Chemistry of inorganic compounds – Phosphorus or compound thereof – Oxygen containing
Patent
1998-08-19
2000-02-29
Langel, Wayne
Chemistry of inorganic compounds
Phosphorus or compound thereof
Oxygen containing
C01B 25165
Patent
active
060305932
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention is that of a process for the manufacture of nickel hypophosphite.
PRIOR ART
Nickel hypophosphite is an inorganic salt known since at least 1828 (Rose, Ann. Physik., [12-87-1828). It crystallizes from its aqueous solutions in the hexahydrate form Ni(H.sub.2 PO.sub.2).sub.2.6H.sub.2 O, It is registered in the Registry file of Chemical Abstracts as RN 13477-97-9. Its constituent components, the hypophosphorous anion on the one hand and the nickel cation on the other hand, are the active species of the well-known chemical nickel plating process which makes use of the autocatalytic oxidation/reduction reaction.
NiSO.sub.4 +2NaH.sub.2 PO.sub.2 +2H.sub.2 O.fwdarw.Ni+2NaH.sub.2 PO.sub.3 +H.sub.2 SO.sub.4 +H.sub.2 .uparw. and the baths of which are manufactured from sodium hypophosphite and a soluble nickel salt, generally the sulphate. It might have been thought advantageous to use nickel hypophosphite for this end, with the obvious advantage of not, for no purpose, charging the baths with sodium and sulphate ions which cause difficulties due to the crystallization of sodium sulphate.
The Nouveau Traite de Chimie Minerale [New Treatise on Inorganic Chemistry] by Paul Pascal cites two processes for obtaining nickel hypophosphite, one by double decomposition between nickel sulphate and barium hypophosphite and the other by dissolving nickel hydroxide in hypophosphorous acid. To convert the double decomposition process to an industrial scale, it would be advisable to use calcium hypophosphite as a realistic source of hypophosphite; this results in a nickel hypophosphite which is unsuitable for chemical nickel plating because it contains an excessively large amount of magnesium, the major impurity contributed by the calcium hypophosphite itself, and of calcium, which is not removed from the reaction mixture due to the not insignificant solubility of the calcium sulphate formed. On the other hand, it is the starting material contributing the nickel to the dissolution process, metallurgic nickel hydroxide or nickel carbonate hydroxide, which is the source of contaminants by contribution of heavy metals or magnesium. Due to the lack of an economically acceptable production process, the use of nickel hypophosphite in chemical nickel plating has remained highly restricted.
DISCLOSURE OF THE INVENTION
The process according to the invention overcomes these disadvantages. It consists in retaining the nickel of an aqueous solution of a soluble nickel salt on an ion exchange resin and in eluting it with an aqueous hypophosphorous acid solution. It is thus possible to obtain hypophosphorous solutions assaying 30-35 g/l of nickel, which can be used directly to prepare or regenerate chemical nickel plating baths or from which nickel hypophosphite hexahydrate can be crystallized.
The resin to be used for the invention is a carboxylic resin (weak acid) in the sodium form. This type of resin can be regenerated by concentrated solutions of strong acids. It is thus possible to draw therefrom regeneration solutions which are concentrated in exchanged ions. After regeneration, the resin is in an acidic form which is unfavourable for adsorbing nickel ions: it is brought back to the carboxylate form, and preferably sodium carboxylate form, by treatment with a strong base, in this case sodium hydroxide. This is a highly exothermic reaction (approximately 80 kcal/mol). The chemical nature of the resin is of little importance but its composition must be such that it satisfactorily withstands the osmotic shocks created by the difference in the concentrations of the various reactants which succeed one another in the column during the operation, the thermal shocks due to the exothermicity of the neutralization of the acid resin, and the physical effects resulting from the fact that, in very concentrated solutions, the resin begins to float.
All water-soluble nickel salts are suitable for the invention. Nickel sulphate is preferred because it is easy to remove the sulphate ion from the
REFERENCES:
patent: 3888971 (1975-06-01), Scheibitz et al.
patent: 4552737 (1985-11-01), Estes
Brunner Paul
Jeanneret Gilbert
Jousset Dominique
CECA S.A.
Langel Wayne
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