 1.5 M sulphamic acid, 40 ml. concentrated phosphoricacid, 5 nil 1.0 M ferrous sulphate 5 nil. of "4 M HNO3/0.1 M sul-phamic acid reagent' and 2 ml of 1% ammonium molybdate solutionin the order given, stirr well after each addition.Wait until the dark brown colour which is produced in the solutionhas disappeared and a pale green colour is produced , then allow thesolution to standard for a further 3 minutes.XI-9The 3 min. standing time is important for high precision results, andshould be timed with a stop clock.Except for the 3 min . waiting time, the procedure once started, shouldbe carried through without delay.Add 25 ml of 9 M H2SO4. 200 ml cold water and 2 ml of 0.04% bar-ium diphenyl amine sulphonate solution in order given, mixing aftereach addition.Within 10 min. of adding water, titrate with N/20 K2Cr2O7 solutionuntill the intense violet colour which lasts at least for one min. with-out fading.The one min. fading time of the indicator is conveniently timed withstop clock.Determine a blank by applying the procedure to a sample consistingof 10 ml of water plus 0.5 ml of 15 M HNO3. The blank value of0.05 to 0.15 of N/20 dichromate is substrated from the titre.Uranium (ing) in sample aliquot = Net titre X 5.951As U308 = Net titre X 7.01784Emission Spectrometry : LABTAM ICP Plasma Scan was used fordetermination of uraniumReagents :(i) Standard UO8 - NBS. USA(ii) Nitric Acid, AR BDFI(iii) Triton X-200, Sigma Chemical USAStandard U3O8 Solution : Take 1.0 gm pure U3O8 standard samplein a 500 ml beaker. Add 20 ml con. HNO3 and 100 ml of distilledwater. Boil to dissolve completely, cool and make up the volume to1000 nil.XI-10Standard Ore Sample : Take 5 gms. of standard ore sample in a400 ml beaker. Add 10 ml cone. HNO3 and 100 ml of distilled water.Boil for 3 to 4 hours. Filter through No.41 filter paper and wash theresidue with 1:99) hot acidified (HNO3) water. Cool and make up thevolume to 250 ml.Different standard ore samples were analysed in ICP at differentrecommended wavelengths and the results were compared with chemi-cal analysis. The values obtained in ICP and by chemical analysisat different wavelength are given in Table-II.Table - IIAnalysis of Standard Uranium Ores in ICP atDifferent WavelengthsWavelength Actual U308 Measured % U308nm concn.ppm U308 Cone.ppm% U308 ICP chemical385.958 13.80 13.78 0.069 0.06911.20 11.26 0.056 0.05610.00 16.87 0.084 0.050409.014 13.80 13.82 0.069 0.06911.20 11.26 0.056 0.05610.00 10.05 0.050 0.050427.167 13.80 9.97 0.050 0.06911.20 8.86 0.044 0.05610.00 7.60 0.038 0.050385.466 13.80 13.53 0.068 0.06911.20 10.64 0.053 0.05610.00 9.42 0.047 0.050XI-11Both standard samples of Jaduguda ore were of same matrices,whereas the uranium Table concentrate of Surda was of differentmatrix.The results in the table No.II show that although the Surda,Uranium Table Concentrate was having a different matrix (containingapproximately 30% Magnetite) than the other two samples of JadugudaOre, it didn't have any effect at 409.014 nm in respect to the accu-racy of the uranium analysis. Although spectral line 385.958 nm wasbetter line for uranium analysis due to this higher SBR upto 1000ppm of Fe content, but when ion was higher than 1000 ppm thespectral line of Fe 385.991 nin interfered at this wave length and gavehigher result. That was why we had chosen the line 409.014 nm,where there was no interference of iron spectral lines in the analysisof uranium ores and Table concentrates. Hundreds of Uranium Oresand other samples of Uranium were analysed for U3O8 content andthe method has now become a routine one for U3O8 estimations Inplace of chemical analysis which was more time consuming. How-ever it had been observed that precision and accuracy of analysis wasbetter in case of lower range of Uranium content, say between 0.5ppm to 150 ppm but above 150 ppm the percent error was more thanthe maximum permissible limit of 0.3%. This was observed in caseof Uranium concentrates which might be due to series of dilution.Some of the uranium ores and concentrates of different gradeswere analysed in ICP at 409.014 nm and results were compared withits chemical analysis and are given in Table-III.Table-IIIComparison of Chemical and ICP-AES Analysis ofDifferent Ores and ConcentratesSample Code1. Jaduguda Ore2. Bhatin Ore3. Jajwal OreChemical Assay ICP-AES AssayU308 U3080.06 0.0680.60 0.0610.064 0.0640.78 0.0770.054 0.0530.270 0.2710.043 0.0410.045 0.0450.050 0.0490.030 0.0300.38 0.0390.050 0.0510.051 0.0510.047 0.0490.052 0.0510.048 0.0474. Rakha Urauluni Table 0.052 0.052Conc. 0.053 0.0540.055 0.0560.060 0.0610.073 0.0725. Surda Uranium Tableconc.6. Magnesium Diuranate0.075 0.0770.063 0.0620.098 0.1000.080 0.0820.078 0.07768.81 69.3268.12 68.40XI-13Interferences:The effect of interference In Uranium analysis by ICP-AES werestudied and it was found that the presence of Fe, Al, Ca, Mg, SI,Cu, Ni, Mo, Na, K, P, S and Mn has no effect on accuracy in theconcentration range given in Table-IVTable-IVElement Conccntration/ppinFe 1000Al 100Ca 100Mg 100Si 100Cu 100Ni 100Mo 50Na 1000K 50P 100S 100M n 100ACKNOWLEDGEMENTSThe author of the paper are extremely grateful to the Chairman& Managing Director of tICII, for his keen interest in the working ofthe Department and allowing us to purchase the Plasma EmissionSpectrometer.XI-14

Analysis of Uranium in the Uranium Ores of India

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Analysis of Uranium in the Uranium Ores of India

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