US2900231A

US2900231A - Process for extracting rare earths from ores and residues

Info

Publication number: US2900231A
Authority: US
Inventors: Howard E Kremers; David W Newman; Frank C Kautzky
Original assignee: American Potash and Chemical Corp
Current assignee: American Potash and Chemical Corp
Priority date: 1952-06-20
Filing date: 1952-06-20
Publication date: 1959-08-18
Anticipated expiration: 1976-08-18

Description

United States Patent PROCESS FOR EXTRACTING RARE EARTHS FROM ORES AND RESIDUES Howard E. Kren ers, David W. Newman, and Frank C. Kautzky, West Chicago, Ill assignors to American Potash 8; Chemical Corporation, a corporation of Delaw re No Drawing. Application June 20, 1952 eri N9! 1 17 Claims. (Cl. 2319) This invention relates to certain innovations and improvernents in processes for extracting rare earths from tires or residues rich in rare earth fluocarbonates or in the mineral, bastnasite. More particularly, the invention relates to novel processes for extracting rare earths from such ores or residues wherein either all or a portion of the rare earth values can be obtained directly as a granular, easily filterable precipitate of rare earth fluoride.

The ores may either be refined or they may be crude or semi-refined and contain variable amounts of mineral bastnasite together with gangue materials such as calcite, harite fluorspar, silicates, etc.

The'first st'ep in the conventional process for extracting rare. earths from ores and residues, e.g. monazite sands, involves reacting the rare earth ore with concentrated sulfuric acid. The reaction mixture is stirred and heated to. a tjemperature of approximately 230350 C. to convert the rare earth compounds in the ore into anhydrous rare earth sulfates. The reaction product is then leached water to, dissolve the rare earth sulfates and the resulting rare earth solutions were treated in various ways to obtain desired rare earth salts and compounds. However, the application of such conventional process to bastnasite type ores involves certain difficulties which malge, it objectionable. There is excessive frothing; the fluorine has to be eliminated to avoid subsequent formation of a slimy, gelatinous rare earth fluoride precipitate; and, additional facilities are required to recover the ex pelled hydrofluoric acid.

Aceording to the present invention it was found that the mineral bastnasite, which is essentially a rare earth fluocarbonate, and ores and residues rich in bastnasite or rare earth fluocarbonates, could be treated by a new and different process which oifered important and unexpected advantages and savings over the conventional process referred to above.

The term bastnasite as used herein designates broadly the group of minerals whose composition includes rare earths, fluoride and carbonate in various proportions with or without other constituents. A pure form of bastnasite would be represented by the general formula RPCO where R designates the rare earth elements. There are closely related bastnasite-type ores which have a somewhat different or more complex composition such, for example, as the mineral parisite. This mineral contains calcium in addition to the rare earths and has the general formula 2RFCO .CaCO

' Briefly, the process of the present invention involves first subjecting an ore or residue rich in bastnasite or in some other form of rare earth fluocarbonates, to a roasting operation so as to drive ofi' a substantial portion of the carbon dioxide content present as the carbonate. It has been found that during the course of such a roasting step when it is properly carried out, a substantial portion of the cerium present in the ore or residue is oxidized to the eerie (i.e. tetravalent) state, Furthermore, it appears that the rare earth fluocarbonate constitutent of the ore or residue is converted to rare earth fluo-oxide er a mixture of rare earth fluoride and rare earthogride. The roas ed e taine can e r ad ly and qu ckly dissolved even without heating in a dilute non-reducing acid, such as dilute nitric acid or dilute sulfuric acid, and the resulting solution separated from the ganglia Q1 insoluble residue. This solution which contains substantielly l f he r re e rth. alue of the. raw mat ia is then treated in one of two ways depending upon whether or not it is desired to obtain all of the rare, earth values in the for n of the flueride or only a part of them as such. In case it is desired to obtain all of the, rare earth values in the form of the fluoride, the, solution so obtained is treated with a soluble substance which furnishes fluoride ions such as, for example, hydrofluoric acid, or an alkali metal fluoride in suflicientquantity to directly precipitate all of the rare earth value, as a granular, easily filterable fluoride precipitate.

