Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1986-12-23
1988-10-04
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204111, C25F 500
Patent
active
047754524
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for dissolving and recovering noble metals from used catalysts and the like by the fluidized or fixed bed electrolytic processes.
BACKGROUND
Noble metals such as the platinum group are in general use as catalysts for automotive exhaust gas purification and organic chemical reactions, and fuel cell electrodes. They are also constituents of electronic parts such as ICs. The recovery of noble metals from used materials is important due to their rarity and expense.
This has hitherto been by the dissolution process. In this process, the metals are dissolved with the carriers in hot concentrated sulfuric acid or an oxidizing acid such as aqua regia, and the metals are separated from the solution by addition of a reducing agent or by electrolyzing the solution in low current density electrolytic cell. In the former case, the noble metals separate out in the solution, which in the latter case, they are deposited on the cathode.
The dissolution process requires a dangerously high oxidizing acid that is difficult to handle, and a large amount of heat to maintain the acid temperature. Additionally, aqua regia, long been used for noble metals dissolution, gives off NOx producing pollution treatment problems. Cyanides, such as sodium cyanide, are effective for noble metals dissolution, but need careful handling and adequate liquid waste treatment due to their high toxicity.
In addition, the dissolution process is uneconomical in noble metals recovery from noble metal catalysts, because it involves the treatment of a large amount of carrier containing solutions as well as noble metals. (Noble metal catalysts are composed of carriers such as silica and alumina and very small amounts of noble metals therein. Therefore, the volume ratio of noble metal to catalyst is very small: 1 g of noble metal to 1 liter in apparent volume of catalyst.) Moreover, at times a portion of noble metal is present as oxides, barely soluble in aqua regia. In such cases, it is necessary to reduce the noble metal oxides before dissolution, or perform the dissolution process in two steps, i.e., noble metal dissolution in acid and noble metal oxide dissolution in alkali (see Japanese Patent Laid-open No. 155333/1982).
On the other hand, several processes are proposed for electrolysis metal dissolution (see Japanese Patent Laid-open No. 37045/1976); however, nothing has been reported on the use of electrolysis to dissolve noble metals supported on granular carriers. In the case of noble metals, the resulting solution would be too dilute to handle economically. The addition of a reducing agent increases the amount of solution to be treated and therefore the operating cost, beyond practical consideration. The use of ordinary flat electrodes in the electrolytic cell creates a dilute solution that does not permit efficient recovery.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a process for recovering noble metals from crushed granules of used catalysts, fuel cell electrodes, and electronic parts. This process utilizes the advantages of the electrolytic process; therefore, it does not need an oxidizing acid and waste acid solution disposal. In this process, the noble metals are dissolved in the electrolyte of the anode compartment of an electrolytic cell; the resulting dilute solution is introduced into the cathode compartment of a fluidized bed electrolytic cell in which the noble metals deposit on the cathode particles.
The crushed granules may be in spherical, cylindrical, plate, or conical shapes, or shapeless which obtained by crushing, pulverizing or from ashes-left after-incineration. They are not restricted as the crushed granules.
As a practical example, the invention will be illustrated below in more detail with the recovery of noble metals from used catalysts.
It is uncertain how noble metals are leached from non-conductive catalyst carriers; but it is considered that the leaching is affected by many factors in combination, such as anodic dissol
REFERENCES:
patent: 961924 (1910-06-01), Wohlwill
patent: 2088250 (1935-01-01), Truthe
patent: 2735810 (1956-02-01), Gagliano
patent: 3673061 (1972-06-01), Kruesi
patent: 3787293 (1974-01-01), Kametani
patent: 3886055 (1975-05-01), Baboian et al.
patent: 3956086 (1976-05-01), Wilkinson et al.
Daidoji Hiroshi
Goto Nobutaka
Kuninaga Tadashi
Andrews R. L.
Chlorine Engineers Corp. Ltd.
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