DE3146035A1 - RECOVERY OF PRECIOUS METALS - Google Patents

Description

Recovery of precious metals

description

The invention relates to a method for recovery recoverable metals from a raw material, for example returned material where the recoverable metal, usually at very low levels

Concentration, is dispersed. The procedure can be A U

can generally be described as a melting process in which the raw material containing the recoverable metal is melted and brought into contact with a molten collector _{metal in which the 2f} -recoverable metal is dissolved. The recoverable metal is then recovered from the collector metal by conventional metal refining techniques.

An increasingly important source of valuable recoverable metals QQ includes refractory oxides containing platinum group metals; For example, spent catalyst, waste from the electronics industry, waste from the manufacture of catalysts and scrap and, in general, any material in which metals, especially precious metals, such as metals of the platinum group, gold and silver in a base or a carrier material in a highly concentrated form Form.

A great and growing source of waste material this type is used car exhaust catalyst and Used catalyst from chemical and petroleum processing processes, all of which are essentially a feuerjo solid oxide as a carrier, such as aluminum dioxide, Contain cordierite or mullite on which one or more precious metals are dispersed. Typically these contain Catalysts one or more metals from the platinum group, the i η very η i less concentration, based on

"LQ is the mass of the supporting carrier, dispersed. The carrier can be a monolithic body of the cell type, typically made of cordierite (an Alumiηiumoxid-Si1iζiumdioxid-magnesia material) or individual beads, typically from Al umiηiumoxid, da rs te 1 th Cordierite monolith usually has a surface coating mainly of gamma aluminum oxide which results in a surface film of large surface area on which the catalytic material, usually platinum with one or more other platinum group metals, is dispersed. The catalysts can contain other components such as, for example a catalytic material of a base metal, for example nickel or nickel oxide, and oxides of rare earths include, stabilize the stabilization of alumina with high surface area to help (see US Patents 35 ⁶ 5830 and ^ I57316 the applicant, the typical Describe catalyst compositions of this type) Noble metal, in this case metals of the platinum group, which is present in some masses, is very small and is often on the order of 0.02 to 1 percent by weight, based on the total weight of the catalyst.

When recovering metals, such as metals of the P1 atine group from a solid starting material, Since it contains the metal in a highly dispersed form, it is common practice to use the solid metal to melt a flux component and the

molten slag, which is the recoverable metal contains to bring into contact with a collector metal, in which the recoverable metal (for example one or more metals of the platinum group, gold, silver, etc.) or into which it migrates in some other way. For example, if a molten slag that Cordierite and / or alumina and platinum group metals contains, as obtained by melting spent catalyst and a suitable FluCmittel can, with molten iron or copper as the collector metal is brought into contact, the platinum group metals migrate by dissolution or by any one another mechanism from the slag to the collector metal. For the sake of convenience, the expression "Loosening" is used hereinafter to describe this phenomenon.

The recoverable metal becomes from the collector metal separated in a separate, conventional process. Treatment is often necessary to increase recovery to repeat on the treated slag in order to remove any remaining recoverable metals from the first Pass not recovered to win. This can be done by cooling and crushing the resulting from the process discharged slag take place, whereby any existing, merged from the melt Metal 1k1umps separates (that is, small inclusions of collector metal that are trapped in the slag are) ffa1ls desired, and the broken Gives slag to a furnace for a second independent melting and contact process.

Conventional electric ovens, such as electric arc or plasma arc ovens, can be used. ^ ° Such furnaces usually have a refractory crucible, which is suitable for receiving the material batch, such as for example a graphite crucible that is in an isolated

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yc.

Cladding is included and is provided with suitable electrodes, plasma guns or the like.

It was found in certain collector metals, in particular Iron, but also nickel, found that if the crucible is made of graphite or some other form of carbon that denotes the molten metal Attacks crucible as coal is soluble to some extent in molten iron. It would be very old beneficiaries if this tendency were reduced or avoided entirely, as there are reasons for it make it desirable to use iron as a collector and graphite as a crucible material. Iron has the advantage that it shares with nickel, and to a lesser extent with cobalt, that it is both an effective collector (in the sense that it yachts platinum group metals from a molten one Starting material dissolves) and is ferromagnetic, so that meta 11 that have merged from the melt clump can easily be magnetically separated from the slag. The use of graphite crucibles is good because of their Resistance to molten slag at very high high temperatures are desirable.

