CA1065122A - Recovery of fluorine, uranium and rare earth metal values from phosphoric acid waste liquors - Google Patents
Recovery of fluorine, uranium and rare earth metal values from phosphoric acid waste liquorsInfo
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- CA1065122A CA1065122A CA241,022A CA241022A CA1065122A CA 1065122 A CA1065122 A CA 1065122A CA 241022 A CA241022 A CA 241022A CA 1065122 A CA1065122 A CA 1065122A
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Abstract
ABSTRACT OF THE DISCLOSURE
A method for recovering substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from brine raffinate obtained as by-product in the production of phosphoric acid by the hydrochloric acid decomposition of tricalcium phosphate minerals. A basically reacting compound is added to the brine raffinate to effect a pH of at least about 9, whereby fluorine, uranium and rare earth metal values are simultaneously precipitated therefrom. These values may then be separately recovered from the precipitate by known processes.
A method for recovering substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from brine raffinate obtained as by-product in the production of phosphoric acid by the hydrochloric acid decomposition of tricalcium phosphate minerals. A basically reacting compound is added to the brine raffinate to effect a pH of at least about 9, whereby fluorine, uranium and rare earth metal values are simultaneously precipitated therefrom. These values may then be separately recovered from the precipitate by known processes.
Description
~o65~z2 RECOVERY OF FLUORINE, URANIUM AND RARE EARTH
METAL VALUES FROM PHOSPHORIC ACID WASTE LIQUORS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
:.
Thls lnventlon relates to the recovery of fluorlne, uranlum and rare earth metal values from waste llquors produced as a by-product ln the production of phosphorlc acid by the hydrochlorlc acld decomposition of tricalclum phosphate mlnerals.
DESCRIPTION OF THE PRIOR ART
The production of phosphoric acid by the hydrochloric acid decomposition of tricalcium phosphate minerals is well known in the prior art. In such a process, of which U.S. Patent
METAL VALUES FROM PHOSPHORIC ACID WASTE LIQUORS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
:.
Thls lnventlon relates to the recovery of fluorlne, uranlum and rare earth metal values from waste llquors produced as a by-product ln the production of phosphorlc acid by the hydrochlorlc acld decomposition of tricalclum phosphate mlnerals.
DESCRIPTION OF THE PRIOR ART
The production of phosphoric acid by the hydrochloric acid decomposition of tricalcium phosphate minerals is well known in the prior art. In such a process, of which U.S. Patent
2,880,063 (issued ln 1959 to Banlel et al.) and U.S. Patent
3,311,450 (issued in 1967 to Alon et al.) are typical, a tri-calclum phosphate mineral ls dlgested wlth hydrochlorlc acld to ~orm a dlge~t solution which is ~iltered to remove insolubles containlng calcium fluorlde and most of the silica from the tricalcium phosphate mlneral, thereby produclng a flltrate termed the aqu00us acidulate liquor, whlch contalns CaC12, HCl and H3P04 in addition to fluorine, uranium and ~are earth metal values present in the trlcalcium phosphate mlneral treated. The acidulate llquor ls contacted wlth a suitable organlc solvent to extPact H3P04 into the organic phase, which is subsequently separated from the aqueous phase and treated to recover phosphoric acid therefrom. During the extractlon operation, some additional HCl is introduced to maintaln a concentration of about 2 weight percent HCl in the aqueous phase throughout the extraction to improve the efficiency of phosphoric acid transfer into the organic solvent.
The aqueous phase obtained following this separation, termed the "brine ra~finate",contains essentially all of the fluorine and rare earth metal values and a portion of the uranium .
values initially present in the acidulate liquor. Mos~ uranium, however, remains ln the oreanic phase containing the H3PO4 and must be recovered therefrom subsequent to the extraction step -reclted above.
Discarding the brine rarfinate thereby produced represents a slgni~lcant loss of valuable rluorlne, uranlum and rare earth metal values. Uranium values, for example, upon recovery, concentration and purification are useful in serving as fuel for atomic reactors. Due to the large tonnages of tricalclum phosphate minerals which are annually produced by industry to obtain phosphoric acid, even the small concen-trations of fluorine, uranium and rare earth metal values which are contained in these minerals represent a substantial source of these valuable elements in the aggregate.
SUMMARY OF THE INVENTION
Accordin~ to the present inventlon, substantially all of the fluorlne and uranium values and at least 90 percent ~`
of the rare earth metal values are recovered from tricalcium phosphate minerals by a process which comprises digesting the mineral with hydrochloric acid to form (1) a digest solution containing fluorine, uranium and rare earth metal values and (2) an insoluble residue, separating said insoluble residue from said solution, thereby producing an aqueous acidulate liquor containing fluorine, uranium and rare earth metal values, contacting said liquor with an organic solvent capable of dissolving phosphoric acid but having limited miscibility with water free of phosphoric acid to extract phosphoric acid from said liquor into the organic phase, separatlng said organic phase from the aqueous phase for subsequent removal of phosphoric acid from said organic phase, admixinK a basically reacting compound with said separated aqueous phase to effect a pH of at least about 9, thereby forming a basic solutlon 1065~22 and precipitated solids containing ~luorine, uranium and rare ~`
earth ~etal values, separating the precipitated solids from the basic solution and recovering the fluorine, uranium and rare earth metal values from the separated solids.
In the process of the present invention, substantially all of the fluorlne and uranium values and at least 90 percent of the rare earth metal values are surprisingly and advantageously coprecipitated by the addition to the brine raffinate of a basically reacting compound in an amount sufficient to effect a pH of at least about 9, and preferably about 9 to 11, in the raffinate. In addition, precipitation of uranium values from the brine raffinate has been found not to be dependent on whether the uranlum values present in the brine raffinate are in the hexavalent or tetravalent state. The present invention provides an efficient and economic recovery of valuable fluorine and ~;
uranium values and, most slgniflcantly, provides an efficient and economic recovery of the much more valuable rare earth metal values from trlcalclum phosphate mlnerals, thus avoldlng the economic penalty of discarding waste liquors produced as by-products from the production of phosphoric acid.
In addition, lt has been found that from about 40 to 5Q% of the fluorine values initially present in the trl-calcium phosphate mineral either remain in the insoluble residue as calcium fluoride following the hydrochloric acid digestion or are volatilized from the dlgest solution during digestion. In accordance with a specific embodiment of the present invention, the portion of the fluorine values present in the tricalcium phosphate mineral which transfers into and remains in the digest solution and which, therefore, transfers 3 to the aqueous acidulate llquor and is recovered by the process of the present invention, may be signlficantly increased by providing in the digest solution an aluminum-containing compound ; 3 -- 106SlZ2 which is soluble in the digest solution. Further, the amount of fluorine values volatilized and thus lost during digestion may be decreased by employing a digestion temperature of not greater than about 110C., preferably about 90 to 100C.
BRIEF DESCRIPTION OF THE DRAWING
Tha accompanying figure is a schematic diagram of the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The term "tricalcium phosphate mineral" as used herein is meant to include any mineral, such as phosphate rock (e.g., apatite) which contains tricalcium phosphate and small amounts of fluorine, uranium and rare earth metal values and which reacts with hydrochloric acid to form phosphoric acid.
Typical of such minerals are phosphate rock, apatite and phosphorite. If phosphate rock is used, it may be either calcined or uncalcined rock.
