HU191827B - Method of preparing high purity tungstate salts by processing tungsten-containing ores or wastes - Google Patents

Abstract

The present invention relates to a process for the preparation of high purity tungsten salts, preferably ammonium para-tungsten, from a tungsten solution obtained by alkaline exploration or dissolution of tungsten-containing ores or waste, by reducing the pH of the tungsten solution, contacting the acidic acidic vcframate solution with a non-aqueous solution of long chain amines or salts thereof. the tungsten is extracted, the tungsten-containing amine solution is stripped with an alkali or ammonium hydroxide solution to form a tungsten salt solution from which the tungsten salt is crystallized. The method is characterized in that the alkaline tungsten solution is electrodialylated at least once using a cation exchange membrane to reduce the pH of the volgramate solution, and the acid tungsten solution obtained by electrodialysis is contacted with the amine solution, and the alkali solution is returned to exploration or dissolution of the ore or waste. -1-

Description

(57) ABSTRACT

The present invention relates to a process for the preparation of high purity tungsten salts, preferably ammonium para tungstate, from a tungsten solution formed during the alkaline digestion or dissolution of tungsten-containing ores or wastes by lowering the pH of the tungstate solution by the tungsten is extracted by stripping the tungsten-containing amine solution with an alkali or ammonium hydroxide solution to form a tungsten salt solution from which the tungsten salt is crystallized.

The process is characterized in that, to lower the pH of the volgramate solution, the alkaline tungstate solution is electrodialyzed at least once using a cation exchange membrane, the acidic tungsten solution prepared by electrodialysis is contacted with the amine solution and the alkali solution is recycled or dissolved.

The present invention relates to a process for the preparation of high purity tungsten salts, preferably ammonium para tungsten (APW), from solutions obtained during the alkaline dissolution or digestion of tungsten ores or tungsten-containing wastes.

It is known that tungsten metal powder is produced predominantly by hydrogen reduction of ammonium para-tungsten (APW). Most users are industries, such as. filament, carbide production, APW is subject to stringent requirements. Chemical purity is particularly important, but the requirements regarding morphology, particle size distribution and phase composition are not negligible. The production of APW is usually based on tungsten ores (tungsten, ferberite, hybnerite, and scheelite), in which various impurities, e.g. As, P, Sb, Si, Sn, Mo, etc. there are some which are a basic step in any manufacturing process. Tungsten ores, which are usually finely ground, are most often discovered in concentrated, autoclave, pressurized solutions. Tungsten, ferberite and hybnite are preferably found in sodium hydroxide, while scheelite in sodium carbonate. After digestion, the insoluble residue is removed by filtration or otherwise to give a solution of sodium tungstate which, depending on the excess used, contains free alkali.

In addition to tungsten ores, large amounts of various tungsten metal scraps or tungsten compounds are used to produce pure tungsten salts. Such materials are e.g. wastes from the various stages of tungsten metal or carbide production, naturally occurring wastes collected from which tungsten is usually leached after solid or liquid oxidation. The acid digestion of tungsten ores also yields tungsten oxide hydrate, which is usually dissolved in alkalis for further purification.

In the prior art processes, the solutions of the majority of the sodium tungstates obtained above are purified in at least two stages. The solutions are usually acidified with sulfuric acid to pH 8-11, first treated with aluminum and magnesium salts to remove impurities from As, P, Si, Sb, and after filtration, further acidified to pH 3 with alkaline sulfides. for the purpose.

Subsequently, APW can be produced in several ways. In what is now considered obsolete, with high W losses, W-oxide hydrate (WO ₃ , H ₂ O) is precipitated with a strong mineral acid (eg HQ). Subsequently, the solid tungsten oxide hydrate is purified by washing and decanting several times with alkaline impurities, and then the APW is crystallized by evaporation to dissolve in ammonium hydroxide.

Many variations of the above-described process are known as pi. use of ion exchange resins in each step. However, all these processes have a number of disadvantages, most notably relatively large losses of tungsten, and the chemical operations employed can only be performed in batch mode, making them less suitable for automation.

