Method for processing of spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts (options)

 

(57) Abstract:

The invention relates to methods for processing of spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts. The present invention is to increase the degree of extraction of silver from spent catalysts in the production of pure metallic silver or its salts, suitable for preparation of new parties catalyst for the simple technology that is easily implemented in terms of catalyst production. Before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700 - 1050oC, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitated impurity introduction precipitator, separating the precipitation of impurities, and from the liquid phase are recovering silver or concentrate liquid phase up to a certain content of nitric acid silver in solution, or from a solution of nitric acid silver precipitate the silver as silver chloride in the presence of surfactants, or from a solution of nitric acid with who I am. The proposed solution allows you to effectively recycle the spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts. 3 S. and 8 C.p. f-crystals, 6 PL.

The invention relates to hydrometallurgy of precious metals and can be used in the processing of spent catalysts containing silver, in particular catalysts used in the synthesis of ethylene oxide.

Exhaust catalysts for the synthesis of ethylene oxide is usually disposed of by leaching from them silver with a solution of nitric acid and subsequent precipitation of silver from leaching solutions in the form of chloride or oxide and processing concentrates on affinage. Significant loss of silver and the long duration of cycle metal make this path is economically inefficient. However, a relatively small content of impurities in the exhaust catalysts for the synthesis of ethylene oxide, as it would seem, allow for the recovery of silver directly on the production of the catalyst, thereby reducing the cycle time of the turnover of the metal and improve the Economics of the recovery process.

POLAND N 269724, class. B 01 J, 1987). Alumina catalyst containing silver, is treated with a solution of sulfuric acid, heated to 90oC, then add a solution of oxidizer KMPO4and get high selection of silver.

The disadvantage of this method is a very large volume of leach solution per unit mass of the raw material due to the low solubility of silver sulfate, the complexity of the subsequent processing of the leaching solutions and limited choice in sustainable production of materials for the manufacture of equipment.

The known method for the recovery of silver from spent catalysts (GDR Patent N 264822, CL 22 In 11/04, 1989), in which the used catalysts in the special conditions are subject to multiple processing HNO3. From the resulting solution the silver is planted in the form of chloride, from which recovery of the heat receiving metal silver purity of 99.9%.

The disadvantage of this method is the low degree of extraction of silver and unusual catalyst production pyrometallurgical process is finished.

The closest solution is the way stated in the German patent N 289414, class B 01 J 23/26, 38/48, 23/89, 1992). The loss is of 15-35% at 27-77oC in a fixed bed. When this is separated 80-99% contained on the media silver. Then another containing silver medium washed, dried, and used for preparation of the catalyst.

The disadvantage of this method is the low degree of extraction of silver.

The present invention is to increase the degree of extraction of silver from spent catalysts in the production of pure metallic silver or its salts, suitable for preparation of new parties catalyst for the simple technology that is easily implemented in terms of catalyst production.

The problem is solved as follows.

In the first embodiment before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700-1050oC, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitated impurity introduction precipitator, separating the precipitation of impurities, and from the liquid phase are recovering silver or concentrate liquid phase up to a certain content of nitric acid silver in solution.

p. The precipitation of the impurities are in the presence of fluoride. After the separation of the silver dissolved in the acid to obtain a solution of a certain concentration.

The second option before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700-1050oC, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitate the silver as silver chloride in the presence of surfactants. The amount of surfactant during the precipitation of silver chloride is from 30 to 500 mg/DM3suspension. As the use of surfactants of the Quaternary ammonium base or neinogennye substances.

By the third variant before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700-1050oC, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitate the silver as silver oxalate, and the precipitation of the oxalate of silver are in excess of the precipitant. Precipitated oxalate of silver in excess of oxalic acid against STE 100 mg/DM3suspension. As the use of surfactants of the Quaternary ammonium base or nonionic substances.

To increase the degree of extraction of silver in the solution and decrease the solubility of the carrier components exhaust catalyst before the leaching of silver is subjected to a preliminary heat treatment in oxidizing or reducing atmospheres at a temperature of 700-1050oC depending on the composition of the media and how to obtain it.

