The method of extracting platinum group metals from slimes

 

(57) Abstract:

The invention relates to hydrometallurgy of precious metals and can be used for extraction of platinum metals from the sludge formed during the manufacture of nitric acid. The method comprises leaching the slimes, which is carried out in two stages with separation of the solution and washing the cake after each stage, the first stage leaching is carried out in hydrochloric acid, and the second in a mixture of concentrated hydrochloric and nitric acids, and the cake after the first stage leaching calcined at a temperature of 800-900C for 1 h, and then sent to the second stage leach. Solutions and rinse waters both stages of leaching combine, adjust the content of platinum metals to 5-50 g/l, and from the resulting solution is extracted platinum metals by precipitation with obtaining a precipitate, which is calcined and fused onto the ingot. Leaching is carried out at a temperature of 80-95C. the Deposition of platinum metals from solution is performed depending on the content of platinum in the following ways: hydrazine at pH 2-4 and a temperature of 70-80C To produce collective concentrate platinum metals; ammonium chloride at a pH of not balabasov allows to significantly increase the degree of extraction of platinum metals and sludge due to the optimum sequence and combination techniques, providing almost complete translation of platinum in the solution during leaching. 5 C.p. f-crystals, 1 table.

The invention relates to hydrometallurgy of precious metals and can be used for extraction of platinum metals from the sludge formed during the manufacture of nitric acid.

The sludge formed during the manufacture of nitric acid, are a fine powder material complex chemical, physical and phase composition in which the total content of platinum metals (platinum, palladium and rhodium) is in the range of 0.5 - 80%. In this regard, the slimes are an additional source of platinum group metals. But at the same time, recycling of sludge is an extremely difficult task, as the present platinum and related metals are in the form of chemical compounds with different chemical properties (interaction with acids).

The method for extracting platinum group metals from the containing material (RF patent N 2120485, C 22 B 11/00, Appl. 03.07.97,, publ. 20.10.98 G., b. "Inventions", No. 29, S. 363). The method includes melting of the raw materials, the processing of the ingot with a solution of Aqua Regia and deposition platinovyi chloropalladite.

The disadvantage of this method is mnogovershinnoe and significant irreversible loss of platinum on pyrometallurgical operations, which reduces the degree of extraction of precious metals. The known method can be effectively used for processing material containing, along with platinum, gold and silver.

The method for extracting platinum together with rhodium from waste generated in the nitrogen industry (patent Poland N 139177, C 22 B 7/00, Appl. 03.06.83,, publ. 31.07.87,, R j "metallurgy", 88,, GP, S. 28). The method involves the fusion of the sludge with an alkali (NaOH or KOH) at a temperature of 450 - 650oC. Water leached with water, the precipitate is repeatedly treated with hydrochloric acid with the addition of an oxidant. From the resulting solution platinum and palladium restore aluminum or zinc. The whole cycle is repeated several times.

However, the disadvantage of this method is the low degree of extraction of platinum metals, as used as reductants aluminum or zinc is not effective for a full selection of platinum metals from the solution.

In addition, re-contamination platinochloride oireet process with subsequent filtration and treatment solution.

The technical nature closest to the proposed object of the invention is a method for the extraction of platinum from sludge - waste nitric acid production (copyright certificate Bulgaria N 45936, C 22 B 11/04, Appl. 31.05.88, publ. 15.09.89,, "Invention of the world", vol. 48, N 2, 92,, S. 1-2).

The way is in the handling of sludge containing platinum and associated elements in the form of various chemical compounds with a mixture of concentrated hydrochloric and nitric acids in a single or portions of the introduction of the sludge. The dissolution is carried out at a temperature of 333-385K, pressure 0 - 6 bar. within 8 to 12 h, and the selection of platinum from a solution is carried out by extraction using organic reagent.

The disadvantage of this method is the low degree of extraction of platinum metals, since the method does not provide a sufficient opening all compounds platinum, and the use of expensive and scarce reagents.

In addition, a known technology is associated with the necessity of neutralizing organic reagents used in the extraction, because they pollute technological solutions.

The technical result of the invention avle of nitric acid.