Therefore, from the age of 60 onwards, liquid-liquid extraction methods have gradually spread. A common feature of these processes is the formation of high molecular weight so-called isopoly acids in acidified alkali tungstate solution, which form complexes with ionic association which are highly soluble with long chain aliphatic or aromatic amines in various organic solvents (mostly kerosene). Using this phenomenon, when a non-aqueous solution of amines is contacted (e.g. shaken) with an acidified tungstate solution, the tungsten enters the organic phase with an efficiency of about 100% and, after mixing the resulting emulsion, can be separated from the aqueous phase. Alkali and other cationic impurities do not complex with amines and are thus insoluble in the organic phase, meaning that they are substantially free of tungsten impurities in the organic phase. The tungsten-containing organic solution can also be removed from contaminants suspended in the form of droplets of colloidal size upon contact with deionized water. The purified solution is then contacted with ammonium hydroxide. the tungsten ammonium paravolframate (APW) is in the form of a solution in the aqueous ammonium hydroxide phase (stripping), from which it can be crystallized by evaporation, while the amine-containing organic phase which is liberated from the tungsten content can be reused to dissolve the tungsten content.

Numerous variants of the described process are known, see U.S. Patent No. 3,052,516. U.S. Patent Nos. 5,902 and 895,402 use secondary and tertiary C8-C22 aliphatic amines in organic solvents, for acidified alkali tungstates as stripping agents and at pH 10 for stripping. Methods disclosed in U.S. Patent Nos. 3,256,057 and 3,256,058, and in U.S. Pat. No. 1,089,913, as well as in U.S. Pat. from the solution give instructions for extraction with aliphatic tertiary amines and stripping with ammonia at pH> 7.5. Ketones and tributyl phosphate have been proposed to facilitate separation of the resulting emulsions and dissolution of the W-amine complex in kerosene. The organic phase is treated with sulfuric acid before being reused. Such a solution is also found in Yih, S.W.H-Wang, C.T., Tungsten (Plenum Press, 1979),

A more advantageous solution for ammonia stripping from the organic phase is proposed in U.S. Pat. No. 684,892. A process for the use of a tertiary amine-enriched organic solvent consisting of tertiary amines containing tertiary amine, pH 10-11, instead of a mixer settler conventionally used for this purpose, using a tungsten saturated organic solvent solution.

Guidance on ore digestion, deprotection of Si with aluminum salts, and extraction with tertiary amines at a pH of 1 to 1.8 is given in U.S. Pat. U.S. Pat. Stripping uses a pH 7.5-8.5 solution at 45-55 ° C and a relatively long contact time of 10 minutes. No. 4,115,513 is similar in nature. U.S. Pat. No. 4,175,109. In the process according to US patent, it is preferred to use aromatic solvents instead of the previously used kerosene, tributyl phosphate mixtures. Instructions for recovering pure APW from W-poor solutions by combining ion exchange and solvent extraction are given in U.S. Patent No. 4,279,869. U.S. Pat. Secondary amines are proposed in U.S. Patent Nos. 3,158,438, and in U.S. Patent Nos. 889,295 and 912,929 for the preparation of APW. The use of secondary and tertiary amines and a pH range of 2.2 to 4.0 is taught in U.S. Patent No. 4,328,190. U.S. Pat.

In addition to the above, a number of studies address the above subject. Of these, mention is made of the study by Chuicliward and Bridges (US Dep. Lnt.Report 6845) which investigates the possibility of W extraction with a primary amine and the preparation of APW. An advantage of the above processes is that they can produce high purity APWs in very high efficiency, 98-99%, highly automated, continuous operation equipment (mixer settlers). Their great disadvantage is that tungsten can only be extracted from an acidic medium and strong mineral acids (mostly sulfuric acids) are used in all known processes to adjust the alkaline solutions resulting from ore digestion to acidic pH. The valuable lye used to make tungsten in solution is converted into salts (Na ₂ SO ₄ ) during the processes, thus being wasted and at the same time appearing as an environmental pollutant as a by-product of the process.

This problem is overcome by the process of U.S. Pat. No. 3,936,362, which utilizes an anion exchange membrane to prepare various ammonium tungstate solutions from an alkali tungstate solution formed by alkaline digestion. However, due to the inadequate selectivity of the ion-exchange membranes, the ammonium tungstate produced is also contaminated with a significant amount of alkaline material and only repeatedly can be obtained with a sufficiently pure ammonium tungstate solution. A further disadvantage of this process is that the concentration of the recovered alkali is not controllable and only a subsequent concentration of the reconstituted alkaline solution can be achieved. The efficiency of the process is also unsatisfactory, since in a highly alkaline medium the hydroxyl ion transport competes with the tungsten ion transport through the membrane, so that even a disproportionate amount of energy cannot be recovered from the dialysis solution.

