US3079226A - Tungsten extraction and purification process - Google Patents

Description

3,079,226 TUNGSTEN EXTRACTION AND PURI- FlCATlON PRGCESS Arthur E. Newlnirlr, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York No Drawing. Filed June 1, 1960, Ser. No. 33,097 20 Claims. (Cl. 23-49) This invention relates to a process of separating tungsten values, substantially free of molybdenum values, from tungsten ores containing molybdenum which comprises digesting the ore in the presence of an acid and extracting this aqueous digestion mixture, either during or after the digestion step, with a ketone having limited solubility in water.

More particularly, this invention relates to a process of separating tungsten values, substantially free of molybdenum values, from their ores which comprises digesting the ore with aqueous hydrochloric acid and extractin this digestion mixture with an .aliphatic ketone. Still more particularly, this invention relates to a process of separating tungsten values substantially free of molybdenum values from tungsten ores, containing molybdenum values as an impurity, which comprises digesting the ore with aqueous hydrochloric acid and extracting the digestion mixture with methyl isobutyl ketone.

This application is a continuation-impart of my application Serial No. 724,898, filed March 31, 1958, assigned to the same assignee as the present invention and now abandoned.

Tungsten minerals can be conveniently divided into two groups, a scheelite group and the so-called black ore group, sometimes referred to as the wolframite group. The black ore group is a generic name for various ores which are a mixture of iron tungstate and manganese tungstate in various proportions from essentially pure iron tungstate to essentially pure manganese tungstate. This generic class of tungsten ores is sometimes broken down into three classes of ores in which those ores containing up to 20 percent by weight of manganese tungstate (MnWO are called fenherite, and those ores containing from 20 percent to 80 percent by weight of manganese tungstate are called wolframite, and those ores containing from 80 percent to 100 percent of manganese tungstate are called hiibnerite. In each of these ores the remainder, except for impurities, is iron tungstate ('FeWO It is thus seen that these three minerals form a continuous series of iron-manganese tungstates, of which the iron end is ferherite and the manganese end is hiibnerite. Pure ferberite and pure hiihnerite are not found as such in nature. The scheelite group contains only one commercially important mineral, scheelite itself, which is a calcium tungstate (CaWO but as used in this specification and claims also includes the synthetic scheelites which also are calcium tungstates known in the art and correspond generally to the formula CaWO scheelite is the most available domestic tungsten ore in the United States.

These tungsten ores and their impurities which cause trouble in processing are discussed in great detail in many of the books available on tungsten, for example, the book by C. I. Smithells, Tungsten, Chemical Publishing Company, Inc, New York, first American edition (1953), and the book by K. C. Li and C. Y. Wang, Tungsten, Rheinhold Publishing Corp, New York, third edition 3,079,226 Patented Feb. 26, 1963 (-1955). On page 116 of the book .by Li and Wang, for example, there is the statement: In most cases, the elements presenting the most serious problem are molybdenum, bismuth and sulfur. Of the three, the removal of molybdenum if present in the form of a chemical combination with tungsten and calcium (powellite type), presents the most difficulty and so far as is known, is not extractable except by chemical treatment.

Under normal procedures, the black ores are usually fused with an alkali such as sodium carbonate or caustic soda or digested with an aqueous solution of these reagents to produce a water-soluble sodium tungstate which can be dissolved away from the major amount of impurities and further purified by conversion to an artificial scheelite ore, e.g., by treatment with calcium ch oride, which is further treated in the same way as the scheelite obtained from the natural ore. The scheelite ores are digested with hydrochloric acid to produce an insoluble tungstic acid which is converted to ammonium paratungstate and finally to tungsten trioxide (W0 Smithells, on page 30, states that the wolframite ores may also be decomposed with acids (for example, hydrochloric acid) but they produce a product of inferior purity. Such a process is valuable When it is desired to recover the iron and manganese content of the black ores.

