us 4454097...

8/3/2019 US 4454097 Process.of.Extracting.both.Uranium.and.Radium.from.Uranium-Containing.ores.1982.Nirdosh.baird.banerjee.muthuswami

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United States Patent [191Nirdosh et al.[54] PROCESS OF EXTRACfiNG BOTH

URANIUM AND RADIUM FROMURANIUM-CONTAINING OR ES

[76] Inventors: Inderjit Nirdosh, 494 RyersonCrescent, Thunder Bay, Ontario,Canada, P7C 5R8; Malcolm H.Baird, 139 Old Ancaster Rd.,Dundas, Ontario, Canada, L9H 3R3;Sanjoy Banerjee, 891 Jimeno Rd.,Santa Barbara, Calif. 93103;Sirugamani V. Muthuswami, 111Clydesdale Dr., Willowdale,Ontario, Canada, M2J 3N3[21] Appl. No.: 435,858(22] Filed: Oct. 21, 1982[51] Int. Cl,l ....................... C01G 43/00; COIF 13/00[52] u.s. Cl. 423/8; 423/2;423/10; 423/20; 423/3[58] Field of Search ......................... 423/2, 3, 6, 8, 10,423/18, 20(56] References Cited

U.S. PATENT DOCUMENTS1,142,153 6/1915 Ehler .................................. .. . 423/21,435,180 11/1922 Schlesinger ............................. 423/21,522,040 1/1925 Thews et al. ........................... 423/22,859,094 11/1958 Schmitt eta!. ................... 423/20 X2,894,804 7/1959 Sawyer et al ........................... 423/24,206,182 6/1980 Lafforgue et al. ................. 423/3 X

[11](45]

4,454,097Jun. 12, 1984

OTHER PUBLICATIONSBaird et al., "Reduction of Radionuclide Levels in Uranium Mine Tailings"; in Proceedings of NEA Workshops at Colorado State University, Fort Collins, USA,Oct. 28-30, 1981: Uranium Mill Tailings Management.Primary Examiner-B. R. PadgettAssistant Examiner-Matthew A. ThextonAttorney, Agent, or Firm-Hirons, Rogers & Scott[57] ABSTRACfFerric chloride leaching at temperatures in the range47"-74" C. is found to remove up to 97% of the uraniumfrom ores occurring in the Elliot Lake area of Canada,but radium removal was found to be poor due to theformation of sulphates from the sulphides present in theore. In processes of the invention the sulphides areinitially removed by flotation, when aqueous acidicferric chloride of relatively low concentration, e.g. 0.1M can extract as much as 92% of the radium, givingtailings which are effectively sulphide-free and withradium levels approaching a desired maximum of 24pCi!g. Radium may be removed by adsorption on manganese dioxide and uranium may be removed by liquidextraction with D2EHPA (DAPEX process). The ferric chloride may be recirculated for further leaching,with reduction before the uranium extraction and reoxidation afterwards. Because of the recycle, it is possibleto keep chloride ion levels in the effluent below theprescribed level in Ontario, Canada of 750 ppm.

10 Claims, 6 Drawing Figures

r------------, YELLOW1-----_..,U RECOVERY VIA CONVENTIONAL CAKEH2so 4 LEACHING PROCESSPYRITIC TAILS

FOR DISPOSAL, COVERED WITH CLEAN TAILS, ORRa REMOVAL BY A COMPLEXING AGENT BEFORE DISPOSAL

F ~ C 1r - - - - - - - ~ ~ ~ ~ ~ R ~ E ~ M ~ O ~ V ~ A ~ L j - . - - - - - - - - - - - - ~ - - MAKEUP

. r - - - -Mg OHJ2r - - - -L-L-- - ,


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GROUND ~ - - - L - - - - , ORE

36

30

FIG. 1

1- - - - . . L . . - - - -EFFLUENTS

~ - - - - - - - - - - - - - - - - - - - - ~ YELLOWI .!u RECOVERY VIA C O N V E N T I O N A L ~ H2S04 LEACHING PROCESStPYRITIC TAILS

FOR DISPOSAL, COVERED WITH CLEAN TAILS, ORRa REMOVAL BY A COMPLEXING AGENT BEFORE DISPOSALFeC1 3so4 REMOVAL I .. I "' MAKE UP

41.