As mentioned above, when acidifying acal tungstates with mineral acid, so-called "tungsten" is used. isopoly acids are formed which are aggregates of high molecular weight 6-12 WO ₄ ^J ions (WO _e octahedron). The composition of most of these isopoly acids, as well as the mechanism of their acidification reactions, are not fully understood, despite extensive studies. Summarized by Tytko, KH Glemser, Ο. Z. Naturforsch. 30b, 834 (1975). It is difficult to create an imbalance system during acidification where short and very long half-life reactions occur simultaneously. Many have shown that e.g. the manner of acidification also influences the composition of the isopoly acids formed. Species formed by mixing with dilute acid under intense mixing differ, e.g. from the addition of concentrated acid, which slowly dissolves when the amount of one base acid per unit tungsten is <2.

At the ρ, and acid / W ratios where the highly extractable W species are formed (pH 1.5-4), according to the latest literature data, the so-called W A specific Y is formed which has a characteristic absorption maximum at 322 nm in its UV spectrum. Its composition according to W ₁₀ O _J ^{2 4 according to} Birkholtz and Fuchs (Z. Naturforsch. 26b, 365, 1971), which is a transient so-called. Through the species Y-meta and X, H ₂ W, ₅ × ₄₀ ⁶ , is slowly converted to metavolframate ion. Kim, in a paper (Separation Sci. 3, 467, 1968), investigated the extraction of isopoly tungstate with tri-caprylamide. He found that both the distribution of the amine-isopolyolic acid complex and the amount of W reacting with a unit amount of amine depend on the charge density (charge-tungsten ratio) of the polyanion specific. This phenomenon partly explains the fact that each patent gives substantially different values of 30 to 150 g / l for tungsten-binding capacity of amine solutions of the same composition.

The lack of knowledge of the formation mechanism of isopoly acids can introduce many uncertain elements into tungstate extraction technology. If the organic phase is not sufficiently saturated with W during extraction, other anions present (mainly sulfate) are soluble in the solvent and when transported to the ammonia stripping solution, the resulting APW solution may be contaminated with sulfate ions. The danger of this is called in No. 3,933,971. U.S. Pat. No. 5,123,195, which recommends washing liquid to remove sulfate prior to stripping. In other processes such as No. 4,328,190; In the US release, as described herein, the organic phase is saturated with tungsten during the extraction steps to displace most of the sulfate ions.

From the foregoing it can be seen that the known processes have many disadvantages:

- the alkali or ammonium hydroxide or carbonate used in the manufacture of 'tungsten' solutions is lost to a waste process which is rendered useless by the processes,

- the acidification of the tungsten solution to be extracted requires a large amount of mineral acid which is also converted into waste,

- the anion of the mineral acids present in the extraction contaminates the highly purified tungsten salts to be produced, and is particularly dangerous since its mineral acids are usually sulfuric acid whose sulfur content in the tungsten salt affects the properties of the tungsten metal produced therefrom.

It has been discovered that these disadvantages can be overcome by the use of known amine-extracting agents which are effective only in acidic media, by utilizing the property of some isopoly acids to dissociate hydrogen ions up to pH 1.5 in sufficiently concentrated solutions. —Can be 2. Such isopoly acids can be prepared from alkaline alkaline tungstates by lysis using a catheter exchange membrane electrode.

The present invention thus provides a process for the preparation of high purity tungsten salts, preferably ammonium paravolframate, from the tungsten solution formed by the alkaline addition or dissolution of tungsten ores or wastes by reducing the plolliamate side, e.g. so acidic! The tungsten solution is contacted with a non-aqueous solution of the long chain amines or salts thereof, the tungsten is extracted, stripping the amine solution containing the recovered tungsten with an alkali or ammonium hydroxide solution to obtain a tungsten salt solution which is crystallized from using at least one membrane, electrodialysis the tungsten solution prepared by electrodialysis, starting with the amine solution έπη and returning the recovered alkaline solution to. for the exploration or removal of ores or waste.

Eljárás In accordance with the process of the invention, The alkali used for the dissolution can be almost completely recovered at a concentration such that it can be directly traced back to the digestion or digestion. This results, on the one hand, in saving alkali and, on the other hand, in reducing the amount of waste salts. The electrodialysis of acidification in the process of the present invention also results in significant acid savings compared to known processes.

