Method of decomposing CMPO

CMPO is safely, reliably and rapidly decomposed under mild conditions. A CMPO-containing substance is emulsified in an electrolyte comprising an oxidation promoter (silver ion) by an emulsifier in an emulsifying tank, this electrolyte comprising the CMPO-containing substance is supplied to an anode chamber, and an electrolytic oxidation reaction is performed by passing an electric current. By emulsifying the CMPO-containing substance, the surface area of CMPO in contact with electrolyte is increased, and electrolytic decomposition is thereby promoted. As sufficient CMPO decomposition is not obtained by passing the emulsion only once through an electrolysis tank 1, a batch oxidation method is employed wherein an anolyte is recirculated by a recirculating pump 3a through the anode chamber, a constant temperature bath 7a and an emulsifying tank 6, so that electrolysis is performed with the CMPO-containing substance permanently emulsified in the electrolyte. To maintain a catholyte in a cathode chamber at the same temperature as the anolyte, the catholyte is recirculated by a recirculating pump 3b between the cathode chamber and a constant temperature bath 7b. The current supplied to an anode 4 and cathode 5 in the electrolysis tank 1 is controlled by a rectifier 8.

BACKGROUND OF THE INVENTION 
This invention relates to a method of decomposing octyl 
(phenyl)-N,N-di-isobutyl carbamoyl methyl phosphine oxide (C.sub.24 
H.sub.42 NO.sub.2 P, referred to hereafter as "CMPO"), a neutral 
organophosphorous compound having a double chair configuration, which is 
used for separating actinoids. 
DESCRIPTION OF THE RELATED ARTS 
CMPO has a high actinoid separating ability, and various studies are being 
carried out to explore its use as a promising new actinoid extracting 
agent. In the TRUEX method, for example, to separate transuranic elements 
and nuclear fission products (FP) containing trivalent actinoids such as 
Am and Cm from reprocessed, highly radioactive effluent, a mixed solvent 
comprising a blend of CMPO and tributylphosphoric acid ((C.sub.4 H.sub.9 
O).sub.3 PO, referred to hereafter as TBP) in a hydrocarbon diluent (e.g., 
n-dodecane, chemical formula: n-C.sub.12 H.sub.26) is used, and the 
transuranic elements are thereby extracted into the solvent. 
However when CMPO which is the extracting agent is used for a long period 
of time, it deteriorates due to radiation damage and hydrolytic 
decomposition, its extracting efficiency declines, and as a result, highly 
radioactive organic effluent containing CMPO is produced. Until now, no 
effective method had been found for treating this CMPO-containing 
radioactive effluent. 
It is therefore an object of this invention to provide a method of safely, 
reliably and rapidly decomposing CMPO under mild conditions. 
SUMMARY OF THE INVENTION 
To resolve the aforesaid problems, the method of decomposing CMPO according 
to this invention has the following features. 
(1) A CMPO-containing substance is added to an electrolyte containing an 
oxidation promoter so as to emulsify the CMPO-containing substance in the 
electrolyte, the emulsion obtained is supplied to an anode chamber in an 
electrolysis cell partitioned by a membrane, and a current is passed to 
electrochemically decompose the CMPO-containing substance. 
This permits oxidative degradation of CMPO under mild conditions. 
(2) In the method of decomposing CMPO mentioned in (1) above, the aforesaid 
oxidization promoter is silver ion, and the aforesaid electrolyte is 
nitric acid solution. 
Silver ion (Ag.sup.2+ /Ag.sup.+ system) which is the oxidation promoter has 
a high redox potential, and since Ag.sup.2+ is a metal ion with a high 
oxidizing power, CMPO can be oxidatively degradated efficiently even under 
mild conditions. Further, nitric acid solution which is widely used for 
actinoid separation is an electrolyte which is easy to handle, and it may 
be used to assist in the safe, oxidative degradation of CMPO.

DESCRIPTION OF THE PRESENT INVENTION 
A preferred form of this invention will now be described. 
In the method of decomposition according to this invention, the 
CMPO-containing substance is indirectly electrolytically oxidized and 
oxidatively degradated. In general, electrolytic decomposition proceeds 
under mild conditions and operating procedures involve no risk. Also, a 
major part of the CMPO molecule is hydrocarbon, so most of the products of 
oxidative degradation are easily discharged into the outside environment 
as carbon dioxide gas and water, and only phosphoric acid is left as a 
residue. Therefore, although CMPO is a large molecule, it is decomposed 
according to the method of this invention leaving only phosphoric acid, so 
generation of waste products is largely reduced (high volume reduction). 
Since phosphoric acid is produced also in the treatment of fertilizers, 
methods have already been established to dispose of phosphoric acid. The 
end product of the decomposition may therefore also be safely, efficiently 
treated. 