In case only a portion of the rare earth values are desired as the fluoride, then the solution of rare earths is treated with a suitable reducing agent such as sulfur dioxide and this treatment results in the formation of a precipitate of rare earth fluoride leaving the solution substantially fluorine free so that it can be treated in known manner to recover the rare earth values. p

The unroasted ores are generally onlysparingly soluble even in large excesses of acid and heating to elevated temperature is necessary in order to solubilize them.

An important object of the invention is an improved process for the extraction or recovery of rare earths from ores and residues rich in bastnasite or other rare earth fluocarbonates, whichcomprises first roasting the ore or residue so as to drive otf a substantial portion of the carbon dioxide content therefrom and oxidize a large portion of the cerium content to the ceric state, and then treat the roasted ore with acid, preferably a dilute nonreducing acid, so as to dissolve the rare, earth. values from the gangue or insolubles.

An important object of the invention is the provision of an improved method of treating ores and residues rich in bastnasite or rare earth fluocarbonates so as to place them in a highly porous condition where they are readily soluble in dilute acid without fine grinding.

Another important object of the invention is theproyision of a process of treating ores and residues richin bastnasite or rare earth fluocarbonates whereby rareearth fluorides can be obtained directly and incidental to the Process of re rin the r e earth. a u sv fr m su h ores and residues.

Another importantobject of the invention is a method Qt eat ng o PIQQQSSL JE; ores. o r siduesri h nbas n s q r a e ea hv fln carb es so a o obtain p ec p ta es o r e th fl o des, ch. aresra u a non-g l ti ous; easily t v ble a d ot er s cct v nienflynd easi y handled.

An he mportant j t. h nvention is provision of a novel method; of solubilizing relafiiYe y in so bl rare ear h fluori es y cond i the siium con en so a t f rm a c mple h hefi otide p esent which isreadily soluble inf dilute, acid.

no e mpo an o ject o he nve t on. a ava me h d. of co rin ra a h l s. item ore and residues, rich in bastnasite or rare earthfiuocarbonate ith the es ity f ha n to pel, the fli a de contentv of the ore.

Still a, further object of the invention is-a novel method, of: a g o e and. es dues richas na ite are; e rth fluc aibenatesse as. to par out he, f uor de; content directly in, the form, of rare earth fluoride, leanng e alanc of the a e ar h valueslin h ere/subs stantially' fluoride free.

.fornia.

obvious andwill, in part, appear hereinafter.

. For a more complete understanding of the nature and scope of the invention, reference may now be had to the following detailed description thereof wherein illustrative and preferred examples are set forth.

Commercial deposits of bastnasite are, among other places, located in the States of New Mexico and Cali- Bastnasite from the deposits in New Mexico is .of much higher purity than that available from the deposits in California. While ores from these or other deiposits of bastnasite are presently the primary raw materials used in the processes of this invention, it will be understood that bastnasite ores from other deposits may be used and also other ores or residues which are rich in rare earth fluocarbonatcs may also be utilized. The invention is also useful in connection with ores and residues containing rare earth fluorides or rare earth fluooxides for the recovery of the rare earth values therefrom.

The first step in the recovery of rare earths from an ore rich in bastnasite or a residue rich in rare earth fluocarbonates, after the ore or residue has been cleaned, is to roast the ore or residue so as to eliminate a substantial portion of the carbon dioxide content therefrom and oxidize at least a substantial portion of the cerium to the ceric state thereby converting the bastnasite or rare earth fluocarbonate into a condition such that it may be readily dissolved by a dilute acid. In general, the ore or residue should be roasted in such a way as to eliminate enough of the carbon dioxide content present as carbonates so that there will be no objectionable frothing when the roasted material is treated with the dilute acid. In addition, the roasting also has to be sufficient to convert an adequate proportion of the cerium from the trivalent to the tetravalent state so that it will form soluble complexes with the fluoride present in the ore and with theranion of the acid used for dissolution. However, the roasting must not be excessive, otherwise rare earth oxides will be formed which are refractory (i.e. dead burnt) in nature and highly resistant to attack with acid, and therefore not readily dissolved. It has also been found that during the roasting operation and as a result thereof the ores or residues acquire a high degree of porosity which further facilitates the rapid solution of the roasted material in the acid.