The tricalcium phosphate minerals treated by the process of the present invention generally contain from about 2 to 4 weight percent fluorine, 50 to 300 ppm uranium and 100 to 1,000 ppm rare earth metals, measured as the respective elements. The mineral generally contains fluorine values in the form of Ca5(PO4)3F, and rare earth metals in the form of oxides, fluorides or phosphates. Typical of rare earth metals which may be present are yttrium, lanthanum, cerium and small amounts of gadolinum, ytterbium, europium, samarium and praseodymium. While the form which uranium takes in tricalcium phosphate minerals has not been precisely determined, uranium is generally thought to be present in both the hexavalent and tetravalent states in the form of calcium uranate or uranyl phosphate (U+6) and calcium uranous fluoride or uranous phosphate (U~4). Tricalcium phosphate minerals typically also contain from about 0.8 to 1.3 weight percent aluminum values as ~0651ZZ
A12O3, 0.8 to 1.5 weight percent iron values as Fe2O3; 7.0 to 9.0 weight percent silicon values as SiO2, 0.1 to 0.5 weight percent Na2O, 0.1 to 0.5 weight percent K2O, 0.2 to 1.0 weight percent sulfur values as SO3, and 3.0 to 7.0 weight percent volati:Le matter (i.e., water, organic carbon, carbonate carbon and nitrogen).
A typical tricalcium phosphate mineral which may be treated by the process of the present invention contains:
Ca values (as CaO) 45 weight percent P values (as P2O5) 32 " "
F values (as elemental F) 3.5 " "
SiO2 8.0 " "
A123 1.0 " "
Fe2o3 1.3 " "
U values (as elemental U)200 ppm Yttrium values (as elemental ~) 300 ppm Lanthanum values ~as elemental La) 70 ppm Cerium valuess (as elemental Ce) 30 ppm Up to about 100 ppm (as the elemental metals) of other rare earths may also be present. These include gadolinium, ytterbium, samarium, praseodymium, dysprosium, europium, lutetium, erbium and thulium. Such minerals also typically contain organic matter, as well as moisture. However, tricalcium phosphate minerals differing very considerably from that indicated either in composition or relative concentrations of components may also be satisfactorily processed.
In the process of the present invention, while any concentration of hydrochloric acid may be employed to digest the tricalcium phosphate mineral, it is preferred to employ an aqueous solution of hydrochloric acid which contains from about 20 to 37 weight percent HCl and most preferably from about 23 to 30 weight percent HCl. The amount of hydrochloric acid which is added to a tricalcium phosphate mineral to be treated is not critical, but is generally from about 100 to 110 percent of the sboichiometric amount required to react with the tri-calciu~ phosphate content of the mineral to form phosphoric acid, and preferably from about 103 to 108 percent. The time of digestion is not critical and varies widely wlth the com-posit,ion of the tricalcium phosphate mineral which is treated, the amount of HCl added during digestion and other factors.
For example, a digestion time of from about 1 to 2 hours is 10 required for substantially complete digestion of a tricalcium phosphate mineral containing 80 weight percent tricalcium phosphate. It has been found that volatilization of fluorine values from the digest solution may be minimized by terminating the digestion step when all the tricalcium phosphate ln the mlneral is reacted. Likewlse, whlle the di~e~tlon may be per~ormed over a wlde range of temperatures, lt has been s found that a temperature of not greater than 110C., and pre~erably about 60 to 100C., provides a substantial decrease in the amount of fluorine values volatlllzed from the digest 20 solution, Since the hydrochloric acid digestion of a tricalcium phosphate mineral typically provides an insoluble residue in the digest solution, separation of the residue is generally necessary before the digest solution is further processed.
The separation of these ~olids may be effected by any standard solid separation process such as filtering, centrifuging or ~ , by decanting the digest liquor. An acidulate liquor results following the removal of the insoluble residue from the digest solution. A typical acidulate liquor contains:
CaC12 27.0 weight percent H3P04 12.6 " "
F values (as elemental F) o.6 HCl 2.0 weight percent 3 7 " "
FeC13 o.8 U values (as elemental U) 80 ppm Yttrlum values (as elemental Y)100 ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) However, it will be appreciated that the composition of such a solution may vary considerably from that indicated depending upon the composition of the original tricalcium phosphate mineral which is treated and upon the conditions of digestion of the mineral. The fluorine values in the typical acidulate liquor described above are thought to be present in the form of complex lons such as fluosilicate (SiF6) and fluoaluminate (e.g , AlF+2, A1~2~, etc.) The acidulate liquor thereby obtained is contacted with a suitable organic solvent. Organic solvents which are suitable in the process of the present invention are those which are capable of dlssolving phosphoric acid but have limited miscibility with water free of phosphoric acid, as well as with water containing phosphoric acid and calcium chloride. The solvents which can be used in the process may be ascertained by reference to data on the mutual miscibility of solvents and water, which ls well-known in the art and is available from the literature~ e.g., Seidell, Solubilities Of Organic Compounds, 3rd Edition, Volume 2, 1941, D. Van Nostrand Co., Inc., New York City and Landolt-Bornstein, Physikalisch-Chemische Tabellen, 1912, Julius Springer, Berlin, Germany.
Representative solvents coming within the above definition are, 3~
for example, lower aliphatic alcohols and ketones of limited mutual miscibility with water, such as alcohols containing 4 to 6 carbon atoms in the aliphatic group, used alone or in mixture, e.g., butanol, amyl alcohol, isoamyl alcohol, and also trialkyl phosphates, particularly those containing 2 to 8 carbon atoms in the lndividual alkyl group, such as tributyl phosphate and mixtures thereor. The contacting of the acidulate llquor wlth the organlc solvent in the extraction step may be er~ected in any Or the standard extraction apparatus employed for slmilar rluids. 'rhe contacting o~ the acidulate liquor with the selected organic solvent produces an organic phase and an aqueous phase. The organic phase has been found to 10 contain essentially all Or the phosphoric acid, hydrochloric ~-~
acid and hexavalent uranium, which was inltially present in the acidulate liquor, in addition to a small portion (up to about ~; -10 weight percent) of the FeCl3 initially present in the -acldulate liquor, as well as most o~ the HCl lntroduced during the extraction operation. The organic phase contalning the pho~phorlc acid is separated from the extractlon apparatus and is processed by known methods to recover the phosphorlc acid , and the organic solvent therefrom. See, e.g., U.S. Patents 2,880,063 and 3,311,450. The recovered organic solvent may be recycled to the extraction step.
A brine rarfinate remains following the separation o~
the phosphoric acid-organic phase. A typical brine raffinate contains:
CaC12 26.0 weight percent HCl 2.0 " "
0.7 C13 .7 F values (as elemental F) 0.~ " "
U values (as elemental U) 30 ppm Yttrium values (as elemental Y)100 ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) Due to the marked tendency of uranium in the tetra-valent state to remain in the aqueous phase and the tendency of hexavalent uranium to transfer into the organic phase durlng the extraction step, most of the uranium values present in the brine raffinate are in the tetravalent state following the extraction step. However, during subsequent processing of the brine raffinate, a small amount of the tetra-valent uranium may be oxidized to the hexavalent state due to the sensitivity of tetravalent uranium to air oxidation at elevated pH. It should be recognized that the concentration of the above constituents in the brine raffinate and the -precise components present in the brine raffinate may vary ~-considerably from that indicated above depending on the composition of the tricalcium phosphate mineral treated by the process o~ the present invention, the conditions Or digestion and the conditions of the extraction step.
An essential feature of thé present invention is the addition to the brine raffinate o~ a basically reacting compound so as to ad~ust the pH of the raffinate to at least about 9, and preferably from about 9 to 11, in order to effect coprecipita-tion of substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from the brine raffinate. The basically reacting compounds which may be employed to effect such precipitation are generally sélected from the group consisting of alkali hydroxides, alkaline earth hydroxides, alkali carbonates, alkaline earth oxides, alkaline earth carbonates, ammonium hydroxide, alkaline earth silicates and mixtures thereof. Preferred basically reacting compounds are sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, calcium oxide and calcium carbonate.
When calcium carbonate or calcium silicate is employed as the basically reacting compound, a pH of 9 cannot be obtained utilizing the calcium silicate or calcium carbonate alone, and therefore, supplementary addition of another basically reactlng compound (as, for example, calclum oxide) ls required ~' ln ord,er to effect the brine raffinate having a pH of at least about ~.
