CH654558A5 - PROCESS FOR THE PRODUCTION OF NIOBIUM OXYFLUORIDE. - Google Patents

Description

The present invention can advantageously be implemented in a discontinuous, semi-continuous or continuous mode. The semi-continuous and continuous modes are the most effective. To this end, a portion of the sludge containing niobium oxyfluoride is removed periodically or continuously from the hydrolysis and crystallization reactor. The crystallized niobium oxyfluoride is then separated from the liquid phase of the portion of sludge thus removed and the liquid filtrate is recycled to the reactor. A new quantity of aqueous starting solution containing niobium is introduced into the reactor periodically or continuously, at a rate sufficient to maintain an appropriate volume of sludge in the reactor and prevent the sludge from evaporating to dryness. By this series of operations, one can produce and collect a niobium oxyfluoride product in a semi-continuous or continuous manner.

As indicated in the aforementioned US Pat. No. 4,164,417, niobium oxyfluoride (Nb02F) can be calcined in the presence of water vapor at a temperature of about 500 to 1000 ° C to form niobium oxide (Nb2Os) according to the equation:

(A) 2 Nb02F + H20 2 Nb2Os + 2 HF

However, it has now been found that, although the reaction appears to proceed according to this equation in the lower part of this temperature range (i.e. 500 to about 600 ° C), another reaction mechanism seems to predominate at temperatures above about 700 ° C, giving a limited yield of Nb2Os. This other reaction is supposed to take place according to the equation:

(B) 3 Nb02F (s) 2 Nb2Os (s) + NbOF3 (g)

At temperatures below about 600 ° C, the reaction mechanism follows Equation A, but the reaction is too slow to be practically useful. Above about 600 ° C, the mechanism according to equation B becomes more important and the gaseous NbOF3 by-product begins to form quickly. This equation is used to explain the reduction in the yield of niobium oxide observed in the implementation of the calcination process of the aforementioned patent at temperatures above approximately 600 ° C. Although the increase in the reaction rate at temperatures above approximately 600 ° C is very desirable for the practical commercial utility of the process, the reduced yields at this temperature make the process practically uninteresting.

The following examples illustrate the invention.

Example 1:

A fluorocarbon beaker containing an agitator rod coated with fluorocarbon and provided with a polypropylene condenser was placed on a hot plate provided with a magnetic stirring device. 400 ml of a preconcentrated fraction of niobium were placed in this beaker, the analysis of which showed that it contained 946.9 g / 1 of Nb205 (662.8 g / 1 of Nb) and 699.2 g / 1 of F (molar ratio F: Nb about 5: 1). To this niobium solution was added 100 ml of water. The mixture was then heated to boiling (130-160 ° C) with stirring to keep the hydrolyzed solids in suspension. During the heating, an aqueous fraction containing hydrogen fluoride (HF) was collected at the outlet of the refrigerant.

Analysis of this 270 ml fraction showed that it contained 305 g / l of F. Then, the residual suspension (230 ml) was cooled and filtered. The solid product was washed with deionized water and dried. 230 g of a granulated, free-flowing product were obtained, the analysis of which showed that it consisted of niobium oxyfluoride. (Nb02F). The amount of filtrate was 145 ml, of which 110 ml was recycled to the reactor, leaving 35 ml of filtrate for analysis. To the filtrate placed in the reactor was added 290 ml of aqueous fraction of preconcentrated niobium and 100 ml of water. The reaction mixture was again heated to boiling with stirring and 240 ml of aqueous HF was collected as condensate (328 g / l F by analysis). The resulting suspension was cooled (252 ml), filtered, washed, dried and 190 g of Nb02F were collected. 182 ml of filtrate were obtained, of which 162 ml was recycled again in reactor 15, reserving 20 ml for analysis.