The ore or residue may be roasted either batchwise or continuously depending upon equipment available and existing facilities and conditions. Commercial type roasting equipment may be utilized. Rotary kilns and furnaces of standard design have been found to be very satisfactory.

After being roasted the ore or other raw material is subjected to treatment with acid to dissolve the rare earth values therein. A non-reducing acid is preferably used and commercially this means that the choice of acid will usually lie between sulfuric acid and nitric acid. However, in certain instances more expensive acids such as perchloric acid or acetic acid may be used in place of sulfuric or nitric acid. Acid-forming gases, such as sulfur dioxide, may be introduced into water suspensions of the roasted ores or residues in lieu of using acids themselves. It has been found that the acids may be dilute and usually dilute sulfuric acid or dilute nitric acid will be used because of the advantages in reduced cost, ease of handling, and less expensive equipment required. However, it will be understood that concentrated acid may be used if desired. Normally, excessive dilution is to be avoided because of the increased costs involved in handling large b-ulks of liquid and it is generally desirable to work with rare earth solutions which are as concentrated as practically possible.

It has been found that optimum results may be obtained in reacting the roasted ore or residue with the acid by following somewhat different techniques depending upon the particular ores or residues being handled. For example, in some cases it has been found to be desirable to add the roasted material to the mixture of the acid in water. However, in other cases it has been found desirable to first make a slurry of the roasted material in water and then add the acid or an acid-forming substance, e.g. S0 to the slurry. Usually the rate of solution will be sufliciently rapid and complete so that heating is not required. However, heating may be used to promote or increase the rate of dissolution and to hasten the reaction with the roasted ore or residue.

Normally, an excess of acid will be used so as to bring about practically complete recovery of the rare earth values and shorten the time of reaction ad dissolution.

After dissolution of the rare earth values from the roasted ore or residues, the insolubles consisting largely of non-rare earth materials present in the ore or residue may be removed either by settling followed by decanting, or by filtration, and the orange colored solution obtained may be further treated as described below to recover the rare earth values present therein.

It has been found that when the roasted ore or residue is solubilized with either dilute or concentrated acids, the portion of the cerium which was oxidized to the ceric state during roasting remains in the ceric state in the aqueous solution obtained by treating the roasted ore or residue with acid, except where acids are used which are capable of reducing the cerium, such as hydrochloric acid, sulfurous acid or sulfur dioxide. Furthermore, when the properly roasted ore or residue is dissolved in a dilute non-reducing acid, such as nitric or sulfuric, it has been found that the resulting solution contains not only practically all of the rare earths originally present in the ore but also practically all the fluoride ions originally present. It is believed that the fluoride content is held in solution as a soluble ceric fluoride complex compound, and it is the formation of such a complex which permits the roasted ore or residue to dissolve so readily and easily even in these dilute acids. The porous structure obtained on roasting increases the area and ease of contact of the acid with the ore and this also promotes easier and faster dissolution.

Ordinarily, when trivalent rare earth fluorides are precipitated from aqueous solution, the precipitate is a bulky, gelatinous mass which is difficult to handle and very difficult to filter off. However, it has been found that rare earth fluorides can be precipitated in the form of a granular, dense, and easily filterable precipitate from the solutions obtained in the present process by dissolving the roasted ores or residues in dilute acids.

Certain simple and easily followed precautions with respect to control and technique which are referred to below should be followed for best results. The solutions obtained by the acid treatment of the roasted ores and residues are treated according to one of the two main techniques referred to above depending upon the type of products to be obtained. There is a considerable commercial demand and market for rare earth fluorides for use as core ingredients of searchlight carbons and also for use in steel making. Accordingly, if rare earth fluorides are desired for these or other purposes, then the rare earth solutions obtained from the roasted ores or residues are treated by adding thereto a soluble material which furnishes fluoride ions. For example, hydrofluoric acid may be added or sodium fluoride or some other soluble fluoride having an unobjectionable cation. Preferably, the soluble fluoride is added slowly with agitation.

