JPH0144647B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for recovering rhodium and at least platinum or palladium as platinum group metal elements (hereinafter simply referred to as platinum group metals) on an activated alumina support, especially from a used platinum-based catalyst. It is related to. Platinum-based catalysts, in which various platinum group metals are supported on carriers such as alumina, are widely used in the chemical industry and for purifying exhaust gas from automobiles and the like.
Since the platinum group metals used in these catalysts are expensive and in short supply, there is a social demand for their recovery and reuse from used catalysts.
Therefore, there is an urgent need to establish a method for recovering these metals. Conventionally, methods for recovering catalyst metals from a catalyst in which platinum, palladium, etc. are supported as catalyst components on an activated alumina support (hereinafter simply referred to as an alumina support) include extracting the catalyst as it is with an inorganic acid, Alternatively, first the alumina of the carrier is pregelatinized by firing at a high temperature of about 1200°C, then the platinum, palladium, etc. that have become oxides are reduced with a reducing agent such as hydrogen or sodium borohydride, and then with a reducing agent such as hydrochloric acid or nitric acid. Platinum is removed from the carrier by an inorganic acid.
A method for extracting and recovering palladium and the like with high yield is known. However, although the above conventional method is convenient for recovering these metals from a catalyst in which only platinum and palladium are supported on an alumina support, it is difficult to recover catalyst metals from a catalyst in which rhodium is also supported along with these metals. It cannot be used to
This is because, in the latter method of the above-mentioned conventional methods, when fired at high temperature in air, the supported rhodium reacts with the alumina support to form a solid solution that is stable in inorganic acids. This is because there is a problem that it cannot be extracted and recovered using an inorganic acid. In order to prevent the formation of this solid solution and increase the recovery rate of rhodium, the metal supported on the catalyst is reduced with sodium borohydride, etc., and then the alumina is dissolved with an inorganic acid by the former method of the above conventional method. By doing so, rhodium can be recovered in high yield. However, in this method, the alumina of the carrier is not pregelatinized and retains its activity, so once dissolved platinum and palladium are re-supported on the carrier, making it impossible to recover platinum and palladium in high yield. I get used to it.
Another method for preventing the formation of a solid solution between rhodium and supported alumina is to calcinate a catalyst supporting rhodium in hydrogen at a high temperature, thereby recovering rhodium in high yield without forming a solid solution. can. However, high-temperature firing in hydrogen is practically impossible on an industrial scale because the equipment and running costs are extremely high. In this way, in the conventional method, if an attempt is made to recover platinum, palladium, etc. with a high yield from a catalyst in which rhodium is supported on an alumina carrier together with platinum or palladium, the recovery rate of rhodium decreases; There was a problem in that if an attempt was made to recover platinum and palladium at a high yield, the recovery rate of platinum and palladium would decrease. The present invention solves the above-mentioned contradictory problems and provides a method for recovering rhodium and all catalytic metals such as platinum and palladium from an alumina-supported catalyst in high yield. The method of the present invention uses a catalyst comprising at least rhodium and platinum and/or palladium as catalyst component platinum group metals supported on an alumina carrier.
First, after reduction, most of the rhodium and some of the platinum, palladium, etc. of the platinum group metals are dissolved in an inorganic acid and recovered primarily, and then the catalyst is calcined at a temperature of 1100°C or higher to transform the carrier into α- After the aluminization, the platinum group metals remaining on the carrier, such as platinum and palladium, are dissolved in the same inorganic acid as described above for secondary recovery. Examples of inorganic acids used to dissolve metals include nitric acid, aqua regia, and hydrochloric acid containing hydrogen peroxide. In the method of the present invention, in order to recover platinum, palladium, etc. in high yield, the catalyst must be calcined at a temperature of 1100°C or higher until the surface area of the carrier after α-aluminaization becomes 20 m ² /g or less. It is desirable to do so. Note that when carrying out the method of the present invention, if carbon etc. are attached to the catalyst, it should be soaked in air beforehand.
It is preferable to carry out a pretreatment at 500 to 700°C to burn off this carbon, etc. However, if the temperature of the pretreatment is higher than 700°C, a solid solution of alumina and rhodium will be formed, which will reduce the recovery rate of rhodium, which is not preferable. In the method of the present invention, when the platinum group metal on the catalyst carrier is not in an oxide state, the initial reduction treatment may be omitted, but if the above-mentioned pretreatment for carbon removal is performed. is reduced at a low temperature of 300-700℃ in a hydrogen atmosphere before extraction, or
By reducing with a reducing agent such as sodium borohydride,
It is necessary to return the platinum group noble metal oxide to its original non-oxidized metal state. Next, the present invention will be explained in detail based on examples. Example 1 6.8 g of catalyst with 0.2% by weight of palladium and 0.02% by weight of rhodium supported on activated alumina support
was calcined in air at 600° C. to burn off the adhering carbon, and after reduction with 20 ml of an aqueous sodium borohydride solution with a concentration of 0.5 g/region, rhodium and some palladium were recovered with aqua regia. Next, the extracted catalyst is calcined in air at 1200℃,
After reduction with an aqueous sodium borohydride solution in the same manner as above, the remaining palladium was extracted with aqua regia. As a result, as shown in Table 1, both palladium and rhodium were recovered with a high yield of well over 95%. Note that Table 1 also shows the results of Example 2 and Comparative Example described later.

[Table] Example 2 6.8 g of a catalyst in which 0.11% by weight of platinum and 0.02% by weight of rhodium were supported on an activated alumina carrier was extracted with aqua regia to recover rhodium and some platinum,
After that, it is baked in air at 1200℃, and the concentration is 0.5g/
After reduction with 20 ml of sodium borohydride aqueous solution,
The remaining platinum was extracted with aqua regia. As a result, the first
As shown in the table, both platinum and rhodium were recovered in high yields exceeding 95%. Comparative Example 6.8g of the same catalyst used in Example 2 was
After calcining at ℃ for 3 hours, the mixture was reduced with 20 ml of an aqueous sodium borohydride solution with a concentration of 0.5 g/region, and rhodium and platinum were extracted with aqua regia. Next, after washing the extracted catalyst with water, a second extraction was performed under the same conditions as the first extraction. As a result, as shown in Table 1 above, the recovery rates of both platinum and rhodium were low, far below 95%. The reason for this low recovery rate is that 800
Since the catalyst was heated at a temperature of 10°C, some of the rhodium formed a solid solution with alumina and was no longer extracted, and the calcination temperature of 800°C was insufficient for alumina to gelatinize. This is thought to be because activity remained in the alumina carrier, and platinum once extracted was re-adsorbed onto the carrier and was not recovered. As explained above, the present invention provides a method for recovering precious metals from a platinum-based catalyst in which platinum group noble metals including rhodium are supported on an activated alumina carrier at a high yield of over 95%. The method of the present invention can efficiently recover rhodium and other platinum group metals without sintering the catalyst at high temperatures in a hydrogen atmosphere, so it is easy to implement and has low running costs, making it a major contribution to resource conservation. be.

Claims (1)

[Claims] 1. A catalyst in which rhodium and at least platinum or palladium are supported as catalyst component platinum group metals on an alumina support is first reduced, and then the platinum group metal is dissolved in an inorganic acid for primary recovery, and then the catalyst is recovered. The above carrier is α-
A method for recovering platinum group metals from a platinum-based catalyst, which comprises dissolving the platinum group metals remaining on the carrier with an inorganic acid after aluminization for secondary recovery.