DE1934406A1 - Method for cleaning sodium silicofluoride - Google Patents

Description

Central Glass Co., Ltd., Ube-shi, Yamaguchi-ken, Japan

Method for cleaning sodium silicofluoride,

The invention relates to a method for purifying sodium silicofluoride (Sodium fluorosilicate) which contains gypsum and / or phosphates as impurities, you "specifically refers on a new method of cleaning sodium silicofluoride, using impure sodium silicofluoride in salty water such as Sea water and natural or artificial brine is slurried in order to remove the impurities present in the sodium silicofluoride how to actually remove plaster of paris and phosphates without a significant loss of sodium silicofluoride.

Sodium silicofluoride is used as a material for making synthetic Cryolite, useful from fluorides and enamel. So far it has mostly been caused by the absorption of silicon tetrafluoride, which was a by-product of the manufacture of fertilizers such as superphosphate, followed by the addition of a sodium compound, manufactured. In recent years, phosphoric acid obtained by the wet process has found uses as Raw material for high purity phosphates, such as sodium ortho-phosphate and condensed sodium phosphate, besides its application as fertilizer. Therefore, a different technical

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drive developed for the production of sodium silicofluoride, according to hydrofluoric acid and hydrofluoric acid contained in phosphoric acid from the wet process, neutralized with a sodium compound in the cleaning process. Because of an increasing demand for sodium silicofluoride In recent years, the sodium silicofluoride produced from phosphoric acid by the wet process tends to be used poses economically more favorably. In general, no sodium silicofluoride is produced. the Wet process phosphoric acid fine gypsum particles, even after a separation process, in a suspended or dispersed state together with organic materials in phosphoric acid, for example because of imperfect filtration. In addition, the solution is saturated or oversaturated with gypsum. Of the

Plaster of paris precipitates together with sodium silicofluoride as soon as the Hydrofluoric acid is neutralized with a sodium compound such as sodium hydroxide, sodium carbonate, and sodium chloride is added to the phosphoric acid of the wet process. At the same time, impurities dissolved in the phosphoric acid fall like iron and aluminum also together with the sodium silicofluoride in the form of their water-insoluble or poorly water-soluble phosphates such as iron phosphate and aluminum phosphate or complex salts thereof.

In technical practice, it is extremely difficult to obtain a complete Ensure that the above-mentioned impurities are filtered off. Even if suspended impurities such as fine gypsum particles are completely removed, it becomes more saturated or oversaturated gypsum precipitated during the addition of the sodium salts and the sodium silicofluoride obtained inevitably contains Plaster. The production of sodium silicofluoride from phosphoric acid by the wet process therefore has the disadvantage that the The resulting sodium silicofluoride tends to contain a considerable amount of plaster of paris. Gypsum has a very low solubility in water or common acids, whereas sodium silicofluoride has a higher solubility than gypsum, except when the acids are in high concentration. Efforts

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Plaster completely after conventional cleaning methods, such as slurrying Removal with water, warm water or acids, therefore, leads to a very large loss of sodium silicofluoride. From an economic point of view, it is practically impossible to use the above-mentioned process on an industrial scale To be carried out on a scale, since it only gives an unsatisfactory yield and the use of large amounts of water or acid required ·.

A process for purifying liatric silicofluoride obtained from phosphoric acid by the wet process is described in US Pat. No. 3,055,733, wherein a 98-99 $ pure sodium silicofluoride is obtained by slurrying sodium silicofluoride from 94 to 97 $ iger purity at 80 ⁰ G under Ver

application of one part of phosphoric acid (30 # .'Silicon hydrofluoric acid, both related

^a - ^part l · based on a part

raw sodium silicofluoride. This method is economically disadvantageous in that expensive hydrofluoric acid and phosphoric acid must be used in large quantities to remove the gypsum and there is a large loss of fluorine associated with it in terms of the total fluorine balance. In addition, there is a problem with respect to the material of the to be used Aufschlämingefäßes since the AufSchlämmtemperatur at 80 ⁰ C. If the plaster of paris in the sodium silicofluoride has to be removed at such a high temperature, some of the plaster of paris reacts with hydrofluoric acid or sodium silicofluoride to form calcium fluoride, and consequently calcium is still present in the sodium silicofluoride. This is believed to be the reason why, in spite of the acid washing at such a high temperature, sodium silicofluoride of more than 99% purity cannot be obtained. If the material is impure sodium silicofluoride with a large amount of gypsum, it will be even more difficult to clean after such a process. The process of this US patent therefore appears to be based on the use of sodium silicofluoride with a purity of 94 to 97 i ° or more.