Upon the addition of the soluble fluoride no precipitate is formed at first until a suflicient amount of fluoride ionshas been added .to exceed the complexing .ability of the soluble ceric fluoride complex compound formed as the result of roasting. However, once this complexing ability or capacity has been exceeded, the rare earth fluorides begin to precipitate and continue to precipitate with the additions of more fluoride ions ,until substantially all of the rare earths present have been precipitated. The precipitate is dense and granular and easily filtered and managed. The quantity of fluoride added is appreciably less than the stoichiometric amount required to combine with the rare earthspr'esent since the fluoride present in the ore or residue itself is also effective in forming the precipitate.

' In the event-that it is not desired to obtain the maximum amount of rare earth fluoride from an ore or residue, then the alternate procedure is followed in handling the solutions obtained by the acid treatment of the roasted ceric fluoride complex is destroyed, whereupon a precipitate of rare earth fluoride is obtained. This precipitate is dense and granular and easily filtered and managed as distinguished from the usual bulky, slimy, unmanageable and unfilterable rare earth fluoride precipitate. By introducing the reducing agent in the proper amounts and in the proper manner, practically all of the fluoride content of the solution can be removed in the .form of rare earth fluorides leaving a solution or filtrate which contains practically no fluoride. The rare earths remaining in the solution or filtrate will be largely rare earth sulfate or nitrate, depending upon whichof these two acids was used for dissolving the roasted ore or residue. The essentially fluoride-free rare earth solutions can be handled in known manner to recover the rare earths therefrom, as for example, by the precipitation of the rare earths as rare earth sodium sulfate or rare earth oxalate.

The rare earth fluoride precipitate obtained by the reduction, technique is not a pure rare earth fluoride but is contaminated with sulfate, nitrate or other anion depending upon the particular acid used and the conditions of precipitation. However, such sulfate or other anion can be rather easily removed to provide a rare earth fluoride of commercial quality by treating the precipitate with aqueous hydrofluoric acid, washing the precipitate to remove excess hydrofluoric acid .and sulfuric or nitric acid, filtering the precipitate and drying.

The following illustrative examples will now be given to more fully acquaint those skilled in the art with practical methods .ofpracticing the invention.

Example 1 A bastnas'ite-containing ore was processed which analyzed 27% rare earth oxide, 6.6% SiO 3.6% MgO, 6.1% 'CaO, 29.4% BaO, 2.8% M (where M=Al, Fe, Ti, etc.), 3.1% F, 13% S03, and 10.6% loss on ignition (largely carbonate). The ore was first roasted in a rotary type furnace at a temperature of about 650 C. until test portions of the roasted product showed that no further appreciable loss on ignition occurred. This roasting period required approximately 3 /2 hours. During the roasting step a major portion of the cerium content of the ore was oxidized to the eerie state and the ore acquired a noticeable porosity.

The roasted ore was then added to a solution of sulfuric acid in water in the proportions by weight of 400 parts of 66 r-B. sulfuric :acid to 1000 parts of water and i000 parts of the roasted 'ore. The mixture was agitated so as to hasten the dissolution of the rare earths in the dilute acid. After the mixture had been agitated for 6 about 3 hours the solution was filtered off. The insolubie residue, consisting largely of the non-rare earth materials present inthe ore, was washed with 1% sulfuric acid solution and the wash liquor combined with the filtrate.

The filtrate was separated into two approximately equal portions. Aqueous hydrofluoric acid was slowly added to one portion with suflicient agitation to insure a fairly uniform mixture. Heating from about 60 C. to boiling promoted the formation of a granular rare earth fluoride precipitate. At first no precipitate forms but on continued addition of the hydrofluoric acid a precipitate of rare earth fluoride begins to form and settle out. Addition of the hydrofluoric acid is continued until a test sample shows that no more rare earth fluoride precipitate forms, at which point the remaining solution is practically free of rare earths. Since there is a substantial portion of fluoride already present in the rare earth solution as derived from the bastnasite ore, only suflicient hydrofluoric acid or other soluble fluoride needs to be added to complete the formation of rare earth fluoride.