As stated above, CMPO is normally used is systems employing n-dodecane and 
TBP as solvents. Like CMPO, TBP also contains phosphorus, and as it can 
clearly be decomposed by the method described hereafter, a detailed 
description of the decomposition of TBP will be omitted. To avoid any 
confusion between the decomposition of CMPO and decomposition of TBP, the 
description given herein applies to a two-component system wherein CMPO is 
dissolved in the organic solvent decalin (decahydronaphthalene, chemical 
formula: C.sub.10 H.sub.18). 
A two-component solution of CMPO/decalin dissolves only slightly in an 
electrolyte (e.g., aqueous nitric acid solution), and it was found to be 
only slowly oxidized unless special measures are taken. To increase the 
oxidation rate, therefore, it is preferable to emulsify an electrolyte 
containing CMPO prior to electrolysis so as to increase the surface area 
of CMPO in contact with electrolyte. 
It is moreover preferable to add silver ion (Ag.sup.+) to the electrolyte, 
this silver ion functioning as an oxidation promoter. Ag.sup.+ undergoes 
anodic oxidation (Ag.sup.+ .fwdarw.Ag.sup.2+ +e.sup.-), thus converting it 
to Ag.sup.2+ which has a high oxidizing power. Further, Ag.sup.2+ reacts 
with water producing oxygen radicals (O.degree.) which also have oxidizing 
properties (2Ag.sup.2+ +H.sub.2 O.fwdarw.2Ag.sup.+ +2H.sup.+ +O.degree.). 
These oxygen radicals accelerate the electrolytic oxidation of CMPO. 
An electrolysis cell 1 used in this invention may have a two-chamber or 
three-chamber construction, however a two-chamber construction is 
preferable since it is simpler, as shown in FIG. 1. As shown in FIG. 1, 
the electrolysis cell 1 is partitioned by a membrane 2 (i.e., cation 
exchange membrane). The electrolyte containing CMPO is supplied to an 
anode chamber housing an anode 4. It should be noted that even if CMPO is 
supplied to a cathode chamber containing a cathode 5, CMPO cannot be 
decomposed. Also, no decomposition of CMPO takes place whatsoever in an 
electrolysis tank which does not make use of the membrane 2, as described 
hereafter. It was found that the electrolyte containing CMPO must be 
supplied to the anode chamber formed inside the electrolysis cell by 
partitioning the tank with the membrane. 
The electrolysis cell 1 used in this invention can be manufactured from the 
following materials. The cell frame (i.e., the frame of the anode chamber 
and cathode chamber) of the electrolysis cell 1 may be formed of an 
acid-resistant metal or a plastic (e.g., PTFE). The anode 4 may be formed 
of platinum, or of titanium which has been electroplated or coated with 
platinum. The membrane 2 may be a perfluorosulfonic acid type ion exchange 
membrane, or it may be made of porous glass, porcelain or the like. 
The electrolyte on the cathode side may be dilute nitric acid, sulfuric 
acid or phosphoric acid, however from the viewpoint of subsequent 
processing, it is preferable to use the same dilute nitric acid as for the 
anolyte. 
According to this invention, phosphoric acid ion produced in the 
electrolyte solution was used as an indication of the progress of 
decomposition of CMPO. Many different products are generated by the 
electrolysis of CMPO, but it is thought that these are finally oxidized to 
carbon dioxide gas, water and phosphoric acid. For example, the following 
reaction has been postulated. 
##EQU1## 
The inventors therefore measured phosphoric acid ion in the solution after 
electrolysis. To perform this measurement, hydrochloric acid was added to 
the effluent after electrolysis to remove excess silver ion, and the 
effluent was evaporated to dryness on the water bath to remove nitric 
acid. Residual phosphoric acid ion was dissolved in water, and 
quantitatively determined by ion chromatography. 
According to this invention, the electrolysis temperature may lie within a 
range of 0.degree. C. to 100.degree. C., but from the viewpoints of 
efficiency and prevention of corrosion of the materials forming the 
electrolysis cell, it is preferably from 40.degree. C. to 60.degree. C. 
The current density used may lie within a range of 1 mA/cm.sup.2 to 3000 
mA/cm.sup.2 from the viewpoints of efficiency and processing speed, it is 
preferably from 200 mA/cm.sup.2 to 500 mA/cm.sup.2. 
According to this invention, silver ion was added only to the anolyte. The 
source of silver ion used here is preferably silver nitrate as it has a 
high solubility and is most commonly encountered in actual practice. The 
concentration of silver ion added to the anolyte lies within a range of 
0.001 mole/liter to 1 mole/liter, but from the viewpoints of efficiency 
and economic viability, it is preferably from 0.1 mole/liter to 0.5 
mole/liter. 
