CA1224415A

CA1224415A - Process for the preparation of a modified aqueous chlorite solution, the solution prepared by this process and the use thereof

Info

Publication number: CA1224415A
Application number: CA000461618A
Authority: CA
Inventors: Peter Berger
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-08-23
Filing date: 1984-08-23
Publication date: 1987-07-21

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the preparation of a stabilized, modified aqueous chlorite solution containing a peroxy compound for use as a biocide is disclosed. The invention overcomes the problems of stability and reduces the cost of equipment necessary in chlorinating drinking and swimming pool water. In addition, a long storage period is possible without a reduction in oxidative action of the solution. Minimal quantities of this chlorite solution, with associated cost savings, can be used to efficiently treat water. The biocidal properties of the solution are effect-ive in treating skin diseases, when used in a bath medium.

Description

~22~5 2~835-10 The invention relates -to a process for the preparation of a stabilized, modified, aqueous chlorite solution with a content oE a peroxy compound, the chlorite solution obtained by this p~ocess and the multiple possible uses thereof as a biocide.
Modified, aqueous, chlorite solutions, particularly aqueous sodium chlorite solutions stabilized by means of peroxy compounds have a large number of different uses in technology and in other fields, such as e.g. for oxidative purposes. Such solu~
tions are inter alia used for the treatment of water to be used as drinking water, as well as swimming pool water and water for industrial use for disinfection purposes.
The stability thereof is not adequate. Therefore, num-erous attempts have been made to obviate this shortcoming. It is generally known to use alkaline stabilizing agents, such as e.g.
sodium carbonate, as well as hydrogen peroxide and inorganic compounds derived therefrom, such as e.g. perborates.
It is also known that aqueous chlorite solutions, in which chlorine dioxide is in equilibrium with chloric acid in the acid range, can be stabilized by means of pyridine tof Holleman/Wiberg "Lehrbuch der anorganischen Chemie", 47-56 edition, 1960, p.l27). The stabilized chlorite solution prepared in this way is also not sufficiently stable. Moreover, pyridine-stabilized chlorite solutions cannot be used in systems, where an additional loading with an organic substance is to be avoided, such as e.g.
in drinking water and swimmlng pool water treatment~ In addition, pyridine is a carcinogenic substance.
Stabilized and even unstabilized chlorite solutions play a particular part in the treatment of swimming pool water. Conven-~Z~4~

