[1]3 ; 1 1 0 , 5 1 7 5 5 " United States Patent Office Patented Oct. 1, 1963 3,105,755 METHOD FOR OBTAINING MORE ECONOMICAL EXTRACTION OF TBE VALUABLE CONSTITUEINTS OF THOSE MINERALS WI-HCH CONTAIN IRON AT LOWER STATES OF OXIDATION THAN 5 Fe2o3 IN THEIR MOLECULAR STRUCTURES George E. Green, Baguio, RepubBe of the Phflippines, assignor to Haalmer Corporation, Dover, Del., a corporation of DeIaware No Drawing. Filed June 18,1959, Ser. No. 821,090 10 4 Clabus. (Cl. 75-1) T'his invention relates to the decomposition, partial or complete, of those minerals which conwn iron at lower states of oxidation than Fe2O3 in their molecular structure and has for its objects the provision of procedures to ob- 15 tain more economical and/or more selective decomposition of such minerals. In many minerals, iron is present as an inherent component of the molecule, usually as ferrous oxide, FeO. In some cases, as in ilmenite, FcO -TiO2 the iron is present 20 as an FeO radical and is in definite pro;,ortion to the oth-,r radical which in this instance is TiO2. Titanium dioxide has considerable value, much greater than that of the iron associated with it, but the combined mineral, ilmenite or FeO.- TiO2 has a relatively low value because of 25 the hitherto expensive procedures necessary to effect decomposition and separation of the iron from the titanium. Another mineral @of this class is chromite, FeO-C'@@.0g. Pure chromite would theoretically be composed of 68% chroniic oxide and 32% ferrous oxide, but p,,ire chromite 30 is not found in @nature. In all natural deposits, some replacement of iron and chromium by aluminum and magnesium has taken place, Chromite for metallurgical use is usually required to have a Cr:Fe ratio of 3:1 or higher and chromite deposits with this Cr:Fe ratio do 35 not exist in the industrialized countries where metaburgical grade chromite is most in demand. The value of chromite in which the Cr:Fe ratio exceeds 3:1 is far geater than the value of chromite in which the Cr:Fe ratio is less than 3: 1, but since chroniite is one of the most refractory 40 of aH natural minerals, previous attempts to alter the inherent Cr:Fe ratio have proved uneconomical. The tungsten minerals fellberite FEWO, (or FeO-WO3) 45 and wolframite (Fe, Mn)WO4 or (FeO, MnO)WO,3, are two minerals which- come into -the above class. The value of the contained W03, per pound increases markedly as the grade of tungsten concentrate increases, but attempts 50 hitherto to cbtain partial decomposition of the natural mineral in order to up-grade the W03 content by extraction or partial extraction of the iron inherently contained in the molecule have not been economically satisfactory. Certain beryuium minerals, such as danalite, 3 (Fe, Zn, 55 Mn)0-3BeO3SiO2(Fe, Zn)S, gadolinite, 2BeOFeO2y2,03-3SiO2 and helvite, 3(Fe, Mn)O-MnS, 3BeO-3SiO2, contain important amounts of beryllium, and, in the case of gadolin- 6o ite, other valuable elenients, but these minerals are quite refractory and have not been hitherto susceptible to decomposition by economically satisfactory methods. I There are certain nickel and/or cobalt bearing minerals such as lusakite, a cobalt-nickel aluminum silicate, 4(Fe, 65 Co, Ni, Mg)0-9(FeAI)20-3-8SiO2-H20, that contain important amounts of cobalt and/or nickel yet have not been profita,bly exploitable heretofore since they were not amenable to economic attack by the usual treatment methods. This invention applies to such cobalt-nickel minerals when 70 FeO is present as a part of the molecular strticture as it is in lusakite. 