FR2494303A1 - PROCESS FOR THE RECOVERY OF PRECIOUS METALS - Google Patents

Abstract

THE INVENTION CONCERNS THE METALLURGY INDUSTRY. IT CONCERNS A PROCESS FOR RECOVERING PRECIOUS METALS FROM A SOURCE SUBSTANCE CONTAINING THEM IN A VERY LOW CONCENTRATION, WHICH IS PLACED IN CONTACT WITH AN IRON OR NICKEL COLLECTOR IN A GRAPHITE CRUCIBLE, ACCORDING TO WHICH THE GRAPHITE CRUCIBLE IS DECREASED. ATTACK OF THE CRUCIBLE BY THE COLLECTOR, BY ADDING SUFFICIENT QUANTITY OF CARBON TO SATURATE IT. APPLICATION TO THE RECOVERY OF METALS OF THE PLATINUM GROUP IN USED CATALYSTS.

Description

The present invention relates to a process for the recovery of metals

valuable recoverable, from

  of a source substance, for example, a substance

  cycled, in which the recoverable metal is dispersed, usually in a very low concentration. The procedure

  of the invention can be considered, in its general aspect

  neral, as a fusion process, whereby the source material containing the recoverable metal is melted and

  in contact with a molten collector metal, in which the metal

  recoverable amount dissolves. The recoverable metal is then collected in the collecting metal, according to the techniques

  conventional refining of metals.

  An increasingly important source of recoverable valuable metals is materials such as refractory oxides containing platinum group metals, for example spent catalysts, electronic residues, residues and rejects from

  the manufacture of catalysts and, in general, of all

  in which platinum group metals, gold and silver are present in a basic or carrier substance in a highly dispersed form. A

  important and growing source of residues of this type

  exhausted catalytic converters from automobile

  used catalysts and catalysts of chemical and

  of the petroleum industry, which all

  a carrier refractory oxide, such as alumina,

  cordierite or mullite, on which one or more

  precious rates are scattered. Typically, these

  The catalysts contain one or more platinum group metals dispersed at a very low concentration relative to the mass of the carrier material. The support may consist of a monolithic material of the honeycomb type, most often composed of cordierite (aluminum magnesium silicate), or it may comprise beads, generally alumina. The monolithic cordierite block generally comprises a surface coating mainly composed of gamma-alumina, intended to provide a large-area film on which is dispersed the catalyst material, generally platinum plus one or more other platinum-group metals. . The catalysts may contain other components, such as a catalytic, metallic, basic substance, e.g.

  nickel or nickel oxide, and oxides of earth

  are rare, to help stabilize alumina of great

  face. We can refer to this subject, for example in the case of

  US Patent Nos. 3,565,830 and 4,157,316, both assigned to the Applicant, which disclose such catalyst compositions. The total content of precious metals, in this case of platinum group metals, present in certain compositions, is very low, often of the order of 0.02.

  to 1% by weight of the total weight of the catalyst.

  To recover metals, like those in the group

  platinum, from a solid source containing the

  In a highly dispersed form, it is usual to melt the solid material with a flux and to put the molten slag containing the recoverable metal in contact with a collector metal in which the recoverable metal (for example one or more platinum group metals). , gold, silver, etc.) dissolves or migrates in another way. By

  example, when a melted slag containing cordierite

  and / or alumina and platinum group metals, as obtained by melting a spent catalyst and a suitable flux, is contacted with molten iron or copper as the collector metal, the Platinum group metals migrate, either by melting or by some other mechanism, slag into the collector metal. By

  convenience, the phenomenon will be referred to below as ter-

me of "dissolution".

  Separate the recoverable metal from the metal col-lec-

  in a separate, conventional process.

  To improve recovery, it is often necessary to repeat the treatment on the slag already

  treated, in order to recover waste metal residues

  not collected in the first pass. This can be done by cooling and spraying the removed slag in the process, by separation, if

  the desire of all metal globules (that is to say

  This is done by introducing the slag into a furnace for a second independent melting and contacting operation.