MAKE UP~ ~ - - - - - - - - - - - - r . - - - S O L V E N T

Na YELLOW CAKEDISSOLUTION ANDco2- co3 2

cVJ.0::s......

?--000en::r(1)(1).....-.....,0..

..f;:l..

Vl..f;:l.....0\0-. l


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U.S. Patent Jun. 12, 1984 Sheet 2 of 6

' ~ l ~ ; we :1 : : ~ f 6ac :I

7 0 ~ - - ~ - - - - - L - - - - i - - - ~ ~ - - ~ - - - - ~ i=U I O O r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~ z 70 60 ~ - - ~ - - - - - L - - - - i - - - ~ ~ - - ~ - - - - ~

Tl ME (hours)

4,454,097

Dependence of uranium leaching on t ime, temperature and ferr icchloride concentration.

FIG. 2


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U.S. Patent

u0 .

Il l...J

200

Jun. 12, 1984 Sheet 3 of 6

I O O L - - - ~ L - - - ~ - - - - ~ - - - - ~ - - - - ~ - - - - ~ . . . J

::e22000q:a:

I O O O L - - - - J ~ - - ~ - - - - ~ , 2 ~ - - ~ , 6 - - - - ~ 2 ~ 0 ~ - - ~ 2 ~ 4 TIME (hours)

4,454,097

226Dependence of Ra leaching on time, temperature and ferr icchloride concentration.

FIG. 3


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U.S. Patent

0zzLL0z0I -u


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U.S. Patent Jun. 12, 1984 Sheet 5 of 6 4,454,097

>Ewu(/ ' )"'

7 0 0 . - - - - - - - - - - - - - - - - - - - - - - - - - ~

400

200

100

PYRITE FLOAT(74C)

0o 4 8 12

' .NoCI0 3 ADDED(O.Ig/IOOg ORE

28 32TIME (hours)

C h a n g e ~ in e.m.f . during leaching of feed with 0.10 H FeC1 3 in0. 10 H HCl.

0 Pyri te-Float-Tails Pyrite-Float-Concentrate

(Oxidant addition as indicated in th e plots . )

Washed class i f ier overflowX No oxidant added6 NaClo 3 added ini t ia l ly (0.]0 g/100 g feed)v NaClo 3 added in i t ia l ly (0.60 g/100 g feed)0 NaC10 3 added after S.S h (0. 10 g/100 g feed)

FIG. 5


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U.S. Patent Jun. 12, 1984 Sheet 6 of 6 4,454,097100

00::tDC\J Uranium extractionC\J0zlL.. Radium extraction0z01-u


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1 4,454,097PROCESS OF EXTRACTING BOTH URANIUMAND RADIUM FROM URANIUM-CONTAINING

ORES

2Ferric chloride has been proposed hitherto in U.S.Pat. No. 2,894,804 of Sawyer and Handley, in the form

of an aqueous solution thereof, as a leachant for therecovery of uranium and radium values from uraniumFIELD OF THE INVENTION

Th e invention is concerned with improvements in orrelating to processes for extracting both uranium andradium from uranium-containing ores.

5 ores, the preferred process operating at about 75 C. to85 C. with a solution containing from 2 to 15 kilos ofFeCl3.6HzO per kilo (0.03 to 0.45M) of uranium to berecovered. Preferably the process is operated at 85 C.and a concentration of 0.4M. The leachate may be

REVIEW OF THE PRIOR ART 10 treated to recover either uranium or radium first, orboth together, and various sub-processes are proposedfor this purpose. In one specific example with an oreassaying 3-4% uranium the leachate (filtrate) was foundto contain 96.7% of the uranium and 89% of the radiumpresent in the treated ore. Th e origins of the ores treated