Because of the great similarity in chemical structure between tungsten and molybdenum, whenever molybdenum appears as an impurity in the tungsten ores, a high percentage of the molybdenum values present in the ore remain with the tungsten values. An additional chemical purification step is required, to separate the tungsten from the molybdenum values. As shown by Smithells on page 37 and page 38 of the above-quoted book, many tungsten ores contain up to 5 percent molybdenum. Owing to the similarity of its chemical properties with those of tungsten this element is difficult to remove. Unless special precautions are taken, the ammonium paratungstate will contain 20 to 25 percent of the molybdenum present in the original ore. Since even very small amounts of molybdenum in tungsten (in the order of USS-0.1%) are undesirable for tungsten to be used for such applications as lamp filaments and tungsten carbide tools, it is highly desirable to have a sim ple, reliable and efficient method of extracting tungsten from scheelite with as low a molybdenum content as possible without having to rely on additional chemical and metallurgical processes to obtain the desired purity.

Soluble molybdenum compounds have been extracted from an aqueous hydrochloric acid solution by the use of oxygen containing organic solvents immiscible with water according to the method described by Nelidow et al., J. Phys. Chem, 59, 710-18 (1955). However, this method is not specific for molybdenum compounds so that certain other metal compounds, if present, will also be extracted. Because of the chemical similarity of tungsten and molybdenum, it would be expected that tungsten and molybdenumcompounds, if present, together, would be simultaneously extracted by these solvents.

l have now discovered a simple, reliable and efiicient method of separating tungsten substantially free of molybdenum from tungsten ores containing molybdenum as an impurity without solubilizing all of the metallic values in the ore, which comprises digesting the ore with hy- 3 s drochloric acid and extracting the digestion mixture with methyl isobutyl ltctone. My invention may be practiced by a preferred method which comprises having methyl isobutyl ketone present during the digestion step or by an alternate method which comprises performing the digestion in the absence of methyl isobutyl ketone.

The alternate method comprises digesting the ore with hydrochloric acid for the usual digestion period, followed by intimatmy contacting the digestion mixture with methyl isobutyl ketone. The organic layer is separated and additional portions of the organic solvent can be used to provide greater removal of the molybdenumwhich is preterentiallyextracted into the organic layer, while substantially all of the tungsten values remain as a precipi-' tate which is insoluble in both the aqueous and organic phases.

In the preferred method of practicing my invention, methyl isobutyl ketone is present during the entire time that the tungsten ore is being digested with the hydrochloric acid. At the end of the digestion period, the reaction mixture consists of three phases: the insoluble precipitate containing the tungsten values in the form ofltungstic acid, H WO mixed with silica and other acid insoluble constituents of the ore, the aqueous acid phase containing the calcium, a minor amount of the iron, manganese, etc., as the corresponding chlorides and excess hydrochloric acid, and the organic phase containing substantially all of the molybdenum values as a molybdenum oxychloride, probably MoO Cl the major amount of iron,'and the manganese, etc. The organic layer is removed from the other two phases. Additional solvent extractions can be made if desired to etfect further removal of the molybdenum values from the aqueous and solid phases. For a given number of steps, the preferred method will produce an exceptionally purer tungsten than the alternate method of practicing my invention.

After the last organic layer is removedv in either of the above two methods of practicing my invention, the aqueous acid layer is separated, for example, by filtration, centrifugation or decant'ation, etc., from the solid residue containing the tungsten values. The solid residue is washed with water containing hydrochloric acid to prevent the tungstic acid from being peptized. Theresulting tungstic acid residue can be converted to tungsten metal by any desired method. For example, it can be treated with ammonium hydroxide to form ammonium tungstate which can'be crystallized as ammonium parat-ungstate, as is well known-in the art, to further purify the tungsten values and separate them from the impurities. Ammonium paratungstate can be converted to tungsten oxide which can be reduced to tungsten metal by hydrogen.

The clean separation of tungsten and molybdenum is unexpected because of the chemical similarity of molybdenum and tungsten and the fact that molybdenum tends to replace tungsten isomorphously in its compounds. At the same time, my process also removes substantially all of the other impurities in the ore so that the tungsten produced by my process is of very high purity. The results are further unexpected because of the superior separation obtained with methyl isobutyl ketone in comparison to other oxygen-containing solvents known to extract molybdenum from its solutions. The results are still further unexpected because of the tremendous advantage obtained by. having the methyl isobutyl ketone present during the digestion period.

