FI59422C - FOER FARING FOR SAFETY RING OF JORDMETALLFOSFATER - Google Patents

Description

uSr ^ l ΓβΙ im ^ u υ * utusjuKÄKKIS BJ (11) UTLÄGGNINGSSKRIFT 59422 • £ (45) Patent granted 10 08 1931

Patent Meddelat (51) Kv.tk.3 / Int, ci.3 c 22 B 59/00 // C 01 F 17/00, C 01 B 25/26 FINLAND — FINLAND (») Patunttlhaktmus - Patcnurodkning 1239/7 ^

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_ __ '_. (44) Date of issue / battery / exterior. - riunt * ocn reglsterstyrelsen Antokin utiagd och Mi-ikrUtm pubikcnd 30. Oli. 8l (32) (33) (31) *> ry4 «<y stuoikuus — Bagtrd prloritat 02.05.73

Norway-Norway (NO) 18lL / 73 (71) Norsk Hydro a. S, Bygd? 5y alle 2, Oslo 2, Norway-Norway (NO) (72) Gl ^ r Thorvald Me jdell, Porsgrunn, Harald St ^ ren, Glomfjord, Norway-Norway (NO) (jh) Oy Kolster Ab (5M Method for enrichment of rare earth phosphates - Förfa-rande för anrikning av sällsynta jordmetallfosfater

The invention relates to a process for the preparation of a rare earth phosphate concentrate from crude phosphate. By crude phosphate in this context is meant naturally occurring calcium phosphates and apatites used in the manufacture of phosphate-containing fertilizers such as colaphosphate (colafphosphates). The content of rare earth metals in the latter phosphate type is between 0.7 and 1% by weight (Re = sum of the elements La, Ce, Pr, ---- Yb, Lu and Y).

It is known that rare earth metals can be produced as a by-product in the preparation of useful phosphates (feed phosphates, fertilizers, etc.). The object of the process according to the invention is to prepare said by-product by partially neutralizing with ammonia a solution of crude phosphate in nitric acid, from which a substantial part of its calcium content has been separated according to the known Odda process as calcium nitrate tetrahydrate crystals. Such a process is known from DDR Patent No. 40739, according to which said crude phosphate solution is neutralized with gaseous ammonia to a pH of between 1.7 and 2.3 at a temperature between 60 and 100 ° C while maintaining the specified concentration limits for P 2 O 2 and weight ratio between CaO and P 2 O 2 sn. This precipitates the machine nitrate of rare earth phosphates, which is separated. The further treatment of the filtrate is carried out in a known manner into fertilizers containing N, P and N, P, K. However, according to this patent, the residence time in the neutralization age is 20 to 90 minutes, and we have found that the precipitate of rare earth phosphates is so difficult to filter that technical manufacturing would require enormous filtration surfaces. Thus, we found a typical permeability value of 0.5 m 2 / h of suspension per square meter of filter surface immersed in the liquid with a suction of 200 mm Eg and a filter cake thickness of 5-6 mm, while the leaching properties according to the present invention under otherwise similar conditions were about 5 m 2 / h per square meter towards the filter surface immersed in the liquid. Moreover, the infiltration properties of the filter cake were very stable in the method of the present invention.

It is known from DDR Patent No. 65075 that the poor leaching properties of the concentrate can be improved by adding 0.1 to 0.2 g of potassium permanganate per liter of solution before neutralization and thereby separating the precipitated flocculant bottom precipitate. Alternatively, the leaching properties can be improved by reducing the silica content of the solution before neutralization by boiling the solution, thereby recovering the silica to be expelled as SiF2, which evaporates with the water vapor. However, alternative variations of the method described in this patent require an additional step of the method, which complicates the method while leaving the effect of these steps modest.