The technical result is achieved in that in the method of extracting platinum group metals from the sludge formed during the manufacture of nitric acid, including acid leaching at portions introduction of sludge and subsequent extraction of platinum metals from the solution, according to the invention, the leaching is carried out in two stages with separation of the solution and washing the cake after each stage, the first stage leaching is carried out in hydrochloric acid, the second in a mixture of concentrated hydrochloric and nitric acids, and the cake after the first stage leaching calcined at a temperature of 800 - 900oC for 1 h, and then sent to the second stage leach solution and rinse water after both stages of leaching combine, adjust the content of platinum metals and carry out the deposition of the platinum metals, the obtained precipitate is calcined and fused onto the bar.

The process of leaching of sludge is carried out at a temperature of 80 - 95oC, the combined solution after leaching and leaching cake adjusting the content amount of the platinum metals to 5 - 50 g/l, and the deposition scheduled metals from the resulting solution is performed depending on the content of platinoidov, or ammonium chloride at a pH of not more than 2 and a temperature of not more than 40oC with getting chloroplatinate ammonium, and/or by electrolysis.

The method consists in the following.

In the inventive method, the leaching process is carried out in two stages. The first stage leaching is conducted at a temperature of 80 - 90oC in hydrochloric acid, is a preparatory and provides translation in the solution of the main part of base metals (mainly iron and its compounds). This avoids agglomeration of sludge on the subsequent firing operation. At the same time at this stage in the solution passes up to 15% platinum and 20% palladium and rhodium from the original number.

The operation of firing sludge before the second stage leaching provides translation of sparingly soluble compounds of platinum metals in soluble form and almost a full transition into the solution during the subsequent second stage of leaching. As shown by differential thermal analysis (DTA), held on the cake, this effect is achieved due to occur during the firing processes of destruction insoluble in hydrochloric acid and Aqua Regia compounds of platinum, which previously C due to the fact, that at these temperatures occur phase transformations and platinum metals become soluble form, with the loss of platinum metals is minimal. At temperatures below 800oC reaction of destruction compounds of platinum group metals and transition them into a soluble form requires a long shutter speed, and at a temperature of more than 900oC possible melting of candle that will reduce the extraction of platinum group metals in solution.

It was established experimentally that the duration of the roasting 1 hour is the best results following the firing of acid leaching were the same, regardless of the increased duration to 1.5, 2 and 3 hours.

The duration of firing is less than 1 hour in the claimed temperature range leads to a decrease in the degree of extraction of platinum metals in solution.

After firing the slurry is directed to the second stage leaching is carried out at a temperature of 80 - 95oC in a mixture of concentrated hydrochloric and nitric acids. At this stage achieves maximum extraction of platinum metals in solution.

The process is most intense runs at the same temperature, but not higher than 95oC, as Balleny the temperature interval is sufficient to established experimentally duration of leaching, which is no more than 1 hour.

Solutions after filtration and washing are combined to adjust the volume corresponding to the content of platinum 5-50 g/l, and from the resulting solution is extracted platinum metals deposition under the conditions defined by the content of their solution, which in turn depends on the composition of the original sludge.

When extracting platinum group metals from a solution containing platinum, palladium and rhodium in significant quantities (up to 50 g/l), the deposition is performed with hydrazine to produce collective concentrate of platinum metals.

To complete the precipitation the best option is the implementation process at pH 2-4 and a temperature of 70 - 80oC, when present in a solution of the chlorides of non-ferrous metals and iron are not hydrolyzed by precipitation.

The limits of pH values is due to the fact that when the pH value falls below 2 extraction of platinum metals from solution, while increasing more than 4 worse filterability of the precipitate due to the formation of iron hydroxide (III).

The temperature range is set experimentally and at a given pH of the solution provides the lowest consumption reactivities from solution by precipitation with ammonium chloride at a pH of not more than 2 and a temperature of not more than 40oC with getting chloroplatinate ammonium, while palladium and rhodium remain in the solution are then retrieved by the known methods.