According to the invention it has now been found that the tendency of molten iron to attack graphite crucibles is considerable can be reduced or even completely eliminated by adding carbon to the collector in an amount at least substantially to saturate the collector at the operating temperature of the stove was enough.

Therefore, according to the present invention, there is a method of recovery of precious metals made available from a starting material containing these, the metals contains in a highly dispersed form, in which one has the Starting material in a charcoal vessel at an elevated temperature in melted form with a melted one

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Collector brings into contact in which the precious metals migrate, the collector metal with an amount of carbon on it the furnace is given, which is at least sufficient, the Saromlermeta 11 mit t carbon at the elevated temperature to saturate.

In general, the inventive methods are each Ofenschmelz- or V> i rhüttungs ve rf ah ren applicable regardless of the rückzu'jewi nnenden metal or the heat source used; However, it has been found that it is particularly applicable to a process for the secondary recovery of platinum group metals dispersed on a support in dilute form, that is, in small amounts based on the mass of the support. The term "platinum group metals" as used herein means platinum, rhodium, ruthenium, palladium, osmium and iridium. For example, the methods of the invention are particularly applicable to the recovery of platinum group metals from spent catalyst containing a platinum group metal dispersed on a monolithic carrier or a carrier in bead form, such as catalysts for car exhaust gas, platinum on alumina-containing petroleum reforming -Catalyst, catalysts containing rhodium on alumina and ruthenium on alumina used for chemical processing, intermediate refined platinum group metals, catalysts, etc. As indicated, the invention can be achieved by using ovens equipped with plasma arcs or others suitable heat sources. The US PS ^! For example, en 339 * »2A2, 3783I67» ^ 0370 ^ 3 and AOO628A show typical plasma arc furnaces.

The collector is suitably iron; it can, however nickel or cobalt can also be used.

The amount of carbon added to the molten collector is generally at least sufficient in

essential to saturate the collector at the furnace operating temperature. The only figure in the accompanying drawing indicates the amount of graph ^r t that dissolves in molten iron at elevated temperatures. In general, a furnace is operated at a temperature between 1400 and 1700 ° C, preferably 1450 to. 16OO ° C operated. The amount of Koh1 enstoff, which is necessary to saturate an iron collector at a special furnace operating temperature can easily be determined from the appended figure. Similar curves can easily be made for other collectors who attack coal crucibles, for example cobalt or nickel. The latter metal forms a 2.2% carbon eutectic; and at 1700 ° C it is saturated by about 3% carbon.

^The fuel in cobalt is similar to that of carbon in nickel.

In general, a flux is used to ensure that the Aüsgangsmaterial melts, a melt of suitable viscosity (for example, about ^ 3 poise) at the furnace temperature, for example 1400 to 1700 ⁰ C, to form to 16oo ° C, preferably 1450 . Lime (CaO) is an example of a suitable flux; However, other fluxes can also be used

Example magnesium oxide or dolomite can be used. 25th

In general, the furnace loading material, for example the starting material and flux, dem Furnace fed in granulated form. It can for example

to a particle size of 100 μm to 5 mm, preferably 30th

15OyMm to 2mm, be broken. However, the particle size is not critical, especially when a Plasma arc furnace is used.

The dwell time can for example be between 5 and 30 minutes

th amount; however, shorter or longer residence times can also be used. The procedure according to The invention can be batch or continuous

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be performed.

The method according to the invention can be used for the first or second recovery from a starting material can be applied. In the first (primary) recovery, it is the starting material itself that is melted and brought into contact with a molten collector. At the second (secondary) recovery becomes a slag that has already been depleted by extracting part of its metal content in a collector is melted again and brought into contact with other collectors.

In operation was a mixture, the broken car exhaust catalyst and contained lime (calcium oxide), melted and with a melted iron collector metal Brought into contact to dissolve the platinum group metals contained in the catalyst in the iron.

A plasma arc furnace was used as follows:

A batch of cast iron and coal was turned into one Graphite crucible placed on the bottom of a plasma arc furnace and melted. A batch that contained spent broken car exhaust catalyst and lime

- ^ ⁰ was put on the stove and melted. A molten slag formed and floated on top of the molten collector metal. The plant was operated continuously, with overflowing slag being removed. The feed rates were such that the

Slag has an average residence time in the furnace

of about 8 minutes. The furnace was operated so that the collector metal remained molten and the molten slag was maintained at a temperature of about 1600 ° C.
35

The withdrawn molten slag was solidified by contact with running water and then

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broke. It was used a second time in the oven in a similar manner, that is, with a fresh one Batch of molten collector metal contacted.