2 Lithium is an element which- has been of considerable recent interest. Certain minerals which contain important quantities of lithium as cryophyllite, 3(Li, K),0-2FeO,-4AIQ,-2OSiO,-3H,0-8(LiK)F and lesser amounts of lithium su-,h as proto-lithionite, K20-Li2O-ZA1203-3FeO-6SiO2-2H20, and zinnwaldite, K20-Li2O-2Fe-2AI203-6Si2O-2-H20, have not been used, to any great extent, as a source of lithium because of the cost of separation of the lithium from the other elements present. Thepresence of the FeO radical in these minerals place -them in the class to which this invention is applicable. The rare earths occur in a large number of minerals which occur at many places around the world. The rare earths have acquired their name because of their rarity in the extracted state, not because of any rarity in M'meral occurrence. The apparent rarity of these elements stems from the exceedingly costly methods hitherto necessary for their extraction from the natural minerals, which cost, in turn, has worked against the development of wider uses for the elements in the rare earth group. Columbium, tantalum, thorium and uranium are four other elements which occur in more minerals than have been used as a source of produc;tion. These four elements, which are strategically very important, could be recovered from more sources if the extraction cost could be made considerably less than that entailed in processes hitherto employed. All such minerals which contain Fe in their molecular struoture as FeO or as in any state or states of oxidation lower than Fe2O'3 fall into the class with which this invention is concerned. Such minerals are: Djalmaite, (U, Ca, @Pb, Bi, Fe) (Ta, Cb, Ti, Zr) 309 - nH20 YttrotanWite, (Fe, Y, 'Ca, ete.)@(Cb, Ta, Za, Sn)0,4 Yttro-columbite (more Cb than above) Nohlite, (Ca, Mg, Fe, Y, etc. U)2(0b, Zr, Fe)3010 Eschynite, (Ce, Ca, Fe, Th) (TiCb) 206 Priorite, (Y, Er, Ca, Fe, Th) ( i-L il Cb) 206 Samarskite, (y, Er, Ce, U, Ca, Fe, Pb, Th) (Cb, Ta, Ti, Sn)20"6 Fergusonite, (Y, Er, Ce, Fe) (Ta, Ob, Ti) 04 Columbo-tantalite (Fe, Mn) (0b, Ta) 206 Polyniignite, (Ca, Fe, Y, etc., Zr, Th) (Cb, Ti, Ta) 0 Zirkelite, (Ca, Fe, Th, U) 2 - (Ti, Zr) 20,5 Brannerite, (U, Ca, Fe, Y, Th)3-Ti5Ol6 Ampangabeite, (Y, Er, U, CaTh)2'(Cb, Ta, Fe, Ti)qO'16 ARanite, 4(Ca, Fe)0-3(Al, Ce, Fe, Di)203.,6SiO2.H20 Knopite, (Ca, Y, Fe, Ce)O-TiO2 Aenigmatite, a titano-silicate of columbium and iron Magnesium-orthite, 7{(Mg, Fe, Ca)O+(Fe, Al, Ce, Ob, La)2,0316SiO2-H20+F Eudialyte, Na2O.Ce2O3-FeO-MnO-Zr2O3-SiO2 Codazzite, (Ca, Mg, Fe, Ce)CO3 . Heretofore, these minerals have been regarded as quite resistant to deconiposition and none of the coniponents incorporated in the molecular structure have been deemed extractable unless total decomposition was acconiplished by prolonged digestion in expensive concentrated solvents, in some cases after costly prior fusion, usually at elevated temperatures and/or with a pressure of many atmospheres. The molecular structure has been regarded as not susceptible to such re-arrangement that a part of the molecule could be subtracted while the rest of the m<)Iecu.1e remained substantially unaffected. In my improved process, when treating minerals which have FeO present dn the moleculo of the mineral, it is possible to, in some instances, preferentially extract the iron and leave the more valuablo constituent, and in theother instances, to preferentially extract the iron together with the most valuable c6nstituents leaving behind the,
[2]3,105,755 3 valueless constituents substantially unattacked. In the latter instance, leaving the valueless constituents unattacked means, of course, a savings in reagent consumption -and a lesser dearee of contarnination in the primary concentration ofthe valuabl,- constituents. 5 'fhe FcO in all the above named minerals is not directly extractable by leaching with economical solvents because in each case, it is protected by the constituents - fornu'ng the rest of -.Lhe molecule. For the FeO to become susceptible to preforential leaching, it is not only necessary 10 to free it from the protection exerted by the natural lattice of the molecule, but also to free it in a readily soluble form. Fe3O4 is readily soluble but the FeO radical cannot be oxidized directly to FC304 because the FeO dnsistently seeks the highest common state of oxidation, 15 Fe2O3 - I have found that in all nlinerals available for testwork which contain an FeO radical (a radical being a group of atoms -w,.hich behave as an entity) the FeO is readily oxidizable to Fe2O3 by roasting in an oxidiz'mg latinosphere at t'@le normal temperatures used for conver- 20 sion of iron compounds -to Fe2O3, that is, at approximately 700 deg. C., the refractory characteristics toward reduction or solubility