DE2555879C3 - Process for the recovery of platinum and iridium as well as aluminum from catalysts containing precious metals - Google Patents

Description

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The invention relates to a method for recovering the components of catalysts which consist of an alumina carrier, platinum and iridium, and variable amounts of iron.

Catalysts containing precious metals such as platinum and iridium on an alumina support are common known and are mainly used for reforming hydrocarbons. the Recovering these metals from the catalyst waste and the spent catalysts is one imperative economic necessity.

There are already various processes for recovering these metals, either only the catalyst support or the entire catalyst being dissolved. The drawbacks of these various methods are based luauf that resulted in an excessive number of work steps and often incomplete separation of the noble metals from each other ⁶ S noble metal losses occur.

An older proposal according to the German Offenlegungsschrift 24 54 647 describes a method in which the catalysts are practically completely dissolved with hydrochloric acid and the Ede'.metalle are retained separately from one another on anion exchange resins by the Validity of these metals in their complex compounds accordingly in the course of the measures will be changed. Although this process gives good results, it is difficult to run on catalysts use that also contain iron or other metals that behave analogously and are retained by the anion exchange resins at the same time as platinum and iridium.

The method according to the invention now avoids these difficulties and makes them possible in practice complete separation and recovery of platinum and iridium from catalysts other than these Noble metals and an alumina carrier or iron and possibly other metals in different ways Quantities included.

According to the invention, the catalyst is also essentially completely in solution with hydrochloric acid and at the same time platinum and iridium in their highest valence level in their complex compounds transferred so that they are retained together on an anion exchange resin be able. Before treatment with exchange resin, the hydrochloric acid solution is depending on its content Iron or other metals and the chlorine ion concentration so diluted that the iron or the other metals are not rebounded from the ion exchange resin. That way treated solution contains aluminum and is used to recover this metal in the form of its chloride treated further. Then iridium and platinum are separated from each other by removing the iridium selectively on the exchange resin itself in the 3 \ vertigen state within its complex compounds is transferred and then eluted with a hydrochloric acid solution. The remaining exchange resin, which only contains platinum is ultimately burned to recover this precious metal.

In practice, the following measures are observed in the individual process stages:

a) so that practically all of the catalyst goes into solution, a 3 to 9 molar aqueous solution must be used Hydrochloric acid are used in sufficient quantities;

b) in order for platinum and iridium to be converted to their highest valence level, this must be An oxidizing agent can be added to the solution; concentrated nitric acid is best in an amount of 1 to 5 ml / 1 hydrochloric acid solution; other oxidizing agents, such as Chlorine, chlorites, chlorates and / or hydrogen peroxide in appropriate amounts can can also be used;

c) dos iron and other metals are made of Anion exchange resin retained when it (she) in the hydrochloric acid digestion solution in Form of anionic complexes is present. To prevent this formation of complexes, the solution must be diluted, the extent of the dilution both from the content of iron or other metals as also depends on the chlorine ion concentration: an omolar hydrochloric acid solution must be diluted to double the amount (2-fold)

if it contains 0.2 to 0.9 g / l iron, but to the threefold menj; e (3-fold), if it contains 1.5 to 5 g / l iron. After the anion exchange resin with Platinum and loaded with iridium, it becomes pure with dilute hydrochloric acid and then mk Washed water until it no longer contains aluminum chloride. To transfer the iridium in its three

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the catalyst is brought into solution as far as possible.

The invention is explained in more detail in the following example:

example

5 kg of a catalyst that had been used for 1 year and 0.34% Pt, 0.049% Ir in addition to 0.8% C

valuable condition on the exchange resin io and the 0.5 weight percent iron on an AhOs-

Carrier (95.5%) as well as traces of Si, Cr and Ni, were fired at 400 ° C. for 2 h in order to remove the organic Destroy substances; the catalyst was then refluxed with 50 liters of 20% strength hydrochloric acid

wisely allow about 50 ° C !, no disturb- 15 (6 molar) and 0.1 1 58% nitric acid in a the oxidation products deliver and finally boiled with glass-lined and externally heated reactor. After three hours of digestion at a temperature of about 110 ^° C., the solution was drawn off and filtered. The dry residue

acid solution. Conveniently made up 10.8 g and contained essentially Usually solutions based on a-AhO3 and some silica as well as traces of

Platinum and iridium; taking into account the very low weight of the residue, this corresponded practically a complete dissolution of the precious metals.

The clear solution obtained became mi ', an equal Volume of demineralized water, mixed with 0.1 l of 58% nitric acid, heated to 70 ° C and over a bed of a strong anion exchange

Very different reducing solutions can be used; Biding is only that they achieve a rapid reduction at a fairly low temperature of for example

lidi act selectively, so that at the same time changes the platinum complexes and during the subsequent washing out of iridium with salt

Formaldehyde and ammonium or sodium acetate or based on hexamethylenetetramine with a pH value of 4 to 6 are used.