0 0 9 8 0 8 / U 9 2

to be limited. In summary, it can be said that this method has so far not proven to be satisfactory has, since, as mentioned above, it is limited to the purification of sodium silicofluoride with a limited purity, the resulting purified product does not have a high degree of purity , expensive hydrofluoric acid and phosphoric acid are required for purification, in view of the need for cleaning on the total balance of fluorine there is a large loss of fluorine and corrosion takes place in the cleaning device.

U.S. Patent 2,883,266 describes a method in which the HpSO. to the phosphoric acid of the hate process, e.g. a phosphorus

phosphoric acid, to which 27.02 # ^ p ^Q 5 " ² ^ °> 5 # ^H 2 ^S0 4 ^en # ^läl ' ^fc » is added in order to adjust the concentration of HpSO. to 1.5 $ , whereby that in the raw Phosphoric acid dissolved gypsum is precipitated, after which the gypsum is separated and sodium hydroxide and sodium silicate are added to thereby recover the fluorine contained in the crude phosphoric acid as sodium silicofluoride. It is admitted that this process is used for the production of gypsum-free sodium silicofluoride However, it is economically disadvantageous that an excess of sulfuric acid is also required after the wet process of phosphoric acid, and it is unsuitable for high-purity phosphoric acid by the hate process, and fine gypsum particles are in the crude phosphoric acid suspended or dispersed unless the crystallized gypsum is completely separated by filtration, and such gypsum becomes from the precipitated sodium iliko-fluorid carried away. As mentioned above, fine gypsum particles suspended in crude phosphoric acid are difficult to completely separate.

An object of the present invention is to provide a method for purifying sodium silicofluoride bis too high purity, through selective removal of gypsum and / ■ or phosphates without significant loss of sodium silicone

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fluoride, from sodium silicofluoride, the plaster of paris and / or phosphates contains as impurities, such as sodium silicofluoride, which is obtained from phosphoric acid by the wet process.

Another object of the present invention is to provide an economical method of production of high purity sodium silicofluoride by cleaning sodium silicofluoride, the gypsum and / or phosphates as impurities without using an expensive reagent and without any trouble such as corrosion of the Devices.

The aforementioned objects of the invention are achieved by a method for purifying sodium silicofluoride, wherein sodium silicofluoride, contains gypsum or phosphates as impurities in an aqueous solution containing sodium chloride is slurried for a time sufficient to remove these impurities practically to remove, and the purified sodium silicofluoride is recovered.

The sodium silicofluoride containing gypsum and / or phosphates used in the cleaning process of the present invention is generally sodium _{silicofluoride precipitated by adding a sodium compound such as NaOH, Na 2} CO ₅ or NaCl to the phosphoric acid of the wet process. The composition of this sodium silicofluoride can vary depending on the composition of the phosphoric acid of the wet process and the method of obtaining the sodium silicofluoride, but in general it has the following composition (calculated as dry matter):

Na ₂ SiP ₆ 70 to 95 %

Approx $ 1 to $ 6>

SO ₄ 3 to 13 %

P ₂ O ₅ 0.5 to 2 %

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In addition to such a large amount of gypsum, the sodium silicofluoride contains water-insoluble or sparingly water-soluble phosphates, such as iron phosphate and aluminum phosphate and complex salts thereof, water-soluble salts such as NaH ₂ PO., Na ₂ HPO ₄ , NaHSO. and Ca (H ₂ PO.) ₂ , and organic colored materials. These impurities can be effectively removed by a slurry method in an aqueous solution containing sodium chloride, as described below. Furthermore, it should be understood that the process of the present invention is also applicable to the purification of contaminated sodium silicofluorides similar to those obtained by the wet process.

