Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-03-09
2003-05-06
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S682000, C210S684000, C210S688000, C502S402000, C521S028000
Reexamination Certificate
active
06558552
ABSTRACT:
DESCRIPTION
The present invention relates to a composite solid material fixing mineral contaminants, with a basis of hexacyanoferrates and cationic polymer deposited in a pellicular layer on a support.
More precisely, the object of the present invention is a composite solid material fixing mineral contaminants formed from a mechanically and chemically stable solid support coated with a pellicle of an anion-exchange polymer to which a thin layer of insoluble hexacyanoferrate is fixed.
The present invention also relates to the method of preparing the said composite solid material fixing mineral contaminants with a hexacyanoferrate basis.
The present invention finally relates to method of fixing at least one mineral contaminant contained in a solution, on the said composite solid material fixing mineral contaminants.
Many mineral fixers have been used for fixing various mineral contaminants such as metallic cations contained in the various effluents and media originating from various industries and in particular from the nuclear industry.
In fact, the nuclear industry uses, for the treatment of low- or medium-radioactivity effluents, purification techniques with volume reduction consisting of the fixing on a mineral solid of radioisotopes present in the solutions. The volumes treated currently are huge and reach several tens of thousands of m
3
/year for France. The liquids treated are also of a varied nature since treatment of both nuclear power station cooling waters and the various effluents coming into contact with radioisotopes such as all the wash water, the resin regeneration solutions, etc. is concerned.
Among the mineral fixers used notably in the nuclear industry can be cited the Manox® type products with an oxides of manganese basis which are used for fixing elements present in solution, in various chemical forms, the said elements being for example Ag, Sb, Ra or Pb; iron hydroxide used for fixing, by coprecipitation, the transuranic elements, and finally the insoluble hexacyanoferrates (II or III).
The hexacyanoferrates, notably the hexacyanoferrates (II) of Cu, Ni and Co, are in fact among the mineral fixers most commonly used, in particular in the nuclear industry owing to the great affinity they have with regard to caesium. Hexacyanoferrate type inorganic fixers have therefore notably been used for separating, recovering and fixing metallic ions and in particular the ions of radioactive alkali metals such as long half-life caesium 137 from various industrial and nuclear effluents, for example from strongly acid solutions originating from the reprocessing of irradiated fuels and from the solutions already referred to above.
At present, insoluble hexacyanoferrates thus enter into the majority of methods of treating liquid radioactive waste by coprecipitation.
Mineral fixers and in particular hexacyanoferrates, although they sometimes have high selectivities, have however the basic failing of having a low intrinsic durability, in other words a poor mechanical strength which makes it difficult, perhaps even impossible, to pack them in a column because of a reduction in the volume occupied by the fixer and a clogging-up which moreover limits the number of applications.
Thus these fixers, when they are prepared in powder form, form mechanically unstable grains; in addition, in compact form in a mass, their small specific surface often leads to slow reaction kinetics which greatly limits their effectiveness.
In fact it is generally difficult to alloy a compact form with a high reaction speed.
At the present time, insoluble hexacyanoferrates in a mass, although otherwise commonly made use of, are used, it seems, industrially in columns only in Finland, as described in the document by R. HARJULA, J. LEHTO, J. WALLACE: “Removal of cesium from nuclear waste solutions by potassium-cobalt hexacyanoferrate (II) columns”, Proc. Symp. Waste Manag., Tucson, Ariz., 1987, 3, p.93, and in the document by J. LEHTO, R. HARJULA, S. HAUKKA, J. WALLACE: “Solidification of
137
Cs into KCo hexacyanoferrate (II) ion exchanger”, Joint Int. Waste Manag Conf., Kyoto, Japan, 1989.
Cobalt hexacyanoferrates (II) in a mass are concerned, which are used for treating only limited volumes of solutions because of clogging-up.
Many publications report researches in order to prepare phases of good mechanical strength from mineral fixing compounds such as hexacyanoferrates.
There has thus been proposed in the documents by K. WATARI, K. IMAI and M. IZAWA, J. Nucl. Sci. Technology, 1967, 4, 190-194 “Isolation of
137
Cs with copper ferrocyanide-anion exchange resin”, by J. STEJSKAL, J. SOUKUP, J. DOLEZAL and V. KOURIM, J. Radioanal. Chem., 1974, 21, 371-379 “Improved inorganic ion-exchangers I. Systems with organic polymers as binding materials”, and in the patent U.S. Pat. No. 4,755,322, the preparation of composite organic resins which can incorporate a high proportion of mineral compound such as a hexacyanoferrate.
The stability of these composite materials is satisfactory but the majority presence of organic compounds greatly limits the possibilities of use, all the more so since the active mineral part retains the bulk of its characteristics and in particular the non-reversibility of the fixing.
In general, the methods concerning improvement in performance of mineral fixers call upon in-situ precipitation in the presence of silica.
This is notably the case of the precipitation of hexacyanoferrates, in the document by K. TERADA, H. HAYAKAWA, K. SAWADA and T. KIBA, Talanta, 1970, 17, 955-963 “Silica gel as a support for inorganic ion-exchangers for the determination of
137
Cs in natural waters”, the Russian patent SU-A-77 8780 by E. K. SPIRIN et al., and the document by C. KONECNY and R. CALETKA, J. Radioanal. Chem., 1973, 14, 255-266 “Adsorption properties of insoluble hexacyanoferrates (II) supported on silica gel”.
Thus, the latter document describes the fixing on silica gel of insoluble hexacyanoferrates in order to improve their mechanical properties and pack them into columns, which allows a continuous treatment of effluents. These products fixed on silica gel are prepared notably by impregnation under agitation of the silica gel with aqueous solutions saturated with potassium hexacyanoferrates (II) until a “moist solid” state is obtained, then, after drying, bringing the solid into contact with solutions comprising an excess of metallic ions, then drying once more and bringing into contact again with 0.1 M solutions of the metallic ions in order to allow precipitation on the silica of the desired hexacyanoferrate.
All the methods and products described above which call upon fixing of the mineral fixer such as hexacyanoferrates on silica have in common a number of drawbacks.
First of all, the bulk of the precipitation of the hexacyanoferrate takes place inside the pores of the silica and not on the surface which greatly reduces the effectiveness of the composite mineral fixer obtained since the surface of contact between this composite mineral fixer and the solution, represented by the specific surface of the composite, is distinctly less than the specific surface of the support, such as silica, preferably chosen from among the finely-divided silicas of large specific surface.
The so-called “coprecipitation” method proves difficult to use for amounts exceeding a few grams since there takes place in particular a phenomenon of salting-out of the excess salts.
Moreover, the composition of the final product is very poorly controlled, and its properties are not very reproducible, the proportion of hexacyanoferrate deposited being very poorly controlled by the coprecipitation. This is because the adhesion of the mineral fixer on the silica is accomplished by a purely mechanical phenomenon which means that the mineral fixer is weakly bonded to the support and can be easily detached, or leached, therefrom.
Moreover, the amounts of mineral fixer such as hexacyanoferrate are relatively high and can reach for example up to 30% by mass with respect to the mass of mineral support such as silica.
These highly
Dulieu Jacqueline
Loos-Neskovic Christiane
Pantazaki Anastasia
Vidal-Madjar Claire
Cintins Ivars
Commissariat a l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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