Uranium-containing ores always includes other radioactive constituents (radionuclides) such as thorium(230Th) and radium (226Ra) and it is radium that princi- 15pally causes environmental concern, since it tends toconcentrate in the bones of animals and humans. Because of the low concentration of uranium in mosturanium-containing ores (typically 0.1%-1%) theirprocessing involves grinding to a relatively fine state of 20division (typically 40 to 75 microns); the tailings resulting from the processing are correspondingly finely divided and contain the majority of the highly radioactiveradionuclides. Because of their fine division the tailingsmay be leached by surface or ground waters as a result 25of which the radioactive materials may be able to enterthe food consumption chain.This has led to the development of tailings management techniques designed to minimize the spread ofradionuclides into the environment either by water 30seepage or wind action in arid areas. These techniquesinclude special liners (clay, plastics) for the tailingsdams, surface covers for the areas such as asphalt orsoils with vegetation, and special surface configurationsdesigned to promote long-term stability and good drain- 35age of rainwater clear of the tailings.

Fo r the same reasons strict environmental standardshave been set for various possible contaminants in waterand foods, and for their levels in the effiuents of processes. For example, in the Province of Ontario, Canada 40the maximum for radium in drinking water is 3 picocuries per liter (pCi/L), while a suggested acceptablemaximum for such tailings is 25 pCi/g.Radium usually occurs in secular radioactive equilibrium with its precursors and daughters in the radioac- 45tive decay series. Its equilibrium atomic concentra tion isin proportion to its half-life, so that an ore containingonly 0.1% of 238U (half-life: 4.47 X J09 a) would containan equilibrium concentration of 342 pCi/g of 226Ra.Uranium extraction by the conventional methods of 50sulphuric acid or alkaline leaching does not removevery much of this radium, which thus remains in thefinely divided tailings in a more labile form than in theoriginal orebody. This implies that over 90% of theradium must be removed to achieve the sugges ted maxi- 55mum. Aqueous solutions of inorganic salts (mainly chlorides and nitrates) and inorganic acids, and organicchelating agents have been used for such removal, butthe target level can only be reached with the use ofprohibitively expensive quantities of reagents, due to 60the interference from other constituents of the tailings,e.g. calcium and other metals competing for chelatingagents.A number of processes for the extraction of uraniumand/or radium have been proposed involving leaches 65with strong inorganic acids, but such processes poseoperating difficulties because of the corrosiveness of thereagents and their relatively high expense.

in this manner are not mentioned in the specification,but since both inventors apparently were residents ofDenver, Colo., it seem logical to assume that they werefrom the Colorado plateau.Attempts to use an aqueous ferric chloride leachantwith other uranium ores have not been as successful inthe matter of radium removal. Th e effectiveness offerric ion as a leachant is well known for many mineralswhose leaching involves an oxidation step. Fo r example, it promotes the leaching of uranium by oxidation ofthe U(IV) form in the mineral to the more soluble U(VI)form:

(I )

It is understandable that the minimum condition forgood radium removal from ores is good uranium removal, since the radium is a daughter of uranium andtherefore occurs at the same positions in the minerallattice. However, because of the different chemicalproperties of uranium and radium, such as the low solubilities of radium sulphate and carbonate, in contrast tothose of uranyl sulphate and carbonate, a good leachantfor uranium is no t necessarily a good leachant for radium.Another problem resulting from the use of ferricchloride is that environmental regulations set the maximum level of chloride ion in the effluent (irrigationwaters) at 750 ppm, and this is difficult to achieve.

DEFINITION OF THE INVENTIONIt is therefore the principal object of the invention toprovide new processes for the extraction of both uranium and radium from uranium ores using an aqueousferric ch loride leachant.In accordance with the present invention there isprovided a process for the extraction of both uraniumand radium from difficultly-leachable low grade uranium ores using an aqueous ferric chloride leachant in

the presence of an interfering sulphate ion resultingfrom the presence of sulphide therein including thesteps of:(a) mechanically treating the finely ground ore forthe removal of sulphide therefrom;(b) leaching the mechanically treated finely groundore with aqueous acidic ferric chloride solution in aconcentration from 0.5M to 0.2M for the removal ofuranium and radium therefrom to result in a liquid ferricchloride leachate containing radium and uranium and awet cake containing retained ferric chloride with uranium and radium dissolved therein;(c) treating the ferric chloride leachate to separate theuranium and radium therefrom;