tional, also stabilized chlorite solutions, must underqo an acid reaction course at a PH-value C3 in such a "chlorine/chlorine dioxic~e ~rocess". For this PurPose, it is necessar~ to use sPecial e~uiPment, which is not directl~ inteqrated into the water cycle.
This a~Plies both to acid Process and to the hYPochlorous acid process, which are subordinate to the aforementioned chlorine/
chlorine dioxide process. If sodium chlorite and hydrochloric acid are used, then sodium chloride and chlorine dioxide are formed in a "hydrochloric acid process" at pH ~3. For the purposes of this reaction, reaction towers with Raschig rings are recommended in a size guaranteeing a corresponding reaction time, in order to obtain a very high conversion rate. This is also intended to ensure that on introducing the reaction product, the residual chlorite content in the swimming pool water is as low as possible, particularly max. 0.1 mg/l. To prevent a redisproportioning to chlorite-chlorate, the chlorine to chlorine dioxide ratio in the swimming pool water is fixed at 10:1. In the aforementioned hypochlorous acid process, the reactions take place in the follow-ing way. For example, a sodium chlorite solution and chlorine are metered into a water tank upstream of the water disinfection process. A reaction then takes place at a pH-value of C3, in which hypochlorous acid is formed as an intermediate stage and finally chlorine dioxide. The thus prepared solution is then metered into the pool water as required.
In both the aforementioned processes (acid process and hypochlorous acid process), high expenditure on equipment is neces-sary and it must also be constantly ensured that in the acid process the hydrochloric acid supply is absolutely ensured and in the hypo-~ZZ~5 chlorous acid process that the chlorine supply is absolutelyensured, in order to avoid a disadvantageous metering of unreacted chlorite into the pool water. However, as occasionally deficienc-ies cannot be reliably prevented, this always constitu-tes a risk for the bather. In addition, the accidental mixing of commercial chlorite solutions with acids leads to explosive phenomena.
Disclosure of the Invention The invention seeks to improve the aforementioned pro-cesses, and to provide a more stable process product, which can be safely and more reliably used for the treatment of water, partic-ularly swi~ing pool water.
According to the invention, a process for the preparationof a weak acid aqueous solution of a peroxy compound which is sub-stantially stable therein is provided. Into this solution is metered an aqueous solution of a chlorite until the pH-value of 7 is exceeded, accompanied by the formation of a greenish solution.
The invention also provides a stabilized chlorite solution obtained by the acid process.
Thus, according to the invention, in order to stabilize the chlorite in the aqueous solution, peroxy compounds are used which stabilize on a long-term basis the oxidation system bas~d on the chlorite whilst retaining the sought oxidative activity. The term "peroxy compounds" is defined in its widest sense and covers hydrogen peroxide (H~02), as well as hydrogen peroxide derivatives, particularly peroxy compounds (preferably in the form of inorganic compounds), which contain the ion 2 as a ligand, or in which -0-is replaced by -0-0-, peroxides and peracids. The peroxy compounds more particularly include inorganic peroxy acids, together with ~2;~4~5 their salts. Preference is given to the usè here of perborates, percarbonates and persulphates. The peracids usable include not only the aEorementioned peroxy acids, but also oxy acids of the perchloric acid type, including their salts. The said salts are preferably alkali metal and alkaline ear~h salts, with particular reference to the corresponding sodium, potassium and calcium com-pounds. The stabilization by peroxides preferably takes place by barium or sodium peroxide.
In the case where the stabilized, modified chlorite solu-tion is used in systems where additionally introduced, organic sub-stances are unobjectionable, the aforementioned peroxy compounds can also be organic. One can readily determine the appropriate concentration oE the stabilizing peroxy compound. It is surprising that preferably relatively small peroxy compound concentrations are adequate for the purposes of the invention and when using the stab-ilized products, particularly favourable effects are obtained. In a preferred embodiment the stabilization is effective with a 0.001 to 0.01 molar concentration of the peroxy compound in the greenish finished solution. It is possible to increase or decrease this range, as a function of the particular aqueous system, the selected starting materials and the field of use, e.g. by a decimal point.
Higher concentrations regularly often have no advantages and freq-uently exclude the sought effects. Moreover, the small stabilizingperoxy compound quantity required by the invention results in sub-stantially no cost increase.
In the process according to the invention, a suitable stabilizing peroxy compound is converted into a weak acid solution.
This solution preferably has a pH value of C3, whilst Cl is partic-~L~Z49~1S

ularly advantageous. In the la-tter preferred ran~e, there is both an optimum performance of the process, and a well-stabilized product.
~cidiication can take place by means of mineral acids such as hyd-rochloric acid, sulphuric acid, etc. as well as by adding hydrogen compounds, i.e. acid, organic salts, particularly alkali metal or alkaline earth salts, or in the form of a combination oF the above compounds. Preference is given to sodium, potassium and calcium salts, particularly in the form of their hydrogen sulphates.
When selecting the acidifying compounds, the end use of the product must be considered. It is particularly advantageous for acidification to take place with sulphuric acid~ In connec-tion with the other uses o~ the product, it has been found that sulphate ions, are particularly favourable. For example, it is possible to add a sulphate and carry out acidification with another acid. Fundamentally, it is possible to use hydrochloric acid.
However, compared with the use of sulphuric acid, there are certain disadvantages. Despite the described in-teraction with chlorite, excessive chloride quantities prematurely result in the formation of chlorine dioxide. This disturbs -the desired equilibrium system, accompanied by gassing out and consequently require chlor-ine dioxide removal. This leads to an undesired weakening of thesystem in the sense of the invention.
Into the weak acid aqueous solution of the peroxy com-pound is metered an aqueous chlorite solution. Its concentration is not decisive. Thus, a commercial aqueous alkali metal and/or alkaline earth chlorite solution can be used, particularly a sod-ium and/or calcium chlorite solution. The pH value of the commer-cial alkali metal chlorite solution is generally above 12.