  Conventional electric ovens can be used

  such as electric arc furnaces or arc furnaces

  with plasma. These furnaces generally comprise a crucible

  fracture adapted to receive the charge, such as a graphite crucible, contained in an isolated enclosure, and they are provided with suitable electrodes and plasma guns, etc. With certain collector metals, particularly iron, but also nickel, it is found that if the crucible is made of graphite, or other forms of

  carbon, that the molten metal attacks the crucible, being

  that carbon is soluble to some extent in molten iron. It would be very beneficial to be able to reduce or eliminate this trend, since there are

  reasons to make it desirable to use iron as a

  tor, and graphite as a material for the crucible. Iron has the advantage, common with nickel, and to a lesser extent with cobalt, of being both an efficient collector (in the sense that it dissolves easily

  platinum group metals from a source

  due) and to be ferromagnetic, so that one can easily

  magnetically separate the small gloubles that form

  in the slag. It is desirable to use graphite crucibles because of their good resistance to

  melted slag at very high temperatures.

  The present invention is based on the discovery that the tendency of molten iron to attack graphite crucibles, when carbon is added to the collector, can be substantially reduced or eliminated.

  an amount at least sufficient to saturate

  Precise the collector at the operating temperature

from the oven.

  The subject of the present invention is therefore a procedure

  for the recovery of precious metals from a source containing them in a highly dispersed form,

  according to which the source is put in the molten state, in a

  carbon container at high temperature, in contact with a molten collector in which the precious metals pass by migration, said method being characterized in that the collector charge is introduced into the furnace with a quantity of carbon at least sufficient to saturate of

  the collector metal, at the elevated temperature

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  In general, the process according to the invention is

  plicable to any melting or foundry operation, in an oven, whatever the recoverable metal or the heat source used, but it is found that it is particularly suitable for a secondary process for recovering platinum group metals, dispersed in diluted form on a support, that is to say in small amounts relative to the mass of the support. Here is meant by "metals of the group

  platinum, platinum, rhodium, ruthenium, palladium

  dium, osmium and iridium. For example, the process of

  vention is particularly applicable, but not limited, to the recovery of platinum group metals from

  of a spent catalyst containing a platinum group metal

  not, dispersed on a monolithic support or in the form of

  pearls, such as automobile exhaust catalysts,

  bile, platinum catalysts on alumina cracking the

  oil, platinum rhodium catalysts and ruthenium

  nium on platinum used in chemical treatments, platinum group metals, purified, used as intermediates, catalysts, etc. As already mentioned, the process of the invention can be carried out using plasma arc furnaces or other suitable sources of heat. U.S. Patent Nos. 3,394,242, 3,783,167, 4,037,043 and 4,006,284, for example, describe

  typical plasma arc furnaces.

  The collector is favorably constituted by iron, but it is also possible to use nickel or cobalt. The amount of carbon that is added, according to the invention, to the molten collector, is at least sufficient to saturate it appreciably at the temperature of 50.degree.

oven operation.

  The single figure of the appended drawing represents the amount of graphite that dissolves in liquid iron at elevated temperature. In general, the furnace is operated at a temperature of 1400 to 1700WC, preferably 1450 to 16000C. It is easy to determine, from the curve shown in the figure, the amount of carbon

  necessary to saturate an iron collector at a temperature

  given data of operation of an oven. We are building

  easily similar curves for other collections.

  attacking carbon crucibles, such as the

  cobalt or nickel. Nickel forms a eutectic

  holding 2.2% carbon, and at a temperature of 17000C, it is saturated with about 3% carbon. The behavior of carbon in cobalt is similar to that in nickel. A flux is usually used to ensure

  that the source melts and forms a melt of a viscosity

  appropriate temperature (eg about 3 poises) at the temperature

  oven, for example from 1400 to 1700 C, preferably from 1450 to 16000C. Lime (CaO) is an example of a fondant

  suitable for the invention, but it is also possible to use

  melting substances, such as magnesia or dolomite

  moth. In general, the feedstock of the oven, i.e. the source material and the flux, is introduced into the oven in granulated form. We can, by

  For example, grinding these substances to a particle size

  from 100 μm to 5 mm, preferably from 150 μm to 2 mm. The dimensions of the particles are, however, not critical, particularly in the case of the use of a plasma arc furnace. The residence time can last from 5 to 30 minutes, but

  shorter or longer durations can also be used

  and the method of the invention can be implemented

  continuously or by successive charges.

  The method of the invention can be applied to a

  primary or secondary recovery from the source.

  In a primary recovery, it is the source itself that is melted and brought into contact with a melted collector. In

  secondary recovery, a slag that has already been

  exhausted of its metal content, passing into the collector, is again melted and brought into contact with

  a new amount of collector.

  In practice, a mixture comprising the automotive exhaust catalyst and lime (calcium oxide) is ground, melted and put in contact with a molten iron collector to dissolve the mixture. platinum group metals contained in the collector

and put them in the iron.