of the original mineral notwithstanding. Then, when this is followed by a strongly - reduc'mg roast, such as one performed in la carbon monoxide oic 25 hy,drogen latmosphere at 900-1260 deg. C., the Fe2O3, totally -or in part, is readily reduced to Fe3O4 orin some cases, partly to Fe3O,, and partly to FeO. A part of the iron, tssentially that part which is reduced to Fe3O4 ' IS freed from the original molecule @by such reduction anci 90 is available for leaching as unprotected iron open to attack by solvents. Tibe solvents necessary to dissolve -this iron can be any of the solvents in quite dilute form that ,are customarily used to dissolve finely divided magnetite, Fe3O4- Special condltions such ias elevated temperatures, 3,-3 extremely fine grinding or pressure leaching is not essential and in some cases, @undesirable, since such extreme measures will, in some instances, cause undue solution of that fraction which is desired to be left unattacked. The @chemical changes that take Piace during -the oxi40 dation and reduction steps that are responsible for re-;arrangement of the molecule and for leaving the irbn vulnerable to attack by solvents are easily demonstrated by taking chromite as an exam-ple. T,he formula for the chromite molecule may be Nvr@itten :as FeO-Cr2p3. The 45 magnesium and aluminum contained therein will be disregarded since they play,absoll ,tely no part in the reactions at any time. Faulty reasonin.- is shown by at@tem@pts to reduce the FeO to Fe since the Fe will still be protected in the chrom-ite molecule against acid attack un- 50 less very finegrinding and hot pressure leaching is resorted to mith concom-itant losses of @chromium. T-he FeO cannot be oxidized directly to iacid soluble Fe3O4 since it cannot be effectively prevented from @going directly to it were If ' the -highest common state o-f oxidation, Fe2O3 55 possible to oxidize the FeO directly to Fe3O4, the iron would still be protected from acid attack because althou.-h the formula forthe molecule would be changed to Fe3O4-3Cr2O3, no iron has actually been set free from t@he molecule, and but little iron can be learhed out un- 60 less hcyt pressure leaching with strong solvents is applied which invariably entails considerable solut-ion and loss Of chromium. If the FeO radical is first oxidized to Fe2O3 then the chromite formiila becomes Fe2O3-2Cr2O3, in ' ' w@hich each iron radical is coupled with two @chr4Dnlic 6D'do radicals. @-Ihave found that when this new larrange ox-i ment has been obtained, by oxidation, the Fe-bearing -radical can be reduced to lower states of oxidation, and that the chromic oxide radicals will be chemically satisfied with - the new arrangement of one Fe-bearing radical 70 ,to tw@o Cr.4bearing radicals even if the number of Fe atoms in the Fe radicial are reduced in number. Thus, ohromite, FeO-Cr2O3, can be oxid . ized to Fe-203-2Cr2O3 as 12(FeO@Cr2O3)+302=6Fe2O3 12Cr2O3. Each Fe radical now is cou@pled with two Cr rad-icals. 75 4 Then 6Fe,03 - 12Cr2O3 can be reduced to ZFe3O4 +@6FeO - 12Cr2O3 as 6Fe,O, - 12CrO, +4CO=2Fe,O, +6FeO- 12cr2(9+4CO2 Haff of the original iron content is now in theform of magnetite, Fe3O4, in a finely-divided condition, free from tho chromite molecule. It is readily ava-ilable for leaching and will leach out complettly in a very short time with dilute solvents at air temperature, at atmospheric pressure;and witliout fine, grinding. I have found, by examination of reduced,calcines under the microscope, that there is considerable -physical migration of iron durinc, ihe reduction roasting. Examination of -the reduced particles discloses many brownish crusty 1! ines!apparently delineating the exposed ed@ges of parting planes, together with a number of roughly circular bronvnish patche . After leaghing, the brownish lines and patches have disappeared, leaving in their place, iop@-n crevices )and minuto craters. I have found that,as much as half of the original iron content can be leached out,of @t-he chrorilite wwch has been crushed to minus ten mesh size, oxidized by roasting in an ic)xidizing atmosphere at iapproximately 700 @deg. C. for 3 hours, reduced by mixing