CA1236981A - Recovery of rhenium from tertiary phosphine oxide- rhenium complexes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to the recovery of rhenium values from tertiary phosphine oxide-rhenium complexes resulting from the leaching of rhenium out of spent hydrocarbon reforming catalysts. The rhenium is recovered by contacting the complex with an aqueous solution of an ammonium salt, typically ammonium chloride.

Description

- l- 1109-7249D

This application is a divisional application from Application 445,116 filed January 11th, 1984.
Application 445,116 relates to the selective extrac-tion of rhenium metal from aqueous sulfuric acid solutlons. More par-ticularly, it relates to -the selective extraction of rhenium metal from sulfuric acid leach solutions, resulting from the leaching of spent petroleum reforming catalysts, by the use of tertiary phosphine oxide extraction compounds.
This Application relates to methods to recover -the rhen-ium from the thus obtained leach solutions.
Rhenium is an essential element, along with platinum, inthe production of petroleum reforming catalysts. Recovery of these valuable metals from spent catalysts is obviously desirable.
One method for recovering the metals is to leach them from the spent catalyst with sulfuric acid. The resulting leach solution contains, ordinarily, less than 100 ppm of rhenium metal, along with various other metals in appreciable amounts, including aluminum, which is generally present at a level of more than 3%.
A satisfactory method is available for the recovery of platinum metal from the catalysts, but rhenium recovery is at present a time consuming operation. A reduction in the time required to recover rhenium metal, particularly in a selective manner, would represent an economically significant improvement.

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Application 445,116 provides an ef~iclent and economical process for the extraction ox rhenium metal from aqueous sulfuric acid solutions and, more particularly, for the selective recovery of rhenium metal from sulEuric acid solutions containing other metals, which process comprises contacting the aqueous rhenium-containing sul-furic acid solution with a tertiary phosphine oxide com-pound, separating the resulting rhenium phosphine oxide complex therefrom, and recovering the rhenium metal from the complex by contacting the complex with a suitable stripping agent.
In accordance with Application 445,116, a rhenium containing sulfuric acid solution is contacted with a tertiary phosphine oxide extractant compound. Tertiary 15 phosphine oxides which are suitable for use in the present invention as rhenium metal extractants are those which are represented by the formula:

Rl 20 R2-P=o l3 wherein Rl, R2 and R3 are each, independently, selected from alkyl containing from 6 to 20 carbon atoms, cycloalkyl, aryl, alkyl-substituted aryl, aralkyl and alkyl-substitued aralkyl. Illustrative examples of suitable tertiary phosphine oxides include, but are not limited to, tri-n-hexylphosphine oxide (TIIPO), tri-n-octylphosphine oxide (TOPO), tris~2,4,4-trimethylpentyl)phosphine oxide (TMPPO), tricyclohexyl phosphine oxide (TCHPO), tri-n dodecyl phos-phine oxide, tri-n-octadecyl phosphine oxide, tris(2-ethyl-hexyl) phosphine oxide, di-n-octylethyl phosphine oxide, di-n-hexylisobutyl phosphine oxide, octyldiisobutyl phos-phine oxide, triphenylphosphine oxide 9 tribenzylphosphine oxide, di-n-hexylbenzylphosphine oxide, di-n-octylbenzyl-phosphine oxide, di-n-octylphenylphosphine oxide, and the like. The preferred tertiary phosphine oxide co~npounds ~36~381 are tri-n-octyl phosphine oxide (TOPO), tri-n-hexyl phos-phine oxide (THPO), and tris(2,4,4-trimethylpentyl)phos-phine oxide (TMPPO).
The extraction of rhenium from aqueous sulfuric acid solutions in accordance with Application 445,116 may be accomplished by (a) solvent extraction, wherein the aqueous rhenium-containing sulfuric acid solution is contacted with a water-immiscible organic solvent solution of the tertiary phosphine oxide compound, whereby the rhenium reports to 10 the organic solution as a rhenium-phosphine oxide complex, or (b) by a supported extraction, whereby the aqueous rhenium-containing sulfuric acid solution is passed over or through an inert support material having absorbed thereon or encapsulated therein the tertiary phosphine 15 oxide compound, whereby the rhenium metal is retained on the support material.
The solvent extraction process is generally preferred for relatively high concentrations ox rhenium metal and the supported extraction for relatively low 20 concentrations.
In the solvent extraction process the tertiary phosphine oxide compound is generally, and preferably, dissolved in a suitable water-immiscible organic hydro-carbon solvent. However, if the tertiary phosphine oxide, 25 or mixture of phosphine oxides, is a liquid at the temp-erature of the extractin, it may be used neat. Suitable water-immiscible organic hydrocarbon solvents include, but are not limited to, aromatic hydrocarbons, such as toluene and xylene; cyclohexane, naphtha, kerosine compositions, 30 and the like. A preferred solvent is an aliphatic or aro-matic petroleum distillate composition of the kind available commercially as, for example, Kermac*470B (Kerr-~lcCee, Inc.~), VarsoL*Dx-364l (Exxon Co.), Ashland*360 (Ashland Oil Co.), or Solvesso*150 (Exxon Co.);
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In general, the tertiary phosphine oxide compound, or mixture thereof, is used in the solution in an amount ranging from about 20 to about 500 grams per liter of solu-tion, and preferably from about 200 to 350 grams per liter.
Usually, it is desirable to contact the aqueous solution with as concentrated a solution of extractant as practicable.
The aqueous sulfuric acid solutions which are extracted in accordance with the invention usually will contain from about 0.1 to about 5000 micrograms of rhenium 10 per milliliter of solution and, more commonly, from about 80 to about 250 micrograms of rhenium per milliliter.
The pH of the aqueous sulfuric acid solution is important, since efficient extraction of rhenium with good phase disengagement is achieved when the pH is in the range 15 of from about -0.5 to about 3.0 and, preferably, from about 0.1 to 0.7.
The ratio oE the aqueous phase (A) to the organic extractant phase (O), i.e., the A/0 ratio, may be in the range of from about 0.1 to 1000, but it is preferably in 20 the range of about 3 to 100.
The solvent extraction process may be conducted at a temperature in the range oE from about 20C to about 85C and contact time between the two phases may vary between about 1 and 60 minutes. In carrying out the process 25 of the invention solvent extraction techniques compatible with an extraction solution include, but are not limited to, liquid-liquid extraction using either mixer-settlers or columns, such as the reciprocating plate extraction column, pulse columns or columns employing rotating impellers.
When the extraction is conducted using a sup ported phosphine oxide extractant, the support material will ordinarily contain from about lQ to 60 weight percent of the phosphine oxide compound encapsulated therein or absorbed thereon. Preferably, the phosphine oxide is 35 encapsulated in a macroporous styrene-divinylbenzene copolymer to the extent oE about 40% by weight. The rat;o of phosphine oxide extractant on the support to the rhenium in solution should range from about 0.5 to about 1000 moles per gram-atom of rhenium and, preferably, 10 to 400 moles per gram-atom of rhenium.
The supported extractant may either be slurried with the aqueous rhenium-containing solution or the solu-tion may be passed over or through the supported phosphin2 oxide in a `column. Contact time between the aqueous solu-tion and the supported extractant may vary widely from 10 about 1 minute to many hours, but in general, the contact time will be in the range of about 15 minutes to 20 hours and will also depend on the temperature of the extraction, which is normally in the range of about 20C to 50C.
Usually the rhenium metal to be extracted from 15 the aqueous solution will be accompanied by other dissolved metals, including aluminum, calcium, iron and magnesium.
Aluminum may be present in high concentration, i.e., greater than 3%. When the extraction process of the invention is used, rhenium is selectively separated from these metals.
20 rhus, when rhenium extraction is high, little to none of the aluminum, calcium or magnesium are co-extracted and only 2-4% of the iron present is co-extracted.
Following extraction of the rhenium metal from solution, either by solvent extraction, wherein the phos-25 phine oxide-rhenium complex is in solution in the organic extractant phase, or by supported extraction, wherein the phosphine oxide-rhenium complex is retained on the support, the rhenium metal must be recovered from the complex by a suitable stripping procedure.
In accordance with the present invention, there is provided a method for stripping the rhenium metal from its phosphine oxide complex, said methocl comprising contacting the organic solvent solution containing the complex, as the inert support containing the complex "with 35 an aqueous solution of an ammonium salt, preferably ammonium sulfate, whereby the rhenium metal is stripped from the complex and reports to the aqueous phase.