It has been found that, among various slurry media, salt water exhibits unique behavior towards sodium silicofluoride, which contains gypsum as an impurity. In particular that in the addition of a mixture of gypsum and Natriumsiliko fluoride to an aqueous solution containing 2.5 g NaCl / 100 cc at 20 ⁰ C contains two, for example, the solubility of gypsum or three times larger than that was found in Water at room temperature, whereas the solubility of sodium silicofluoride is reduced to 1/10 or less of that in water. The solubilities of gypsum and sodium silicofluoride in water and for various sodium chloride concentrations are given in Table I below:

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193A406

Table I (unit: g / 100 ecm solution at 2O ⁰ C)

- ^ _ ^ ___ ^ Substance to be dissolved Na ₂ SiF ₆ CaSO ₄ * NaCl-Concentration- ~~ "-—— ■ —____ ^^ tration ~~ "" ~ --— 0 0.670 0.212 2.5 0.043 0.475 5.0 0.026 0.6.00 10.0 0.015 0.695 15.0 0.011 0.723 20.0 0.007 0.692 25.0 0.006 0.645

The values in this column are those of calcium sulfate dihydrate, calculated as calcium sulfate anhydride. The solved Amounts of calcium sulfate dihydrate can therefore be increased by multiplying these numbers with

CaSO

2H ₂ O

CaSO,

be calculated.

Accordingly, it enables the use of an aqueous sodium chloride solution as the slurry medium, the actual removal of Gypsum made from sodium silicofluoride, which contains large amounts of impurities contains like plaster of paris without significant loss of sodium silicofluoride.

The concentration of sodium chloride in the aqueous sodium chloride solution should be such that it _{inhibits the dissolution of Na 2} SiEg, but facilitates the dissolution of gypsum, it should therefore be at least 0.5 % . However, too high a concentration delivers not an increased effect, but rather it lowers the amount of dissolved calcium sulfate dihydrate, which leads to an economic disadvantage. Preferably, therefore, the

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the upper limit of the concentration is 25 f ° . The most preferred concentration is in the range from $ 2.0 to $ 10. The aqueous solution containing sodium chloride includes not only a solution of sodium chloride in water in the concentrations given above, but also sea water and natural or artificial brine. The lake water and natural or artificial brine are easily accessible and are particularly preferred from an economic point of view.

Lower amounts of substance (1 to 70 g / ltr., If one of the Substances used alone and 1 to 100 g / ltr. as the combined total when used in combination) that contain the Increase the solubility of gypsum and other impurities, such as mineral acids, e.g. hydrochloric acid, nitric acid and sulfuric acid, magnesium chloride, magnesium nitrate and ammonium chloride, are added to an aqueous sodium chloride-containing one Solution used as the slurry medium in the present Invention is used, whereby it is possible to obtain a high purity sodium silicofluoride even if the so obtained aqueous solution is used in an amount smaller than that of an aqueous solution of sodium chloride alone. When these additives are used together to accelerate the dissolution of impurities, especially mineral acids then the removal of water-insoluble or poorly water-soluble phosphates becomes easy and the loss of sodium silicofluoride can be drastically reduced compared to the use of an aqueous solution of these mineral acids alone.

Furthermore, in addition to sodium chloride, smaller amounts, e.g. 0.01 to 20 g / ltr. Additives to inhibit going into solution of sodium silicofluoride, such as sodium carbonate, sodium nitrate, sodium tetrafluoroborate (NaBF,) and organic sodium salts Acids are added individually or in combination to the slurry medium used according to the invention. This ensures a further reduction in atrium-silicone-fluoride losses. These inhibiting additives prove to be special

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effective when you deal with the aforementioned contaminants dissolving accelerators combined.

According to the invention, contaminated sodium silicofluoride is added to the slurry medium, which consists of an aqueous solution containing sodium chloride, and slurries it until practically the removal of the impurities in the sodium silicofluoride is achieved.