with 2096 6f its own we,,tght of minus ten @mesh ordinaxylow-grade coal and roasting the inixture at approximiately 1200 deg. C. for four hours and leached for as little as 20 minutes with l@0% suliluric aid or by a,6% S02 gas in water solution; furthermore, that this can be done at air temperature, at atmospheric pressure, iand without any meichanical reduction in particle size - between any of the sev@ eral steps 6.f the process, wi@th only trace or negligible amounts of chromium goin, into solution. This nearly 100% recovery of chromite is important to the beneficiation because, b@eyond avoiding a ch'ar@ge for non-recovery, it meazis that the total degree of iron removal accrues to the benefit of improved Cr: Fe ratio. I prefer to @allow three hoiirs for the oxidizing roast, maintainin.- the temperature atapproximately 700 deg. C. with constant rabbling of the charge in order to insure free access of air to all particles. Particles that will pass through,a ten mesh screen are sufficiently fine for effective oxidation, -reduction and leaching. Test runs made on chromite that was 100% plus ten mesh and 100% minus, one-fourth inch resulted in about half as much iron being removed as duplicate tests r3iade on minus ten mesh material. Subsequent investigation showed that poorer results on the plus ten mesh sample were attributable to less-effective oxidation primarily, less effective reduction secondarily, and that the ,coarse siz I es hindere-d leaching to only a small extent. A sample of minus ten mesh chromite gravity concend found to contain 28.28% Cr, 12.42% Fe, 2.45% SiG2 trate marked "Lumnec Chromite Cone." was assayed an @andhadaCr:Feratioof2@28:1 Approximatelyone,kilo of this chromite was oxidized by hand-rabbling on an iron plate on top of a butane-fired furnace at approxirnately 700 deg. C. for 3 hours. At the end of the oxidation period, the charge was allowed to cool, then was mixed with 20% of its own weight of minus ten mesh low-grade coal and was poured loosely into a 3" x 14" :ffre-clay tube. One end of the tube was plugged and one end was. partially restricted, leaving a small, opening for gas escape. The charge was reduced in the butane furnace for four hours at 1200 deg. C. At the endof the reduc-tion period, the charge was quenched in water, washed free of un. consumed coal, dried and weighed@ The reduced product@ was very magiietic to a hand magnet, and the slight increase in weight indicated that reduction had been to magnetite rather than to elemental Fe. 100 grams of this minus ten@ mesh reduced caleine was leached by rolling in a bottle for 20 minutes with 500 cc. of 10% (by voltifyid) sulphuric acid. The fil-tered, washed, and dried residu6 assayed 30.27% Cr and 8.979@o Fe, showing,a Cr:-Fe ratio'
[3]5 of 3.37: 1. An assay of the filtrate for Cr disclosed that only 0.08% of the original:Cr had gone into solution. Several formulae are commonly ascribed to minerals known as "ilmenite." These are: (1) FeO-Fe2O3-3TiO2 (2) FeO-TiO2 (3) Fe3O4-3TiO2 No. 1 should be very slightly magnetic to a hand ma,-net, No. 2, the formula most commonly encountered, should be slightly magnetic, and No. 3 should be very magnetic to a hand magnet. It should be easily possible to oxidize by an oxidizing roast at 700 deg. C., any form of true ilmenite to a new molecular structure in which the iron is present as Fe2O3 as(No. 1) 4(FeO-Fe2O3-3TiO2)+02=6Fe2O3'12TiO2 (No. 2) 4(FeO-TiOz-) +02=2Fe2O3-4TiO2 (No. 3) 4(Fe3O4-3TiO2)+02=6Fe2O3'12TiO2 In this oxidized product, we have a new condition similar to that created by oxidizing chromite; here, each iron radical is now coupled with two titanium radicals. I have found that the oxidized iron radical can only be preferentially reduced t.0 Fe3O4 and metallic Fe as 6FeIO3-12TiO,+4CO=2Fe,O,+6FeO- 12TiO,+4CO2 and Fe3O4+4CO=3Fe+4CO2 There is evidently a substantially measurable amount of iron reduced to metallic Fe since the reduced product is extremely magnetic, more so than would be expected of an equivalent amotint of iron present as magnetite, since the loss of weight during the reduction is greater than could be accounted for by reduction of Fe2O3 to Fe3O4, and since the reduced product releases its iron more rea:dily to reagents adapted to metallic Fe solution than it does to solvents ordinarly used for Fe3O4 solution. Another reaction possible durin.