The invention is illustrated by the following example 1i cht. '

example 1

Carbon powder (80 g) and cast iron (3.5 kg) were placed in a graphite crucible in a plasma arc furnace and melted to form a collector. A mixture of calcium oxide powder and broken catalyst (1:10) Was then placed on the oven at a rate of 0.5 kg / min. The catalyst was broken monolithic Car exhaust catalyst, the cordierite with about 10% Alumina containing a total of about 1700 ppm Pt, Rh and Pd. The oven was on with continuous Sch 1ackeüberl operated on, taking samples of slag (150 to 250 g) at intervals starting when the process temperature reaches (approximately 160 ° C) was taken. The content of each slag sample on metals of the platinum group was determined; the results of this are summarized in Table 1.

Ά *.

Table 1

Time (min) ^X Pt (ppm) Pd (ppm) Rh (ppm) 30th 180 10 30th 60 185 \ k η. a. 90 210 10 30th 120 293 21st η. a. 150 130 90 20th 165 160 12th η. a.

Note: time elapsed from reaching process temperature,
na: not analyzed.

At the end of the experiment it was found that the crucible very little of the iron had been attacked. On a similar run using Iron was carried out solely as a collector, one noticed a clear visible sign of dissolution of the Crucible where it is in contact with the melted Had been iron.

Example 2

In this example, slag from Example 1 was further treated by the method according to the invention. Carbon powder (rg g) and iron (1 _S 75 kg) were placed in a crucible in the furnace used in Example 1. In this example, the starting material was the slag of Example 1 (hereinafter referred to as "primary slag"). It was broken and added as such in a total amount of 250.3 kg. As in Example 1, samples were taken at intervals and tested for their platinum group metal content. The results are compiled in Table 2.

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Table 2

Time (m " η) X Pt (ppm) Pd (ppm) Rh (ppm) PGM overall 5 31 20th 1 3 76 10 2 5 92 O 5

Note: time elapsed from reaching process temperature.

Total PGM: total of 11 metals in the Plating group.

Again, there was essentially no visible sign of crucible subsidence attack by the molten iron to notice.

Example 3

This run was carried out with a primary slag consisting of 40 kg of pressed catalyst (mainly Aluminum oxide) and 40 kg of calcium oxide had been carried out; the collector contained ^ O g Coal powder and 2 kg of cast iron. The resulting primary slag contained 20 ppm platinum and 5 ppm Pal 1 ad i um.

In the experiment itself, which lasted k8 minutes, the collector contained 50 g of carbon powder and 2.5 kg of cast iron. The feed contained kO kg of primary slag as such. The results are shown in Table 3.

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Tabel

Time (m " η) Pt (ppm) Pd (ppm) ρ ri mä re Sch 1acke 20th 5 38 20th 1 kS <1 <1 60 n.d. n.d. 90 < ¹ <1

nd .: not measured.

Again the crucible was melted by the Collector not attacked.

L e r «e i t e

Claims (1)

Patent claims 1. A process for the recovery of precious metals from a starting material _a containing the metals in highly dispersed form * characterized geke η nz e ichnet that the starting material in a vessel made of carbon at elevated temperature in molten form with a molten collector metal, in which the Precious metals migrate, brings into contact, wherein the collector metal with an amount of carbon at least sufficient to saturate the collector metal with carbon at the elevated temperature, -2- gives up on the stove. 2. The method according to claim 1, characterized in that g e k e η n-Ze! c h η e t that one ice collector metal iron or give up nickel. 3 · Method according to claim 1 or 2, characterized in that - Mark T chnet that the starting material is mixed with a flux.
10 k. Method according to Claim 3, characterized in that lime is used as the flux. 5. The method according to any one of claims 1 to * », characterized gekennzei chnet that the starting material with the collector metal in a plasma arc furnace brings in contact. 6. The method according to any one of claims 1 to 5> characterized in that one is used as the starting material Slag from a previous recovery process, in which precious metals are extracted from a molten primary feedstock in a molten collector meta11 has been recovered, begins.