The term "slurry" used in the present description stands for a process in which impure sodium silicofluoride is mixed with an aqueous solution containing sodium chloride is slurried and the slurry is stirred. Sodium silicofluoride can be used to slurry sodium silicofluoride in the form as it is from phosphoric acid using the wet process is obtained, can be added to an aqueous solution containing sodium chloride. Sodium silicofluoride can also be pulverized to a particle size of e.g. less than 100 microns before placing it in an aqueous sodium chloride-containing one Solution slurries.

The ratio of the slurry medium to the starting sodium silicofluoride can be such that the gypsum concentration in the aqueous solution containing the sodium chloride is below the saturation concentration. In general, 10 to 350 liters, in particular 20 to 80 liters, of an aqueous sodium chloride-containing solution are preferably used per kg of sodium silicofluoride. The use of the slurry medium in an amount exceeding the above range results in a large loss of sodium silicofluoride, and the impurities are not completely removed with an amount of the slurry medium smaller than the above range. The Ausschlämmtemperatur is preferably in the range from room temperature to 70 ⁰ C. At temperatures above 70 ⁰ G takes place between the reaction gypsum and Natriumsiliko fluoride and calcium fluoride and silicon dioxide tend to precipitate.

009808 / H92

Temperatures above 7O ⁰ C are not preferred. No particular limitation is imposed on the pressure, and the objects of the invention can be satisfactorily achieved using normal atmospheric pressure. The slurry time will vary depending on the temperature and the amount of contaminants, but it can range from 5 minutes to an hour to substantially remove the contaminants.

The slurry operation is carried out by placing a mixing vessel, equipped with a stirrer is used and a slurry of sodium silicofluoride among those mentioned above Conditions stirs. The operation can either be continuous in a single stage or in two or more stages or be carried out on a rudimentary basis. For example, sodium silicofluoride becomes a large amount in a first stage added to aqueous solution containing sodium chloride, slurried and allowed to stand to separate the resulting supernatant liquid, and in a second stage is the resulting slurry directly or after adding a substance such as mineral acid, which increases the solubility of the impurities increased, slurried. Slurrying can also be effected by adding sodium silicofluoride and an aqueous sodium chloride-containing one Contacted solution in cocurrent or in countercurrent.

According to the invention, the sodium silicofluoride purified in this way can be separated from the slurry medium by known methods separated from the pesticide and liquid such as filtration, centrifugation and decanting. The severed If desired, sodium silicofluoride is washed with water and dried to prepare an end product.

Thus, the practice of the present invention enables the recovery of sodium silicofluoride with a purity of $ 99> or more from raw sodium silicofluoride that is 80 yo or more

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contains less impurities such as plaster of paris and phosphates. Of the Loss of sodium silicofluoride is low and amounts to E.g. $ 4.6 if a material with a purity of $ 80 is up to a Purified product of 99.4% purity. The cleaning process The present invention is advantageous over the known methods as it is performed in simple operation and sea water and natural or artificial brine, which is cheap, can be used as the slurry medium can.

The sodium silicofluoride obtained according to the present invention is high Purity and is useful as a material for synthetic cryolite and fluoride and for other applications.

The following examples explain the invention without it however, limit it. Unless otherwise stated, the percentages in the examples and elsewhere refer to that Based on weight.

Comparative example

1.50 kg sodium silicofluoride containing impurities (water content: $ 21.29>) was 45 ltr. Given water and slurried for 30 minutes at 20 ⁰ G or at 50 ⁰ O, then separated, with 2 ltr. Washed water per kg of sodium silicofluoride and ^{dried at 110 0} C, as indicated in Table II.

The same sodium silicofluoride was added to 25 liters. a solution containing 5 g / ltr. HCl contained and 9 ltr. a solution containing 40 g / ltr. HGl contained, and slurried for 30 minutes at room temperature in a mixing vessel equipped with a stirrer, then separated, washed .with 2 ltr. Water are per kg llatriumsiliko fluoride and dried at 110 ⁰ G. The nature dos obtained Natriumsiliko-fluorides before and after slurrying and the loss of fluoride Natriumsiliko

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given in Table II.

From the results obtained, it can be seen that if water or an aqueous hydrochloric acid as the slurry medium is used, a considerable loss of sodium fluosilicate occurs.

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Table II

sample

category

Amount of Aufschläimn medium (ltr.)