Two additional cycles were repeated according to this general method. The aqueous fraction of preconcentrated niobium (238 ml) and water (100 ml) were introduced into the reactor containing the recycled filtrate from the previous recovery of Nb02F. This reaction mixture was heated to boiling (130-160 ° C) with stirring and 230 ml of aqueous HF condensate was collected (containing 347 g / l F). A new quantity of preconcentrated niobium fraction (214 ml) was added to the suspension with a new quantity of 100 ml of water. The reaction mixture was brought to the boil with stirring and 200 ml of aqueous HF (containing 372 g / l of F) was collected. The 360 ml of suspension obtained was filtered to collect Nb02F as product. 245 ml of filtrate remained. The washed and dried, granulated, non-hydrated, free flowing product weighed 340 g.

30

Example 2:

In a fluorocarbon distillation flask, a 1000 ml sample of an aqueous niobium fraction [containing 180 g / l of Nb205 (126 g / l of Nb) and 213 g / l of F (F: Nb) was placed 8: 1)] 35 obtained by liquid / liquid extraction of an ore digestion solution. This niobium fraction was evaporated to half its volume (500 ml), after which another 550 ml of niobium fraction was introduced into the reactor. The contents of the reactor were then evaporated until 550 ml of distillate were collected. Two more 550 ml portions of niobium fraction were successively added and successively evaporated and 550 ml evaporated after each addition niobium fraction Analysis of the final concentrate showed that it contained 914.3 g / l of Nb205 (640 g / l of Nb) in solution.

Three cycles of crystallization by hydrolysis were then carried out. For each cycle, 690 ml of niobium fraction was added to the concentrated niobium fraction placed in the reactor. Each reaction mixture was then heated to boiling (105-125 ° C) with sufficient stirring to keep the hydrolyzed solids in suspension, until the volume of distillate collected was 50,645 ml. After each evaporation, the reaction mixture was cooled and filtered to separate the unhydrated, granulated, free flowing niobium oxyfluoride (Nb02F). The filtrate was recycled to the reactor by introducing an additional fraction of niobium and the next cycle was started. Table A below 55 collects the results obtained.

(Table at the top of the next page)

Example 3:

282 kg of a niobium solution were introduced into a reactor of 601 1701 equipped with a turbine agitator and electric heating bodies. The niobium solution had a density of about 1.8 g / cc at 25 ° C and contained about 493 g / 1 of Nb and 565 g / 1 of F (an F: Nb molar ratio of 5.6). The niobium solution was boiled and the Nb02F crystallized as a suspension of a granulated so-65 lide, easy to filter. The steam was condensed in a shell and tube heat exchanger, cooled with water. At equilibrium, the normal boiling point of the solution was 155 ± 5 ° C. About 20% by volume of the suspension was withdrawn from the reactor.

654 558 4

Table A

Step N °

Volume (ml) Nb Fraction '"at the reactor

Volume (ml) evaporated

Distillate analysis

Analysis of the aqueous content of the reactor

Product collected

1

1000

0

-

126 g / 1 Nb

-

2

0

500

-

250 g / 1 Nb (est)

-

3

550

550

-

390 g / 1 Nb (est)

-

4

550

550

-

540 g / 1 Nb (est)

-

5

550

550

-

640 g / 1 Nb'2 '

-

6.7

690

645

145 g / 1 HF

638 g / 1 Nb'3 '

140 g Nb02F

8.9

690

645

138 g / 1 HF

666 g / 1 Nb'31

86 g Nb02F

10, 11

690

645

163 g / 1 HF

656 a / 1 Nb'3)

119.5 g Nb02F

Analysis: 126 g / 1 Nb, 213 g / 1 F.

121 35 ml sample of the reactor contents taken for analysis.

m Contents of the filtered reactor, precipitated product collected, sample of 35 ml of filtrate taken for analysis and remaining of the filtrate recycled in the reactor.

