JP2002255563A - Method for purifying by crystallization of rhodium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying rhodium by crystallization facilitating re-purification by recrystallization, capable of separating and recovering rhodium selectively and at a high yield from an aqueous solution of a rhodium compound even when an impurity such as iridium is co-existing. SOLUTION: This method for purifying rhodium comprises the steps of adding sodium nitrite to an aqueous solution containing a rhodium compound, reacting it with the rhodium compound in the presence of sodium ions of 100 g/l or more, and selectively separating and recovering rhodium as a crystalline precipitate of sodium hexanitro rhodate (III). Adjustment of sodium ion quantity is carried out by adding another water soluble sodium salt together with addition of sodium nitrite, or by concentrating the aqueous solution. The crystal of sodium hexanitro rhodate (III) is dissolved in water, and by adding a water soluble sodium salt, rhodium is again selectively separated and recovered as a crystalline precipitate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the crystallization of rhodium from platinum group concentrates produced in the smelting process of nickel, copper, etc., or from platinum group concentrates generated as a result of recycling of platinum group content. The present invention relates to a method for separating and recovering.

[0002]

2. Description of the Related Art Since it is difficult to separate rhodium in an aqueous solution selectively and in a high yield with either a solvent extractant or an ion exchange resin, first, impurities coexisting with rhodium are extracted by solvent extraction or ion extraction. After separation by exchange, etc.
A method for purifying the final residual rhodium by crystallization and separation is widely used.

[0003] As a method for separating and crystallizing rhodium, R.S.
J. Dowsing: MetalsMater, (19
80), No. 7, pp. 32/42, etc., sodium nitrite and ammonium chloride are added to an aqueous solution containing a water-soluble rhodium compound, and hexanitrorhodium (III) which is hardly soluble in water is added. Ammonium); (NH ₄ )
₃ a method for separating as crystals _{[Rh (NO 2) 6]} , or, S. A. Johnson, F.C. Basolo: In
orog. Chem. 1, (1962), PP. 925 /
32, ammonium chloride and ammonium carbonate, an aqueous solution of a water-soluble rhodium compound,
Or, by adding aqueous ammonia, pentaamminechlororhodium (II) chloride which is hardly soluble in water; [RhCl (NH ₃ ) ₅ ] C
How to separate as crystals l _2, or is known a method with improved selectivity by combining the two,
All are practiced industrially.

However, the former method of separating rhodium as ammonium hexanitrorhodate (III) is a method originally devised to collectively separate iridium and rhodium from a mixture of various ions. However, there is a problem that it is difficult to separate rhodium and iridium when there is much iridium.

[0005] In addition, recrystallization is necessary because crystals of sufficient purity cannot be obtained by a single crystallization, and ammonium hexanitrorhodate (III) is difficult to dissolve in water even at high temperatures. However, it is necessary to once add an acid to decompose and then re-crystallize by adding sodium nitrite and ammonium salt, which is extremely uneconomical.
Furthermore, toxic nitrogen oxides are generated in large quantities when decomposed with this acid. However, since nitrogen oxides are hardly absorbed by alkali, there is a problem that it is difficult to absorb the exhaust gas.

Accordingly, the former method of separating rhodium as ammonium hexanitrorhodate (III) is applicable as a method of purifying rhodium to a target purity and then collecting rhodium as crystals, but the method of purifying rhodium is not limited. There were many problems as a means of doing so.

On the other hand, in the latter method of separating rhodium as pentaamminechlororhodium (II) chloride, since the pentaamminechlororhodium (II) chloride is synthesized at a high pH, it is difficult to form a water-soluble hydroxide. There is a problem that all co-existing impurities that easily form a substance co-precipitate with rhodium and are easily contaminated. Therefore, prior to the synthesis of this compound, it is necessary to precipitate and separate a co-existing impurity that easily forms a hydroxide that is hardly soluble in water.However, in the step of precipitating this impurity, rhodium is co-precipitated as a hydroxide.
This resulted in loss of rhodium.