The selected basic reacting compounds may be added to the brine raffinate either as a solid or as an aqueous solution ~ ;
of the compound, or, in the case of ammonium hydroxide, ,may be added by bubbling gaseous NH3 through the raf~inate. The -10 amount of the basically reacting compound added to the brine ' raffinate, varies according to the pH of the raffinate, -which in turn varies according to the amount of HCl remaining in the brine raffinate after extraction, the relative basicity of the selected basically reacting compound and other factors.
In ~eneral, the selected basically reacting compound wlll be added in an amount of from about 2 to 5 weight percent of a ~' brine raffinate containing 26 weight percent CaC12, 2 weight percent HCl, 0.7 weight percent FeC13, 0.7 weight percent AlC13, o.6 weight percent fluorine values, 30 ppm uranium values and 160 ppm rare earth metal values. Various known sources of the above basically reacting compounds may be employed in the process of the present invention. For example, sea shells and limestone are effective sources of calcium carbonate. In addition, calcium silicate may be used in the form of spent bed sand discharged from a fluidized bed pyrohydro-lizer unit which may be used for recovery of HCl from the basic solution containing CaC12, as discussed below.
The temperature of the brine raffinate to which the , selected basically reacting compound is added is not critical, but is preferably below the boiling point of the brine raffinate, which is generally from about 105 to 110C. To effect sub-stantially complete precipitation of the fluorine, uranium -- 10 - ' .
and rare earth metal values o~ the brlne raffinate and to increase the rate at which the fluorine, uranium and rare earth metal values are preclpitated, the brine rafrinate may be agitated (as by use of a mechanical stlrrer) in the presence of the selected basically reactlng compound. Such a~ltatlon ls, however, not essential.
The period of time requlred to effect precipitation of substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from the brine raffinate varies according to the relative amounts of these 10 values lnltlally present ln the brine raffinate, the selected ~
basically reacting compound added to the brine raffinate and ~-other factors.
The precipitated solids, obtained by the addition to the brine raffinate of the basically reactln~ compounds as discussed above, generally contaln from about 95 to 100 percent of the uranium values (as elemental uranium), 95 to 100 percent of the fluorine values (as elemental fluorlne), and 90 to 100 percent of the rare earth metal values (as elemental rare earth metals) which were initially present in the brlne raffinate. -In addition, the precipitated solids also contain up to approximately 100 percent of the aluminum and 100 percent of the iron values present in the brine raffinate. The fluorine values in the precipitate are thought to be in the form of calcium fluoride, and the aluminum to be present as a complex compound of the formula A12O3 CaC12 3CaO 10H2O. The form which the uranium and rare earth metal values take in the precipitated solids has not been established with certainty, but is believed that such elements are present as hydrous uranium oxides, calcium uranate, and rare earth metal hydrous oxides, which may contain uranium in both the hexavalent and tetravalent states due to the sensitivity of tetravalent uranium to oxidation.
The precipitated solids obtained by the addition to the br:Lne raffinate of the selected basically reactlng compound as discussed above may be separated from the aqueous solution, herein termed the "baslc solution", by any standard solld separatlon procedure, such as by flltration, centrlfuglng or by decanting the aqueous baslc solutlon. The separated solids may then be processed by known methods to individually recover the fluorine, uranium and rare earth metal values present in - ~
the precipitated solids. For example, if the precipitated ~ -solids are slurried with a solution of HCl, all the components of the mixture are leached out with the exception of calcium fluoride precipitate, thus isolating the fluorine values. The leach liquor from the above treatment for isolating CaF2 contains uranium and rare earth metal values whlch may be concentrated or isolated by a number Or methods. For example, the liquor may be concentrated by evaporatlon and the uranlum values recovered by adsorption on an anion exchange resin accordlng to the ;~
process of U.S. Patent 2,770,520. The rare earth metal values in the effluent from the exchange resin treatment can then be isolated by known methods such as the solvent extraction method set forth in Chemical and Nuclear Technology (S. Peterson and R. Wymer, ed., Addison-Wesley Publishing Co., 1963) p. 359, wherein the rare earth values present in the effluent are extracted therefrom as rare earth chlorides by use of di-2-ethyl-hexyl phosphoric acid, yielding an aqueous phase containlng CaC12 and AlC13 which may then be recycled to the digest solution for the process of the present invention to provide a source for an aluminum-containlng compound which is soluble in the digest solution.
The basic solution containing C~C12 which is produced by the addition to the brine raffinate of the selected basically reacting compound as discussed above, may be calcined by known 10~5~Z:2 methods to produce hydrochloric acid which may then be recycled to the digestion step for admixtuxe with additional tricalcium phosphate mineral. In addition, the ba$ic solution may be passed through a fluidized bed pyrohydrolysis unit to recover hydrochloric acid. Since spent bed sand may from such a unit contain calcium silicate, it is employed as the basically reacting compound added to the brine raffinate, as discussed above.
As indicated above, an aluminum-containing compound which is soluble in the digest solution may be added to the `
digest solution during the digestion of the calcium phosphate mineral in order to increase the portion of the fluorine values present in the mineral which dissolves in the digest solution.
Aluminum-containing compounds which are especially preferred are AlC13, Al(OH)3 and A12(SO4)3 and mixtures thereof. The selected -aluminum-containing compound should be added to the digest solution in an amount of from about 2 to 5 weight percent of the tricalcium phosphate mineral to be digested, and may be added as a solid or as an aqueous solution. The concentration of aluminum-containing compound in the aqueous solution is not critical and generally ranges from about 10 to 30 weight percent aluminum-containing compound.
As disclosed and claimed in U.S. Patent 3,880,980 (issued April 29, 1975) the amount of uranium which transfers from the acidulate liquor into the brine raffinate may be in-creased by treating the aqueous acidulate liquor (before the extraction thereof with the organic solvent) with a reductant, such as H2S, to reduce the hexavalent uranium present in the acidulate liquor to the tetravalent state. Since uranium in the tetravalent state transfers into the aqueous phase more readily than does hexavalent uranium, a more complete transfer of uranium into the aqueous phase during extraction r -is efrected, thereby allowing an increased recovery by the `;: ;
process Or the present invention of uranium initially present -~
in the tricalcium phosphate mineral.
Referring to the drawing, whereln a process of the present invention is diagrammatlcally lllustrated, trlcalclum phosphate mlneral, e.g., phosphate rock, containing 2 weight percent fluorlne, 50 ppm uranlum and 0.1 welght percent rare earth metal values, is lntroduced through llne 13 into reactor 12 whereln the mlneral ls dlgested wlth hydrochloric acid, e.g., .-a 25 weight percent solution of HCl, introduced through llne 10.
An alumlnum-containing compound, soluble in the digest solutlon, . .
e.g., an aqueous solutlon comprlslng 30 weight percent Or AlC13, may be optionally introduced into reactor 12 through line 11.
The dlgest solutlon is wlthdrawn from reactor 12 through llne 14 and waste sollds removed from the solution in separator 15 and discarded f~om the sy~tem through llne 35. The remaining solution, i.e. the acidulate liquor, is passed from separator 15 via line 16 to solvent extraction column 22 wherein the acidulate liquor ls admixed wlth a sultable organlc solvent, e.g. butanol, which is introduced into column 22 via line 17, thereby forming organlc phase 23 and aqueous phase 25. Organic phase 23 is withdrawn from extraction column 22 vla line 24 and is treated by known processes to recover phosphoric acid therefrom.
Aqueous phase 25, i.e. the brine raffinate, is wlthdrawn from extraction apparatus 22 via line 26 and passed to vessel 28 into which a basically reacting compound, e.g., a mixture of flnely ground calcium carbonate and calcium oxide, is introduced through line 27 to form solutlon having a pH
3~ of at least about 9 and to simultaneously precipltate solids containing fluorine, uranium and rare earth metal values.
The basic solution and solids are withdrawn from vessel 28 vla 14 _ ~065~Z2 line 29 and passed to separator 30 wherein the solids are separated from the aqueous solution containin~ CaC12. The separated solids are removed rrom separator 30 via line 32 and may then be treated by known processes to recover the uranium, rluorlne and rare earth metal values therefrom. Followlng the separatlon of the above sollds therefrom, the CaC12 solution may then be withdrawn ~rom separator 30 via llne 31 and may be further treated by known methods to recover HCl therefrom.