Nb02F every 2-4 h, it was filtered and the filtrate was reintroduced into the reactor. The NbO, F cake was washed with 10% by weight of water and the washing solution was also introduced into the reactor. The volume in the reactor was kept essentially constant during the test by adding new amounts of niobium solution as required. This test was continued continuously for 116 h and during this time a total of 2821 kg of niobium solution and 112 kg of washing water were added. A total of 1384 kg of condensate was collected. This condensate titrated on average 50% by weight of HF in water. The wet cake of Nb02F collected in the filter weighed 1292 kg (as filtered) and 1187 kg after drying at 120-240 C. The dried Nb02F was granulated, flowed freely and titrated 13.8% by weight of F and 64 % by weight of Nb. At the end of the test, the mother liquor weighed 20 kg.

The total weight loaded during the test was 2821 kg of niobium solution and 112 kg of water for a total of 2933 kg loaded. The total weight collected was 1384 kg of condensate, 1292 kg of Nb02F in the form of a cake on the filter, 210 kg of mother liquor for a total of 2886 kg collected. A quantity of 6 kg was not justified.

20

25

R

Claims (6)

654,558 2 1. Process for the production of niobium oxyfluoride, characterized in that an aqueous starting solution containing hydrofluoric acid and dissolved niobium is heated to boiling, in a reactor, with stirring. evaporation and hydrolysis of the starting aqueous solution, with the formation of a sludge containing niobium oxyfluoride, the stirring being sufficient to keep the hydrolyzed product in suspension; and in that the niobium oxyfluoride is collected from the mud, as formed, by separating the niobium oxyfluoride from the liquid phase of the mud. 2. Method according to claim 1, characterized in that the aqueous starting solution contains niobium dissolved in a concentration of 25 to 700 g / 1. 3. Method according to claim 1, characterized in that the aqueous starting solution contains hydrofluoric acid and niobium dissolved in concentrations such that the molar ratio of fluorine to niobium in the aqueous starting solution is at least 4 . 4. Process for the production of niobium oxyfluoride, characterized in that: a) an aqueous starting solution containing hydrofluoric acid and dissolved niobium is heated to boiling in a reactor, with stirring, in order to cause evaporation and hydrolysis of the starting aqueous solution, with formation a slurry containing niobium oxyfluoride, the stirring being sufficient to keep the hydrolyzed product in suspension; b) in that the niobium oxyfluoride is collected from a portion of the sludge, as formed, by separating the niobium oxyfluoride from the liquid phase of the sludge portion; c) in that the liquid phase thus separated is recycled into the reactor, and d) in that a new quantity of starting aqueous solution is introduced into the reactor at a rate sufficient to maintain an appropriate volume of sludge and prevent the mud to evaporate to dryness. 5. Method according to claim 4, characterized in that the aqueous starting solution contains niobium dissolved in a concentration of 25 to 700 g / I. 6. Method according to claim 4, characterized in that the aqueous starting solution contains hydrofluoric acid and niobium in concentrations such that the molar ratio of fluorine to niobium in the aqueous starting solution is at least 4. Niobium ores have already been treated by digestion with hydrofluoric acid to dissolve niobium and tantalum. The separation and purification of these metals are carried out by means of liquid / liquid extraction techniques, with the use of an appropriate solvent, generally methylisobutylketone (MiBK). The hydrofluoric digestion solution is brought into contact with the ketone and, in a strongly acid medium, niobium and tantalum both pass into the organic phase while the other elements remain in the raffinate. When the organic extract is brought into contact with an aqueous hydrofluoric acid solution of lower acidity, the niobium preferentially returns to the aqueous phase, while the tantalum remains in the organic phase. To recover niobium from the aqueous phase, the latter, which is essentially a saturated aqueous solution of MiBK containing an oxyfluoroniobic acid (H2NbOF5) and hydrogen fluoride (HF), has generally been treated with ammonia for precipitating niobium hydroxide, Nb (OH) 5, which can then be transformed into niobium oxide, Nb2Os, by calcination at high temperature. However, ammonium fluoride formed as a by-product poses a disposal or recovery problem. Another technique, avoiding the use of ammonia, is described in