The acid digestion is carried out in a manner Well known to those skilled in the art. An example of a suitable rnethod of digestion is described in Smithells, C. 3., Tungsten, Chemical Publishing Co, New York, first American edition (1953), page 30 et seq, which gives the procedure for the digestion of tungsten ores with hydrochloric acid. In order to oxidize the impurities present, small amounts of concentrated nitric acid are usually added toward the end of the digestion period. Eecause of the known ability of nitric acid to oxidize or nitrate organic compounds, it is surprising to find the nitric acid does not destroy any'significant quantity of ".e methyl isobutyl ketone if it is present during the digestion period.

When the alternate method is used, I have also discovered that the molarity of the hydrochloric acid at the end of the digestion period is critical for maximum separation of the molybdenum in the tungsten values. Generally, in the digestion of tungsten ores with hydrochloric acid, two parts by weight of 12 molar (12 M) aqueous hydrochloric acid are used for each part by weight of ore. Under these conditions the concentration of hydrochloric acid in the aqueous phase at the end of the digestion period is approximately 9 molar. By reducing this molarity to a range of 6 to 8 before extracting with methyl isobutyl ketone the amount of molybdenum impurity present in the residual tungstic acid can be reduced by a factor of 3. This adjustment in molarity of the hydrochloric acid can be done simply by addition of water, by neutralization with a base such as sodium, potassium, or calcium hydroxides, or carbonates. Because of the simplicity of the method, I prefer to adjust the molarity by the addition of water. As would be apparent to one skilled in the art, the final molarity of the acid in the aqueous layer also can be controlled by either starting with less than 12 molar hydrochloric acid, or by using a smaller amount of 12 molar acid. My experiments show that I obtain a greater separation of the molybdenum values from the tungsten values if I choose conditions such that at the end of the digestion period the acid molarity will be the maximum. However, proc ess losses of the tungsten are apparently directly proportional to the volume of aqueous digestion layer under otherwise equal reaction conditions. Since 12M is the most concentrated hydrochloric acid available commercially, I have found that these two opposing effects are compromised best by so choosing the reaction conditions that the acid molarity at the end of the digestion period is approximately 9 M. After the digestion period I adjust the molarity to be in the range of 6 to 8, preferably 7, before adding the methyl isobutyl ketone to extract the molybdenum. Although this adjustment in molarity can be performed after the methyl isobutyl ketone is added, it is more time consuming because some of the acid extracts into the organic layer. Under such conditions it would be necessary to determine the amount of acid present in both the aqueous and organic layers and calculate the molarity as though all the acid was in the aqueous layer. If longer digestion times are not objectionable, reaction conditions resulting in molarities as low as 4 at the end of the digestion'period are not objectionable, but the losses are higher and the tungsten purity is lower than when higher molarities are obtained, with other process conditions being equal.

The amount of aqueous acid used for the digestion can be varied within Wide. limits, taking into consideration that the theoretical amount of acid required is 2 moles of acid for each mole of tungsten. In practice, I have employed 1.95 to 8 moles of hydrochloric acid for each mole of tungsten present in the ore. Preferably, I employ a minimum of 4 moles of HCl per mole of tungsten in the ore, since the use of less acid results in less than recovery of the tungsten. Although greater than 10 moles of acid can be used per mole of tungsten, no apparent benefit is attained thereby.

Table I shows the relationship between time of digestion, the acid normality at the start, the ratio of the moles of acid to moles of tungsten and the acid molarity at the end of the digestion. Some deviation from this table can be expected because of variations in actual normality of the acid used and the amount of acid escaping from the digestion vessel vent.

TABLE I Digestion time, hrs. at 80 0.

Acid molarity at end of digestion Acid molarity at start 6 8 Moles H01 per mole o! tungsten The temperature and time at which maximum digestion is efiected is well known in the art, for example, from 40 C. to 110 C., but preferably from 75 C. to 85 C. for 1 to 24 hours, but preferably from 2 to 8 hours. Although atmospheric pressure produces excellent results the use of superatmospheric or subatmospheric pressures is not precluded. In order to minimize loss of the agents by evaporation, I prefer to carry out the acid digestion under conditions whereby the maximum amount of reagent vapors is condensed and returned to the reaction mixture.