Further, since rhodium has a property of forming various ammonia complexes other than pentaamminechlororhodium (II) chloride, the condition range in which pentaamminechlororhodium (II) chloride can be selectively formed is narrow. The solubility was difficult to stabilize. Furthermore, since the mother liquor after separating the precipitate of pentaamminechlororhodium (II) chloride contains a stable ammonia complex that is difficult to decompose even in an acidic condition, it decomposes to form a starting material such as chloride or chlorocomplex. It is difficult to form and therefore difficult to recycle, resulting in a decrease in the overall yield.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and when rhodium is crystallized and separated and purified from an aqueous solution of a rhodium compound, rhodium is selected even in the presence of various impurities such as iridium. It is an object of the present invention to provide a method which can be separated and recovered by crystallization with high yield and high yield, does not generate toxic gas or consumes expensive chemicals even during recrystallization, and can easily recycle mother liquor.

[0010]

In order to achieve the above object, the present invention provides a method for crystallization and purification of rhodium, which comprises adding sodium nitrite to an aqueous solution containing a water-soluble rhodium compound, and adding 100 g / l of sodium nitrite. It is characterized by reacting with a rhodium compound in the presence of the above sodium ions, and selectively separating and recovering rhodium as sodium hexanitrorhodate (III) crystalline precipitate.

In the method for purifying rhodium according to the present invention, sodium nitrite in an amount of at least 6 times the mol of the rhodium compound in the aqueous solution and a water-soluble sodium salt other than sodium nitrite are added. In addition, 100 g / l or more of sodium ions can be present in the aqueous solution. Further, while concentrating the aqueous solution,
Sodium nitrite can be added to the concentrated aqueous solution so that 100 g / l or more of sodium ions are present in the aqueous solution.

[0012] The method for crystallizing and purifying rhodium provided by the present invention comprises dissolving sodium hexanitrorhodate (III) crystals produced by the above method in water and adding a water-soluble sodium salt. It is characterized in that rhodium is selectively separated and recovered again as a crystalline precipitate of sodium hexanitrorhodate (III).

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Sodium hexanitrorhodate (III) obtained by reacting rhodium ion with sodium nitrite has a solubility of about 110 g / l in water. Solubility decreases due to the common ion effect of cations. The present invention utilizes this principle to react rhodium ions with sodium nitrite under high sodium concentration, selectively crystallize rhodium as sodium hexanitrorhodate (III), and separate and recover it from the aqueous solution. Things.

FIG. 1 illustrates the relationship between the concentration of sodium ions in an aqueous solution and the concentration of rhodium ions dissolved as sodium hexanitrorhodate (III). FIG. 1 shows that a certain amount of sodium hexanitrorhodate (III) crystals are dissolved in the minimum amount of water that can be dissolved, and the amount of sodium chloride is added and dissolved, and then the amount of the aqueous solution is reduced to 50 ml. It was determined by measuring the concentrations of rhodium and sodium in each of the adjusted sample solutions. From these results, it was found that when rhodium in the aqueous solution was present as sodium hexanitrorhodate (III), the solubility of rhodium was continuously reduced as the sodium concentration was increased.

Further, as can be seen from FIG. 1, if the sodium concentration in the aqueous solution after crystallization is 90 g / l or more, the rhodium concentration in the mother liquor can be reduced to 5 g / l or less. However, even if sodium ion equivalent to 90 g / l is added from the beginning, it is taken into the generated crystals and the sodium ion concentration in the aqueous solution is reduced. It is necessary to coexist.

In the method of the present invention, in order to precipitate sodium hexanitrorhodate (III) crystals, the sodium ion concentration is adjusted to 100 g by any of the following methods.
It is practical to increase it to more than / l. First, a first method is to add, to an aqueous solution containing rhodium, sodium nitrite in an amount of rhodium equivalent to or greater than that capable of forming sodium hexanitrorhodate (III), that is, 6 times or more mol of the rhodium compound. And adding a water-soluble sodium salt.

The higher the rhodium concentration in the stock solution, the greater the amount of sodium nitrite required to form sodium hexanitrorhodate (III), and conversely, the amount of sodium salt added separately from sodium nitrite Is reduced. The sodium salt used here is 90 g / sodium equivalent such as sodium chloride and sodium nitrate.
Any compound can be used as long as it is a sodium salt having a solubility of 1 or more, is neutral, and has no risk of decomposing sodium nitrite.

The sodium ion of 100 g / l or more may be present when sodium hexanitrorhodate (III) is formed. Therefore, the sodium salt to be added separately from sodium nitrite may be added before, simultaneously with, or after the addition of sodium nitrite. When the sodium salt is added before the sodium nitrite, there is no effect whether the sodium salt is added immediately before the addition of the sodium nitrite or even before several steps.

