Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Platinum group metal
Patent
1991-10-30
1994-05-24
Lewis, Michael
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Platinum group metal
423463, C01G 5500, C22B 1100, C01B 900
Patent
active
053146700
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to rhodium chemistry. More particularly, it relates to the recovery of soluble rhodium values from process liquors used in the preparation of a compound employed in photographic chemistry. The rhodium values are recovered as a substantially insoluble precipitate which can be used as an additive to silver halide emulsions.
BACKGROUND ART
Ammonium pentachloromonoaquorhodate(III) is useful in photographic chemistry. A small amount of rhodium as a soluble species remain in solution after synthesis. Most of the soluble rhodium values are present as the aforementioned ammonium complex; however there are traces of the cis and trans isomers of ammonium tetrachlorodiaquorhodate(III), and traces of the fac and/or mer isomers of rhodium(III) chloride triaquo complexes are present in the process liquors from which the ammonium pentachloromonoaquorhodate(III) is precipitated.
Rhodium compounds are expensive: and therefore, recovery rather than discharge in an effluent, is desired. Furthermore, recovery is also desirable from an environmental viewpoint. Therefore, need exists for a method to conveniently recover rhodium values from the process liquor. This invention satisfies that need.
The following references disclose the Cs.sub.2 RhCl.sub.5 (H.sub.2 O) product produced by the process of this invention: Ferguson et al., Australian J. Chem., No. 7, 30, (July 1977), pp. 1445-1460, Thomas et al., J. Coord. Chem. 1973, 2 pp. 231-234, Prokofersa et al., Koord. Khim., 4, No. 1, (1978), pp.32-34. These references do not disclose the process of the invention.
U.S. Pat. No. 3,531,289 discloses a use of ammonium hexachlororhodate. Also U.S. Pat. Nos. 2,448,060, 2,566,245, 2,566,263, 4,477,561, 4,857,450; Australian 134,725; German Offen. 2,226,877; and Japan 59/171,947 relate to uses of alkali metal rhodium compounds in photographic emulsions.
DISCLOSURE OF INVENTION
In one aspect, this invention relates to a process for the preparation of Cs.sub.2 RhCl.sub.5 (H.sub.2 O) said process comprising reacting cesium chloride with (NH.sub.4).sub.2 RhCl.sub.5 (H.sub.2 O) in an aqueous reaction mixture having about 80 percent ethanol, and sufficient HCl to make the content of acid in the aqueous portionins 4-5N. In a preferred embodiment of this invention, the process is carried out in an acidic; organic-aqueous solution in which the (NH.sub.4).sub.2 RhCl.sub.5 (H.sub.2 O) is present together with traces of the cis and trans isomers of ammonium tetrachlorodiaquorhodate(III) and traces of the fac and/or mer isomers of rhodium(III) chloride triaquo complexes. An aqueous material of such a composition can be prepared by the reaction of ammonium chloride, HCl and rhodium (III) chloride, and removal of the (NH.sub.4).sub.2 RhCl.sub.5 (H.sub.2 O), which precipitates from the alcohol water mixture used as a reaction solvent.
In another aspect, this invention provides a silver halide emulsion containing from about 0.5 to about 50 mg of Cs.sub.2 RhCl.sub.5 (H.sub.2 O) per each 100 grams of silver in the emulsion.
The dual function of the Cs.sub.2 RhCl.sub.5 (H.sub.2 O) i.e., a means of recovery of rhodium values, and an additive for silver halide emulsions was unexpected, and makes this invention readily adaptable by industry.
BEST MODE FOR CARRYING OUT THE INVENTION
The process of this invention, for the preparation of Cs.sub.2 RhCl.sub.5 (H.sub.2 O) by the reaction of cesium chloride, can be conducted by reacting two moles of the cesium compound per each one mole portion of (NH.sub.4).sub.2 RhCl.sub.5 (H.sub.2 O). However, it is not necessary to use stoichiometric quantities, and non stoichiometric properties can be used. Thus an excess of either reactant can be used, if desired. For example, an excess of the cesium compound can be use to help drive the reaction to completion, and/or aid in the precipitation of the product cesium/rhodium complex. The amount of excess is not a critical part of this invention, and it is governed by such secondary considerations as process economics. In general fro
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Kuhr, W. et al, "Preparation . . . cesium trans-aquabromotetrachlororhodate(2-)," Z. Anorg. Allg. Chem., 1990, 581, pp. 153-158.
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Kiehl Gary G.
White Weimar W.
Bos Steven
Eastman Kodak Company
Janci David F.
Lewis Michael
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