Analysis values of sodium silico-fluoriae (fo _t based on gross weight)

Oa

SO

P ₂ O ₅

Loss of remarks

liqueur fluoride * (G-ew, -

Sheoretic marriage Fourth

100.0

60.62

CD CD OO O CO

Before slimming down

84.8

51.40

2.79

6.67

1.24

X-ray diagrams

showed 'the presence of v.

and

CO S approx

h ω

σ? ο S approx

■ _ö JUL ₂ O loading

pj iiandlung at 20 ⁰ C

45

HpO-Bchandlune

^ at 50 ⁰ C

96.6

58.5-5

0.67

1.59

0.16

5 g / ltr. HCl added

.95.2

57.75

1.12

2.66

0.07

25th

99.6

60.41

no

40

HCl added

99.8

60.49

no

track

0.06

track

0.05

30.2

55.6

Röiitgendiagramia showed the presence of

CaSO

30.0

■ L-

2H ₉ O

15.9

X-ray diagrams only showed Ha ₉ SiEg. The niicro- sic op iß before Ana Iyse showed that about 5 Hin. no plaster of paris available after the beginning of the winding process.

* = Loss of sodium silicofluoride due to. to go into solution

end of the slurry _e 100

Pure sodium silicofluoride in impure sodium silicofluoride

example 1

1.54 kg of sodium silicofluoride (water content: $ 18.58) containing 8.45 Io SOT ~ ($ 15.15 calculated as CaSO. · 2H ₂ O) and 0.89 1 » PpOc, both on a dry weight basis , which had been obtained by adding anhydrous soda or sodium hydroxide to the phosphoric acid of the wet process and filtering off and washing the crystals formed, were added to 30 ltr. a 3 # aqueous sodium chloride solution or 21 ltr. a 10% aqueous sodium chloride solution and slurried for 30 minutes at room temperature in a mixing vessel provided with a stirrer, then separated off, washed with 2 liters. Water per kg of sodium silicofluoride and dried at 110 ⁰ O.

The nature of the sodium silicofluoride obtained before and after the slurry and the loss of sodium silicofluoride are given in Table III. ·

It is clear from the results obtained that by using an aqueous sodium chloride solution as a slurry medium, the complete removal of gypsum contaminants possible · is borrowed.

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! Table III

\
Per D category 5 5δ ITaCl
treatment itfsnge at
On-
muddy
Medium
(ltr.) Analytical values for sodium silicofluoride
(yo, based on dry weight) I \ ^T a 60.62 Approx so ₄ P 0
^£ 9 ^u r;
C- J Loss at
Katriunzsi-
co-fluoride
(Gev -.- £) 3 comments theoretical
fourth 10 $ FaCl-I
treatment
ι - ITa ₂ SiPg 24.46 48.51 - - - Gate aera open
muddy - 100.0 19.75 60.21 3.40 8.45. 0.89 X-ray slide
grcm showed
the presence
v. Ha ₀ SiIv and
2 ο
CaS0 _A -2H ₂ O ·, '. CJ
ρ:
ε
: ü
H
• s
approx
<j
'S
O;
I. 30th 80.0 24.30 60.05 no track 0.16 2.3 X-ray diagrams
gram showed
the Anv; eg anh e11
from only ITa ^ SiSV
The nikrosiropi-
see analysis he
gave that
et v / a 5 minutes
after the beginning of dec
On G chlli.rr.nens
Ice in plaster of paris.
was dealt. < 21 99.3 24.25 no track 0.18 0.5 99.1

Example 2

Sodium silicofluoride samples A, B and C of 1.37 kg (water content: 19.61 fo), 1.50 kg (water content: 21.29 1 °) and 1.54 kg (water content: 18.18 %) were added accordingly 20 ltr., 45 ltr. "or 58 liters of sea water with an NaCl concentration of 27.34 g / liter and slurried for 15 minutes at room temperature in a mixing vessel equipped with a stirrer, then separated, washed with 2 liters of water per kg of sodium silicofluoride and dried at 110 ⁰ g.

The nature of the sodium silicofluoride obtained and after slurrying and loss of urodium silicofluoride are given in (Table IV.