The amount of methyl isobutyl ketone used to extract the molybdenum from the digestion mixture can be varied within wide limits, for example from /2 to 3 volumes of methyl isobutyl ketone per volume of aquous layer to be extracted. Although the number of times I may extract with fresh portions of methyl isobutyl ketone is not limited, for practical purposes I usually use 3 separate portions of methyl isobutyl ketone, each portion of ketone being equal in volume to the volume of the aqueous solution being extracted. The organic layers containing the molybdenum values may be combined and the molybdenum values recovered by evaporation of the organic liquid which can be reused in the process. The molybdenum values can be treated by known metallurgical techniques for conversion into metallic molybdenum.

If the preferred method is utilized, I have found that I do not need to adjust the molarity of the acid at the end of the digestion period, although such a step is not precluded. In this case,-however, some of the hydrochloric acid will be in the organic layer and molarity should be adjusted to the preferred range of 6-8 M by determining the acidity of the organic and aqueous phases and calculating the acid concentration as though it were all in the aqueous phase. The presence of the organic liquid during the digestion period evidently causes the digestion and extraction of the molybdenum to proceed in a somewhat diiierent fashion than if the methyl isobutyl ketone is added after the digestion period, since 1 have found that if the organic liquid is present during the digestion period, the amount of molybdenum impurity present in the tungsten is markedly less than can be attained in the same number of steps and combination of conditions utilizing the first way of applying my invention. amination of the examples illustrating how my invention may be carried into effect. The amount of methyl isobutyl ketone present during the digestion can be varied within wide limits; for example, from /2 to 3 parts of organic liquid by weight for each part by weight of ore, although the use of higher amounts of organic liquid is not precluded. Preferably, I use 1% to 2 parts of organic liquid per part of ore. The amount of acid used for digesting the ore is the same as described above for the first means of carrying my invention into eiiect.

After separating the organic layer present during the digestion the aqueous layer and solid residue is preferably extracted with one or more additional portions of methyl isobutyl ketone to insure more complete separation of the molybdenum from the tungsten. The volume of these portions of organic liquid is preferably of equal This diiference will be evident by exvolume with the volume of the aqueous layer being extracted. However, as the examples will illustrate, the organic liquid present during the digestion period will have removed a high percentage of the molybdenum, so there is nothing critical about the amount of organic liquid used in the later processing steps.

' The solid tungstic acid from either of my means of carrying my invention into efiect, is separated from the aqueous acid layer, for example by filtration, centrifugation, or decantation. The solid material is washed first with water and finally with water containing a small amount of hydrochloric acid to prevent peptizing the solid material in the washwater. The resulting substantially pure tungstic acid can be separated from the silica and other insoluble matter by treatment with ammonium hydroxide to form ammonium tungstate which is soluble in water. The ammonium paratungstate is crystallized from solution and can be recrystallized if further purification is desirable, converted to tungsten oxide, and then reduced to tungsten metal with hydrogen by any of the methods well known in the art, for example by methods described in the above-identified book by Li and Wang.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation.

There are three stages in the processes described in Examples l-lO. Stage I.The Digestion of the Ore; Stage Ii.--The Washing of the Tungstic Acid Precipitate; and Stage Ill-The Preparation of Ammonium Tungstate Solution.

Stage I.--The Digestion of the Ore parts by weight of 100 mesh scheelite ore are added to 240 parts by weight of concentrated (1?. molar) hydrochloric acid and heated to 80 C. for about 7 to 8 hours with vigorous stirring. Approximately 7 parts by weight of concentrated nitric acid are added slowly and the reaction mixture digested at 80 C. for an additional 30 minutes. Where methyl isobutyl ketone is present during the digestion period, approximately parts by weight, are used.