Another method for increasing the sodium ion concentration is to concentrate an aqueous solution containing rhodium and add sodium nitrite. Since the solubility of sodium hexanitrorhodate (III) as rhodium ion is 25 g / l, if the aqueous solution is concentrated to this concentration, it is possible to crystallize rhodium by reaction with sodium nitrite.

The form of rhodium in the aqueous solution is Rh
In cases other than (NO ₂ ) ₃ , as shown in the following chemical formula 1,
Since excess sodium salt is by-produced simultaneously with the formation of sodium hexanitrorhodate (III), the solubility of sodium hexanitrorhodate (III) can be reduced by the by-produced sodium salt.

[0021]

Embedded image Na ₃ [RhCl ₆ ] + 6NaNO ₂ → Na
₃ [Rh (NO ₂ ) ₆ ] + 6NaCl

In the above chemical formula 1, sodium hexanitroiridate (III) Na ₃ [Ir (NO ₂ ) ₆ ], which is a compound obtained by substituting iridium for rhodium, is replaced with sodium hexanitrorhodate (III) sodium Na ₃ [ Rh (NO
₂ ) Since it is less susceptible to the common ion effect of sodium ions as compared to ₆ ), even if iridium coexists in the aqueous solution, it is possible to selectively precipitate and separate only rhodium.

Further, in general, a sodium compound is often used in the purification process of the platinum group. In such a case, the concentrations of rhodium and sodium increase simultaneously at the stage of simple concentration. Can further increase the yield of rhodium.

When the rhodium crystals recovered by the crystallization purification method of the present invention described above have sufficient purity for the purpose, it is not necessary to further purify the crystals, and other compounds or metals may be purified by a known method. Can be converted to However, when it is necessary to further reduce the impurity content, repurification can be performed by the following method.

First, the recovered hexanitrorhodium (II
I) Water is added to the sodium acid crystals to dissolve them. At this time, if precipitation of hardly soluble impurities is mixed in water,
Separate by filtration or the like. The amount of water used for dissolution is usually about 9 times the amount of the crystal, but the higher the temperature, the more the amount of liquid can be reduced. If solid-liquid separation is necessary, crystals may precipitate during operation and mix with sedimentation of impurities,
It is desirable to carry out solid-liquid separation while keeping the temperature. After that, by adding the water-soluble sodium salt again to the obtained aqueous solution, depending on the amount of addition, crystals of sodium hexanitrorhodate (III) having a smaller amount of impurities than the crystals precipitated first crystallize out. .

The crystals of sodium hexanitrorhodate (III) precipitated after the impurity precipitates are once separated as described above are repeatedly subjected to a common recrystallization method of hot water dissolution-cooling-crystal separation. Alternatively, it can be further purified by repeated concentration-cooling-crystal separation.

As described above, it is possible to easily purify rhodium to a purity of 99.9% on a metal / metal basis by repeating crystallization of rhodium from an aqueous solution and dissolution and recrystallization of the obtained crystals. Can be. If it is not necessary to purify again in the final stage of purification, recrystallization can be carried out using an ammonium salt instead of a sodium salt.

[0028]

【Example】Example 1  In ion concentration (g / l), Rh: 56.8, Pb: 0.0
5, Cu: 0.001, Ir: 0.001, Ru: 0.0
06, Pt: 0.008, Te: 0.001, Fe: 0.00.
004, Bi: 0.001 and Na: 59
80 ml of an aqueous solution having a pH of 1.47
Temperature, and added 21.4% sodium nitrite to this aqueous solution.
g was added to neutralize to pH 6.56. at this point,
The total amount of sodium ions added to the aqueous solution is 199g
/ L.

After the aqueous solution was allowed to cool to 20 ° C., it was filtered to obtain 63.5 ml of mother liquor (1) and crystals (1).
The crystals (1) were dissolved in the minimum amount of water in which the whole amount was soluble, and the precipitate of the remaining impurities was filtered. After that, sodium chloride was added to the obtained filtrate up to 310 g / l to precipitate crystals. The crystals were filtered to obtain 248 ml of mother liquor (2) and 23.2 g of crystals (2). At this point, the total amount of added sodium ions was equivalent to 151 g / l.