The inventive method offers the great advantage that catalysts with any iron content can be treated; the iron content

can be extremely low or practically 0, 3 ° resin given; Platinum and Iridium were from the

for example in the case of waste from new or fresh catalysts. Furthermore, only one ion exchange resin bed is required and the iridium is also directly recovered as chloroiridic acid; this is therefore more interesting than the recovery in finely divided metallic form tr because iridium may be brought into the latter Freq ig difficult in solution, such as even with the aforementioned method of the prior right. It can exchange resin strongly bound; the solution flowing out contained the aluminum and practically all iron and was further treated in a manner known per se to obtain AlCb. The iron was bound as a [FeChI complex by an ion exchange resin and separated off. Practically all of the Al of the catalyst support was recovered.

The exchange resin, which contained the precious metals,

However, be that when digesting or dissolving the 40 was with a dilute aqueous hydrochloric acid catalyst some of the existing iridium sung (0.1 m) washed to remove the last traces of iron does not go into solution, but in the residue to remove and then with deionized water until Sludge remains; In this case, the refluxing solution will have a pH of 4 to 5

exhibited.

The outfeed bed was then slowly filled with a reducing solution containing 0.2 m Formaldehyde. 0.2 M sodium acetate and hydrochloric acid up to

would be treated in a manner known per se for the recovery of this metal.

Certain catalysts also contain metals such as bismuth, antimony, tin, ruthenium, Palladium and rhenium. The first three of these metals are exzu along with the precious metals a pH of 5.5 washed out until all of the solution contained in the interstices

tracted, but can easily be exchanged from these by at 5 °; the reducing solution

known procedures separate. The three other metals (ruthenium, palladium and rhenium) are only slightly extracted along with the precious metals; this can be neglected if your Proportion in the catalyst is low.

Of course, the original condition of the catalysts that are being worked up also applies should have a strong influence on the solution process: Above all, the used catalysts are had previously been heated to 70 ° C. Then, within 1 hour, the equivalent of 1 volume solution Exchange resin was added per volume and allowed to react for 2 hours. The reducing solution was desalted with Washed out water until the wash water no longer contained sodium ions.

The iridium was then eluted with a 2M hydrochloric acid solution at 70 ° C. The eluate that contains the three

more or less heavily loaded with carbon contains 60 valent iridium, is yellow-green in color; from the-

and must be roasted to a greater or lesser extent in an oxidizing manner in order to be freed from carbon; this makes the precious metals more difficult to dissolve. The same thing happens when the catalysts have been used under severe thermal conditions; in this case the invention proves to be Process due to the clearly oxidizing digestion as advantageous because it allows Increasing iridium content can therefore be determined continuously spectrophotometrically and the elution interrupt when the residual iridium content in the exchange resin can be neglected Im In the present case, 20 l of hydrochloric acid solution were required for elution. This solution contained 2.35 g Iridium and has been concentrated to form the iridium hydrochloric acid crystallize out.

The ion exchange resin with bound therein Platinum was washed out with deionized water, dried and placed in an oxidizing atmosphere at gradually Rise to 800 ° C! he temperature burned. Were recovered this way 17.6 g of a metallic powder that is predominantly

consisted of platinum and contained only very small amounts of iridium.

The recovered amounts of precious metals essentially corresponded to the total amount of precious metals, which was present in the treated catalyst.

Claims (3)

Patent claims: 1. Process for the recovery of platinum and iridium as well as aluminum from catalysts, which, in addition to these precious metals and an alumina carrier, also iron and possibly contain other metals by digesting the catalyst under reflux with a 3- to 9 molar hydrochloric acid solution with the addition of an oxidizing agent, characterized in that that the solution obtained is diluted to such an extent that the iron or other similarly behaving metals are not in the solution present as a complex, whereupon this solution is treated with an anion exchange resin, that the platinum and iridium hold back, that the aluminum as Aluminum chloride wins, the exchange resin with dilute hydrochloric acid and then with water washes, treated with a reducing solution and washed again with water that reduced Iridium is eluted with an Im- to 3M-hydrochloric acid solution and by concentration of the eluate as iridium hydrochloric acid isolated and finally as that by burning the exchange resin Platinum bound in it wins. 2. The method according to claim I _1, characterized in that 1 to 5 ml of concentrated nitric acid or an equivalent amount of another oxidizing agent such as chlorine, a chlorite, chlorate or hydrogen peroxide is added to the hydrochloric acid digestion solution. 3. The method according to claim 1 or 2, characterized in that there is a reducing solution on the basis of formaldehyde and ammonium or sodium acetate or on the basis of hexamethylenetetramine with a pH of 4 to 6 is used. 40