Rare earth metal phosphates are known to begin to precipitate at a pH of about 1.5 (measured diluted 1:10 with water). The elements with the lowest atomic numbers precipitate first and at pH 2.2 (measured diluted 1:10 with water) most of the rare earth metals (by weight) have precipitated. However, only those with higher atomic numbers, as well as yttrium, have been partially precipitated from lanthanides. However, at pH 2.5, La, Ce and Nd have precipitated about 100 fo, while Y has precipitated 75 fa · If the pH is further increased, a rapidly increasing amount of dicalcium phosphate, iron and aluminum phosphates precipitates and dilutes the concentrate.

It is known from Norwegian Patent No. 52,397 to precipitate lime as gypsum by adding sulphate ions to a nitric acid crude phosphate solution from which lime has been substantially separated as calcium nitrate crystals by cooling.

3 59422

The process according to the invention relates to the preparation of a rare earth phosphate concentrate from crude phosphate by partial neutralization with ammonia of a crude nitric acid solution from which a substantial part of its calcium content has been separated as calcium nitrate tetrahydrate crystals and part of the calcium content remaining in the solution The method is characterized in that said amount of sulphate ions corresponds at least to the ordinate y in curve 1 in the drawing, which curve shows said amount of sulphate, calculated as equivalent percentages of solution calcium as a function of solution fluoride content, calculated as x , and the resulting suspension is neutralized with ammonia in a reactor using a short residence time, after which the precipitated concentrate containing rare earth metal phosphates is separated by filtration.

As far as the residence time in the reactor is concerned, contrary to the usual experience that the permeability of the precipitated suspension improves with the residence time, it has surprisingly proved that within practical limits the best permeabilities are achieved with the shortest residence times.

In the process according to the invention, the best results are obtained when the amount of calcium sulphate precipitated corresponds to the ordinate y in curve 2 in the drawing. When the fluoride content of the solution corresponds to 0.5% by weight of fluorine, in this case it is only necessary to precipitate calcium content. In addition, it has been found advantageous that the neutralization with ammonia and the separation of the concentrate by filtration are carried out in less than 15 minutes, preferably in less than 5 minutes. Namely, it has been found that the infiltration properties of the concentrate deteriorate substantially as the time spent on neutralization and filtration increases beyond 15 minutes.

In addition, it has been found advantageous to neutralize the suspension with anhydrous ammonia, e.g. with a view to further processing the filtrate into fertilizers. In this case, dilution caused by water is avoided, while the heat of reaction generated in the reactor can cause the suspension to boil, and the generated water vapor can then be separated, e.g. in a cyclone, before the concentrate is separated by filtration.

By carrying out the process according to the invention, a very easily filterable precipitate of rare earth phosphates is obtained, as will be seen in the following examples. If the crude phosphate contains sulfur compounds, these may, due to the oxidizing effect of nitric acid, be converted into sulphate ions in an amount which may be sufficient to compound the amount of calcium sulphate mentioned 4 59422. This amount of calcium sulfate is so finely divided that it passes through a relatively coarse filter before separating the calcium nitrate tetrahydrate. However, the aga-phosphate normally contains only small amounts of sulfur, which is why the precipitation of calcium sulphate usually takes place when soluble mineral sulphate, such as ammonium and / or alkali sulphate, is added to the solution. Sulfuric acid can also be used for this purpose.

As can be seen from curve 1 in the drawing, it is not necessary to remove fluorine from the solution, since useful results are also obtained at the concentration which occurs naturally, which corresponds to a maximum of about 2% by weight of fluorine in the solution. However, the curve shows that with a high fluorine content in the solution, it becomes necessary to precipitate a larger part of the calcium content remaining in the solution as calcium sulphate, which of course reduces the content of rare earths in the concentrate. Substantially for this reason, it may be desirable to reduce the fluorine content of the solution before the calcium is precipitated as sulphate, which can be done in a number of ways known per se. For example, separating the doped fluorides from the crude phosphate solution, which are mainly CaSiF 4, gives a crude phosphate solution containing about 0.5% w / 6 P. It is possible to reduce the fluoride content even more from the solution as SiO 2 by blowing water vapor into the solution.