It has further been found that the acidic acid produced by this electrodialysis solution, when tungstated with a non-aqueous amine solution, is capable of transferring the majority of the tungsten into a non-aqueous solution, and this transfer has a low acidity compared to prior art processes. can be completed. Thus, it is very advantageous to carry out the present invention in which the acidic tungstate solution is contacted with a small amount of strong mineral acid.

Without wishing to be bound by or limited to any theory regarding isopolyolic acid formation, although no specific data are available on the physical, chemical and extracellular properties of the acid tungsten We would like to draw a parallel between acidification with mineral acid and electrodialysis.

Conventional processes for the preparation of strong mineral acids in alkaline voliramate solutions include the following general equation: _P HCbqNa ² WO ₄ > Na, _qp H _p . ₂ W _q O _{4q rT} NaClnH _a O

The above reaction equation satisfies the formal requirements of stoichiometry.

In the electrodialysis procedure, a Na ₂ W0 ₄ solution, which may contain excess alkali in excess of the amount required by stoichiometry, is placed in the anode space of the cation exchange membrane-separated cell, while a completely dilute sodium hydroxide solution (e.g. . using a flat platinum plate, using a sheet of steel as the cathode and passing current from the DC supply to the cell, the sodium ions are transferred from the anode space to the cathode exchange membrane and converted to sodium hydroxide in the reactions described below.

Well * <e '-> Well

Na * II ₂ O * NaOH - 1/2 H ₂

The hydroxyl ions remaining in the anode space are botanized to water and oxygen in the following reactions.

There was blood OH

011 1/2 0 ₂

Λ As the process progresses, as the sodium ions gradually leave the anode space, W-isopolyolic acid species, which are increasingly poor in sodium, are formed, as indicated by the gradual acidification of the anode space.

The following processes occur during elec- trical odialization:

<, Na ₂ WO ₄ 'pNa * rNa _2l . _p W _q O _4q

I migrates through the membrane into the cathode space

Numerical determination of the stoichiometric coefficients \ p, q and e of the reaction at ^the anode OP O ₂ * P ^e , thus, it is very difficult to determine the actual reactions and to determine the composition of the resulting isopoly acids, and as described above, even with mineral acid solved task.

Of course, the composition of the isopoic acid species produced by acid or electrodialysis is not necessarily the same. This is supported by our observation that the ultraviolet spectra of the two solutions produced at the same concentration and pH show marked differences. To the best of our knowledge, there is no data available in the literature for the identification or testing of tungstate-containing isopoly acids produced by electrodialysis, however, we do not find the observed difference surprising since numerous data indicate that the acidity of the acid and the formation. Electrodialysis of tungsten-containing isopoly acids, as shown in the reaction equations, does not result in the formation of salts other than the tungsten compound (e.g. NaCl or Na ₂ SO ₄ ). or minimized.

In parallel with the process in the anode space, the sodium hydroxide formed in the cathode space is gradually concentrated. According to our measurements, the concentration of the alkali formed during the process may exceed 10 mol / l in the anode or in the aqueous solution. by choosing the appropriate volume ratio of the cathode space or by periodically replacing the sodium voifram in the anode space. It has been found that more than 95% by weight of sodium in the anode space can be removed and the electrodialysis can continue until a solid precipitate of tungstic acid is formed.

The tungstic acid precipitate in the anode space drops below 1.5 pH and at 2 ρΗ does not begin to precipitate. No precipitation was observed in the anode space during stationary operation with continuous supply of sodium tungstate in the anode chamber. The resulting acidic tungsten solutions of pH 2, up to 150-200 g W / l, are unusually stable. Even after several months of standing, no precipitation of tungstic acid was observed. Their sodium content is approximately 5% by weight of the stock solution. Similarly, the majority of the alkali or ammonium ions may be removed from other alkali or ammonium tungstate solutions, except that in the case of ammonium hydroxide, due to its low conductivity, it is preferable to dilute place.

Table 1 shows some measurement data for the extraction of tungsten contents of acidic voiframate solutions prepared by electrodialysis with kerosene solutions of long amines.

Table 1

Primary amine Secondary amine Tertiary amine

5% Primene JMT ⁺ 5% Amerlite LAl ^x 5 Lower

336 °

37 24

Extractable W% by weight

Tungsten content of aqueous phase: 20 g / l, pH 1.8 (before extr.)