The recovered HCl may be recycled to line 10 for admixture with 10 additional tricalcium phosphate mineral. -The process of the present inventlon may be further illustrated by reference to the followlng examples, wherein parts are by weight unless otherwlse lndlcated.
EXAMPL~ 1 . . ~
2000 Parts of a brlne raffinate containlng:
CaC12 25.7 welght percent HCl 1.8 " "
FeC13 75 AlC13 0.62 " "
F values (as elemental F) 0.63 U values (as elemental U) 70 ppm Yttrium values (as elemental Y) 100ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) is obtained as a by-product from the production of phosphoric acid by the hydrochlorlc acid decomposition of a tricalcium phosphate mineral. With continual vigorous stirring, 70 parts of ground clam shells containing 97.2 weight percent CaCO3 is added to the brine raffinate over a period of 20 minutes.
Subsequently, 10 parts o~ powdered slaked lime, containing greater than 98 weight percent Ca(OH)2, ls added to the raffinate, thereby effecting a pH of 9. The mixture is maintained at 70C. for three hours with continuous agitation, during which period a precipitate is formed. At the conclusion of the three hour period the precipitate is separated from the basic solution by filtration, drained by suction and dried in an oven at 120C., yielding 97 parts of solids which are found by chemical analysis to contain:
F values (as elemental F) 12.8 weight percent U values (as elemental U) 0.14 " "
Rare earth metal values 0.3 " "
(as the elemental metals) Fe values (as Fe2O3) 7.6 " "
Al values (as A12o3) 4.8 CaCO3 25. " "
Thus, about 98 percent of the fluorine, 97 percent of the uranium and 90 percent of the rare earth metal values present in the brine raffinate are precipitated. Analysis of the precipitated solids by X-ray diffraction shows the fluorine values to be in the form of CaF2 and a substantial amount of the aluminum to be in the form of A12O3-CaC12.3CaO-lOH2O.
2000 Parts of brine raffinate having the composition shown in Example 1 is heated to 70C. and contacted with gaseous ammonia which is bubbled through the continuously stirred brine raffinate. A total of 25 parts of ammonia is passed into the solution over a period of about 2 hours. At periodic intervals, samples of the reaction mixture are withdrawn for pH measurement and chemical analysis to determine the fluorine and uranium values (as elemental fluorine and uranium, respectively) and rare earth metal values (as mixed oxides).
After 17.4 parts of NH3 have been added to the 2~00 parts of brine raffinate, the pH of the raffinate is determined ~06S122 to be 7.5 and the percent of the rare earth metal values present in the raffinate which are precipitated is determined to be 60 percent. Approximately 100 percent of the fluorine and uranium values and 92 percent Or the rare earth metal values are determined to be precipitated at a pH of 8.4 which corres-ponds to the addition to the 2000 parts of brine raffinate of 20.0 parts of NH3. The addition to the 2000 parts of brine raffinate of 22.2 parts Or NH3 is determined to effect a pH of 9.1 and the precipitation of 100 percent of the rare earth metal values, in addition, to 100 percent of the fluorine and uranium values, present in the brine raffinate.
2000 Parts of brine raffinate having the composition shown in Example 1 is heated to 70C. and continuously stirred whlle 71.5 parts of eround oyster shells contalning 96.5 weight percent CaC03 are added to the rafflnate over a period of four hours. At perlodic intervals, samples of the mixture are with-drawn for chemical analysis.
The following data are obtained.
Parts Oyster Shells Added Percent F Precipitated 22.6 63 27.0 75 31.7 82 -~
36.9 87 47.0 90 .
58.4 96 ~-71.5 98 After the last addition of oyster shells, the solids are pre-cipitated by filtration and dried at 100C., yielding 92 parts of material which contained 13.2 percent by weight fluorine.
106512Z : i ;:.` ' ' EXAMPLE 4 ~ -1000 Parts Or brine raffinate having the composition of ExaLmple l is heated to 70C. and stirred continuously while 100 pa~rts of an aqueous solution containing 30 parts of NaOH are added at a uniform rate over a period of one hour. The mixture ls allowed to react for an additional hour at 70C., and the solids are then separated from the mixture by filtration and dried at 100C., yielding 27.5 parts of solids containing 21.8 percent by weight fluorine, corresponding to a recovery of 10 about 95 percent of the fluorine initially present in the brine ;
raffinate. X-ray diffraction analysis indicated that the ma~or component of the solid is CaF2.
The following example illustrates the effect of adding an alumlnum-containlng compound to the hydrochloric acid digest solution which is soluble in that ~olution.
Three 100 part portions of a ground Florida phosphate rock containing:
Ca values (as CaO) 45 weight percent P values (as P2O5) 30.2 " "
F values (as elemental F) 3.5 " "
SiO2 7.62 " "
A123 0.85 " "
Fe203 1.30 " "
U values (as elemental U) 270 ppm Rare earth metal values 650 ppm (as the elemental metals) are digested for 2 hours at a temperature of 100C. The first , 100 part portion of the rock is digested with 270 parts of an aqueous hydrochloric acid solution containing 23 weight percent HCl. The second 100 part portion of rock i8 digested with 270 parts of a 23 weight pereent HCl solution and 4.0 parts AlCl3 6l~2O, and the third 100 part portion is digested with 270 parts Or a 23 weight percent HCl solutlon and 8.0 parts of AlCl3 5H20.
Each digest llquor ls filtered to yield about 330 parts ~
Or a clear acidulate liquor. Upon analysis, each of the acidualte ~ `
liquors is found to contaln the following components ln the amounts indicated:
CaC12 27.0 weight percent H3P04 12.6 " "
FeC13 0.8 U values (as elemental U)75 ppm Rare Earth Metal Values185 ppm HCl 2.0 weight percent The acldulate liquors, however, differ in compositlon ln fluorine and aluminum content. The acidulate liquor obtained from the first lO0 part rock portion to which no alumlnum-contalnin~ compound is added during digestion is found to contain 0.58 welght percent fluorine values (as elemental F) and 0.67 weight percent Al (as AlC13). The acidulate liquor obtained following the digestion of the 100 part rock portion to which 4.0 parts AlC13 6H2O is added during digestion is found to contain o.8 weight percent ~;
fluorine and 1.34 welght percent Al (as AlC13). ~he acldulate liquor which is obtained from the third 100 part roc~ portion, to which 8.0 parts AlC13 6H2O is added durlng digestion, is found to contain 0.92 weight percent fluorine and 2.01 weight percent Al (as AlCl3).
Thus, the addition to the second and third 100 part rock portions of 4.0 parts and 8.0 parts, respectively, of AlCl3 6H2O, effec~ed a transfer to the acidulate liquor of 76 percent and 87 percent, respectively, of the total fluorine content of the rock, as compared with a transfer to the acidulate liquor of only 55 percent of the fluorine present in the flrst 100 part rock portion to which no aluminum~
containlng compound was added during digestlon.
Although certain preferred embodiments of the invention have been disclosed for purpose Or illustration, it will be evi-dent to one skilled in the art that various changes and modifica-tlons may be made therein without departing from the scope and ,.
spirit of the invention.
' ' ,
The aqueous phase obtained following this separation, termed the "brine ra~finate",contains essentially all of the fluorine and rare earth metal values and a portion of the uranium .
values initially present in the acidulate liquor. Mos~ uranium, however, remains ln the oreanic phase containing the H3PO4 and must be recovered therefrom subsequent to the extraction step -reclted above.
Discarding the brine rarfinate thereby produced represents a slgni~lcant loss of valuable rluorlne, uranlum and rare earth metal values. Uranium values, for example, upon recovery, concentration and purification are useful in serving as fuel for atomic reactors. Due to the large tonnages of tricalclum phosphate minerals which are annually produced by industry to obtain phosphoric acid, even the small concen-trations of fluorine, uranium and rare earth metal values which are contained in these minerals represent a substantial source of these valuable elements in the aggregate.