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5 4,454,097at a constant L/S ratio of 2. 5 mL/g. Leaching improvesmonotonically with contact time, temperature and fer-ric chloride concentration, with a maximum 97% extraction obtained with 1.0 M FeCI3 at 75 ' C. for 24hours. It may be noted that 60-70% of the final extrac- Stion occurs in the first 15 minutes, even at the lowertemperatures. It will also be noted that both the rate ofextraction and the final extraction value are relativelyunaffected by the concentration of the ferric chloridesolution, and that good results are obtained with con- 10centrations as low as O.lOM and temperatures in the lowrange of 47 ' .C.-74' C., as contrasted with the respectivevalues of 0.40M and 85' C. of Sawyer and Handley.

Th e kinetics of radium leaching under these conditions, as shown in FIG. 3, are therefore quite different 15from that of the corresponding uranium leaching. Th eordinate of FIG. 3 is the radium content of the solidresidue (tails) so that the minima seen in some of thecurves represent maximum values of the percent radiumextraction. Th e average 226Ra in the feed material was 20409 pCi/g and the highest extractions observed wereonly about 67% and these occured at 58' C. after onlyI hour and at 47' C. after about 4 hours, as indicated byarrows. Contrary to normal expectation, as the temper- 25atures and contact times are increased, the trend of mostof the data is towards reduced radium extraction. InFIG. 3 the radium content in the leach residues is plotted rather than the percent radium extraction so as toshow that leach residues with acceptable low radium 30levels (approaching 25 pCi/g) are not obtained in any ofthese tests.

The following explanation for the data in FIG. 3 issuggested. As leaching commences, uranium and radium start to dissolve at approximately the same rate. 35However, the concentrations of Ba2+ and Pb2+ alsobegin to rise because of the dissolution of their respective minerals from the ore; sulphate ions are formed insolutions from the partial oxidation of pyrite (FeS2) andpyrrhotite (FeS) by the ferric chloride. This leads to the 40formation of BaS04 and PbS04 with partial coprecipitation of the radium as the relatively insoluble sulphate.The rate of pyrite oxidation is known to be slow, andthe above mechanism explains the slow reversal of theradium dissolution. Some sulphate ions were also ini- 45tially present in the classifier overflow sample due tosulphates in the water added and due to the oxidation ofsulphides in the preparatory grinding process. However, prewashing of the classifier overflow with distilled water just prior to ferric chloride leaching gave soonly a marginal improvement in radium extraction, andsuch prewashing in a commercial installation is economically not justifiable. This difficulty with radiumdissolution apparently did not arise in the work of Sawyer and Handley, presumably because of the above- ssmentioned fact that the Colorado ores have much lowersulphide contents than those from Elliot Lake.In accordance with this invention the finely groundore material is subjected to a mechanical treatment stepfor the removal therefrom of the interfering sulphide 60minerals, or at least the reduction of the concentrationthereof to an economically reasonable level, i.e. below0.45% by weight. Because of the already finely dividedstate of the ore this mechanical separation step preferably is a mechanical froth flotation, indicated in the flow 65chart of FIG. 1 as sulphide flotation step 10. The material used for experiments in accordance with the invention was the overflow slurry from the rake classifier

6that normally is fed to a thickener and filters fromwhich the usual leach feed is derived.A 10 kg sample of the classifier overflow slurry wascollected and its density was adjusted to give 66 wt% ofsolids. It was then ground in a ball mill for 1 hour,giving solids of 80% less than 46 microns (- 325 meshsize). Flotation was carried out in a Denver flotationmachine with potassium amyl xanthate at a rate of 0.04kg/tonne solids and Dowfroth 250 (Trade Mark) at arate of 0.025 kg/tonne of solids.