~22~5 Solutions of this type regularly contain approximately 300 g/l.
However, it is possible to drop below this value. Since often a stron~ concentrated, stabilized and modified chlorite solution is sought, one can use a strong, concen-tration chlorite solution as the starting material. The metering in of the startiny chlorite solution preferably takes place with stirring until the original partly gassing, dark brown solution has assumed a greenish yellow or greenish shade. This is generally the case when the pH-value is above 7. Preference is given to a p~-value of approximately 7 to 8 and particularly 7.5 to 8.
It has surprisingly been found that in the process accor-ding to the invention, the peroxy compound quantity can be reduced greatly if small quantity of a water-soluble phosphate, e.g. sod-ium metapolyphosphate is incorporated into the finished solution.
An excessive reaction in the form of explosIve phenomena can occur if the aqueous starting solutions used have only a limit-ed carbonate hardness, or when demineraliæed water is involved.
In such cases, it is advisable to work under an inert gas atmos-phere. Preferably, prior to -the metering in of the chlorite solu-tion, an adequate small quantity of a hydrogen carbonatel e.gO
sodium hydrogen carbonate, is metered into the acid aqueous solu-tion. In the case of aqueous starting solutions with an average or high carbonate hardness, such a measure is not generally neces-sary, because a type of inert gas layer of carbon dioxide is formed bet.ween the slightly gassing chlorine dioxide and the air.
Thus, no explosive air/chlorine dioxide mixture can form. In the case of an air to chlorine dioxide ratio of approximately 10:1, such a mixture tends towards an explosive decomposition of the chlo.rine dioxide .into chlorine and oxygen.
The stabilized modified chlorite solution according to the invention has an extremely favourable storage period of sever-al months, without there being any significant reduction to the desired oxidative action. After some time, there is a yellow-brown colouring as a result of the proportionately released chlor-ine dioxide, however, this does not significantly impair the des-ired activity. I the released chlorine dioxide proportion is removed from the aqueous solu-tion, e.g. by extraction by shaking, then after a short time the desired greenish colouring of the clear aqueous solution reappears. In the sense of an equilibrium react-ion, the chlorite solution always re-forms chlorine dioxide during the removal thereof. This occurs with high dilution, also e.g.
when the chlorine dioxide formed has used up its oxidative action through the influence of reducing suhstances, particularly organic substances.
Unlike the conventional prior art chlorite solutions, the stabilized modified chlorite solution according to the invention, has a positive redox potential between approximately 450 and 500 mV, as a function of the light action. It is important for the subsequent action, as well as for the action ranges.des.cribed hereinafter that a stabilizing effect is obtained with a minimum, controllable ~uantity of a peroxy compound. As the stabilizing action of peroxy compounds with respect to chlorine dioxide or chlorite solutions is highly p~ dependent according to the known procedure, a relatively large amount of peroxy compound must be ~2~

added to an acid chloride dioxide solution to be stabilized. This also applies for stabilization in the alkaline range. In this case, larye peroxy compound excesses must be added, because this compound decomposes strongly in the alkaline range. Following pII-reduction, it is no longer possible to establish what peroxy proportions are still present in the finished solution. In prin-ciple, larger peroxy compound proportions lead to an unacceptable interEerence to the subsequent use of the two last-described, prior art chlorite solutions in the aforementioned use ranges. In addit-ition, a chlorite solution in specific use ranges should be approx-imately pH-neutral which is not possible in the aforementioned prior art solutions. The technological background will be clearer in subsequent comments with respect to the prior art.
For example, the following procedure is used in the process of the invention. A very small quantity of a peroxy comp-ound is added to an acid (particularly sulphuric acid) solution, whose pH-value is preferably ~1, so that there is an approximately 0.0022 mol peroxy compound concentration in the finished chlorite solution. This finished solution contains approximately lOOg of chlorine dioxide per litre. In order to stabilize such a chlorine dioxide quantity with minimum amounts of peroxy compounds in the pH-range of 7 to 8, the following procedure is adopted. Approxi-mately 6 kg of a bubbled sodium hydrogen sulphate is incorporated, accompanied by stirring, into approximately 200 litres of tap water with a carbonate hardness of 18. Appxoximately 100 ml of a 30% H202 solution is added to the aforementioned solution. After stirring for roughly 10 minutes, 200 litres of an approximately 30% sodium chlorite solution is added to the aforementioned solu-:~2~g~1~