  A plasma arc furnace is employed in the following manner

  In a graphite crucible, in the bottom of a plasma arc furnace, a charge of cast iron and carbon is introduced and melted. A filler comprising the spent catalyst and the lime is introduced into the furnace, which is melted to form a molten slag which floats above the molten collector metal. It operates continuously, with too much evacuation of the slag. The load regime is such that the contact time of the slag is

  about 8 minutes. The oven is operated

  keeping the molten metal in the molten state and keeping the slag melted at a temperature of about

16000C.

  The molten slag removed from the furnace is solidified by contact with a stream of water, then ground and treated a second time in the furnace.

  similar, that is to say, put it in contact with a new

  the load of molten metal collector.

  The invention is illustrated by the following examples.

Example 1

  Powdered carbon (80 g) and cast iron (3.5 kg) are placed in a graphite crucible in a plasma arc furnace and melted to form a collector. We then introduce into the oven a

  a mixture of calcium oxide powder and catalytic

  milled (1:10), at a rate of 0.5 kg / minute. The cap

  talyseur is a monolithic catalyst ground for gas

  automobile exhaust, comprising cordierite with about 10% alumina, and containing in total about 1700

  ppm of Pt, Rh and Pd. The oven operates in an operating mode

  Continuous evacuation of the slag by overflow, and samples are taken at intervals of time

  measured from the moment the operating temperature

  (approximately 16000C) is reached. The platinum group metal content is measured in each sample, the results obtained being shown in Table I.

Table I

  Time (min.) X Pt (ppm) Pd (ppm) Rh (ppm)

180 10 30

185 14 N.Ae

210 10 30

293 21 N.A.

150 130 90 20

160 12 N.A,

  Notes: X Time measured from the moment when the temperature

  oven operation is reached.

N.A. Not analyzed.

  At the end of the test, it is found that the iron has only very little attacked the crucible. In a similar test, but iron alone is used as a collector, there is clearly a dissolution of the crucible in the areas of contact with the molten iron.

Example 2

  We continue the treatment of the slag of the exem-

  ple 1, according to the method of the invention. Carbon powder (40 g) and cast iron (1.75 kg) are introduced

  in a crucible, in the oven used in Example 1. I-

  here, the source substance is the slag coming from

  Example 1 (hereinafter referred to as "primary slag").

  After grinding, a total amount of 52.3 kg is introduced. As in Example 1, samples are taken at intervals of time, subjected to measurement tests

  of their platinum group metal content. The results

  States obtained are shown in Table II.

Table II

  Time (min.) X Pt (ppm) Pd (ppm) Rh (ppm) Total MGP

31 20 1 3

76 10 2 5

92: 1 5

  Notes: X Time measured from the moment when the temperature

  operating temperature of the oven is reached,

  Total PGM: Total platinum group metals.

  Here again, no effective attack of the substance of the crucible by the molten iron is observed visually. Example 3

  The test is carried out on a primary slag pro-

  from 40 kg of granulated catalyst (mainly alumina) and 40 kg of calcium oxide, the collector comprising 40 g of carbon powder and 2 kg of cast iron, the resulting primary slag contains 20 ppm of

platinum and 5 ppm of palladium.

  In the same operation, which lasts 48 minutes, the collector comprises 50 g of carbon powder and 2.5 kg of cast iron. The feedstock includes 40

  kg of the primary slag itself.

  The results obtained are shown in Table III.

Table III

  Time (min.) Pt-ppm) Pd (ppm) Primary slag 20 5

38 20 1

46 C 1 <1

N.D. N.D.

<1 1

  Here again, the crucible is not attacked by the

melted collector.

Claims (5)

  1) Process for the recovery of precious metals   from a source containing them in a highly distorted state   persé, according to which the source is melted in a high temperature carbon container in contact with a molten collector into which the precious metals migrate, said method being characterized in that the oven the load of the collector   with a quantity of carbon at least sufficient to saturate   remove the carbon from the collecting metal at the high temperature used.   2) Process according to claim 1, characterized in   the collector is iron or nickel.   3) Method according to one of claims 1 and 2,   characterized. in that the substance of the source is mixed with a fondant.   4) Process according to claim 3, characterized in what the fondant is lime.   Method according to one of Claims 1 to 4,   characterized in that the substance of the source is   contact of a collector, in a plasma arc furnace.   6) Method according to one of claims 1 to 5,   characterized in that the substance of the source comprises   a slag resulting from a preliminary operation of   in which precious metals have been recovered   extracted from a primary source, and a melted collector.