Silver prepared as described above, the spent catalyst is leached with a solution of nitric acid followed by rinsing with water to remove the metal in solution in the form of nitric acid salt. At the same time to reduce the amount of leaching solutions it is advisable to use the counterflow principle.

Then depending on the chemical nature and concentration of impurities in the solution of nitric acid silver obtained after leaching, offers options for its further processing:

1. Precipitation of impurities from the solution, followed by separation of silver by the method of chemical or electrochemical reduction and isolation of pure silver or dissolution of the deposited metal in chemicalization and for other purposes.

2. Selection of silver from a solution leaching in the form of silver chloride in the conditions when the impurities remain in solution. Then restore the silver chloride by known methods, for example, the precipitate of silver chloride is separated from the mother liquor and washed it from the residue of the mother liquor, restore chloride to metallic silver and emit pure silver or after washing the dissolved metal in H. H. nitric acid to obtain pure nitric acid silver or provide a selection of silver from a solution leaching in the form of oxalate of silver in the conditions, when the impurities remain in solution.

Recycling of spent catalyst in the first embodiment is as follows.

If necessary, the spent catalyst is subjected to a preliminary heat treatment in an oxidizing atmosphere at a temperature of 700-1050oC. Of the thus prepared material silver almost completely leached 12-20% aqueous solution of nitric acid followed by rinsing with water to remove residual nitric acid silver.

Solution leaching of silver contains impurities partially dissolved material carrier and dirt from getting in CA precipitator.

Separating the precipitated impurities from the solution and get solution of nitric acid silver required concentration by evaporation, which impurities are suitable for the preparation of new parties of the silver catalysts or from the liquid phase are recovering silver in crystalline form.

By dissolving silver in acid get solution of silver salts of the desired concentration.

The following examples illustrate a first variant embodiment of the invention.

Example 1 (prototype)

Leaching of silver from spent catalyst in mullite-corundum media spend in a known manner by treatment with 15% solution of nitric acid at a temperature of 70 and 100oC followed by rinsing with hot water.

The leaching process is conducted according to the counterflow principle. Total recovery of silver in the solution is 98-99% of which is in the source material, the solubility of the material of the medium is 1.5 to 3.5%.

The leaching solution with the wash water evaporated until the concentration of silver 30-150 g/DM3. In the filtered solution restores nitric acid silver by ammonium formate or sodium formate.

The output of metallic silver is 95-96% of the contained in the solution, which will carry out the restoration.

The silver content in the resulting product of 98.2-99,0%, the content of impurities (in terms of element),%:

Aluminum - 0,1-0,4

Silicon - 110-2< / BR>
Iron - 110-2< / BR>
Copper - 110-3< / BR>
Nickel - 110-3< / BR>
Chrome - 110-3< / BR>
Example 2

Solution leaching of silver from spent catalyst obtained as described in example 1 and containing 30-50 g/DM3silver, carefully neutralize 20-25% aqueous solution of ammonia (grade analytical grade). With gelegenen precipitate of aluminum hydroxide seacadets impurity compounds of silicon, iron, Nickel, chromium, copper, and other Precipitate separated from the solution and washed with water.

From purified as described above solution leaching produce metallic silver recovery, as in example 1.

Unlike example 1, the metallic silver is obtained in the form of small granules of crystals of the metal. The precipitate of silver legcy of 99.5%, the silver content in the resulting product is 99.8 to 99.9%.

The content of impurities % in terms of element:

Aluminum is less than 0.02

Silicon is less than 110-3< / BR>
Iron - less than 510-4< / BR>
Copper is less than 110-4< / BR>
Nickel is less than 110-4< / BR>
Chrome - less than 110-4< / BR>
Example 3

A sample of spent catalyst based on silica-alumina-refractory carrier before the leaching of silver is subjected to heat treatment for 6-8 hours at a temperature of 700-1000oC in air or in a reducing atmosphere (nitrogen +8-15% hydrogen).

Leaching of silver carried out as in example 1.

Table 1 shows the influence of thermal treatment on the degree of extraction of silver from catalysts.