SUMMARY OF THE INVENTION
Accordin~ to the present inventlon, substantially all of the fluorlne and uranium values and at least 90 percent ~`
of the rare earth metal values are recovered from tricalcium phosphate minerals by a process which comprises digesting the mineral with hydrochloric acid to form (1) a digest solution containing fluorine, uranium and rare earth metal values and (2) an insoluble residue, separating said insoluble residue from said solution, thereby producing an aqueous acidulate liquor containing fluorine, uranium and rare earth metal values, contacting said liquor with an organic solvent capable of dissolving phosphoric acid but having limited miscibility with water free of phosphoric acid to extract phosphoric acid from said liquor into the organic phase, separatlng said organic phase from the aqueous phase for subsequent removal of phosphoric acid from said organic phase, admixinK a basically reacting compound with said separated aqueous phase to effect a pH of at least about 9, thereby forming a basic solutlon 1065~22 and precipitated solids containing ~luorine, uranium and rare ~`
earth ~etal values, separating the precipitated solids from the basic solution and recovering the fluorine, uranium and rare earth metal values from the separated solids.
In the process of the present invention, substantially all of the fluorlne and uranium values and at least 90 percent of the rare earth metal values are surprisingly and advantageously coprecipitated by the addition to the brine raffinate of a basically reacting compound in an amount sufficient to effect a pH of at least about 9, and preferably about 9 to 11, in the raffinate. In addition, precipitation of uranium values from the brine raffinate has been found not to be dependent on whether the uranlum values present in the brine raffinate are in the hexavalent or tetravalent state. The present invention provides an efficient and economic recovery of valuable fluorine and ~;
uranium values and, most slgniflcantly, provides an efficient and economic recovery of the much more valuable rare earth metal values from trlcalclum phosphate mlnerals, thus avoldlng the economic penalty of discarding waste liquors produced as by-products from the production of phosphoric acid.
In addition, lt has been found that from about 40 to 5Q% of the fluorine values initially present in the trl-calcium phosphate mineral either remain in the insoluble residue as calcium fluoride following the hydrochloric acid digestion or are volatilized from the dlgest solution during digestion. In accordance with a specific embodiment of the present invention, the portion of the fluorine values present in the tricalcium phosphate mineral which transfers into and remains in the digest solution and which, therefore, transfers 3 to the aqueous acidulate llquor and is recovered by the process of the present invention, may be signlficantly increased by providing in the digest solution an aluminum-containing compound ; 3 -- 106SlZ2 which is soluble in the digest solution. Further, the amount of fluorine values volatilized and thus lost during digestion may be decreased by employing a digestion temperature of not greater than about 110C., preferably about 90 to 100C.
BRIEF DESCRIPTION OF THE DRAWING
Tha accompanying figure is a schematic diagram of the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The term "tricalcium phosphate mineral" as used herein is meant to include any mineral, such as phosphate rock (e.g., apatite) which contains tricalcium phosphate and small amounts of fluorine, uranium and rare earth metal values and which reacts with hydrochloric acid to form phosphoric acid.
Typical of such minerals are phosphate rock, apatite and phosphorite. If phosphate rock is used, it may be either calcined or uncalcined rock.
The tricalcium phosphate minerals treated by the process of the present invention generally contain from about 2 to 4 weight percent fluorine, 50 to 300 ppm uranium and 100 to 1,000 ppm rare earth metals, measured as the respective elements. The mineral generally contains fluorine values in the form of Ca5(PO4)3F, and rare earth metals in the form of oxides, fluorides or phosphates. Typical of rare earth metals which may be present are yttrium, lanthanum, cerium and small amounts of gadolinum, ytterbium, europium, samarium and praseodymium. While the form which uranium takes in tricalcium phosphate minerals has not been precisely determined, uranium is generally thought to be present in both the hexavalent and tetravalent states in the form of calcium uranate or uranyl phosphate (U+6) and calcium uranous fluoride or uranous phosphate (U~4). Tricalcium phosphate minerals typically also contain from about 0.8 to 1.3 weight percent aluminum values as ~0651ZZ
A12O3, 0.8 to 1.5 weight percent iron values as Fe2O3; 7.0 to 9.0 weight percent silicon values as SiO2, 0.1 to 0.5 weight percent Na2O, 0.1 to 0.5 weight percent K2O, 0.2 to 1.0 weight percent sulfur values as SO3, and 3.0 to 7.0 weight percent volati:Le matter (i.e., water, organic carbon, carbonate carbon and nitrogen).
A typical tricalcium phosphate mineral which may be treated by the process of the present invention contains:
Ca values (as CaO) 45 weight percent P values (as P2O5) 32 " "
F values (as elemental F) 3.5 " "
SiO2 8.0 " "
A123 1.0 " "
Fe2o3 1.3 " "
U values (as elemental U)200 ppm Yttrium values (as elemental ~) 300 ppm Lanthanum values ~as elemental La) 70 ppm Cerium valuess (as elemental Ce) 30 ppm Up to about 100 ppm (as the elemental metals) of other rare earths may also be present. These include gadolinium, ytterbium, samarium, praseodymium, dysprosium, europium, lutetium, erbium and thulium. Such minerals also typically contain organic matter, as well as moisture. However, tricalcium phosphate minerals differing very considerably from that indicated either in composition or relative concentrations of components may also be satisfactorily processed.
In the process of the present invention, while any concentration of hydrochloric acid may be employed to digest the tricalcium phosphate mineral, it is preferred to employ an aqueous solution of hydrochloric acid which contains from about 20 to 37 weight percent HCl and most preferably from about 23 to 30 weight percent HCl. The amount of hydrochloric acid which is added to a tricalcium phosphate mineral to be treated is not critical, but is generally from about 100 to 110 percent of the sboichiometric amount required to react with the tri-calciu~ phosphate content of the mineral to form phosphoric acid, and preferably from about 103 to 108 percent. The time of digestion is not critical and varies widely wlth the com-posit,ion of the tricalcium phosphate mineral which is treated, the amount of HCl added during digestion and other factors.
For example, a digestion time of from about 1 to 2 hours is 10 required for substantially complete digestion of a tricalcium phosphate mineral containing 80 weight percent tricalcium phosphate. It has been found that volatilization of fluorine values from the digest solution may be minimized by terminating the digestion step when all the tricalcium phosphate ln the mlneral is reacted. Likewlse, whlle the di~e~tlon may be per~ormed over a wlde range of temperatures, lt has been s found that a temperature of not greater than 110C., and pre~erably about 60 to 100C., provides a substantial decrease in the amount of fluorine values volatlllzed from the digest 20 solution, Since the hydrochloric acid digestion of a tricalcium phosphate mineral typically provides an insoluble residue in the digest solution, separation of the residue is generally necessary before the digest solution is further processed.
The separation of these ~olids may be effected by any standard solid separation process such as filtering, centrifuging or ~ , by decanting the digest liquor. An acidulate liquor results following the removal of the insoluble residue from the digest solution. A typical acidulate liquor contains:
CaC12 27.0 weight percent H3P04 12.6 " "
F values (as elemental F) o.6 HCl 2.0 weight percent 3 7 " "
FeC13 o.8 U values (as elemental U) 80 ppm Yttrlum values (as elemental Y)100 ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) However, it will be appreciated that the composition of such a solution may vary considerably from that indicated depending upon the composition of the original tricalcium phosphate mineral which is treated and upon the conditions of digestion of the mineral. The fluorine values in the typical acidulate liquor described above are thought to be present in the form of complex lons such as fluosilicate (SiF6) and fluoaluminate (e.g , AlF+2, A1~2~, etc.) The acidulate liquor thereby obtained is contacted with a suitable organic solvent. Organic solvents which are suitable in the process of the present invention are those which are capable of dlssolving phosphoric acid but have limited miscibility with water free of phosphoric acid, as well as with water containing phosphoric acid and calcium chloride. The solvents which can be used in the process may be ascertained by reference to data on the mutual miscibility of solvents and water, which ls well-known in the art and is available from the literature~ e.g., Seidell, Solubilities Of Organic Compounds, 3rd Edition, Volume 2, 1941, D. Van Nostrand Co., Inc., New York City and Landolt-Bornstein, Physikalisch-Chemische Tabellen, 1912, Julius Springer, Berlin, Germany.
