JPH05255771A - Reduction method for noble metal - Google Patents

Abstract

PURPOSE:To provide the improved reduction method which is safer and easier in operation than the methods practiced heretofore and is equal to or higher in the recovery rate of the noble metals obtd. by the method than by the conventional methods as the reduction of a pretreatment to be executed at the time of recovering the noble metals from noble metal scrap. CONSTITUTION:This reduction method for the pretreatment to be executed at the time of recovering the noble metals from the scrap contg. the noble metals and/or the compds. of the noble metals consists of reducing the noble metals by an aq. gas reaction effected at the time of burning the scrap in the state in which the scrap, carbon contents and steam coexsit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction method used as a pretreatment when recovering precious metals from scrap containing precious metals.

[0002]

2. Description of the Related Art Scraps containing precious metals are often produced as used catalysts or in the electronics industry or physical processing such as polishing of precious metals.

These scraps are often mixed with those carried on activated carbon, oil components, filter aids, and the like. In order to remove these contaminants, usually after burning the combustible components, reduction is performed to modify the surface oxidation state of the noble metal as a pretreatment, and then a wet recovery process such as extraction treatment with an acid solution is performed. I often enter.

[0004]

Conventionally, as a general reduction method, a wet reduction method using a chemical or a dry method using hydrogen gas or the like has been used. However,
In the wet method, uniform reduction is difficult, and in addition, depending on the chemical, it is extremely troublesome to control the liquid property, which is troublesome. On the other hand, in the dry method, hydrogen gas is extremely active and explosive, so sufficient safety measures must be taken when using it, such as the installation of frame curtains and alarm devices. It is necessary to ensure the structural safety of the furnace including the above, and there is a drawback that the maintenance cost for this is high.

An object of the present invention is to provide a reduction method which has a reduction effect equal to or higher than that of the above-mentioned conventional reduction method, is easy to maintain and is highly safe. ..

[0006]

The present invention for attaining the above-mentioned object provides a scrap in a pretreatment reduction method for recovering precious metals from scrap containing precious metals and / or compounds of precious metals (hereinafter referred to as scrap). ,
A noble metal reduction method characterized in that reduction is carried out by a water gas reaction generated by firing in a state where a carbon-containing substance and water vapor coexist.

[0007]

The operation of the present invention will be described in detail below. The present invention replaces the conventional wet reduction method or the dry reduction method using hydrogen, and performs reduction by a water gas reaction. That is, reduction is carried out by a water gas consisting of carbon monoxide gas and hydrogen gas generated when the scrap is heated and calcined in the presence of a carbon-containing substance and steam.

In carrying out the present invention, the mixture of the scrap and the carbon-containing material may be roasted once, or may be carried out as it is. Noble metals and / or oxides of noble metals in scrap are usually less than 0.
Since it is dispersed in an amount of about 0 n% to 10%, the reduction reaction is completed if the nascent reducing water gas is present in an amount equal to or more than the substance to be reduced.

Therefore, the reduction can be carried out very easily by controlling the amounts of the carbon-containing substance and steam added, the reaction temperature and the time. At this time, the water vapor not only decomposes carbon to generate a reducing gas, but also has the effect of reducing the oxygen partial pressure in the gas atmosphere during the reaction to stably complete the reduction reaction. There is.

As the carbon-containing substance, it is not necessary to newly add it when the activated carbon, the organic compound or the like is present in an appropriate amount in the scrap. If there is no carbon-containing material in the scrap, or if the carbon-containing material is present in a very small amount, the carbon-containing material such as charcoal, activated carbon, coke, sugar and corn starch can be used as a precious metal in the scrap. It may be added in an amount equal to or more than 30% of the amount.

When a large amount of carbon-containing material is present in the scrap, as a method other than the above, the scrap is once heated and roasted to remove the carbon-containing material to reduce the amount of the material,
A suitable amount of carbon-containing material may be newly added. In this case, the added amount is preferably about 30 to 50%, which is equivalent to the amount of the noble metal.

It is desirable to use the same amount of steam as the amount of carbon contained in the scrap, including the added steam, or 100 times as much. If the amount is less than the same amount as carbon, the generated steam will escape to the outside of the system without contributing to the reaction, so the reduction reaction may be insufficient. Otherwise, the amount of water vapor that goes out of the system wastefully increases, which is not economical.

40 m when steam is added to the atmosphere
Add in the range of mHg to 760 mmHg. The addition method is generally a method of continuously flowing into the atmosphere, and it is preferable that the flow rate is about 0.1 to 7 liters per 1 kg of scrap material. After sufficient mixing of the scrap and the additives, the scrap and the additive are put into a furnace and heated in a temperature range of 200 ° C. to 940 ° C. for 20 minutes to 3 hours for reduction.

The furnace used can be any type of furnace commonly used, for example tubular furnaces, rotary kilns, muffle furnaces, etc., but the rotary kiln is suitable for continuous processing. After completion of the reduction pretreatment, the scrap can be subjected to a wet treatment by an ordinary extraction method to purify and recover the precious metal.

[0015]

EXAMPLES Next, examples of the present invention will be described.

Example 1 100 g of a used catalyst in which activated carbon powder was loaded with 5% by weight of rhodium was placed in a tray and charged in a tubular furnace, and 100 ml / 100 ml of water was added while controlling the partial pressure of steam to 700 mmHg. Sample A was obtained by performing a reduction reaction at 600 ° C. for 2 hours while flowing at a flow rate of min.