Example 4

Spend cleaning solutions leaching of silver from spent catalyst on a silica-corundum media, subjected to preliminary heat treatment mode 3.3 example 3. The concentration of silver in solution is 28-35 g/DM3, aluminum 8-12 g/DM3and "free" nitric acid 5-12 g/DM3.

After adding reagent-precipitator (NH4OH), the suspension is subjected to aging, cooled to 20-30oC and the Department of the I formation of cracks in the cake." The total volume of wash water in each experience equal to the amount taken for the cleaning solution leaching.

Examples 5-9

Similar to example 4, only differ in the conditions of deposition of impurities.

The results of the experiments on the deposition of impurities from the solution given in table 2.

From purified leaching solutions, obtained as described in examples 4, 8, 9,), precipitated metallic silver chemical recovery by ammonium formate or sodium formate. The reductant solution with a concentration of 30-40 wt. % gradually added with stirring to the heated to 70-90oC a purified solution leaching to full recovery and deposition of silver. Weight deposition of silver is controlled by the absence of silver chloride precipitate by adding a solution of sodium chloride to profilirovannoj the sample stock solution, the outward sign of the completion of the recovery process and the deposition of silver is almost complete transparency of the solution of the mother liquor over fast settling the precipitate of metallic silver. The precipitate is washed by decanting method - hot water, diluted 1:50 by volume sulfuric acid and then repeatedly with hot water to the absence of ions SO4and NO4

The results of the experiments are given in table 3. From table 3 it can be seen that satisfactory results when chemical reduction of silver can be obtained if the initial solution concentration of aluminum is not greater than 0.05%.

Processing spent catalyst according to the second option.

The precipitation of silver chloride with subsequent flushing of sediment and restoration to metal is a classical method of separation of silver from impurities. However, as we found, during the precipitation of silver chloride from solutions of leaching of spent catalyst with nitric acid precipitate captures the solution contains impurities, mainly in the form of alumagrips. Wash the precipitate until the required condition is not possible. In addition, the sediment has unsatisfactory properties - forms massive clumps, which makes transportation of the suspension and washing the precipitate. Apparently, these difficulties led the authors of the abovementioned patent GDR N 2648822, 1989 to the need for restoration melting of silver chloride precipitate, which, as is well known, a number of impurities passes into the slag.

In the present invention the precipitation of silver chloride from the solution which enables you to significantly improve the technological properties of silver chloride precipitate and helps to hold in solution the particles alumagrips and other impurities.

The precipitate of silver chloride obtained in the presence of surfactants, not crumpled, easily washed away impurities and subsequent chemical recovery allows to obtain pure metallic silver, suitable for re-preparation of catalysts for the oxidation of ethylene to ethylene oxide.

Example 10

Silver chloride is precipitated by 15% solution of sodium chloride from a solution of leaching of spent catalyst to alumosilicate-corundum media. The leaching solution with the concentration of silver 32 g/DM3, aluminum 11,5 g/DM3and free nitric acid 12 g/DM3receive, as described in example 4.

The deposition is carried out at a temperature of 45-50oC with mechanical stirring, an excess of the precipitant 3-7% versus stoichiometry. After injection of sodium chloride solution, stirring is continued until coagulation of the suspension of silver chloride, which occurred within 10-15 minutes the Precipitate is washed by decantation until neutral reaction of water (universal indicator paper).

Then the washed precipitate of silver chloride may be restored with formaldehyde in alkaline solution.

Recovery of silver chloride and washing the obtained m the content of impurities.

Examples 11-16

The precipitation of silver chloride and subsequent production of metallic silver is produced as in example 10, but the deposition of silver chloride is produced in the presence of surfactants. Type, surfactant concentration, and the results are shown in table 4.

Processing spent catalyst according to the third variant.

Oxalate of silver are usually obtained in the form of a thick sludge in the interaction of nitric acid with silver oxalate alkali metals. It is known that the solubility of oxalate of silver increases, if the solution is free of nitric acid.

However, as we have found, neutralization of excess nitric acid in the leaching solutions of silver at the same time increases as the output of the oxalate of silver, and the content of impurities in the sludge.

Further studies have shown that sufficiently pure silver oxalate with a good yield can be precipitated from acidic leaching solutions containing up to 20 g/DM3free nitric acid, if the precipitator to use oxalic acid, taken with a considerable excess against stoichiometry. This forms a crystalline precipitate of oxalate saruchevo oxalate of silver can be improved by the introduction of surfactant.