- the reduction is. 6Fe,O,- 12TiO,+2CO@4Fe3O','12TiO2+2CO2 and 4Fe3Ol'l2TiO2+12CO=8Fe+4FeO- 12TiO2+12CO2 'nis reaction indicates that two-thirds of the original iron wil,l be in free elemental form. Since tests have shown that approxiinately tivo-thirds of the iron does become acid-soluble, and since the reduced product exhibits such marked magnetic susceptibility, this is the @reaction that is believed to indicate the greater part of the chemical change duringreduction. Tests have disclosed that removal of @pproximately t,"7o,-thirds of the iron is not prejudicial.to repeating the process and making a further extraction of iron f@-om the remaining one-third of the original iron content. A sample of minus ten mesh ilmenite concentrate recovered by gravity concentrat,.on methods from beach sands on the islaiid of Palawan, Republic of the Philippines and cleaned of contaminants by rep@ated passes through an induced-roll r@ia.-netic separator was found by assay to contain 49.95% TiO2 and 27.72% Fe. The sample was oxidized for three hours at 700 deg. C. with :constant handrabbling on an iron plate on top of a butane-fired furnace. At the end of the three hour oxidation period the charge was allowed to cool and was mixed with 200% of its own weight of minus ten mesh coal. The mixture was poured loosely into two 30-,-ram fire-clay crucibles and reduced at 1260 deg. C. for 4 hours. At the end of the reduction period, the charge-s were quenched in water, washed free of unconsumed coal and dried. TNventy-five grams of reduced calcine was then leached, at ten mesh size, for 20 minutes with 10% (by volume) sulphuric acid at air temperature and at atmospheric pressure. The filtered, washed and dried residue assayed 64.41% TiO2, 13.86% Fe and weighed 19.0 grams, showin.- a recovery in residue of 98.0% of the TiO2 and only 38% of the Fe. The 19 grams of residue, less the small 3,105,755 6 quantity taken out for assay purposes was re-oxidized,,rereduced and re-leached as before. The filtered, washed and dried residue from the second leaching weighed 12.5 grams and assayed 6.65% Fe and 75.84% TiO2 and .5 showed a TiO2 recovery in the residue of 98% while that of the iron was 40%. A small sample of minus ten mesh ferberite, said to have ori-,inated in the Republic of Korea and assaying 73.01% W03 and 18.40% Fe with small amount of Mn, 10 SiO2 and CaO waS Toasted for 3 hours at 750, de-. C. with free access of air and constant hand-rabblingo At the end of the oxidation period the charge was alloived to cool and was then mixed with 15% of its own weight of low-grade bituminous coal. The mixture was poured 15 into a 30-giram fire-clay crucible, covered with a loose fitting porcelain cover and reduced in the butane furnace at 1260 -deg. C. for four hours. At the end of the four hour reduction period, the charge was quenched in water, washed free of unconsumed coal and dried. 10 grams of 20 the reduced calcine was leached for 3 hours with 30% (by volume) sulphuric acid at air temperature and at atmospheric pressure,without further grinding. A@t the end of the threehour leaching period, the leached calcines were filtered, washed, dried and weighed. Leaching was 25 found to have caused a loss in weight -of 1.2 gramg or 12% of the original. The. clean residue assaye-d 83.00% W03 and 12.55% Fe. No W03 was lost by leaching but a very small amount of free yellow W03 was seen as very fine crystals in the residue. 