Th e sulphide float (pyrite concentrate) constituted7% of the solid mass and contained substantially all ofthe sulphides and about 10% of the uraniuim and radium; the sulphide float tail therefore comprised about93% of the solids fed, and contained about 90% of theuranium and radium. This sulphide float must subsequently be treated for removal of the uranium and radium values to acceptable residual levels, and the radium extraction will be made more difficult because ofthe high concentration of sulphide ion and consequentformation ofsulphates . However, because of the greatlyreduced quantity of material to be treated the use ofmore expensive leaching processes and leachants iseconomically justifiable. It is found that 98% of theuranium content can be leached with a dilute solution offerric sulphate. The radium from this reduced mass maybe removed with a chelating agent.

It will be seen that uranium extraction of 97% fromthe sulphide float tail is slightly better than the value of94% from the classifier overflow. This may be due tothe effect of the pyrite in the classifier overflow in forming Fe2+ ions and lowering the solution e.m.f., whichwill be discussed below.

Th e radium extraction from the washed classifieroverflow shows the same trends as were noted for theunwashed materials (see FIGS. 2 and 3), declining withtime and not exceeding 73% in the best case. The radium extraction is significantly improved when theleaching is applied to the sulphide float tail. The extraction is best at the highest temperature where it improveswith time to a level of 90% after 24 hours. However, itmust be noted that it still is significantly less than the97% extraction of uranium obtained under the sameconditions.FIG. 4 shows the comparison between the uraniumand radium extractions from the washed classifier overflow, and from the sulphide float tail at two temperatures 74 ' C. and 47 ' C. which are the extremes of therange at which this invention has been tested. Uraniumextraction is indicated by solid lines and radium extraction by broken lines respectively. Th e tests were performed at a fixed L/S dratio of 2.5 mL/g and with aleachant consisting of O.OlM FeCl3 in 0.1 M HCL Th epercentage extraction is plotted against time of contact.Experiments to determine the effect of L/S ratio onthe extractions were carried out at a temperature of 74 C., a contact time of I hour and using a leachant consisting of 0.1 M FeCl3 in O.IM HCI. These showed thaturanium extraction is quite insensitive to L/S ratio, butthe inhibiting effect of the sulphides in the classifieroverflow are evident. The radium extraction, on theother hand, is improved as the L/S ratio is increased,particularly in the case of the washed classifier overflow. This is however believed to be due simply to adilution effect which reduces the coprecipitation ofradium sulphate with BaS04, PbS04, etc. The equilibriaof the type


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9 4,454,097REMOVAL OF URANIUM FROM LEA CHANT

This can be effected by a modified form of theDAPEX process as described in "The Extractive Metallurgy of Uranium" by R. C. Merrit t published 1971 by 5the Colorado School of Mines Research Institute atpages 204-205, whereby liquid-liquid extraction is usedto remove uranium from sulphate leach liquors. Theorganic extractant is a solution of 5% by volume di-2-ethyl-hexyl-phosphoric acid (D2EHPA) and 2.5% tri- 10butyl phospha te (TBP) in kerosene. Th e aqueous phasemust first be treated (as at 30) with a reducing agent toconvert a!! the ferric iron to ferrous, thereby preventingthe uptake of iron in the organic phase. Sulphur dioxidewas used as a reducing agent in the present processes, 15but in a practical circuit, the sulphate levels must beminimised so the use of sulphur dioxide is possible onlyif the S042- can be effectively removed from the solution before its recycle. The uranium-loaded organicphase is stripped at 38 with a 10% aqueous solution of 20sodium carbonate, giving a uranyl carbonate solution,from which uranium may be precipitated at 40 as asodium yellow cake by the addition of sodium hydroxide. The sodium yellow cake is relatively difficult tofilter and a magnesium yellow cake is preferred instead. 25However, the precipitation of magnesium yellow cakefrom the carbonate strip solution will inevitably beaccompanied by the simultaneous precipitation of theinsoluble magnesium carbonate. Fo r this reason, thesodium yellow cake slurry is first thickened at 42 and 30the clear overflow is recycled to strip stage 38 for further stripping, after treatment with carbon dioxide andadding the make-up sodium carbonate. The densifiedslurry from thickener 42 is treated with sulphuric acid 35at 44 to dissolve the sodium yellow cake; the acid alsodecomposes the carbonate present and carbon dioxide isevolved in this operation. This acid solution is nowtreated with magnesia at 46 and the magnesium yellowcake is precipitated. This yellow cake is filtered ~ t _48. 40and sent for drying. The filtrate from 48 contammgsome unprccipitated uranium is directed to stage 24 via25 as described above to be treated in the low leveluranium recovery step 24, where it is mixed with thewashings of step 18 and the mine water. . 4 I d n 5Extraction and strippmg resu ts are summanseTable 2.