The stripping solution generally will contain the ammonium salt in an amount oE Erom about 1 to 80% by weight, preferably 5 to 20% by weight. The ratio of stripping solu-tion to organic extractant solution may vary widely from l to 100 volumes of stripping solution per volume extractant solution.
However, 1 - 2 volumes per volume of organic extractant sol-ution is preferred. When the rhenium-phosphine oxide com-plex is retained on a support material, the stripping solution is passed through or over the support material to recover the rhenium from the complex.
The rhenium metal may be recovered from the strip-ping solution by conventional electrowinning or concentra-tion methods.
The following non-limiting examples further illustrate the invention.
Example 1 Aqueous solutions of perrhenate were prepared from potassium perrhenate (KReO4) and SN sulfuric acid, providing a solution containing 232 micrograms (~g) of rhenium per milliliter at pH 1.8 and a solution containing 223 ~g/ml at pH 0.7.
These solutions were contacted with tri-n-octyl-phosphine oxide (TOPO) dissolved in Kermac 470B (Kerr-McGee);
The extractions were conducted at 50C using an A/O ratio Of 3.3 and a contact time of 30 minutes. Data are given in Table I.

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Example 2 The aqueous perrhenate solutions Erom Example 1 (33 ml. each) were slurried with 5.75 grams of macroreticular polystyrene beads containing encapsulated therein 40% by weight oE TOPO. Contact was achieved by mechanical stirring at 25C for 19 hours. Data are given in Table II.

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Example 3 A leach liquor obtained by leaching a spent petro-leum reEorming catalyst with sulfuric acid contained the following elements:
Element Concentration, ~g/ml Rhenium 86.1 5 Aluminum 35,700 Calcium 128 Iron . 405 Magnesium 43 Titanium 10 Nickel I .
Chromium each C10 ppm manganese ¦
zinc J
The solutions had a pH of 1.6 and a sp. gr. of 1.23 g/l.
The procedure of Example 1 was followed to extract rhenium from the solution directly (at pH 1.6) and following pH adjustment to 0.4 with sulfuric acid. Data are given in Table III.

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Example 4 The procedure of Example 2 was followed to extract rhenium from the leach liquor described in Example 3. Data are given in Table IV.

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o a o o o Example 5 The aqueous leach liquor described in Example 3 was contacted with solutions of TOPO in Kermac 470B at various A/O ratios. The pH was adjusted with H2SO4. Data are given in Table V.

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- Example 6 The organic extractant solutions containing the phosphine oxide-rhenium complexes from Table V were then stripped with several stripping solutions. 'rhe organic solutions (18 ml) were contacted with 36 ml of the stripping solutions in a stirred flask. The aqueous stripping sol-tions were then analyzed for rhenium recovered. Data are given in Table VI.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for recovering rhenium metal from a tertiary phosphine oxide-rhenium complex which comprises contacting said complex with an aqueous solution of an ammonium salt, and recover-ing the rhenium metal from said aqueous solution.

2. A process according to claim 1 wherein the tertiary phos-phine oxide-rhenium complex is in solution in a water-immiscible hydrocarbon solvent.

3. A process according to claim 1 wherein the tertiary phosphine oxide-rhenium complex is absorbed on an inert support material.

4. A process according to claim 3 wherein the support mater-ial is a styrene-divinylbenzene copolymer.

5. A process according to claim 1 or 2 wherein the ammonium salt is ammonium sulfate.

6. A process according to claim 3 or 4 wherein the ammonium salt is ammonium sulfate.