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Table IY

^ \ "Rubric
Probes. . Sample A Amount of recording
pr »h 1 ητητη — TVff» «. Analysis values of the sodium silicofluoride
($, based on dry weight) N / A Έ Approx so ₄ P ₂ O ₅ Loss at
Sodium
liko-fluo-
rid (weight Remarks Before the
Sludge
men Sample B dium (ltr.) Na ₂ SiF ₆ 22.52 55.06 1.26 5.10 0.65 - X-ray diagrams
gram showed
the property
called V.
Na ₂ SiIV and
CaSO. 2H _o 0
4 pounds After slurrying Sample C - 90.8 20.84 51.40 2.79 6.67 1.24 - X-ray diagrams
gram showed
only the application
sness of
Na ₉ SiIV. the
mifcrosKopi-
see analysis
revealed that
about 5 minutes
ten according to Be
start of the
muddy
no plaster before
was dealt. Sample A - 84.8 19.75 48.51 5.40 8, / 45 ^ 0.89 . - 009808/1 A Sample B - 80.0 24.55 60.42 no track 0.14 1.6 co
to Sample C 20th 99.6 24.26 60.19 no track 0.14 5.5 45 99.5 24.29 60.25 no track 0.16 4.6 58 99.4

J ^ i

September 19, 89

Example 3

1.50 kg (water content: 21.29 %) of sample B used in Example 2 (sodium silicofluoride of low purity before slurrying) were added to 45 Itr. the same seawater used in Example 2 and slurried for 15 minutes at room temperature in a mixing vessel equipped with a stirrer. The suspended product was allowed to stand for 30 minutes, and when part of the supernatant liquid was removed, about 30 % of the sodium silicofluoride slurry was obtained. The slurry was slurried again for 30 minutes at ψ 55 ⁰ O, then separated, with 2 Itr. Water per kg Natriumsiliko fluoride washed and dried at 110 ⁰ C.

The nature of the obtained sodium silicofluoride before and after the slurry and the loss of sodium silicofluoride are given in Table Y.

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Table V

^. category Analysis values of the sodium silicofluoride
(%, based on the dry weight) N / A P. Approx so ₄ P ₂ O ₅ Loss of sodium
silicon fluoride ■
(Wt .- ^) Remarks Before opening
muddy
(Sample B) Ha ₂ Si ^ ₆ 20.84 51.40 2.79 6.67 1.24 - X-ray diagram
showed the application
sheit V.
Na _o SiP _c and CaSO.
2h | o ^{6 4} After the opening
muddy 84.6 24.27 60.21 no track 3.8 X-ray end i agram
showed that alone
Presence γοη
Na ₂ SiP ₆ 99.3 '

Example 4

1.50 kg (water content: 21.29 ^) of sample B used in Example 2 (before slurrying) was slurried in the same sea water as used in Example 2 and also in a mixture of sea water and each of hydrochloric acid, magnesium chloride , Ammonium chloride, nitric acid and magnesium nitrate in the amounts given in Table YI, slurried for 50 minutes at room temperature using a mixing vessel equipped with a stirrer, then separated, with 2 ltr. Water per kg of dried Natriumsiliko fluoride gewasehen and at 110 ⁰ O. The amounts of the slurry medium, the concentration of the additives, the nature of the sodium silicofluoride before and after the slurry and the loss of the sodium silicofluoride are given in Table YI.

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Table YI '

Ό O LD OO O OO

to

category

Pr QD

Before slurrying. (Prcbe B)

Amount of ac

On-

muddy

medium

(ltr.)

Concentration of additives (g / ltr.)

CQ

rs δ

Γ1

"ο

Seawater

this to-

HCl surplus

added

MH ₂ , Ol

HITO-added

45

21

24

27

26 analysis values of the sodium silicate fluoride
(^, based on dry weight)

Ha

20.84

24.26

24.35

24.31

24.25

27 10.0

24.38

24.23

Approx

51.40

60.19

60.47

60.26

60.15

60.3S

60.09

2.79

no

no

no

no

no

no

SO,

6.67-

Stubborn

Stiur

track

track

^P 2 ° 5

1.24

0.14

0.06

0.19

0.13

0.07

track

0.18

Yerlust
at 2Tatriuinsiliko-

fluoride

Remarks

tlöntgendi c: ram shows the presence of ν.