Electrochemical deposition method using electrolysis is effective for dilute solutions, in which the total content of platinum is less than 5 g/l For the extraction of platinum group metals from such solutions used volume-porous electrodes used solutions electrolysis contain unrecoverable amounts of platinum metals, so you only need to carry out their neutralization and neutralization.

Obtained after deposition of each specific method, the powder was filtered, washed, dried at a temperature of 150oC, and then melted to obtain high-grade ingot.

Information confirming the possibility of carrying out the invention (examples).

Example 1.

The original sludge, containing platinum, palladium and rhodium, were loaded portions heated to 40oC strong hydrochloric acid with constant stirring brought the temperature of the slurry to 90oC, which was carried out by the leaching process. Then the slurry was cooled to a temperature of ~40oC, was filtered, the precipitate (KEK) prior for 1.5 - 3 hours to a temperature of 850oC and annealed at this temperature for 1 hour.

Annealed material (cinder) were subjected to repeated leaching in a mixture of concentrated hydrochloric and nitric acids (tsarskovodochnom leaching) under the same conditions as in the first stage of leaching.

After leaching, the slurry was filtered, the cake washed with water.

The obtained solutions and wash water were combined and evaporated to a volume appropriate to the content of the sum of the platinum metals, which can be implemented processing solution.

Extraction of platinum metals was carried out by precipitation, which was carried out as follows.

The solution is pre-neutralized to pH 2 by addition of a solution of caustic soda. At a temperature of 70 - 80oC slowly and with continuous stirring solution was added hydrazine. Precipitated powder of platinum metals were filtered off, washed and dried at 150oC, then melted into bullion.

Example 2.

The roasting and leaching of the original sludge was carried out in the same conditions as in example 1.

The resulting solution containing the predominant amount

With constant stirring portions solution was added ammonium chloride. The deposition process was carried out at a temperature of ~40oC at pH = 2. Sediment HPA was filtered and washed with acidified with a 5% solution of ammonium chloride until the discoloration of the wash water.

From washed HPA received platinum metal by known methods, and then melted.

The mother solution containing palladium and rhodium, processed by the known methods of deposition.

Example 3.

Tests were subjected to a sludge with a low content of platinum metals.

Roasting and leaching was performed in the same conditions as in example 1.

Obtained in the leaching solution had a total content of platinum 5.9 g/l

For extraction of platinum group metals from such solution used electrochemical deposition method with the use of the cell with flow-through volume-porous electrodes.

Example 4.

To obtain comparative data the degree of extraction of platinum metals from the tailings were tested under conditions known way, in the absence of operation of the firing sludge.

Experience included leaching original sludge predanie platinum from the solution obtained.

The results obtained when testing different samples of sludge, their original composition, the composition of intermediate and final products are presented in the table.

Thus, the proposed method can significantly improve the recovery of platinum metals from the tailings due to the optimum sequence and combination techniques, providing almost complete translation of platinum in the solution during leaching and to obtain an ingot with a high content of precious metals.

1. The method of extracting platinum group metals from the sludge formed during the manufacture of nitric acid, including acid leaching at portions introduction of sludge and subsequent extraction of platinum metals from solution, wherein the leaching is carried out in two stages with separation of the solution and washing the cake after each stage, the first stage leaching is carried out in hydrochloric acid, the second in a mixture of concentrated hydrochloric and nitric acids, and the cake after the first stage leaching calcined at a temperature of 800-900oC for 1 h, and then sent to the second stage leach solution and rinse water after both stages of leaching unite, the calcined and fused onto the bar.

2. The method according to p. 1, wherein the leaching is carried out at a temperature of 80-95oC.

3. The method according to p. 1, characterized in that the deposition of platinum metals from solution is performed with hydrazine at pH 2-4 and a temperature of 70-80oWith obtaining collective concentrate of platinum metals.

4. The method according to p. 1, characterized in that the deposition of platinum from a solution spend ammonium chloride at a pH of not more than 2 and a temperature of not more than 40oWith obtaining chloroplatinate ammonium.

5. The method according to p. 1, characterized in that the deposition of platinum metals from solution is carried out by electrolysis.

6. The method according to p. 1, characterized in that the deposition of lead from solution with the total content of platinum metals 5-50 g/L.

 

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