The precipitate of rare earth fluoride obtained may contain up to several percent of sulfate ion. By adding an excess of hydrofluoric acid to the reaction mixture containing the precipitate until it smells distinctly of hydrofluoric acid and then boiling the solution, the sulfatecontaminated rare earth fluoride may be converted to rare earth fluoride of commercial quality. The precipitate of rare earth fluoride as formed also may be freed of sulfate by filtering off the residual solution and reslurrying the precipitate with additional hydrofluoric acid. The rare earth fluoride precipitate is granular in nature and is easily filtered and handled.

The cerium in the rare earth fluoride precipitate is practically all in the eerie state. If it is desired to have substantially all of the cerium in the cerous state, the precipitate may be treated with a reducing agent either before or after separation from the precipitation solution. Suitable reducing agents for this purpose are sulfur dioxide, oxalic acid, hydrochloric acid, etc.

The second portion of the rare earth solution obtained by dissolving the roasted ore in the dilute sulfuric acid was heated to a temperature of between 40 C. and boiling and sulfur dioxide gas was introduced into the solution so as to reduce the eerie ions to the cerous state. After a suflicient amount of the sulfur dioxide had been introduced, a rare earth fluoride precipitate began to form and continued to form on addition of sulfur dioxide until practically all of the fluoride content of the solution was removed therefrom as the rare earth fluoride precipitate. The rare earth fluoride so precipitated was very granular, settled well, and was extremely easy tofilter and wash. Such a precipitate is usually contaminated with various amounts of rare earth sulfate, the extent of contamination depending primarily upon the temperature at which the precipitation is made. If the precipitations are made at boiling or near-boiling temperatures, increased amounts of rare earth sulfate are present in the rare earth fluoride precipitate .due to the inverse solubility of rare earth sulfates with increase in temperature. Accordingly, the amount of rare earth sulfate in .the precipitate can be reduced by carrying out the precipitation at a lower temperature of around 40 C. Furthermore, it has been found that the amount of rare earth sulfate in the precipitate can also be reduced by diluting the rare earth solution obtained by dissolving the roasted ore in dilute acid, with either water or with dilute acid before the addition of the reducing agent so .as to produce a concentration of the solution such that the rare earth sulfate will not;precipitate from the solution under the conditions .of heating employed.

After the precipitation of the rare earth fluorides complete, they may be separated from the solution by filtration or other means and ,the filtrate will contain largely rare earth sulfate. The rare earth values can '7 be recovered from such filtrate by conventional or known methods. For example, the rare earths may be precipitated from the filtrate as rare earth oxalates or as rare earth sodium sulfates, and these precipitates may be treated in known and conventional manners to produce other rare earth salts.

In one experiment, one liter of rare earth sulfate filtrate solution obtained by dissolving roasted ore in dilute sulfuric acid in the manner described and analyzing 133 grams per liter of rare earth oxide and having a density of 27 B., an acidity of 0.6 N H 50 and having 92% of the cerium in the ceric state, was heated to 60 C. while stirring. Sulfur dioxide gas was introduced into the solution at the rate of 0.2 gram per minute for a period of 50 minutes. At the end of this time the cerium was completely reduced and a granular precipitate of rare earth fluoride was removed by filtration and washed with water. The dry precipitate weighed 68 grams and analyzed 67.3% rare earth oxide (including 31.9% CeG 16.9% F, and 8.0% S The filtrate contained practically no fluoride.

Certain modifications and variations may be made in carrying out the process as described in the foregoing example. First of all, with respect to the roasting of the ore, the roasting temperature may range from approximately 400 to 800 C. The exact temperature and degree of roasting in any instance will depend upon several factors including the nature of the particular ore being processed, the type of equipment available and the time limits on the roasting operation. The amounts of acid and water used to dissolve the roasted ore may be varied within rather wide limits but it is usually desired for practical purposes to have the rare earth solution obtained as concentrated as possible so as to reduce the bulk of the solution that has to be handled and worked with. While concentrated acids, such as sulfuric or nitric, may be employed so as to still further minimize the bulk of the solutions handled, it has been found economical and practical to normally employ either dilute sulfuric or dilute nitric acid. The mixture of acid and water and roasted bastnasite may be either hot or cold, and if a sufficient excess of acid is used, the dissolution of the rare earth values will be complete in a period of time ranging from a few minutes to two or three hours depending upon conditions and nature of the ore.