The process according to the invention is also excellent because it can be carried out continuously, e.g. by separating the concentrate by filtration in a rotating vacuum filter embedded in the suspension *

Other advantages of the invention will become apparent from the following examples, which are not to be construed as limiting, although they are based on a relatively fluorine-poor solution.

Example 1

A substantial portion of its calcium content was removed from a solution of colaphosphate in nitric acid in a manner known as CaiNOjJg.dHgOsna, so that the solution contained 10% by weight of P and 3 * 5% by weight of Ca. The solution was treated with steam until the fluoride content dropped to 0.11 wt% P. To this fluorine-poor solution was added a 50 wt% solution of KgSO 4 in 60 wt% nitric acid in an amount corresponding to 10 equivalents of sulfate solution. control of the calcium content of the solution. The resulting suspension containing calcium sulfate was neutralized with NH 4 gas to pH 2.20 (measured by diluting 5 59422

with water in a ratio of 1:10) in the reactor with a residence time of 5 minutes, at which time the temperature rose to approximately 110 ° C. The precipitate was immediately separated by filtration and the weight of the filter cake (including the addition of mother liquor) was 120 g per kilogram of neutralized suspension. The composition of the filter cake was as followsJ

Ca 6.4 weight- ^ P 12 "N 7.8" K 0.7 "SO. 7" 4 P 0.2 "

Re 2 O 3 4.1 95 ° / ° of the serum content of the crude phosphate and 50% of its yttrium content was in the filter cake. The content of rare earths in the filter cake was, as mentioned above, 4.1% by weight, calculated as RegOjJ, which corresponds to 25% of the total content of rare earths in the phosphate phosphate.

The filtration properties of the precipitate corresponded to about 3 m 2 / h of suspension per square meter in the liquid-immersed filter surface in a rotary vacuum filter with a vacuum of 100 mm Hg and a filter cake thickness of 5-6 mm.

Example 2 The same solution, addition of sulphate and method of fluoid reduction as in Example 1 were used in this experiment. However, neutralization with gaseous NH 4 was carried out to pH 2.50 (measured diluted 1:10 with water). The residence time in the reactor was the same as in Example 1 and the precipitate was immediately separated by filtration. The weight of the filter cake (including the mother liquor supplement) was 120 g per kilogram of neutralized suspension. The composition of the filter cake was as follows:

Ca 5.5 weight- ^ P 10.8 "N 9.1 K 0.8" SO. 6.0 "P 0.24"

Heg0 4.4 "

Approximately 100% of the serum content of the crude phosphate and 75% of its yttrium content was in the filter cake. The cake contained a total of 95 Ί ° of the rare earths contained in the crude phosphate. The filtration properties corresponded approximately to 2 m 2 / h of suspension per square meter of filter surface immersed in the liquid when a rotary vacuum filter was used at a vacuum corresponding to 100 mm Hg, with a filter cake thickness of 5-6 mm.

Claims (3)

7 59422 A process for preparing a rare earth phosphate concentrate from crude phosphate by partially neutralizing with ammonia a nitric acid solution of crude phosphate, a substantial part of the calcium content of which is separated as calcium nitrate tetrahydrate crystals, and a portion of corresponds at least to the ordinate y of drawing curve 1, which represents said amount of sulphate, calculated as the equivalent of the calcium content of the solution as a function of the fluoride content of the solution, calculated as the weight - $ of fluorine shown as abscissa x the residence time after which the precipitated concentrate containing rare earth phosphates is separated by filtration, whereby neutralization and filtration are carried out in less than 15 minutes. A method according to claim 1, characterized in that said amount of precipitated calcium sulphate corresponds to the ordinate y of the curve 2 shown in the drawing. A method according to claim 1, characterized in that said neutralization and separation by filtration is performed in less than 5 minutes. U A method according to claim 1, characterized in that said suspension is neutralized with substantially anhydrous ammonia.