The concentration of nitric acid in the anolyte used in this invention lies 
within a range of 0.1 mole/liter to 10 mole/liter, but from the viewpoints 
of efficiency and suppression of corrosion of the component materials of 
the apparatus, it is preferably from 2 mole/liter to 4 mole/liter. The 
nitric acid concentration of the catholyte preferably lies within the same 
range as that of the anolyte. 
The decomposition of CMPO according to the method of this invention may be 
performed in an apparatus of which a typical construction is shown in FIG. 
1. First, the CMPO-containing substance is emulsified in an electrolyte by 
an emulsifier in an emulsifying tank 6, and this emulsion is supplied to 
the anode chamber. The emulsification of the CMPO-containing substance 
increases the surface area of CMPO in contact with electrolyte, and 
thereby promotes electrolytic decomposition. However, as sufficient CMPO 
decomposition is not obtained by passing the emulsion through the 
electrolysis cell 1 only once, a batch oxidation method is used wherein 
the anolyte is recirculated through the anode chamber, a constant 
temperature bath 7a and the emulsifying tank 6 by a recirculating pump 3a. 
In this way, electrolysis is performed continuously with the 
CMPO-containing substance constantly in contact with electrolyte. To 
maintain the cathode chamber at the same temperature as that of the anode 
chamber, the catholyte is also recirculated through the cathode chamber 
and a constant temperature bath 7b by a recirculating pump 3b. The current 
supplied to the anode 4 and cathode 5 in the electrolysis cell 1 is 
controlled by a rectifier 8. 
There is no particular limitation on the emulsifier in the emulsifying tank 
6, it being possible to use various types of device known in the art. It 
will be understood that in practice, when CMPO-containing effluent is 
treated by the TRUEX method, the emulsifier used will be manufactured from 
materials conforming to specifications indicating their resistance to 
radioactivity. 
Due to differences in electrolysis conditions, no specific rules can be 
given regarding the amount of CMPO added to the anolyte according to this 
invention, however it is preferable that the amount added is equivalent to 
or less than the amount of electricity passed. According to this 
invention, the oxidation of CMPO does not take place selectively, and in 
practice, the decomposition of CMPO is also accompanied by various 
side-reactions. It is therefore preferable that the amount of CMPO added 
is determined by the electrolysis conditions. 
The apparatus used to decompose CMPO according to this invention is not 
limited to the apparatus shown in FIG. 1, the apparatus shown in FIG. 2 
being one alternative. The same component elements of the CMPO 
decomposition apparatus are assigned the same symbols, and their 
description will not be repeated herebelow. 
In the apparatus shown in FIG. 1, a separate emulsifying tank 6 was 
provided, and the CMPO-containing substance was recirculated between the 
anode chamber and emulsifying tank 6 so that it was supplied to the anode 
chamber while permanently emulsified in the electrolyte. However in the 
apparatus shown in FIG. 2, an ultrasonic homogenizer 9 for example may be 
provided in the anode chamber of the electrolysis tank 1 to constantly 
emulsify the anolyte in the chamber. Examples of such an ultrasonic 
homogenizer are "VP-5S", "VP-15S", VP-30S" and VP-60S" (Commercial name of 
Taitech K. K.) having an ultrasonic frequency of 20 kHz. 
DESCRIPTION OF THE ACTUAL EXAMPLES 
Next, this invention will be described in detail with reference to specific 
examples. The CMPO decomposition apparatus used in the examples has the 
construction shown in FIG. 1. A small-scale experimental CMPO 
decomposition apparatus was manufactured. The specification of the 
electrolysis tank was as follows. 
Electrolysis Cell 
Anode chamber: capacity 100 ml, PTFE 
Cathode chamber: capacity 100 ml, PTFE 
Anode 4: platinum electroplating/coating (platinum electroplated on 
titanium) 
Cathode 5: platinum electroplating/coating (platinum electroplated on 
titanium) 
Membrane 2: perfluorosulfonic acid membrane (commercial name: Nafion 450, 
commercial name of Dupont) 
Gaskets: Gore-tex.RTM. (PTFE) (commercial name of Japan Gore-tex) 
Pipes: PFA 
The emulsifier in the emulsifying tank 6 was a "VIBRO MIXER" (commercial 
name of Reika Kogyo K. K.). The electrolyte was pre-treated at a vibration 
frequency of 70 for an emulsification time of 15 min. 