30 There are many minerals which contain the rare earths such as cerium, lanthanum, prasedymium, neodymium, etc., and/or columbium, tantalum, thorium, and/or uranium. Practically all of,these minerals are very complex and quite refractory to attack both to heat treatment and 35 to acid attack. T-he usual method of attack is by total fusion with an expensive amount of alkaline reagents. f ha@ve found that when any of these minerals contains the FeO radical in its formula, the FeO, can be oxidized to Fe2O3 as described above, reduced to Fe3O4 as described, 40 and then successfully leached with dilute sulphuric acid at air temperature and without grinding to extreniely fine sizes. The iron can be caused to go into solution accompanied by a satisfactorily co-inplete percentage of the contained rare earths and/or columbium, tantalum, thorium and/or uranium. Silica and alumina are left be4 '3 hind unattacked, as are zirconitim and titanium when present. T-he solute contains essentially the valuableconstituents along with the iron, which can then be separated by convent-ional means. The disclosure here is not pretended to extend beyond provision of an economical 50 means of putting the valuable constituents of such minerals into solution. I do not intend to convey that tests have been made on all the minerals listed below, but because of the similarity 55 of the molecular structure of all these minerals, it is clearly evident that,disclosure of a method of economical attack on some of them constitutes a disclosure of a method applicable to all of them. Some of the minerals in this class are60 Dialmaite, (U, Ca, Pb, Bi, Fe) (Ta, Cb, Ti, Zr)309.nH20 Yttrotantalite, (Fe, Y, U, Ca, etc.) (Cb, Ta, Zr, Sn)04 Yttro-columbite-more Cb than the above Nohlite, (Ca, Mg, Fe, Y, etc., U)2(Cb, Zr, Fe Eschynite, (Ce, Ca, Fe, Th) (Ti, Cb) 206 )3010 65 Priorite, (Y, Er, Ca, Fe, Th) (Ti, Cb) 206 Samarskite, (Y, Er, Ce, U, Ca Fe, Pb, Th) (Cb, Ta, Ti, Sn)206 Fergusoni-te, (Y, Er, Ce, Fe) (Ta, Cb, Ti) 04 Columbo-tantalite, (Fe, Mn) (Cb Ta) 2,06 7o Polymignite, (Ca, Fe, Y, etc., i;, Th) (Cb, Ti, T,) 0 Zirkelite, (Ca, Fe, Th, U) 2 (Ti, Zr) 205 Brannerite, (U, Ca, Fe, Y, Th)3,Ti5Ol6 Ampangabeite, (Y, Er, U, Ca, Th)2-(Cb, Ta, Fe, Ti)7016 Knopite, (Ca, Y, Fe, Ce)O.TiO2 75 Aenigmatite-titano-silicate of columbium and iron
[4]7 Hellandite, 3 (A], Fe, Mn, Ce)203.2CaO.4SiO2.3H20 M agnesium-orthi,te, 7[(Mg, Fe, Ca)O+(Fe, Al, Ce. Cb. La)20316SiO,.H,O+F Eudialyte, Na2O-Ce2O3.FeO.MnO-Zr2O@3,SiO2 Codazzite, (Ca, Mg, Fe, Ce)CO3 Allanite, 4(Ca, Fe)0.3(Al, Ce, Fe, Di)203.6SiO2.H20 A sample of a rninus ten mesh variety of allanite, concentrated by gravity methods from beach sands on the Island of Palawan, was found to be infusible and unattack-ed by ordinary acids under any con@ditions. This allani,te concentrat@- assayed 21.5% rare calth oxides, 1.5% thoria, 8.82% Fe, 16.06,% A1203 and 31.00:% sio,. One kilo of this minus ten mesh allanite was oxidized by roasting for tbree hours on an iron plate on top of a butane-fired furnace with free access of air and constant hand-rabbling. At tlie end of the oxidation period, the charge was allowed to cool and was -then mixed with 20% of its onvn weight of minus ten mesh coal. The mixture was pol-ired loosely into a 3" by 14" fire-clay tube, wbose lower end was plugged with refractory cement. The upper end was left open, The charge was reduce,d for four hours at 1200 deg. C. At the end of the reduction perio,d, the charge was quenched in water, washed free of i,.nconsumed coal and dried. 50 grams of the reduced allanite was leaci@ed by rolling in a bottle for 16 hours -with 10% (by volume) sulphuric acid. At t,'@ie, end of the leaching period the charge was filtered, and the residue was well-washed. Assay of the products disclosed that, of the rare earths, 74% was @n the filtrate and 26% was in @the residue. Thoria recovery was 76% in filtrate, and 24% in residue. Iron was 65% in -filtrat-- and 35% in residue. Calciurn was almost 100% in filtrate while alumina and silica were almost 100% recovered in residue. Furth,-r exp.-rimental work will doubtlessly lead to better rare earth and thoria recovery in filtrate. If it does beconie evident that complete recovery can only come from fusion of the residue with suitable reagents, the tonnage necessitating such trea.tment wiH have been greatly reduced. Because of the simflarity of the m(>Iecular structure of the rareearth and/or columbium, tantalum, thorium and/or uraniumbearinminerals wl-iich contain an FeO ra@dical in such molecular structure, it is evident that disclosure of a method for economical attack on one constitutes disclosure of a method applicable to all. What is