Representative solvents coming within the above definition are, 3~
for example, lower aliphatic alcohols and ketones of limited mutual miscibility with water, such as alcohols containing 4 to 6 carbon atoms in the aliphatic group, used alone or in mixture, e.g., butanol, amyl alcohol, isoamyl alcohol, and also trialkyl phosphates, particularly those containing 2 to 8 carbon atoms in the lndividual alkyl group, such as tributyl phosphate and mixtures thereor. The contacting of the acidulate llquor wlth the organlc solvent in the extraction step may be er~ected in any Or the standard extraction apparatus employed for slmilar rluids. 'rhe contacting o~ the acidulate liquor with the selected organic solvent produces an organic phase and an aqueous phase. The organic phase has been found to 10 contain essentially all Or the phosphoric acid, hydrochloric ~-~
acid and hexavalent uranium, which was inltially present in the acidulate liquor, in addition to a small portion (up to about ~; -10 weight percent) of the FeCl3 initially present in the -acldulate liquor, as well as most o~ the HCl lntroduced during the extraction operation. The organic phase contalning the pho~phorlc acid is separated from the extractlon apparatus and is processed by known methods to recover the phosphorlc acid , and the organic solvent therefrom. See, e.g., U.S. Patents 2,880,063 and 3,311,450. The recovered organic solvent may be recycled to the extraction step.
A brine rarfinate remains following the separation o~
the phosphoric acid-organic phase. A typical brine raffinate contains:
CaC12 26.0 weight percent HCl 2.0 " "
0.7 C13 .7 F values (as elemental F) 0.~ " "
U values (as elemental U) 30 ppm Yttrium values (as elemental Y)100 ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) Due to the marked tendency of uranium in the tetra-valent state to remain in the aqueous phase and the tendency of hexavalent uranium to transfer into the organic phase durlng the extraction step, most of the uranium values present in the brine raffinate are in the tetravalent state following the extraction step. However, during subsequent processing of the brine raffinate, a small amount of the tetra-valent uranium may be oxidized to the hexavalent state due to the sensitivity of tetravalent uranium to air oxidation at elevated pH. It should be recognized that the concentration of the above constituents in the brine raffinate and the -precise components present in the brine raffinate may vary ~-considerably from that indicated above depending on the composition of the tricalcium phosphate mineral treated by the process o~ the present invention, the conditions Or digestion and the conditions of the extraction step.
An essential feature of thé present invention is the addition to the brine raffinate o~ a basically reacting compound so as to ad~ust the pH of the raffinate to at least about 9, and preferably from about 9 to 11, in order to effect coprecipita-tion of substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from the brine raffinate. The basically reacting compounds which may be employed to effect such precipitation are generally sélected from the group consisting of alkali hydroxides, alkaline earth hydroxides, alkali carbonates, alkaline earth oxides, alkaline earth carbonates, ammonium hydroxide, alkaline earth silicates and mixtures thereof. Preferred basically reacting compounds are sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, calcium oxide and calcium carbonate.
When calcium carbonate or calcium silicate is employed as the basically reacting compound, a pH of 9 cannot be obtained utilizing the calcium silicate or calcium carbonate alone, and therefore, supplementary addition of another basically reactlng compound (as, for example, calclum oxide) ls required ~' ln ord,er to effect the brine raffinate having a pH of at least about ~.
The selected basic reacting compounds may be added to the brine raffinate either as a solid or as an aqueous solution ~ ;
of the compound, or, in the case of ammonium hydroxide, ,may be added by bubbling gaseous NH3 through the raf~inate. The -10 amount of the basically reacting compound added to the brine ' raffinate, varies according to the pH of the raffinate, -which in turn varies according to the amount of HCl remaining in the brine raffinate after extraction, the relative basicity of the selected basically reacting compound and other factors.
In ~eneral, the selected basically reacting compound wlll be added in an amount of from about 2 to 5 weight percent of a ~' brine raffinate containing 26 weight percent CaC12, 2 weight percent HCl, 0.7 weight percent FeC13, 0.7 weight percent AlC13, o.6 weight percent fluorine values, 30 ppm uranium values and 160 ppm rare earth metal values. Various known sources of the above basically reacting compounds may be employed in the process of the present invention. For example, sea shells and limestone are effective sources of calcium carbonate. In addition, calcium silicate may be used in the form of spent bed sand discharged from a fluidized bed pyrohydro-lizer unit which may be used for recovery of HCl from the basic solution containing CaC12, as discussed below.
The temperature of the brine raffinate to which the , selected basically reacting compound is added is not critical, but is preferably below the boiling point of the brine raffinate, which is generally from about 105 to 110C. To effect sub-stantially complete precipitation of the fluorine, uranium -- 10 - ' .
and rare earth metal values o~ the brlne raffinate and to increase the rate at which the fluorine, uranium and rare earth metal values are preclpitated, the brine rafrinate may be agitated (as by use of a mechanical stlrrer) in the presence of the selected basically reactlng compound. Such a~ltatlon ls, however, not essential.
The period of time requlred to effect precipitation of substantially all of the fluorine and uranium values and at least 90 percent of the rare earth metal values from the brine raffinate varies according to the relative amounts of these 10 values lnltlally present ln the brine raffinate, the selected ~
basically reacting compound added to the brine raffinate and ~-other factors.
The precipitated solids, obtained by the addition to the brine raffinate of the basically reactln~ compounds as discussed above, generally contaln from about 95 to 100 percent of the uranium values (as elemental uranium), 95 to 100 percent of the fluorine values (as elemental fluorlne), and 90 to 100 percent of the rare earth metal values (as elemental rare earth metals) which were initially present in the brlne raffinate. -In addition, the precipitated solids also contain up to approximately 100 percent of the aluminum and 100 percent of the iron values present in the brine raffinate. The fluorine values in the precipitate are thought to be in the form of calcium fluoride, and the aluminum to be present as a complex compound of the formula A12O3 CaC12 3CaO 10H2O. The form which the uranium and rare earth metal values take in the precipitated solids has not been established with certainty, but is believed that such elements are present as hydrous uranium oxides, calcium uranate, and rare earth metal hydrous oxides, which may contain uranium in both the hexavalent and tetravalent states due to the sensitivity of tetravalent uranium to oxidation.
The precipitated solids obtained by the addition to the br:Lne raffinate of the selected basically reactlng compound as discussed above may be separated from the aqueous solution, herein termed the "baslc solution", by any standard solld separatlon procedure, such as by flltration, centrlfuglng or by decanting the aqueous baslc solutlon. The separated solids may then be processed by known methods to individually recover the fluorine, uranium and rare earth metal values present in - ~
the precipitated solids. For example, if the precipitated ~ -solids are slurried with a solution of HCl, all the components of the mixture are leached out with the exception of calcium fluoride precipitate, thus isolating the fluorine values. The leach liquor from the above treatment for isolating CaF2 contains uranium and rare earth metal values whlch may be concentrated or isolated by a number Or methods. For example, the liquor may be concentrated by evaporatlon and the uranlum values recovered by adsorption on an anion exchange resin accordlng to the ;~
process of U.S. Patent 2,770,520. The rare earth metal values in the effluent from the exchange resin treatment can then be isolated by known methods such as the solvent extraction method set forth in Chemical and Nuclear Technology (S. Peterson and R. Wymer, ed., Addison-Wesley Publishing Co., 1963) p. 359, wherein the rare earth values present in the effluent are extracted therefrom as rare earth chlorides by use of di-2-ethyl-hexyl phosphoric acid, yielding an aqueous phase containlng CaC12 and AlC13 which may then be recycled to the digest solution for the process of the present invention to provide a source for an aluminum-containlng compound which is soluble in the digest solution.