Instead of using hydrofluoric acid as the fluoride ion furnishing material for precipitating rare earth fluoride, other soluble fluorides may be used, such as sodium fluoride or the less soluble calcium fluoride.

Many other reducing agents besides sulfur dioxide may be used in carrying out the phase of the process wherein the solution of roasted bastnasite ore is handled so as to precipitate its fluoride content such as starch, sugars, oxalic acid, carbon and carbonaceous materials, metals such as iron and zinc, reducing acids such as hydrochloric acid and formic acid, hypo, sulfites, thiosulfates, and hydrogen peroxide.

Example 2 A sample of the roasted ore obtained in accordance with Example 1 above was slurried with water and sulfur dioxide gas was bubbled into the slurry until the slurry was saturated and there was no further dissolution of rare earths. After introduction of the S0 had gone part way a precipitate of rare earth fluoride began to form. At the end of the experiment there was an in soluble portion consisting of rare earth fluoride precipitate and residue from the ore, and a soluble portion comprising a solution of rare earth sulfate. The rare earths in both portions can be separated or recovered in known manner.

While the invention is largely useful in connection with the processing of ores containing bastnasite, it may also be used in processing various residues which may be 'rich in rare earth fluocarbonates and which therefore correspond generally to bastnasite.

The discovery that ceric or tetravalent cerium forms soluble complexes with fluoride and additional anions, such as the sulfate and nitrate anions, may be employed in other connections than in the extraction of rare earth values from bastnasite ores or residues rich in fluocarbonates. Another such use is illustrated by the following example:

Example 3 A residue containing a substantial quantity of rare earth fluoride is treated with ceric sulfate in a solution of sulfuric acid. The rare earth fluoride dissolves in such a solution apparently due to the complexing capacity of the ceric ion. The rare earth fluoride may then be precipitated from the resulting solution by the addition of a reducing agent, such as hydrogen peroxide, which reduces the cerium to the cerous state. Alternately, hydrofluoric acid or some other soluble fluoride may be added to precipitate the rare earth fluoride. In either case, the precipitate of rare earth fluoride obtained is granular and is very easy to filter and wash.

In view of the foregoing disclosure, those skilled in the art will be able to carry out the processes of the invention according to the examples set forth above or with such variations and modifications as will be readily apparent. Therefore, it will be understood that all matter describw above is to be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive ofi a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with a non-reducing acid so as to dissolve the rare earth metal values of the material.

2. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive olf a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with a dilute non-reducing acid so as to dissolve the rare earth metal values of the material.

3. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with sulfuric acid so as to dissolve the rare earth metal values thereof.

4. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with nitric acid so as to dissolve the rare earth metal values of the material.

5. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with dilute sulfuric acid so as to dissolve the rare earth metal values of the material.

6. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roast ing such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, and treating the roasted material with dilute nitric acid so as to dissolve the rare earth metal values of the material.

7. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, treating the roasted material with a non-reducing acid so as to dissolve the rare earth metal values of the material, and adding a water soluble fluoride to the resulting solution of rare earth metal values to obtain an easily filterable precipitate of rare earth fluoride.

8. The process of claim 7 wherein the water soluble fluoride is added in a suflicient amount to substantially completely precipitate the rare earth metal values of said solution.

9. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, treating the roasted material with a dilute nonreducing acid so as to dissolve the rare earth metal values of the material, and adding a water soluble fluoride to= the resulting solution of rare earth metal values to obtain an easily filterable precipitate of rare earth fluoride.

10. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive E a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, treating the roasted material with dilute sulfuric acid so as to dissolve the rare earth metal values of the material, and adding a water soluble fluoride to the resulting solution of rare earth metal values to obtain an easily filterable precipitate of rare earth fluoride.

11. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, treating the roasted material with dilute nitric acid so as to dissolve the rare earth metal values of the material, and adding a water soluble fluoride to the resulting solution of rare earth metal values to obtain an easily filterable precipitate of rare earth fluoride.

12. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, treating the roasted material with a non-reducing acid so as to dissolve the rare earth metal values of the material, treating said resulting solution of rare earth metal values with a reducing agent capable of reducing ceric cerium so as to precipitate rare earth fluoride therefrom, and separating the substantially fluoride-free filtrate from the rare earth fluoride precipitate.