The compositions of the above mother liquor (1) and mother liquor (2), a solution (24 ml) obtained by dissolving the impurity precipitate with hydrochloric acid, and the crystal (2) are shown in Table 1 below. From the results in Table 1, it was confirmed that the rhodium grade of the crystal (2) was purified to 99.9%. The yield of the rhodium from the stock solution was 99.0% calculated from the recovered crystals, and 98.8% calculated from the removal.

[0031]

[Table 1]

[0032]Example 2  A stock solution (sodium chloride 150) having the composition shown in Table 2 below
g / l, pH 1.26), and the equivalent of 222 g / l
Add sodium nitrate and neutralize to pH 7 to obtain crystals
Was. At this point, the amount of sodium ions present in the stock solution
Corresponds to 133 g / l.

The crystals recovered by filtration were dissolved in water and filtered to obtain a crystal solution. After sodium sulfide was added to the solution until no precipitate was formed, the solution was filtered again to obtain a solution after sulfurization. Finally, ammonium chloride was added to the liquid after sulfidation, and the generated purified crystals were collected by filtration. Table 2 shows the composition of the crystal solution, the solution after sulfurization, and the purified crystals, together with the composition of the stock solution.

[0034]

[Table 2]

As can be seen from Table 2, even if the stock solution contains a relatively high concentration of iridium together with rhodium, it is possible to selectively separate and purify only rhodium.

[0036]Comparative example  Same composition as in Example 2, but with sodium chloride content of 1
Using an aqueous solution of 0 g / l, 22
When 2 g / l of sodium nitrite was added,
No crystals were precipitated. At this time, the sodium present in the liquid
Mion was 84 g / l.

When ammonium chloride was added to this aqueous solution, the composition (ppm) was Rh: 22.7%, Pb: 1
00, Cu: 1, Ir: 250, Ru: 40, Pt:
4. Bi: crystals of 1 or less were obtained. From this,
It was confirmed that only the crystals in which a large amount of iridium remained could be obtained without passing through sodium hexanitrorhodate (III).

[0038]

According to the present invention, rhodium can be separated as a crystalline precipitate of sodium hexanitrorhodate (III) by sodium nitrite by keeping the sodium concentration in the aqueous solution high. In the method of crystallizing ammonium nitrorhodate (III), it is possible to separate iridium and other impurity elements, which are difficult to separate, and to easily recrystallize with water and sodium salts. It can be purified to a rate.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the concentration of sodium ions in an aqueous solution and the concentration of rhodium ions dissolved as sodium hexanitrorhodate (III).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 9/02 611 B01D 9/02 611A 615 615A 618 619A (72) Inventor Hidemasa Nagai Nishihara-cho, Niihama-city, Ehime 3-5-3 Sumitomo Metal Mining Co., Ltd. Besshi Office (72) Inventor Minoru Tsukiyama 3-5-3 Nishiharacho, Niihama-shi, Ehime Prefecture Sumitomo Gold Mining Co., Ltd. Besshi Office F-term (reference) 4G048 AA01 AB02 AB08 AD06 AE03 AE05

Claims (4)

[Claims] 1. An aqueous solution containing a water-soluble rhodium compound is added with sodium nitrite and reacted with the rhodium compound in the presence of 100 g / l or more of sodium ions to convert rhodium to sodium hexanitrorhodate (III). A method for crystallizing and purifying rhodium, which is selectively separated and recovered as a crystalline precipitate of Rhodium. 2. The amount of rhodium compound in the aqueous solution is 6
The method according to claim 1, wherein sodium nitrite is added in a molar amount of at least twice, and a water-soluble sodium salt other than sodium nitrite is added, so that 100 g / l or more of sodium ions are present in the aqueous solution. The method for purifying crystallization of rhodium according to the above. 3. The aqueous solution is concentrated, and sodium nitrite is added to the concentrated aqueous solution.
The method for crystallizing and purifying rhodium according to claim 1, wherein sodium ions of at least 00 g / l are present. 4. The crystals of sodium hexanitrorhodate (III) separated and recovered by the method of claim 1 are dissolved in water, and a water-soluble sodium salt is added thereto, whereby rhodium is again converted to hexanitrorhodium (III). ) A method for crystallizing and purifying rhodium, which is selectively separated and recovered as a crystalline precipitate of sodium acid.