Stage II.-Washing of the Tungstic Acid Precip'itate In order to provide a control standard against which to measure the efiicacy of the methyl isobutyl ketone in reducing the amount of molybdenum in the final tungsten product, an extraction was carried out whereby, after the acid digestion in the absence of methyl isobutyl ketone, the aqueous layer was decanted from the precipitate in such a way that the decanted liquid was filtered to insure complete removal of all solid suspended matter and substantially all of the precipitate was left in the reaction vessel. The precipitate was washed 4 times, each time with a volume of water equal to the volume of the original aqueous layer, and the washwater was decanted through the same filter so that all of the filtrates were combined into one receiving vessel. The precipitate was washed 4 times with separate portions of 0.01 molar hyagoraaae drochloric acid equal to the volume of the original aqueous layer. The Water and acid washings were all com bined to produce what is referred to as first filtrate, which, in this case, contains a substantial amount of the molybdenum values.

Where no methyl isobutyl ketone is present during the digestion step, the following is the method used for extracting the molybdenum values from the digestion mixture. A volume of the methyl isobutyl ketone equal to 1% times the volume of the aqueous layer is added to the digestion mixture after it is cooled to room temperature. The three phases are intimately mixed by vigorous stirring for V2 hour. After the layers separate the solvent layer is isolated. Two additional washings with methyl isobutyl ketone are performed, using a volume of liquid equal to the volume of the aqueous layer. The methyl isobutyl ketone portions are combined and stored for the recovery of the solvent and the contained molybdenum values. The aqueous acid layer is decanted through a filter and the solid residue washed with water and aqueous 0.01 molar hydrochloric acid as described for the control. Two water washes and 4 dilute acid washes are used in this case. In this case, if the extraction with methyl isobutyl ketone has been efiective the aqueous filtrates are substantially free of molybdenum values and are discarded.

Stage IIZ.-The Preparation of Ammonium Tzmgstate Solution The solid residue remaining from the decantations and also any solids caught on the filter are brought into contact with a volume of 28% aqueous ammonium hydroxide equal to the volume of the original aqueous layer and stirred for 1 hour. The tungstic acid present in the solid residue dissolves in the ammonium hydroxide to form ammonium tungstate which is soluble, leaving behind the silica and other acid insoluble components of the ore as a solid residue which is removed by filtering. The residue remaining on the filter is washed once with a 14% aqueous ammoniumhydroxide solution to free it from any ammonium tungstate. These two filtrates are combined and are designated as second filtrate. The results of 6 separate extraction experiments are presented in Table II. The results are compared on the basis of the molybdenum equivalence (Me) in the ammonium tungstato solution contained in the second filtrate as described above. The molybdenum equivalence of a material is determined as the weight of molybdenum present in the material times 100 divided by the sum of the weight of the molybdenum and the weight of the tungsten present in the material. In other words, the molybdenum equivalence of a substance as used here expresses the percent of metallic molybdenum that would be in the tungsten metal prepared from that substance. In the first six examples the scheelite ore used had a molybdenum equivalence of 5.45. In the table, MIK, stands for met. yl isobutyl ketone.

TABLE 11 Me (2nd filtrate) Stage I acid digestion Tungstic acid washing conditions in Stage II Water .i 1. O MIK9 M H01... 0.19 MIX-7.5 M ESL 0.06 MIK-GI) M H01 0.08

Stage I acid-MIK digestion NCO Water 0.1 MIIGQ M 1101 0. 0

Exmnple l is in the nature of a control. The method used has been described above.