The basic solution containing C~C12 which is produced by the addition to the brine raffinate of the selected basically reacting compound as discussed above, may be calcined by known 10~5~Z:2 methods to produce hydrochloric acid which may then be recycled to the digestion step for admixtuxe with additional tricalcium phosphate mineral. In addition, the ba$ic solution may be passed through a fluidized bed pyrohydrolysis unit to recover hydrochloric acid. Since spent bed sand may from such a unit contain calcium silicate, it is employed as the basically reacting compound added to the brine raffinate, as discussed above.
As indicated above, an aluminum-containing compound which is soluble in the digest solution may be added to the `
digest solution during the digestion of the calcium phosphate mineral in order to increase the portion of the fluorine values present in the mineral which dissolves in the digest solution.
Aluminum-containing compounds which are especially preferred are AlC13, Al(OH)3 and A12(SO4)3 and mixtures thereof. The selected -aluminum-containing compound should be added to the digest solution in an amount of from about 2 to 5 weight percent of the tricalcium phosphate mineral to be digested, and may be added as a solid or as an aqueous solution. The concentration of aluminum-containing compound in the aqueous solution is not critical and generally ranges from about 10 to 30 weight percent aluminum-containing compound.
As disclosed and claimed in U.S. Patent 3,880,980 (issued April 29, 1975) the amount of uranium which transfers from the acidulate liquor into the brine raffinate may be in-creased by treating the aqueous acidulate liquor (before the extraction thereof with the organic solvent) with a reductant, such as H2S, to reduce the hexavalent uranium present in the acidulate liquor to the tetravalent state. Since uranium in the tetravalent state transfers into the aqueous phase more readily than does hexavalent uranium, a more complete transfer of uranium into the aqueous phase during extraction r -is efrected, thereby allowing an increased recovery by the `;: ;
process Or the present invention of uranium initially present -~
in the tricalcium phosphate mineral.
Referring to the drawing, whereln a process of the present invention is diagrammatlcally lllustrated, trlcalclum phosphate mlneral, e.g., phosphate rock, containing 2 weight percent fluorlne, 50 ppm uranlum and 0.1 welght percent rare earth metal values, is lntroduced through llne 13 into reactor 12 whereln the mlneral ls dlgested wlth hydrochloric acid, e.g., .-a 25 weight percent solution of HCl, introduced through llne 10.
An alumlnum-containing compound, soluble in the digest solutlon, . .
e.g., an aqueous solutlon comprlslng 30 weight percent Or AlC13, may be optionally introduced into reactor 12 through line 11.
The dlgest solutlon is wlthdrawn from reactor 12 through llne 14 and waste sollds removed from the solution in separator 15 and discarded f~om the sy~tem through llne 35. The remaining solution, i.e. the acidulate liquor, is passed from separator 15 via line 16 to solvent extraction column 22 wherein the acidulate liquor ls admixed wlth a sultable organlc solvent, e.g. butanol, which is introduced into column 22 via line 17, thereby forming organlc phase 23 and aqueous phase 25. Organic phase 23 is withdrawn from extraction column 22 vla line 24 and is treated by known processes to recover phosphoric acid therefrom.
Aqueous phase 25, i.e. the brine raffinate, is wlthdrawn from extraction apparatus 22 via line 26 and passed to vessel 28 into which a basically reacting compound, e.g., a mixture of flnely ground calcium carbonate and calcium oxide, is introduced through line 27 to form solutlon having a pH
3~ of at least about 9 and to simultaneously precipltate solids containing fluorine, uranium and rare earth metal values.
The basic solution and solids are withdrawn from vessel 28 vla 14 _ ~065~Z2 line 29 and passed to separator 30 wherein the solids are separated from the aqueous solution containin~ CaC12. The separated solids are removed rrom separator 30 via line 32 and may then be treated by known processes to recover the uranium, rluorlne and rare earth metal values therefrom. Followlng the separatlon of the above sollds therefrom, the CaC12 solution may then be withdrawn ~rom separator 30 via llne 31 and may be further treated by known methods to recover HCl therefrom.
The recovered HCl may be recycled to line 10 for admixture with 10 additional tricalcium phosphate mineral. -The process of the present inventlon may be further illustrated by reference to the followlng examples, wherein parts are by weight unless otherwlse lndlcated.
EXAMPL~ 1 . . ~
2000 Parts of a brlne raffinate containlng:
CaC12 25.7 welght percent HCl 1.8 " "
FeC13 75 AlC13 0.62 " "
F values (as elemental F) 0.63 U values (as elemental U) 70 ppm Yttrium values (as elemental Y) 100ppm Lanthanum values (as elemental La) 20 ppm Other Rare Earths (as elemental 40 ppm (total) metals) is obtained as a by-product from the production of phosphoric acid by the hydrochlorlc acid decomposition of a tricalcium phosphate mineral. With continual vigorous stirring, 70 parts of ground clam shells containing 97.2 weight percent CaCO3 is added to the brine raffinate over a period of 20 minutes.
Subsequently, 10 parts o~ powdered slaked lime, containing greater than 98 weight percent Ca(OH)2, ls added to the raffinate, thereby effecting a pH of 9. The mixture is maintained at 70C. for three hours with continuous agitation, during which period a precipitate is formed. At the conclusion of the three hour period the precipitate is separated from the basic solution by filtration, drained by suction and dried in an oven at 120C., yielding 97 parts of solids which are found by chemical analysis to contain:
F values (as elemental F) 12.8 weight percent U values (as elemental U) 0.14 " "
Rare earth metal values 0.3 " "
(as the elemental metals) Fe values (as Fe2O3) 7.6 " "
Al values (as A12o3) 4.8 CaCO3 25. " "
Thus, about 98 percent of the fluorine, 97 percent of the uranium and 90 percent of the rare earth metal values present in the brine raffinate are precipitated. Analysis of the precipitated solids by X-ray diffraction shows the fluorine values to be in the form of CaF2 and a substantial amount of the aluminum to be in the form of A12O3-CaC12.3CaO-lOH2O.
2000 Parts of brine raffinate having the composition shown in Example 1 is heated to 70C. and contacted with gaseous ammonia which is bubbled through the continuously stirred brine raffinate. A total of 25 parts of ammonia is passed into the solution over a period of about 2 hours. At periodic intervals, samples of the reaction mixture are withdrawn for pH measurement and chemical analysis to determine the fluorine and uranium values (as elemental fluorine and uranium, respectively) and rare earth metal values (as mixed oxides).
After 17.4 parts of NH3 have been added to the 2~00 parts of brine raffinate, the pH of the raffinate is determined ~06S122 to be 7.5 and the percent of the rare earth metal values present in the raffinate which are precipitated is determined to be 60 percent. Approximately 100 percent of the fluorine and uranium values and 92 percent Or the rare earth metal values are determined to be precipitated at a pH of 8.4 which corres-ponds to the addition to the 2000 parts of brine raffinate of 20.0 parts of NH3. The addition to the 2000 parts of brine raffinate of 22.2 parts Or NH3 is determined to effect a pH of 9.1 and the precipitation of 100 percent of the rare earth metal values, in addition, to 100 percent of the fluorine and uranium values, present in the brine raffinate.
2000 Parts of brine raffinate having the composition shown in Example 1 is heated to 70C. and continuously stirred whlle 71.5 parts of eround oyster shells contalning 96.5 weight percent CaC03 are added to the rafflnate over a period of four hours. At perlodic intervals, samples of the mixture are with-drawn for chemical analysis.
The following data are obtained.
Parts Oyster Shells Added Percent F Precipitated 22.6 63 27.0 75 31.7 82 -~
36.9 87 47.0 90 .