Example 17

From the leaching solution containing silver and 22.6 g/DM3, aluminum 8,03 g/DM3and free nitric acid 16,01 g/DM3precipitated oxalate of silver by the addition of crystalline oxalic acid brand X. h (COOH)2H2O.

The mixture is stirred for 15-20 min, 15 min and defend potentiometric titration to determine the residual concentration of silver in the clarified mother solution above the sediment. The results are shown in table 5.

Example 18

The precipitate of silver oxalate obtained in the mode of deposition 7 example 17, washed with distilled water by the method of decanting when the ratio W/TV. = 5:1 to achieve in the wash water pH 6(9 leaching), dried at a temperature of 70oC and examined for the content of impurities.

Examples 19-21

The silver oxalate precipitated and washed as in example 18, but before deposition of oxalate of silver in the solution leaching add surfactant (OP-10).

The results are shown in table 6.

Thus, the essential distinguishing features of the proposed solution are the following features:

under the first option:

before leaching the catalyst is subjected to heat treatment in a until complete dissolution of silver;

- separate the remainder of the catalyst carrier;

- then from a solution of nitric acid silver precipitated impurity introduction precipitator, separating the precipitation of impurities;

- from the liquid phase are recovering silver or concentrate liquid phase up to a certain content of nitric acid silver in solution;

the second option:

before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700-1050oC, leaching with nitric acid leads to the complete dissolution of silver;

- separate the remainder of the catalyst carrier;

- from a solution of nitric acid silver after leaching precipitate the silver as silver chloride in the presence of surfactants;

third option:

before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700-1050oC, leaching with nitric acid leads to the complete dissolution of silver;

- separate the remainder of the catalyst carrier;

- precipitate the silver as silver oxalate, and the deposition of silver oxalate is carried out with an excess of the precipitant.

As can be seen from the presented examples, the proposed reslices silver or its salts, suitable for making new batches of catalyst.

1. Method for processing of spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts comprising leaching in nitric acid solution, washing, and subsequent selection of silver or solutions of its compounds by known methods, wherein before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700 - 1050oWith, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitated impurity introduction precipitator, separating the precipitation of impurities, and from the liquid phase are recovering silver or concentrate liquid phase up to a certain content of nitric acid silver in solution.

2. The method according to p. 1, characterized in that as a precipitator of impurities using a weak alkali, such as NH4OH, carbonates of metals of the second group.

3. The method according to PP.1 and 2, characterized in that the deposition of impurities is carried out in the presence of fluoride.

4. The method according to p. 1, is concentratie.

5. Method for processing of spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts comprising leaching in nitric acid solution, washing, and subsequent selection of silver or solutions of its compounds by known methods, wherein before leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700 - 1050oWith, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitate the silver as silver chloride in the presence of surfactants.

6. The method according to p. 5, characterized in that the amount of surfactant during the precipitation of silver chloride is from 30 to 500 mg/DM3suspension.

7. The method according to p. 5, characterized in that as the use of surfactants of the Quaternary ammonium base or nonionic substances.

8. Method for processing of spent silver catalysts with obtaining pure silver or solutions of its compounds suitable for the preparation of catalysts comprising leaching in nitric acid solution, rinsing, D. leaching the catalyst is subjected to heat treatment in an oxidizing or reducing environment at a temperature of 700 - 1050oWith, leaching with nitric acid leads to the complete dissolution of silver, separating the remainder of the catalyst carrier, then from a solution of nitric acid silver precipitate the silver as silver oxalate, and the deposition of silver oxalate is carried out with an excess of the precipitant.

9. The method according to p. 8, characterized in that the precipitated oxalate of silver in excess of oxalic acid against stoichiometric not less than 2.5 times.

10. The method according to p. 8, characterized in that the deposition of oxalate of silver are in the presence of surfactants in amounts of from 20 to 100 mg/DM3suspension.

11. The method according to p. 8, characterized in that as the use of surfactants of the Quaternary ammonium base or nonionic substances.

 

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