Examples 2, 3 and! use the regular acid digestion in the absence of methyl isobutyl ketone followed by the Stage II procedure using methyl isobutyl ketone to extract the molybdenum. Example 2 shows the effect of not adjusting the molarity after the digestion of the 12 molar hydrochloric acid, while Examples 3 and 4 show the effect of adjusting the molarity by the addition of water after digestion. In Example 2 the HCl was at a concentration of 9 M at the end of digestion, whereas in Examples 3 and 4 it was adjusted to 7.5 and 6.5 M as indicated in the table before extracting with methyl isobutyl ketone. Examples 5 and 6 show the beneficial effects of having methyl isobutyl ketone present during the digestion reaction. The results of Example 5 are to be compared with Example 1 since after the digestion and removal of the organic layer there was no further treatment with additional methyl isob-utyl ketone. The aqueous layer was decanted from the insoluble residue without additional extractions with methyl isobutyl ketone and the insoluble residue washed with water in the same Way as in Example 1. Example 6 shows the excellent result obtained even without the adjustment of the aci dmolarity after the acid digestion, by the presence of methyl isobutyl ketone during the digestion period. The reaction mixture was extracted with additional methyl is'obutyl ketone as described under the Stage II procedure, in the same way as was done for Example2, which is the comparable experiment in which methyl isobutyl ketone is not present during the digestion reaction. An Me of 0.03 represents a purity of tungsten which, after standard processing to metallic tungsten, is entirely satisfactory for use in lamp filaments, and therefore there would be no necessity for preparing a purer tungsten at this stage of the process.

In order to test whether my method is applicable to ores of varying molybdenum content with equally good results, Example 5 was repeated, using two'ores of lower molybdenum content. The results are shown in Table III.

The process of Example 5 was repeated using the same ore but during the 8 hour digestion period the organic layer was withdrawn and replaced with an equal volume of fresh methyl isobutyl ketone at the end of 2, 4 and 6 hours. While other conditions of Example 5 were the same, the Me of the second filtrate using this method was less thn 0.02 showing that removal and replenishing of the solvent during digestion greatly improves the purity of; the tungsten.

This example shows that a method of carrying out the invention which would continuously add and remove some of the methyl isobutyl ketone layer during the digestion would give exceptionally good results. In other words, the process of my invention is amenable to continuous processing.

EXAMPLE 10 When the batches of ammonium paratungstate from Examples 3, 4, 6, 7, 8 and 9 were recrystallized from water, it was found that the Me of each batch was now below 0.005, indicating that extremely high purity tungsten could be obtained from this process.

EXAMPLE 11 Two synthetic scheelite ores having the following analyses were processed according to my process.

Synthetic Scheelite 1 Scheelite 2 pppppp s s w OQOOYNH aeaetswww The reaction conditions wereas follows: 322 grams of the low molybd'enumartificialscheelite and 346 grams of the'high molybdenum scheelite ore weree'ach digested separately with 333 milliliters of 12 M hydrochloric acid, 3 milliliters'of concentrated (70% byweight) nitric acid and 666 milliliters-of methyl isobutyl ketone for a period of 3 hours at 80 C. The digested mixture-wasfiltered on avacuum filter, the solid residue on the filter was, washed with 50 milliliters of methyl isobutyl 'ketone, and then with 6 liters of, a dilute hydrochloric acid solution'containing 1 to 2 grams of hydrochloric acid per liter. The tungstic acid in thewashed solids was dissolved in aqueous ammonia, unde'composed ore and ammonia insolubles were removed by filtration. The aqueous solution was evaporated to produce crystalline ammonium paratungstate. Spectrographic analysis of the metal made from the ammonium paratungstate of each sample was as follows:

1 Impurities in metal from- Residual amount Scheelite 1 Scheellte 2 None detectable Si,- Cr, N l, Mu, Su, Cr, Ni, Mn, S11.

00, Ag, Pb, Zr, Ti. A Al, Mg. M0, Fe, Mg Ca, Si, Fe, Cu.

EXAMPLE 12 This example illustrates that my process is applicable to a typical black ore. Analysis of this black ore showed the following percentage composition:

A two-hundred gram sample of the above ore was ground and was digested with 416 milliliters of 12 M hydrochloric acid in the presence of 832 milliliters of methyl isobutyl ketone, at a temperature of 8082 C. for a period of 6 hours. The digested mixture was filtered on a vacuum filter, the solid residue on the filter was washed with 50 milliliters of methyl isobutyl ketone, and then with 6 liters of a dilute hydrochloric acid solution containing 1 to 2 grams of hydrochloric acid per liter. The tungstic acid in the washed solids was dissolved in aqueous ammonia, undecomposed ore and ammonia insolubles were removed by filtration. The aqueous solution was evaporated to produce crystalline ammonium paratungstate. Spectrographic analysis of the metal made from this ammonium paratungstate showed that there were no detectable amounts oli aluminum, silicon, chromium, nickel, manganese, tin, cobalt, or silver. There was only a trace of magnesium and less than 0.001 percent calcium, molybdenum and iron. There was only 0.003 percent copper.