US Patent No. 4164417. In this method, niobium is separated from aqueous hydrofluoric acid solutions by evaporation of these solutions to dryness, followed by calcination of the residue to obtain a product containing niobium oxyfluoride (generally represented by the formula NbO, Fj. In accordance with the present invention, a novel improved process has been discovered for the recovery of niobium from a hydrofluoric acid solution containing niobium. It has been discovered that an aqueous hydrofluoric acid solution containing niobium can be heated, with stirring, in a reactor to cause evaporation and hydrolysis, forming a sludge containing niobium oxyfluoride, from which Nb02F can be easily separated and recovered. Unexpectedly, such a process provides a free-flowing, non-hydrated, granulated product. This recovery of Nb02F from a solution can be carried out according to a batch, semi-continuous or continuous process. For example, for a batch operation, a solution of hydrofluoric acid containing niobium is heated, with stirring, in a reactor, to form a slurry of Nb02F, which can then be separated from the liquid phase and thus recovered. In a semi-continuous process, the Nb02F can be separated from a portion of the sludge, after which the liquid phase can be recycled in the reactor and a new quantity of starting aqueous solution can be introduced into the reactor at a rate sufficient to maintain an appropriate volume. By repeating this sequence of operations, a semi-continuous production is carried out. In a continuous process, a slurry stream containing Nb02F can be continuously withdrawn from the reactor, the Nb02F can be separated from the liquid phase and the liquid phase can be recycled in the reactor with simultaneous introduction of new quantities of aqueous starting solution , at a rate sufficient to maintain an appropriate volume in the reactor. In a preferred implementation of the invention, a niobium ore is firstly subjected to digestion and a fraction of purified niobium is obtained according to conventional production methods. For example, the ore can be digested with hydrofluoric acid and niobium can be recovered by liquid / liquid extraction based on MiBK. The saturated aqueous solution of MiBK, containing niobium and hydrogen fluoride, thus obtained has a composition the concentration of which can vary. In general, the solution may contain from about 25 to about 150 g / l of dissolved niobium, with a molar ratio of fluorine (F) to niobium (Nb) of at least about 4, in order to keep the niobium in solution. Most often, the solution contains from about 80 to about 110 g / l of dissolved niobium with a molar ratio of fluorine to niobium of about 8; 1 to about 10; 1. The niobium-containing fraction is preferably preconcentrated. This can be done by heating the aqueous solution to the boil, that is, at a temperature of at least about 100 C, usually about 120: C. The fraction is evaporated to the point where the concentrated niobium fraction contains up to about 700 g / l of dissolved niobium. Preferably, the concentrated fraction contains from approximately 250 to approximately 600 g / l, more particularly approximately 500 g / l of dissolved niobium, with a molar ratio of fluorine to niobium of at least 4.5, preferably approximately 5.5 to about 6.0. During this concentration step, the solvent (for example MiBK) as well as the aqueous HF can be condensed from the vapor phase to be recycled. The niobium-containing fraction, preferably preconcentrated, is then heated to boiling in a reactor in order to cause further evaporation and hydrolysis of the aqueous niobium solution. Under agitation conditions sufficient to maintain the hydrolyzed solids in suspension, a fine granulated niobium oxyfluoride crystallizes from the solution. To carry out this hydrolysis-crystallization at atmospheric pressure, the solution is maintained at a temperature of at least about 100; C, preferably 5 10 15 20 25 30 35 40 45 50 55 60 65 3 654,558 from about 100 to about 180 ° C. It has been found that a particularly preferred hydrolysis temperature is from about 150 to about 160 ° C. Reduced or increased pressure can be used to lower or raise the treatment temperature, if desired. The agitation can be of any type suitable for keeping the hydrolyzed solids suspended in the mud. Typical means of agitation include agitators, circulation pumps, etc. When an economically useful amount of crystallized product has formed in the mud, it is easy to separate the niobium oxyfluoride from the liquid phase. Filtration has proven to be a convenient and efficient separation technique, for example using a fluorocarbon filter medium.