Comparative Example 1 100 g of the same catalyst used in Example 1 was added to 600 g in air.
After firing at ℃, insert into a quartz boat and add nitrogen gas to
After confirming that there is no gas leak from the piping while flowing at 0 ml / min and flowing for 40 minutes, hydrogen gas is heated to 250
600 ml over 20 minutes while flowing at a rate of ml / min
The temperature was raised to ℃ and kept for 30 minutes. At this time, the flow rate was adjusted while monitoring so that hydrogen was not consumed due to the rapid reaction and a negative pressure was not generated. After cooling to room temperature, add nitrogen gas to 250
Sample B was obtained by flowing at a rate of ml / min for 20 minutes.

Comparative Example 2 A sample C was obtained by subjecting 100 g of the same catalyst used in Example 1 to a reduction treatment in which it was roasted at 600 ° C. for 2 hours without coexisting steam.

Experimental Example 1 Samples A to C obtained in Example 1, Comparative Example 1 and Comparative Example 2 were placed in beakers, respectively, and 8N hydrochloric acid 100 was added.
ml was added, and an extraction treatment was carried out at about 100 ° C. for 2 hours while flowing chlorine gas at a rate of 100 ml / min. After the extract was filtered off, rhodium was analyzed by ICP to obtain the extraction rate. The results are shown in Table 1.

[0020]

[Table 1] Extraction rate of sample rhodium A 94% B 93% C 65% Example 2 0.13% by weight of platinum on spherical alumina having a diameter of about 3 mm,
0.08% by weight of palladium and 0.00 of rhodium
100 g of a used automobile exhaust gas purifying catalyst loaded with 9% by weight was taken and calcined in air at 900 ° C. for 3 hours.
5 g of a suspension prepared by adding 5% by weight of activated carbon to a 20% by weight aqueous solution of sugar was added thereto.

This was placed in a tray and inserted into a tubular furnace, while controlling steam so that the partial pressure was 540 mmHg and flowing at a flow rate of 100 ml / min, 480 ° C.
Then, the reduction reaction was performed for 20 minutes to obtain Sample D.

Comparative Example 3 Sample E was obtained by the same procedure as in Comparative Example 1 except that 100 g of the same catalyst used in Example 2 was used and the reduction time was 15 minutes.

Comparative Example 4 100 g of the same catalyst as used in Example 2 was placed in a beaker, 100 ml of 0.5 N formic acid solution was added, and the mixture was heated on a steam bath to dryness. Further, heating was continued until the odor of formic acid disappeared to obtain sample F.

Test Example 2 Samples D, E and F obtained in Example 2, Comparative Example 3 and Comparative Example 4 and the used catalyst used in Example 2 were treated as Sample G, respectively. Place each separately in a beaker and add 5 L of hydrochloric acid to 100 L of nitric acid.
Extraction treatment was carried out at 102 ° C. for 4 hours using a mixed acid containing ml. The extract was filtered off and then analyzed by ICP to obtain the extraction rates of platinum, palladium and rhodium.
The results are shown in Table 2.

[0025]

[Table 2] Sample extraction rate (%) Platinum Palladium Rhodium D 96 97 97 88 E 95 97 97 87 F 94 95 78 G 95 54 43 Example 3 Used catalyst 50 in which 1% of platinum was supported on powdered activated carbon 50
0 g was put in an electric furnace and roasted in the air for 1 hour to obtain 35 g of a roasted product. Next, 10.0 g of this roasted product was placed in a quartz boat, and 0.5 g of activated carbon suspended in 5 ml of water was placed in a tube furnace and steam was added at a partial pressure of 100 m.
100ml / while controlling to mHg
Sample H was obtained by firing at 200 ° C. for 40 minutes while flowing at a flow rate of min.

Example 4 Sample I was obtained by the same procedure as in Example 3 except that the temperature and time were 500 ° C. and 30 minutes, respectively.

Example 5 Example 3 was repeated except that the partial pressure of water vapor was 700 mmHg and the temperature and time were 900 ° C. and 20 minutes, respectively.
Sample J was obtained in the same procedure as described above.

Test Example 3 Samples H to J obtained in Examples 3 to 5 were separately placed in a beaker, 50 ml of 6N hydrochloric acid and 1 ml of nitric acid were added, and extraction treatment was carried out at 95 ° C. for 4 hours.

After the extract was filtered, platinum was analyzed by ICP to obtain the extraction rate. The results are shown in Table 3.

[0030]

Table 3 Samples Extraction rate of platinum H 91% I 92% J 88% As can be seen from the results of Examples 1 to 5 and Comparative Examples 1 to 3 and Test Examples 1 to 3, according to the method of the present invention. In this case, reduction treatment can be performed in a general furnace without taking any special safety measures and without cumbersome control of liquid properties such as chemicals. is there.

[0031]

According to the method of the present invention, it is possible to perform a pre-reduction treatment for recovering precious metals with a simple facility without the need to take special safety measures against gas explosion and the like when performing work. Then, after performing the pretreatment method of the present application, the extraction rate in the case of performing the extraction treatment of the noble metal with an acid is at least equivalent to that in the case of performing the pretreatment by the conventional hydrogen reduction method, and by the wet reduction method. Better than the case.

Claims (1)

[Claims] 1. A water-gas reaction produced by calcining a scrap in the presence of a carbon-containing material and water vapor when performing pretreatment reduction when recovering a noble metal from scrap containing a noble metal and / or a compound of a noble metal. A method for reducing a noble metal, which is characterized by reducing with.