<y > - * » w ν /, · C" - - ο ν

R-öntgendia

3.5

2.6

only. the being

The niirro-

..lalys.e he 1,4 'gave that

grooves after 1.7 [beginning of '' Ά u τ s η h 1 1 \ t, -i

2.8

Information no 3-ips before-

1.6

193U06

Example 5

1.50 kg (water content: $ 21.29) of sample B used in Example 2 (before slurrying) were added to 45 ltr. the same seawater used in Example 2 and slurried for 15 minutes at room temperature in a mixing vessel equipped with a stirrer. After standing for 30 minutes, the supernatant was partially removed, forming a 30% slurry of sodium silicofluoride. It was added to the slurry so that there was obtained a 0.5 n-Lö'sung sulfuric acid, and the sample was slurried an additional 30 minutes at 55 ⁰ C and 70 ⁰ C, then separated, washed with 2 liters. Water per kg of sodium silicofluoride washed and dried at 110 ⁰ C. The nature of the obtained sodium silicofluoride before and after the slurry and the loss of sodium silicofluoride are given in Table TII. ^Λ

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Table YII

CD UJ OO O OO

^ • v. category treatment
at 55 ⁰ C Analysis values of the sodium silicofluoride
(#, based on dry weight) SiP ₆ N / A P. Approx so ₄ 1 P ₂ O ₅ Έ e ₂ 0 Al 2 ° 3 Loss at
Sodium Remarks Sample ^^ \. treatment
at 70 ⁰ C Well ₂ 8th 20.84 51. 2.79 6.67 0 , 24 O, 032 O, 18th liko-flub-
rid
(Wt .- $) X-ray diagrams
gram showed
the property
called V.
Na ₂ SiP ₆ and
CaSO ₄ 2H ₂ O Before opening
muddy
(Sample B) 84, 8th 24.35 60, no track 0 , 028 O, 005 O, 05 - X-ray diagrams
gram showed
only the application
sness of,
Na ₂ SiP ₆ After this
Sludge. 99 7th 24.37 60, no track , 019 O, 005 O, 05 4.1 99 ■ 4.3 , 40 48 41

Claims (7)

- 24 patent claims 1. Method for purifying sodium silicofluoride, thereby characterized that sodium silicofluoride, which gypsum and / or contains phosphates as impurities, is suspended in an aqueous solution containing sodium chloride for so long until the impurities are practically removed and then the purified sodium silicofluoride is recovered. 2. The method according to claim 1, characterized in that the concentration of sodium chloride in the aqueous solution is in the range from 0.5 to 25 % . 3. The method according to claim 2, characterized in that the aqueous llctriumchlorid-containing solution is sea water or natural or artificial brine. 4. Process according to Claim 1, characterized in that the slurrying is carried out at a temperature in the range from room temperature to 70 ^° C. 5. The method according to claim 1, characterized in that the aqueous sodium chloride-containing solution is sodium chloride in one Concentration from 0.5 to 25 # and a substance or substances such as mineral acids, magnesium chloride, magnesium nitrate or Contains ammonium chloride and the quantities of these substances are 1 to 70 g / ltr. if used individually, and 1 to 100 g / ltr. as the combined total when used in combination. 6. The method according to claim 1, characterized in that the aqueous sodium chloride-containing solution 0.5 to 25 1 ° sodium chloride and 0.01 to 20 g / ltr., Either alone or in combination, of sodium nitrate, sodium carbonate, Na BF, and water-soluble sodium salts of organic acids. 003808 / U92 7. A method for cleaning sodium silicofluoride, characterized in that sodium silicofluoride, which contains gypsum and / or phosphates as impurities, in 10 to 350 ltr. per kg of sodium silicofluoride of an aqueous solution which contains sodium chloride in a concentration of 0.5 to 25 °, at a temperature in the range from room temperature to 70 ^° C. and over a period of 5 minutes to 1 hour and thereafter the purified urodium silicofluoride is obtained. OD 9 80-87-1 43