As this example has illustrated, my process although designed to remove the troublesome molybdenum, also is capable of purifying tungsten ores from many other metal ions in addition to'molybdenum, and therefore my process is applicable to the purification of tungsten ores containing the other metallic impurities even in the absence of molybdenum.

Attempts to "substitute diethyl ether, fi,[3'-dichlorodiethyl ether, 'or tri-n-butyl phosphate for the methyl isobutyl ketone were ineffective in producing the excellent results obtained'with methyl isobutyl ketone. Diethyl ether does not produce low molybdenum values in the tungsten, fi,,B'-dichlorodiethyl ether produces stable emulsions 'with'the aqueous layer that are not tolerable while tri-(n-butyl)phosphate produces high tungsten losses.

From the foregoing description and examples, it is evident that a versatile, simple and efficient method of separating tungsten values, substantially free of molybdenum values, from scheelite and wolframite ores has been discovered. The foregoing detailed description is given by way of illustration, it being understood that obvious modifications can be made, as will be evident to those skilled in the art. For example, although my process has been described as applicable to natural scheelite ores, artificial scheelite ores, and wolframite type ores, my process can be used for other tungsten ores containing a molybdenum impurity, which at the present time are not found abundantly in nature. The process is also applicable for recovery of tungsten from scrap tungsten compounds and metal which contain molybdenum.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A process of treating tungsten ores selected from the group consisting of scheelite and Wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore with an aqueous solution containing sufiicient hydrochloric acid that the solution is at least 4 molar with respect to hydrochloric acid at the end of the digestion period, (2) extracting molybdenum values from the mixture with methyl isobutyl ketone, and (3) separating the solid, purified tungsten values from the reaction mixture.

2. The process of claim 1 wherein the extraction step is performed after the digestion step.

3. The process of claim 2 in which the molarity of the hydrochloric acid is adjusted to a value of 6 8 before extracting the digestion mixture with methyl isobutyl ketone.

4. The process of treating tungsten ores selected from the group consisting of scheelite and wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore in the presence of methyl isobutyl ketone with an aqueous solution containing sufficient hydrochloric acid that the solution is at least 4 molar with respect to the hydrochloric acid at the end of the digestion period, and (2) separating the solid, purified tungsten values from the reaction mixture.

5. The process of claim 1 in which the initial acid concentration in the aqueous layer is 12 molar.

6. The process of treating tungsten ores selected from the group consisting of scheelite and. wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore in the presence of methyl isobutyl ketone with an aqueous solution which is initially l2 molar with respect to hydrochloric acid, and (2) separating the solid, purified tungsten values from the reaction mixture.

7. A process of treating tungsten ores selected from the group consisting of scheelite and wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (I) converting substantially all of the tungsten values to tungstic acid by digesting the ore with an aqueous solution containing sufficient hydrochloric acid that the solution is at least 4 molar with respect to hydrochloric acid at the end of the digestion period, (2) oxidizing the impurities with nitric acid, (3) extracting the molybdenum values from the mixture with methyl isobutyl ketone, and (4) separating the solid, purified tungsten values from the reaction mixture.

8. A process of treating tungsten ores selected from the group consisting of scheelite and wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) digesting the ore in the presence of methyl isobutyl ketone with. an aqueous solution containing suflicient hydrochloric acid that the solution is at least 4 molar with respect to hydrochloric acid at the end of the digestion period, (2) oxidizing the impurities with nitric acid, and (3) separating the solid, purified tungsten values from the reaction mixture.

9. A process of treating scheelite ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore with an aqueous solution containing suflicient hydrochloric acid that the solution is at least 4 molar with respect to hydrochloric acid at the end of the digestion period, (2) extracting molybdenum values from the mixture with methyl isobutyl ketone, and (3) separating the solid, purified tungsten values from the reaction mixture.