TABLE2

10TABLE 2-continued

Solvent Extraction and Stripping of Uranium% U stripping: 11.1 99.7 97.4

It may be noted that the uranium concentration canbe increased substantially, both in the extraction andstripping operations, by using small and large organic/aqueous phase ratios respectively.The pyrite concentrate obtained from the sulphideflotation step 10 contains about 10% each of the uranium and radium initially present in the ground ore.This mass constitutes nearly 7 wt% of the ground orefed to the flotation cell at 10. The thickened slurry from24, containing uranium in the hydroxide form, is mixedwith this pyrite concentrate and the solids are leachedwith a dilute solution of ferric sulphate at 50. Afterleaching the leach slurry may be subjected to the sametreatment as for a conventional sulphuric acid leachingprocess for the recovery of the dissolved uranium. Noradium is leached in this operation. The leach residue

from this uranium leaching step is essentially the sulphides (pyrite) present in the ore. I t may be furthertreated with a suitable complexing agent to remove theradium present in it, or it may be stored separately, or itmay be disposed of under a massive cover of the nonsulphidic clean tailings obtained at 20.OTHER TREATMENTS OF LEA CHANT PRIOR

TO RE-USEThe raffinate from the uranium extraction process at32 is an acid ferrous chloride solution and an oxidationstep is required, such as air with oxidising bacteria.A test made on the repeated contact of fresh solids bya single sample of ferric chloride leachant solution

shows the need for the sulphate removal step 32. Initially, 375 mL of a leach solution of O.IOM FeCh andO.lOM HCI was contacted with 150 g of sulphide floattail, for 24 hours at 74" C. After 5 hours of contact,sodium chlorate was added in the ratio 0.1 g per 100 gsolids. The filtrate from this contact was contacted with125 g of fresh sulphide float tail, under the same c ~ n d i tions. Th e procedure was repeated four more timesusing 100, 80, 70 and 60 g of fresh solid feeds. Th e useof these masses ensured that L/S ratio remained thesame at 2.5 mL/g in each contact, making due allowance for the retention of some of the leach liquor on thefilter cake. Hefore each leach stage, a very small amount____ ::o:::.lv.:::e::::n::..t : : E : : : _ x t : : . r a c : : : : : ; t i : : : o n : : . . . . : a n : : d : . . S : ; t : ; r i : ! : p p ~ i : ; ; n g ~ o f : . . . U : . : . : r a : : . : n : ; . : ; i u : ; . : ; m ____ 50 ofNaC103 was added to the leach liquor to maintain the(a) Extraction initial e.m.f. at 650 mV. The results indicate that, whileAqueous feed approximately 0.10 M FeCiz, pH 0.90, 0.362 g U/L. uranium extraction remains in excess of 90% even afterSolvent: 5 vol.% D2EHPA, 2.5 vol. % TBP in odorless six passes of the solution, the radium extraction de-kerosene.Volume of aqueous feed used in each test: 40 mL. creases rapidly. The occurrence of negative percent~ = : : . . . . : : : : . . : : ! : : : : : : : . : : : . . . : : : : : : . . . : : : : : : : . . . . : : ; ~ = : : = . ; . . . . . . . . . ; . . ~ : - - - - E : : : ; - 3 - - 55 radium extractions in passes 4, 5 and 6 denotes thatTest No. El E2 radium is depositing from solution onto the solids inSolvent vol. (mL) ~ . 5 ~ ~ these cases. The conclusion is that sulphate ion build-upAqueous/org. volume ratio Joo 2900 1455 ln the solution is causing this deposition and it must bein extract (ppm) Ju in raffinate (ppm) 33.2 3.3 0.7 removed.: % ~ U ~ e ~ x ~ t r = a c ~ t ~ o ~ n = : _ _ _____ ~ 9 ~ l . : ; . : ; o __ . . . . ; . . 9 ~ 9 . _ I ___ _9_.s_ _ 60 EFFECT OF OXIDANT ON THE LEACHANTb) Strippingu concentration in loaded organic solvent: 955 ppm. The role of ferric ion in uranium leaching is well-Strip solution: 10 mass % aqueous solution of NazC03 known and has been noted in equation ( 1) above. Our-Volume of loaded organic phase used in each test: 20 mL. ing the leaching stage the ferrous ion concentration~ T _ : e s : _ t _ : : N : : ; : o : : _ - - - - - - - - - : S - : 1 - - - - : S ; - : 2 ~ - - ; - ; : S : - : ; ; - _ 65 must be kept as low as possible and it is common prac-Strip Solo. (mL) 2.5 5.0 10.3 tice to add an oxidant such as sodium chlorate to theOrg./aqueous volume ratio 8 4 2 leach for this purpose. It is found that the effect. ofu in loaded aq. (ppm) 900 4000 1795 sodium chlorate on uranium extraction is benefictal,U in stripped organic (ppm) 890 31 23.9