The volume ratio of aqueous to kerosene was 1: 1. Before the experiment, the amines were in the form of a natural amine base.

Table 2 compares the amount of sulfuric acid needed to extract more than 99% by weight of tungsten in the case of voiframate acidified by electrodialysis and not previously treated with electrodialysis,

Table 2 5% Primene JMT

Amount of sulfuric acid 20% by weight required for extraction of more than W% by weight of non-electrodialysed W

From the data in the tables, it can be seen that some of the tungsten can be extracted without the addition of acid, using only the amine base, and the extraction can be completed using 10 to 20% by weight of the acid required by the conventional method.

Rohm and Haas make x Fluka make o Henkel make

Table 1 shows that the extraction efficiency with the amine base ranges from 20 to 40% by weight without addition of acid. However, it has been found that if the aqueous solution obtained after extraction of W containing from 60% to 80% by weight of the original tungsten is re-electrodialyzed by returning the aqueous solution to the dialyzer, operating parameters at which the amount of tungsten extracted with the amine can be set equals the amount of tungsten fed to the dialyzer, and at the same time water transport through the cation exchange membrane is sufficient to remove the amount of water introduced into the dialyser by the voiframate solution.

Another very advantageous embodiment of the process according to the invention makes it possible to economically utilize the mother liquor remaining in the crystallization. To do this, the mother liquor is electrodialyzed using a cation exchange membrane, and the voiframate solution obtained from the cathode space of the electrodialysis containing excess alkali or ammonium ions is recycled, after optionally enriched with ammonia gas formed during crystallization, to an and the ionic acidic voiframate solution is recycled to contact the amine solution.

The process for producing the APW of the present invention has the following advantages over known methods:

- the majority of the solution of alkali hydroxide or alkaline carbonate used for the digestion of tungsten ore is economically recoverable in the form of a concentrated alkaline solution which can be reused for ore exploration,

- the amount of mineral acid required for the extraction of tungsten does not exceed 10 to 20% by weight of the quantity required by conventional extraction processes,

- homogeneous solutions containing the same species of tungsten can be prepared by electrodialysis in a highly controllable manner, thus precisely adjusting the amount of amine required for the extraction of the tungsten, thereby minimizing the undesired ion transport during z extraction and providing a higher purity APW solution

- the valuable tungsten and ammonia content of the mother liquor remaining after crystallization of the APW can be utilized more efficiently and with greater efficiency than known processes,

- the amount of waste and by-products generated during the process is negligible compared to known processes.

Eljárás APW or other tungsten salts can be prepared by a variety of processes according to the invention, and the electrodes may be selected in a number or order of digestion or extraction operations depending on the starting material contamination, desired purity and other desired operating parameters.

Without limiting ourselves to any of these, the invention will now be described by reference to the process illustrated in the drawings, wherein

Figure 1 is a flow chart of a possible process, and Figure 2 is a flow chart illustrating a preferred embodiment of the extraction step of Figure 1.

In Figure 1, sodium tungstate solution containing excess alkali obtained after routine ore digestion and filtration operations is fed to a first cation exchange electrodialysis machine, where the pH of the solution in the anode space is maintained at 7 by controlling the current and the sodium tungstate solution. It should be noted that it is desirable to perform the electrodialysis in stationary mode, i.e. at a constant pH, since in certain pH ranges, depending on the impurities, precipitation occurs (eg Si), which is dissolved to change the pH (decrease or increase). , P, Si, demineralization), the pH of the solutions can be restored to the desired value with a little alkali. The dialyzed solution is continuously removed from the anode space and prepared for the usual operation of Al, Cl, and MgCl ₂ removal of the As, P, Si buffer buffer (not shown).

The decontaminated tungstate solution is re-electrodialysed and after the removal of the molybdenum contamination with Na ₂ S, the pH of the solution to be extracted is adjusted to 1.5-4 by further electrodialysis and optionally by adding acid to the solution. The resulting acidic tungsten-containing solution is passed through a desired step (2- or 3-step) mixer settler to extract the tungsten.