10. The process of claim 9 wherein the extraction step is performed after the digestion step.

11. The process of claim 10 in which the molarity of the hydrochloric acid is adjusted to a value of 68 before extracting the digestion mixture with methyl isobutyl ketone.

12. The process of treating scheclite ores to obtain tungsten values substantially free of molybdenum values which consists essentially of.( 1) converting substantially all of the tungsten values to tungstic acid by digesting ore in the presence of methyl isobutyl ketone with an aqueous solution containing sufiicient hydrochloric acid that the solution is at least 4 molar with respect to the hydrochloric acid at the end of the digestion period, and (2) separating the solid, purified tungsten values from the reaction mixture.

13. The process of claim 9 in which the initial acid concentration in the aqueous layer is 12 molar.

14. The process of treating scheelite ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore in the presence of rnethyl isobutyl ketone with an aqueous solution which is initially 12 molar with respect to hydrochloric acid, and (2) separating the solid, purified tungsten values from the reaction mixture.

15. A process of treating wolfrarnite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (l) converting substantially all of the tungsten values to tungstic acid by digesting the ore with an aqueous solution containing suflicient hydrochloric acid that the solution is at least 4 molar with respect to hydrochloric acid at the end of the digestion period, (2) extracting molybdenum values from the mixture with methyl isobutyl ketone, and (3) separating the solid, purified tungsten values from the reaction mixture.

16. The process of claim 15 wherein the extraction step is performed after the digestion step.

17. The process of claim 16 in which the molarity of the hydrochloric acid is adjusted to a value of 6-8 before extracting the digestion mixture with methyl isobutyl ltetone. V

18. The process of treating wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore in the presence of methyl isobutyl ketone with an aqueous solution containing suflicient hydrochloric acid that the solution is .at least 4 molar with respect to hydrochloric acid at the end of the digestion period, and (2) separating the solid, purified tungsten values from the reaction mixture.

19. The process of claim 15 in which the initial acid concentration in the aqueous layer is 12 molar.

20. The process of treating Wolframite type ores to obtain tungsten values substantially free of molybdenum values which consists essentially of (1) converting substantially all of the tungsten values to tungstic acid by digesting the ore in the presence of methyl isobutyl ketone with an aqueous'solution which is initially l2 molar with respect to hydrochloric acid, and (2) separating the solid, purified tungsten values from the reaction mixture.

References Cited in theiile of this patent UNITED STATES PATENTS 2,202,525 Hixson a a1. May 28, 1940 FOREIGN PATENTS 241,399 Great Britain Oct. 22, 1925 OTHER REFERENCES Nelidon et al.: Journal of Physical Chemistry, vol. 59, August 1955, pp. 71G-718.

Hampel, C. A; Rare Metals Handbook, pub. by Reinhold Publ. Corp, N.Y., 1954, pp. 483-487.

Waterbury et al.: Analytical Chemistry, vol. 29, No. 1, January 1957, pp. 129-135.

West: Mettalurgia, vol. 4, July 1956, pp. 47 to 57.

Claims (1)

1. A PROCESS OF TREATING TUNGSTEN ORES SELECTED FROM THE GROUP CONSISTING OF SCHEELITE AND WOLFRAMITE TYPE ORES TO OBTAIN TUNGSTEN VALUES SUBSTANTIALLY FREE OF MOLYBDENUM VALUES WHICH CONSISTS ESSENTIALLY OF (1) CONVERTING SUBSTANTIALLY ALL OF THE TUNGSTEN VALUES OF TUNGSTIC ACID BY DIGESTING THE ORE WITH AN AQUEOUS SOLUTION CONTAINING SUFFICIENT HYDROCHLORIDE ACID THAT THE SOLUTION IS AT LEAST 4 MOLAR WITH RESPECT TO HYDROCHLORIC ACID AT THE END OF THE DIGESTION PERIOD, (2) EXTRACTING MOLYBDENUM VALUES FROM THE MIXTURE WITH METHYL ISOBUTYL KETONE, AND (3) SEPARATING THE SOLID, PURIFIED TUNGSTEN VALUES FROM THE REACTION MIXTURE.