58.4 96 ~-71.5 98 After the last addition of oyster shells, the solids are pre-cipitated by filtration and dried at 100C., yielding 92 parts of material which contained 13.2 percent by weight fluorine.
106512Z : i ;:.` ' ' EXAMPLE 4 ~ -1000 Parts Or brine raffinate having the composition of ExaLmple l is heated to 70C. and stirred continuously while 100 pa~rts of an aqueous solution containing 30 parts of NaOH are added at a uniform rate over a period of one hour. The mixture ls allowed to react for an additional hour at 70C., and the solids are then separated from the mixture by filtration and dried at 100C., yielding 27.5 parts of solids containing 21.8 percent by weight fluorine, corresponding to a recovery of 10 about 95 percent of the fluorine initially present in the brine ;
raffinate. X-ray diffraction analysis indicated that the ma~or component of the solid is CaF2.
The following example illustrates the effect of adding an alumlnum-containlng compound to the hydrochloric acid digest solution which is soluble in that ~olution.
Three 100 part portions of a ground Florida phosphate rock containing:
Ca values (as CaO) 45 weight percent P values (as P2O5) 30.2 " "
F values (as elemental F) 3.5 " "
SiO2 7.62 " "
A123 0.85 " "
Fe203 1.30 " "
U values (as elemental U) 270 ppm Rare earth metal values 650 ppm (as the elemental metals) are digested for 2 hours at a temperature of 100C. The first , 100 part portion of the rock is digested with 270 parts of an aqueous hydrochloric acid solution containing 23 weight percent HCl. The second 100 part portion of rock i8 digested with 270 parts of a 23 weight pereent HCl solution and 4.0 parts AlCl3 6l~2O, and the third 100 part portion is digested with 270 parts Or a 23 weight percent HCl solutlon and 8.0 parts of AlCl3 5H20.
Each digest llquor ls filtered to yield about 330 parts ~
Or a clear acidulate liquor. Upon analysis, each of the acidualte ~ `
liquors is found to contaln the following components ln the amounts indicated:
CaC12 27.0 weight percent H3P04 12.6 " "
FeC13 0.8 U values (as elemental U)75 ppm Rare Earth Metal Values185 ppm HCl 2.0 weight percent The acldulate liquors, however, differ in compositlon ln fluorine and aluminum content. The acidulate liquor obtained from the first lO0 part rock portion to which no alumlnum-contalnin~ compound is added during digestion is found to contain 0.58 welght percent fluorine values (as elemental F) and 0.67 weight percent Al (as AlC13). The acidulate liquor obtained following the digestion of the 100 part rock portion to which 4.0 parts AlC13 6H2O is added during digestion is found to contain o.8 weight percent ~;
fluorine and 1.34 welght percent Al (as AlC13). ~he acldulate liquor which is obtained from the third 100 part roc~ portion, to which 8.0 parts AlC13 6H2O is added durlng digestion, is found to contain 0.92 weight percent fluorine and 2.01 weight percent Al (as AlCl3).
Thus, the addition to the second and third 100 part rock portions of 4.0 parts and 8.0 parts, respectively, of AlCl3 6H2O, effec~ed a transfer to the acidulate liquor of 76 percent and 87 percent, respectively, of the total fluorine content of the rock, as compared with a transfer to the acidulate liquor of only 55 percent of the fluorine present in the flrst 100 part rock portion to which no aluminum~
containlng compound was added during digestlon.
Although certain preferred embodiments of the invention have been disclosed for purpose Or illustration, it will be evi-dent to one skilled in the art that various changes and modifica-tlons may be made therein without departing from the scope and ,.
spirit of the invention.
' ' ,
Claims (9)
1. A process for simultaneous recovery of fluorine, uranium and rare earth metal values from a tricalcium phosphate mineral containing same, which comprises:
(a) contacting said mineral with hydrochloric acid to digest said mineral, thereby forming (1) a digest solution containing phosphoric acid, calcium chloride, fluorine, uranium and rare earth metal values and (2) an insoluble residue;
(b) separating said insoluble residue from said digest solution;
(c) contacting said separated digest solution with an organic solvent capable of dissolving phosphoric acid but having limited miscibility with water free of phosphoric acid, thereby forming an organic phase containing phosphoric acid and an aqueous phase containing calcium chloride and fluorine, uranium and rare earth metal values;
(d) separating said organic phase from said aqueous phase;
(e) admixing said separated aqueous phase with an amount of a basically reacting compound sufficient to effect a pH of at least about 9, thereby forming (1) a basic solution containing calcium chloride and (2) precipitated solids containing fluorine, uranium and rare earth metal values;and (f) separating the precipitated solids containing fluorine, uranium and rare earth metal values from said basic solution.
(a) contacting said mineral with hydrochloric acid to digest said mineral, thereby forming (1) a digest solution containing phosphoric acid, calcium chloride, fluorine, uranium and rare earth metal values and (2) an insoluble residue;
(b) separating said insoluble residue from said digest solution;
(c) contacting said separated digest solution with an organic solvent capable of dissolving phosphoric acid but having limited miscibility with water free of phosphoric acid, thereby forming an organic phase containing phosphoric acid and an aqueous phase containing calcium chloride and fluorine, uranium and rare earth metal values;
(d) separating said organic phase from said aqueous phase;
(e) admixing said separated aqueous phase with an amount of a basically reacting compound sufficient to effect a pH of at least about 9, thereby forming (1) a basic solution containing calcium chloride and (2) precipitated solids containing fluorine, uranium and rare earth metal values;and (f) separating the precipitated solids containing fluorine, uranium and rare earth metal values from said basic solution.
2. A process according to claim 1 wherein said tri-calcium phosphate mineral is apatite.
3. A process according to claim 1 wherein the basically reacting compound is added in an amount sufficient to effect a pH of about 9 to 11.
4. A process according to claim 1 wherein said basic-ally reacting compound is selected from the group consisting of alkali hydroxides, alkaline earth hydroxides, alkali carbonates, alkaline earth carbonates, ammonium hydroxide, alkaline earth silicates, alkaline earth oxides and mixtures thereof.
5. A process according to claim 1 wherein said basically reacting compound is selected from the group consisting of alkali hydroxide, alkaline earth carbonate, alkaline earth oxide, and mixtures thereof and wherein the basically reacting compound is added in an amount sufficient to effect a pH of about 9 to 11.
6. A process according to claim 1 wherein said separated digest solution is treated to reduce the hexavalent uranium content thereof to the tetravalent state prior to con-tacting said separated digest solution with said organic solvent.
7. A process according to claim 1 wherein an aluminum-containing compound soluble in said digest solution is admixed with said digest solution.
8. A process according to claim 7 wherein said aluminum-containing compound is selected from the group consisting of AlCl3, Al(OH)3, Al2(SO4)3 and mixtures thereof.
9. A process according to claim 5 wherein said mineral is contacted with said hydrochloric acid at a temperature of not greater than about 110°C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA241,022A CA1065122A (en) | 1975-12-04 | 1975-12-04 | Recovery of fluorine, uranium and rare earth metal values from phosphoric acid waste liquors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA241,022A CA1065122A (en) | 1975-12-04 | 1975-12-04 | Recovery of fluorine, uranium and rare earth metal values from phosphoric acid waste liquors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065122A true CA1065122A (en) | 1979-10-30 |
Family
ID=4104656
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA241,022A Expired CA1065122A (en) | 1975-12-04 | 1975-12-04 | Recovery of fluorine, uranium and rare earth metal values from phosphoric acid waste liquors |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1065122A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115389283A (en) * | 2022-06-24 | 2022-11-25 | 赣州艾科锐检测技术有限公司 | Internal control sample in rare earth metal or alloy detection, preparation method and application |
-
1975
- 1975-12-04 CA CA241,022A patent/CA1065122A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115389283A (en) * | 2022-06-24 | 2022-11-25 | 赣州艾科锐检测技术有限公司 | Internal control sample in rare earth metal or alloy detection, preparation method and application |
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