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4,454,09711~ v e n in the case of sulphide float tails. However, the~ f f e c t of chlorate is sharply negative as far as radium~ x t r a c t i o n from classifier overflow is concerned, due to~ n h a n c e d formation of sulphate from the pyrite.

The e.m.f. of the leach solution (versus standard calo- 5lllel electrode) is a measure of oxidising power, andjepends mainly on the ratio of [Fe3+ ]/[Fe2+] in theleach solution.

Curves 2 through 5 in FIG. 5 refer to leaches ofwashed classifier overflow and show a gradual decline, 10rndicating reduction of Fe3+ to Fe2+. Th e decline isreversed (curve 3) when sodium chlorate is added, bu tresumes eventually. Sulphide float tails (curve I) show::mly a small decline, bu t again, an improvement in e.m.f.IS given by sodium chlorate addition. Th e sulphide float 15~ o n c e n t r a t e leach (curve 6) shows the greatest declinein e.m.f., as ma y be expected from the high pyrite levelspreset in the solid phase. Chlorate addition has a prorlOunced bu t short-lived beneficial effect. The indicationis that effective uranium extraction from the concen- 20trate can only be achieved with substantial additions of)xidant.

12for leaching and the mechanisms by which the radium isretained on the solids.We claim:1. A process for the extraction of both uranium andradium from difficultly-leachable low grade uraniumores in the presence of an an interfering sulphate ion

resulting from the presence of sulphide therein by use ofan aqueous ferric chloride leachant including the stepsof:(a) mechanically treating the finely ground ore for

the removal of sulphide therefrom;(b) leaching the mechanically treated finely groundore with aqueous acidic ferric chloride solution in aconcentration from 0.05M to 0.2M for the removalof uranium and radium therefrom to result in aliquid ferric chloride leachate containing radiumand uranium and a wet cake containing retainedferric chloride with uranium and radium dissolvedtherein;(c) treating the ferric chloride leachate to separate theuranium and radium therefrom;(d) separately treating the wet cake for removal ofretained ferric chloride and the dissolved uraniumand radium therefrom; and(e) recycling the ferric chloride leachate from step (c)for the leaching of more of the mechanicallytreated finely ground ore.

A leach with 0. IM FeCI3 and 0. IM HCI for I hour at74 ' C. gave 74% uranium extraction with the initialaddition of 4 g NaCI03 per 100 g of solids. Radium 25~ x t r a c t i o n under these conditions was negligible, due toexcessive sulphate formation. 2. A process as claimed in claim 1, wherein the saidacidic solution is in hydrochloric acid of concentration

30 0.05M to 0.2M and equal to the concentration of theferric chloride.