Examples 1-5 
Batch oxidation was performed varying the CMPO addition amount in an 
electrolysis apparatus having the construction shown in FIG. 1. The 
current density was 500 mA/cm.sup.2, electrolysis time was 3 hours, 
electrolysis temperature was 50.degree. C., anolyte composition was 2M 
nitric acid and 0.5M AgNO.sub.3, catholyte composition was 2M nitric acid, 
anolyte amount was 300 ml and catholyte amount was 300 ml. CMPO was added 
to the electrolyte in the form of a 0.2M solution in decalin. After 
treatment, the amount of phosphoric acid ion in the electrolyte was 
measured, and the decomposition rate of CMPO was calculated. Table 1 shows 
the relation between the CMPO addition amount and CMPO decomposition rate. 
TABLE 1 
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CMPO addition 
CMPO decomposition 
Examples amount (g) rate (%) 
______________________________________ 
1 0.27 60 
2 0.48 63 
3 0.96 67 
4 1.97 53 
5 2.97 32 
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Examples 6-8 
Electrolysis was performed based on the methods described in the aforesaid 
examples 1-5 under the conditions of current density 500 mA/cm.sup.2, 
electrolysis time 3 hours, anolyte 3M nitric acid and 0.5M AgNO.sub.3, 
catholyte 3M nitric acid, anolyte amount 300 ml, catholyte amount 300 ml 
and CMPO addition amount 0.48 g, at different electrolysis temperatures. 
The amount of phosphoric acid ion in the electrolyte was measured. Table 2 
shows the relation between the electrolysis temperature and CMPO 
decomposition rate. 
TABLE 2 
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Electrolysis 
CMPO decomposition 
Examples temperature (.degree. C.) 
rate (%) 
______________________________________ 
6 35 60 
7 50 94 
8 60 79 
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Examples 9-12 
Electrolysis was performed based on the methods described in the aforesaid 
examples 1-5 under the conditions of current density 500 mA/cm.sup.2, 
electrolysis time 3 hours, anolyte silver ion concentration 0.5M, anolyte 
amount 300 ml, catholyte amount 300 ml, CMPO addition amount 0.48 g and 
electrolysis temperature 50.degree. C., at different anolyte and catholyte 
nitric acid concentrations. The amount of phosphoric acid ion in the 
electrolyte was measured. Table 3 shows the relation between the anolyte 
and catholyte nitric acid concentrations, and CMPO decomposition rate. 
TABLE 3 
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Anolyte and catholyte 
nitric acid CMPO decomposition 
Examples concentration (M) 
rate (%) 
______________________________________ 
9 1.8 63 
10 3.0 94 
11 4.0 73 
12 5.0 67 
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Examples 13-19 
Electrolysis was performed based on the methods described in the aforesaid 
Examples 1-5 under the conditions of current density 500 mA/cm.sup.2, 
electrolysis time 3 hours, anolyte nitric acid concentration 3.0M, 
catholyte nitric acid concentration 2.0M, anolyte amount 300 ml, catholyte 
amount 300 ml, CMPO addition amount 0.48 g and electrolysis temperature 
50.degree. C., at different anolyte silver ion concentrations. The amount 
of phosphoric acid ion in the electrolyte was measured. Table 4 shows the 
relation between the anolyte silver ion concentration and CMPO 
decomposition rate. In Example 19, electrolysis was performed under the 
same conditions as those of Examples 13-18 excepting that silver ion was 
not added. 
TABLE 4 
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Anolyte and catholyte 
nitric acid CMPO decomposition 
Examples concentration (M) 
rate (%) 
______________________________________ 
13 0.005 76 
14 0.01 82 
15 0.10 88 
16 0.30 97 
17 0.50 94 
18 0.70 91 
19 0 50 
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Comparative Example 1 
Batch oxidation or processing was performed under the conditions of current 
density 500 mA/cm.sup.2, electrolysis time 3 hours, electrolysis 
temperature 50.degree. C., anolyte composition 2M nitric acid and 0.5M 
AgNO.sub.3, anolyte amount 600 ml and CMPO addition amount 0.48 g, without 
using a membrane. Table 5 shows the CMPO decomposition rate. 
Comparative Example 2 
Electrolyis was performed under the same conditions as those of Example 16 
excepting that an emulsifier was not used. 
TABLE 5 
______________________________________ 
Comparative CMPO decomposition 
Examples rate (%) 
______________________________________ 
1 0 
2 5 
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From the above results, it was found that CMPO can be easily decomposed 
according to the method of this invention. 
It will be understood however that the invention is not to be construed as 
being limited by the above examples. 
Therefore according to this invention, the substance CMPO for which no 
disposal method existed in the prior art can be oxidatively degradated 
safely and efficiently under mild conditions. Moreover, as the oxidation 
products are phosphoric acid ion, carbon dioxide gas and water, the amount 
of highly radioactive waste produced can be reduced.