tion over a period of approximately 10 minutes until the neutralpoint is reached. In this strong acid phase, the small peroxy compo~md quantity is adequate to keep the small chlorine dioxide proportion stable. As the p~I-value rises the stabilizing nature of the peroxy compound with respect to chlorine dioxide increases;
thus, the processes take place in accordance with a self-controlling equivalent. Possibly a complex compound of chlorine dioxide forms where, unlike in other known processes, the peroxy compound does not act in the chemical reaction mechanism (such as e.g. in accor-dance with the equation 2 C102 + 2 HO + H202~2 C102 + 2 H20 -~

2) On reaching a pH-value of approximately 7, the previously dark brown solution changes to lime green and has an oxidation potential of approximately 300 m~. If this solution is exposed to direct or indirect daylight for 24 hours, after a certain time a so-called kick reaction occurs and the solution assumes a golden yellow colour. This is linked with a potential jump to approxi-mately +450 to 550 mV.
If the solution prepared in the aforementioned manner is now treated with carbon tetrachloride, the free chlorine dioxide proportion is consequently extracted by shaking, which means that the free chlorine dioxide passes into the carbon tetrachloride phase, accompanied by yellow colouring, whilst the aqueous phase is pale. However, after a short time, chlorine dioxide is reintro-duced into the remaining aqueous phase (yellow colouring). This procedure can be repeated until the aqueous phase is exhausted.
If the stabilized chlorite solution is added to warm water, there is a slight ozone odour, apart from the typical chlorine-like odour.