Figure 2 shows a preferred multistage connection of an extraction mixer-settler. The acidic tungsten solution from the electrodialyzer is fed to the mixer-settler stage 3, where the amine solution from the mixer-settler stage 2 is completely saturated with tungsten and from there to the mixer-settier for water washing shown in Figure 1. The acidic tungsten solution passes from mixer-settler stage 3 to mixer-settler stage 2 and from there to mixer-settler stage I, where it is countercurrently contacted with the amine solution. The amine solution enters the mixer settler stage 1, from there to the mixer settler stage 2 and then to the mixer settler stage 2. During countercurrent contact, the acidic tungsten solution gradually loses its tungsten content, and the tungsten content of the amine solution gradually increases. A small amount of sulfuric acid is introduced into the mixer-settler stage 1 to facilitate perfect tungsten extraction. However, this small amount of kensic acid is removed from the mixer-stage 1 mixer together with the aqueous solution already freed from voucher gum. It can be seen that sulfuric acid is not introduced into mixer settler stages 2 and 3, so if the amine solution in mixer settler stage 1 dissolves little sulfate ions due to the formation of amine salt, this sulfate is completely contained in mixer settler stages 2 and 3. loses it because it dissolves the increasingly concentrated tungsten containing only sulfate ions! contacts.

Returning to Figure 1, after extraction, the tungsten saturated amine solution is washed in one or two stages with deionized water to remove any impurities (particularly sodium) suspended in the amine solution. It is then contacted with ammonium hydroxide or with ammonium tungstate containing excess ammonia in the following (stripping) mixer settler where the tungsten content of the amine solution is released. The tungsten-free amine solution is returned to the extraction mixer setter. Concentrated ammonium tungstate solution (150-300 g / lW) formed during stripping was crystallized and the APW crystals formed were separated from the mother liquor by filtration. The mother liquor, which still contains a significant amount of tungsten, is divided into two parts. One part is introduced into the cathode compartment of an electrodialyzer and the other part into the anode compartment. The ammonium ions are. migrate from the anode space to the cathode space through a cation exchange membrane separating the two spaces. An acidic tungsten solution is formed in the anode space which is recycled to the extraction mixer-settier to recover its tungsten content and the ammonium tungstate solution containing excess ammonia formed in the cathode space is used to strip the ammonia gas liberated during stripping crystallization.

In addition to the embodiments shown in Figures I and 2, many other preferred embodiments of the process of the invention are possible, including those that do not use any mineral acid at all. In the latter case, the aqueous solution resulting from the extraction step is not tungsten-free and is recycled according to the dashed line to the last electrodialysis agent prior to extraction.

The following examples are intended to illustrate some important steps of the process of the invention without limiting our claims.

Example I

Two cells, cathode and anode compartments, were prepared with a Du Pont Nafion 125 cationic membrane (400 cm @ ²⁾ and electrodialyzed using a platinum plate and a stainless steel plate as the anode. The solutions in the cathode and anode compartments were moved using a centrifugal pump. Sodium vololliamate solution containing 144 g / l tungsten and 40 g / l free alkali in the cathode space? diluted 0.1 N NaOH in anode space. Using a current density of 0.125 Λ / cm ² and a voltage of 9.0 V, the electrodialysis was continued until about 90 ′ of the sodium content of the sodium tungstate solution was discharged into the anode space and the pH of the initially strongly alkaline solution dropped to 2. As a result, the initially dilute sodium hydroxide in the anode space gradually becomes concentrated.

The pH 2 acid tungsten solution thus prepared was converted into an APW solution in a five-stage mixer-settler with a metering control system.

Otherwise, the first four stages of the mixer settlers had a volume of about 300 ml, while the fifth stage, the aliol ammonium paravefrainate solution, formed 600 ml. From the solution containing the acidic tungsten compounds fed in the first two stages, the tungsten compounds were extracted with a countercurrent solution of long chain amines at pH 2 η. The kerosene solution was washed with water in the next two stages and cc in the fifth mixer. ammonium hydroxide solution, pH 10.1, the tungsten content of the kerosene solution was converted to ammonium voiframate. The tungsten-free kerosene solution was recycled to the first mixer-settier.