FIG. 6 shows how the extractions of uranium andradium are affected by the concentration of ferric ion inthe initial leachant. Th e leachant has a pH of 1.0 andincludes 0.1 g NaCI03 per 100 g as oxidant. The L/Sratio is 2.5 mL/g and the temperature employed is 74 'C. Th e curve for uranium extraction resembles an ad>orption isotherm, suggesting that Fe3+ ions undergo:tdsorption before oxidising U(IV) to U(VI) at the min~ r a l surface. Th e curves show that ferric chloride con:entrations above 0.2M are unnecessary with the pro:esses of the invention.

3. A process as claimed in claim 1 or 2, wherein thesulphide is in the form of the minerals pyrite and pyrrhotite and the mechanical treatment consists of nota-

35 tion removal thereof.

RELATIONSHIP BETWEEN RESIDUAL U AND 4QRA CONCENTRATIONSAs noted above the concept of secular equilibriumleads to a constant ratio between uranium and radium:.:oncentrations in ores. If the percentage extractions ofuranium and radium in a leaching process were the 45>arne, this ratio of concentrations would remain in the>olid residue.In the case of sulphide float tails, radium is extracted

!!most, but not quite as effectively as uranium. I f theresidual concentrations of radium are plotted against 50the corresponding residual uranium concentrations fora variety of conditions (temperature, time, leachant~ o n c e n t r a t i o n ) , it is found that the data can be fitted:tuite well by a straight line plot. Regression analysis ofthe data points gives the following relationship: 55

Ra assay in leach residue (pCi/g) =20.7+0.34XUassay in leach resudue (ug/g) (4)The slope (0.34) of the experimental plot is the same 60

lS that predicted from th e half-lives of 238U and 226Ra1ssuming (i ) initial secular equilibrium an d (ii) that the:wo elements are leached to an equal extent, bu t thisJTedicted line passes through the origin. This calcula:ion also indicates that 20.7 pCi!g of 226Ra would re- 65nain in the leach residue even after all the uranium iseached from the ore. This level of 20.7 pCi/g is deternined by the type of solids treated, th e reagents used

4. A process as claimed in claim 1 or 2, wherein theacidic ferric chloride leachant solution is used inamounts to give an effective liquid to solid ratio of fromI to 2.5 mL/g of ore.5. A process as claimed in claim 1 or 2, wherein th esaid wet cake is washed separately with an acidic solution of hydrochloric acid so as to maintain a pH about2.5 during washing.6. A process as claimed in claim 1 or 2, wherein theradium is separated by adsorption thereof by an adsorbent.7. A process as claimed in claim 1 or 2, wherein th euranium is separated by liquid-liquid extraction with anorganic solvent.8. A process as claimed in claim 1 or 2, wherein theferric chloride leachate is treated to remove radium,subsequently is reduced to convert ferric ion to ferrousion, the uranium therein is removed by liquid-liquidextaction with an organic solvent, and the ferrous chloride solution is then oxidised to convert the ferrous ionto ferric ion for reuse thereof.

9. A process as claimed in claim 1 or 2, wherein theferric chloride leachate is treated to remove radium,subsequently is reduced to convert ferric ion to ferrousion, the uranium therein is removed by liquid-liquidextraction with an organic solvent, and the ferrous chloride solution is then oxidised to convert the ferrous ionto ferric ion for reuse thereof, and including the step ofremoving sulphate from the ferric chloride solutionsubsequent to its oxidation and prior to its reuse as aleaching agent.10. A process as claimed in claim 1 or 2, wherein thesaid ferric chloride leachate containing radium and


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4,454,09713uranium constitutes about 80% the original ferric chloride leach solution and is recycled for releaching, theremainder of the original ferric chloride leach solutionis retained by the wet cake, the wet cake is washed toremove the remainder of the ferric chloride leach solu- 5

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14tion and the dissolved uranium and radium therefrom,and the washing liquid from the wash of the wet cakeconstitutes a bleed stream for removal of unwantedleached components.* * * * *

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