~2Z~

If the solution is highly diluted with water, then the equi:librium thereof is displaced in the direction of the chlorine dioxide, which still applies in the pH-range of approximately 7 to ~.5.
If the stabilized, modified chlorite solution is used, then the desired action of the neutral or weak alkaline solution by acidification or accompanied by the action of a random reactant, e.g~ chlorine, accompanied by the release of chlorine dioxide, ta~es place in such a way that under normal conditions a yellowish-reddish gas is provided. Due to the presence of chlorine, particu-larly with an elevated chloride proportion, or mineral acids in atreated aqueous system, the chlorine dioxide formation reaction takes place more readily than the undesired chlorate reaction. The desired reaction sequence is not disturbed, even on adding strong mineral acids in high concentration. This is not the case wi-th the known chlorite solutions. Under the action of strong mineral acids, the prior art solutions still exhibit the aforementioned explosive phenomena.
There are cases where the chlorite solution is subject to destabilization, in that the system to be treated contains a react-ant for the peroxy compound present in small quantikies and reducesthe latter and consequently eliminates the stabilization of the chlorite solution. Such a reactant can for example be the peroxi-dases and catalases present in germ cells, i.e. enzymes of the animal and vegetable metabolism belonging to the group of peroxi-doreductases. The action thereof leads -to the spontaneous release of chlorine dioxide. As a result~ the stabilized, modiried chlor-ite solution gives high selectivity when used biocidally in small quantitiesO
The chlorite solution particularly in the form of a sod-ium chlorite solution can be used advantageously in water treat-me.nt, i.e. the treatment of drinking water, water for industrial use and swimmin~ pool water for disinfecting purposes. This disin-Eection preferably takes place accompanied by the simultaneous use of chlorine, so that chlorine dioxide, which is highly effective for disinfection purposes, is formed. For example, a sodium chlor-ite solution with approximately 300g of sodium chlorite per litre is used Eor preparing the chlorite solution. The finished solut-ion generally contains 8 to 15% by weight of chlorine dioxide, therange 10 to 12% by weight being par-ticularly advantageous. It is also possible to add to this solution various other constituents, such as sodium chloride, sodium sulphate and sodium chlorate. The sodium chlorite solution can be adjusted by dilution, such that it satisfies the KOK (coordination committee for swimming pool con-struction and operation) guidelines, which stipulate a residual chlorite content in swimming pool water of max. 0.3 mg/l of pool water. It also satisfies the DIN draft 19643 of max. 0.1 mg/l.
The above comment also applies to other chlorite solutions, such as other alkali metal and alkaline earth chlorite solutions.
The chlorite solution is particularly advantageous in the treatment of swimming pool water, as will be described in greater detail hereinafter.
The explosive phenomena referred to hereinbefore in connection with known processes are eliminated when the chlorite solution of the present invention is used. Even on mixing with concentrated sulphuric acid, an explosion cannot occur. Its ~Z4~5 particular suitability for the treatment or conditioning of swim-mincJ pool water has been proved by an expert opinion of the Gelsenkirchen Institute of Hygiene. In connection with an equiv-alence proof, ik was found that the chlorite solution of the pres-ent invention behaves quite differently ~o commerclal chlorite solu-tions or solutions stabilized in some other way. In the tests perormed by the Institute of ~Iygiene, the solution of the present invention was metered by means of a fine metering pump via an inoc-ulation point between the flocculation inoculation point and the filter directly into the pool water circuit (pH-value of 7.5). All the water samples taken revealed chlorine dioxide, but not the chlo-rite (C10 2) to be avoided. Even very small amounts of peroxy com-pounds have a disturbing action in chlorinated pool water. With respect to st~ong oxidizing agents, such as chlorine, peroxide~
assume a reductive character. Thus, they considerably reduce the oxidation potential in swimming pool water, lessening the germ kil-ling rate. Nowadays, in many swimming pools, the addition of disin-fectant is automatically controlled via this parameter. In the case of an artificial change (reduction) of the oxidation potential, vast quantities of e.g. chlorine were passed uncontrolled into the pool water. This risk is largely eliminated by the use of the chlorite solution of the present invention. The small peroxy comp-ound quantities introduced into the pool circuit can be eliminated by e.g. finely divided metal impurities on the filter or peroxida-ses occurring in certain germs. As a result of the chlorine diox-ide spontaneously selectively released in this way in contaminated filter material, additional phenomena occur which do not take place in conventional chlorine/chlorine dioxide processes.