The process yielded a concentrated solution of ammonium tungstate, suitable for crystallization, from which solid APW crystals were obtained by evaporation. The main parameters of our process are summarized in Table 3 below:

191 827

Table 3

Used extractant

Alamine 336 5% w / w Primene JMT 5% w / w n-octanol 5% w / w n-octanol 5% w / w soluble kerosene

The volume of the solution containing the acidic tungsten compounds is 100 l / hr / hr

The concentration of the feed solution was 162 g / l

W loss during extraction 0.3 wt%

The tungsten content of the resulting solution of animonium tungstate is 159 g / l

306 ml / h 180 g / l 0.1 wt%

220 g / l

The amount of sulfuric acid used in the process was reduced by 82% compared to the 20 conventional methods.

The amount of tungsten in the recovered APW crystal and in the mother liquor formed by crystallization was greater than 99% by weight relative to the initial sodium tungstate solution. 25

Example 2

The 220 g W / L ammonium tungstate solution prepared in Example I is introduced into the anode space of an electrodialysis membrane separated in Example 1 using a cation exchange membrane. The cathode space is diluted, e.g. 50 g of a solution of ammonium tungstate in W / L are prepared and can be prepared in various ways. In the present example, the mother liquor after evaporation of the ammonium tungstate solution prepared according to Example 1 and separation of the solid APW crystals was used. The solutions in the cells were moved by centrifugation pump through heat exchangers so that the system was thermostated at 60 ° C. During the circulation of the anode liquid, even a buffer tank was inserted where the crystals formed during the process were settled.

A DC power supply of 0.13 A / cm ^{3 with a} current of 40 V and a voltage of 6 V was applied to the cell. During the process, NH ₄ * ions gradually migrated to the cathode space, where the concentration of ammonium hydroxide increased. As NH ₄ * ions disappear in the anode space, the pH of the solution gradually decreases and APW crystals begin to precipitate. 45

Continuing the electrodialysis to pH 7.3, the resulting crystals were collected from the buffer tank and dried in an oven. The electrodialysis was then continued with decreasing pH, and the crystals remaining in the buffer vessel were redissolved and the cn process was continued until the anode space pH reached 1.8.

The solution containing the acidic tungsten compounds in the anode space was used for extraction as in Example 1, while the dilute ammonium tungstate solution containing excess ammonium in the cathode was used for extraction.

Example 1 Introduced into a fifth mixer settler, it was used to prepare a concentrated ammonium tungstate solution.

The amount of tungsten present in the final product formed in the process (APW crystal, solution containing tungsten compounds, which is poor in armonia, ammonium tungstate containing excess ammonia) did not change significantly compared to the initial solutions. It has been estimated that the loss of tungsten in the process due to slight leakage of the electrodialyzer is less than 0.1% by weight.

Claims

Claims (6)

A process for the preparation of high purity tungsten salts, preferably ammonium paravolframate, from a tungsten solution obtained by the alkaline digestion or dissolution of tungsten-containing ores or wastes by lowering the pH of the tungsten solution to a solution of acid extracting the tungsten by stripping the tungsten-containing amine solution with an alkali or air ammonium hydroxide solution to obtain a tungsten salt solution, from which the tungsten salt is recrystallized by applying a solution of at least tungsten ions of alkaline tungsten to reduce the t once electrodialysed, the acidic tungstate solution prepared by electrodialysis is optionally contacted with fz amine solution after addition of an acid and the resulting alkaline solution is recycled k for the exploration or removal of ores or waste. 2. A process according to claim 1, wherein the electrodialysis is carried out several times in succession by intervening to remove the contaminants by precipitation filtration. 3. A process according to claim 1 or 2, wherein the at least one electrodialysis step adjusts the pH of the tungsten solution to be contacted with the amine solution to between 1.5 and 4. Aces 1-3. A process according to any one of claims 1 to 3, characterized in that the acidic tungstate solution is contacted with the amine solution by the addition of a strong mineral acid. The process according to any one of claims 1 to 4, characterized in that the acid tungstate solution and the amine solution are contacted in several stages during the extraction, wherein the first stage comprises the addition of the amine solution and optionally a strong mineral acid. and to the final stage the acidic tungsten solution is introduced. 191 827 6. A process according to any one of the claims, wherein the aqueous solution containing tungsten obtained after contacting the acidic tungstate solution and the amine solution is recycled to the last electrodialysis device prior to extraction. 2 drawing Published by: National Office of Inventions Responsible publisher: Zoltán Himer o.v. CODE -8191.827 International Classification: C 01 G 41/00 Stock, APW Solution k. ftXkűu -9191.827 International Classification 01 G 4 1/00 For extracting ^vol ^ ^r ^ ^m