13. The process of extracting rare earth metal values from ores rich in bastnasite which comprises roasting the ore to drive 01f a substantial amount of carbon dioxide therefrom and impart a porous structure to the ore and oxidize at least a portion of the cerium, treating the roasted ore with an excess of dilute sulfuric acid so as to dissolve the rare earth metal values, separating the resulting solution of rare earth metal values from the insoluble material, and adding to the solution a substance capable of furnishing fluoride ions in an amount suflicient to precipitate substantially the entire content of rare earth metal values as rare earth fluoride.

14. The process of extracting rare earth metal values from ores rich in bastnasite which comprises roasting the ore to drive 01f a substantial amount of carbon dioxide therefrom and impart a porous structure to the ore and oxidize at least a portion of the cerium, treating the roasted ore with an excess of dilute sulfuric acid so as to dissolve the rare earth metal values, separating the resulting solution of rare earth metal values from the insoluble material, and adding to the solution a fluoride compound selected from the group consisting of hydrofluoric acid, alkali metal fluorides and alkaline earth fluorides in an amount sufficient to precipitate substantially the entire content of rare earths as rare earth fluoride.

15. The process of extracting rare earth metal values from ores rich in bastnasite which comprises roasting the ore to drive off a substantial amount of carbon dioxide therefrom and impart a porous structure to the ore and oxidize at least a portion of the cerium, treating the roasted ore with an excess of dilute sulfuric acid so as to dissolve the rare earth metal values, separating the resulting solution of rare earth metal values from the insoluble material, introducing sulfur dioxide into the solution to produce a precipitate of rare earth fluoride, sufficient sulfur dioxide being added so that practically all of the fluoride content of the solution is consumed in said precipitate, and separating the rare earth fluoride precipitate from the remaining solution of rare earth metal values.

16. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive off a substantial portion of carbon dioxide therefrom and oxidize at least part of the cerium, slurrying the roasted material in water, and treating the slurry with an acid-forming gas so as to dissolve the rare earth metal values of the material and form a precipitate of rare earth fluoride.

17. The process of extracting rare earth metal values from a material rich in a substance selected from the group consisting of bastnasite and cerium-containing rare earth fluocarbonates which comprises the steps of roasting such a material to drive ofl a substantial portion of carbon dioxide therefrom and oxidize at least part of the eerie cerium, slurrying the roasted material in water, and treating the slurry with sulfur dioxide so as to dissolve the rare earth metal values of the material and form a precipitate of rare earth fluoride.

References Cited in the file of this patent UNITED STATES PATENTS 'Ihews Mar. 16, 1926 OTHER REFERENCES Yoshiga et al.: Chemical Abstracts, vol. 47, col. 7173(0), abstracted from Japan. 2266 (1952), June 18.

Browning: Introduction to the Rarer Earth Elements, pub. by John Wiley and Son, Inc., N.Y., 1914, page 43.

Hopkins: Chemistry of the Rarer Elements, pub. by D. C. Heath and Co., NY. 1923, page 98.

Levy: Rare Earths, pub. by Longmans, Green and Co, N.Y., 1924, page 154.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 5, pages 521, 522, 545 and 564 (1924).

Claims

9. THE PROCESS OF EXTRATING RATE EARTH METAL VALUES FROM A MATERIAL RICH IN A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF BASTNASITE AND CERIUM-CONTAINING RARE EARTH FLUOCARBONATES WHICH COMPRISES THE STEPS OF ROASTING SUCH A MATERIAL TO DRIVE OFF A SUBSTANTIAL PORTION OF CARBON DIOXIDE THEREFROM AND OXIDIZE AT LEAST PART OF THE CERIUM, TREATING THE ROASTED MATERIAL WITH A DILUTE NONREDUCING ACID SO AS TO DISSOLVE THE RARE EARTH METAL VALUES OF THE MATERIAL, AND ADDING A WATER SOLUBLE FLUORIDE TO THE RESULTING SOLUTION OF RARE EARTH METAL VALUES TO OBTAIN AN EASILY FI RABLE PRECIPITATE OF RARE EARTH FLUORIDE.