~f~44~

The aforementioned equivalence proof revealed that the time between the necessary filter bac]~washes after differential pressure could be doubled or the pool water quantity required for backwashing could be reduced by half. It was also found that the Eilter treated with the solu-tion according to the invention can discharye double the pollutant quantity in half the time. This is possibly due to a better flocculation of the organic/inorganic loading substances and to a prevention of the adhering over of the filter material. This permits an easier, faster discharge of the collected pollutant particle. The chlorite solution according to the invention also prevents strung contamination of highly loaded filters. Thus, in the specifically adjusted manner it acts as a filter aid. Its described use leads to considerable savings in fresh water, waste water, heating and treatment costs. The follow-ing occurred in connection with the Bockum/Hovel, Hamm indoor swim-min~ pool used for the equivalence proof. During the normal treat-ment, flocculation - filtering - chlorination, the necessary amount of fresh water per bather is 0.11 m3, whilst when using the chlorite solution according to the invention on average 0.03m3 of fresh water are required for each bather. Thus, the saving for each bather is 0.08m3.
Thus, the following statements can be made in connection with the use of the chlorite solution for the treatment of swim-ming pool water. This solution can be directly added to the chlor-inated swimming pool water~ chlorine dioxide being directly formed in the pH-range of approximately 7 to 7.8. However, the treatment with the solution preferably ta~es place between the flocculation and the filtering stages. There can e.g. be approximately 24 ml of ~2~4~3~5 a roughly 10% by weight chlorite solution for approximately 180 m3 o circulated swimming pool water. The 100% conversion to chlor-ine dioxide ta]ces place so rapidly -that in the case of crude water-side meteriny, no chlorite but only chlorine dioxide could be detected on the pure waterside. The water quality obtained is superior to that of known processes (acid or hypochlorous acid processes). As shown, the treatment process operating with the agent of the invention is very inexpensive.
The stabilized, modified chlorite solutions of the pres-ent invention have further advan-tageous uses. In particular dil-ute chlorite solutionshavingexcellent biocidal action occurs. Thismore particularly applies to a dilute sodium chlorite solution, preferably with an approximately 0.1 to 0.5% by weight concentra-tion. It can be used for hygienic, disinfecting personal hygiene, e.g. for foot care in swimming pools, saunas, etc. particularly in the treatment of perspiring feet. It is also very suitable in the case of externally treatable skin diseases and irritations, particularly skin eruptions, psoriasis, eczema, lupus, hymenomy-cetes or generally in inflammatory skin diseases, which are caused by bacteria and protozoa, viruses or fungi (candidamycosis, trich-ophytia, pityriasis, herpes, etc.). The agent of the present invention and particularly the sodium chlorite solution can also be used for treating skin diseases in the throat or mouth, such as bleeding of the gums. Thus, these agents are a type of medicine.
In addition, the chlorite solution can be considered a cosmetic, which can be added in small concentra-tions to the bath water when bathing. Certain of the aforementioned uses will be described in greater detail hereinafter.

_ 14 ~2~

In the pharmaceu-tical field, it has been found that the solutlon is highly compatible with the skin. It can even be sup-plied in concentrated form to healthy skin, without allergic reactions being detected. The skin generally acts highly allergi-cally to normal chlorite solutions of the same concentration. It was found that a dilute chlorite solution of the present invention led to surprising improvements in allergy conditions. In dilutions of the concentrated solution to water of 1:10, there was found to be very good antimycotic action. The chlorite solution also proved to be effective in healing severe neurodermititis, which had in part persisted for some years. However, the solution must be highly diluted here, e.g. 20 to 30 ml per bath with a slow increase up to the limit of the compatibility of the particular patient.
A very surprising phenomenon occurs in the treatment of psoriasis. With baths every day or every two days (approximately 100 ml/bath, whilst excluding other additives) the scales were detached in 80% of the patients after the first few baths without any mechanical action. Itching generally rapidly decreased. The raised skin parts became flatter and the dark red colouring turned pale pink. Following a stagnation phase of approximately 2 to 3 months, the previously attacked skin parts normalized. During this treatment the giving off of small ozone quant-ties during bathing (metabolism regulation via the large-area skin contact) possibly aids in the process. Persistent perspiration odours were elimin ated by bathing the body and feet. An other use of the solution is for mouthwashes with a 3% solution. This eliminates bleeding of the gums.

A further surprising action was found during the treat-ment of diabetic gangrene. In one case, a wound as wide as the thumb and about 7 cm long healed on bathing with a dilute sodium chlorite solution (dilution with water in ratio 1:100) following treatment for abou-t 8 weeks.
Finally, chlorite solutions obtainable according to the invention, preferably the sodium chlorite solution, can be used industrially, e.g. in combatting slime in water systems~ This particularly applies to the conservation of drinking water in var-ious containers or tanks, particularly on ships. Such a solution can be used very effectively without application problems. The drinking water treated with the solution according to the invention remained germ-free for several months in closed containers. With the ppm range quan~ities used, there was no deterioration to the taste of the water. There were also no toxicological objections.
The oxidizing effect of the chlorite solutions can be used in other technical fields, e.g. in combination with mineral acids or chlorine. Thus, they can be used in the production of cellulose, the bleaching of oils, fats, waxes and leather and for disinfecting or deodorizing evil-smelling waste and sewage. A
special application is the stagewise b]eaching of pulp.
In conclusion, the stabilized, modified, aqueous chlorite solution can be advantageously used wherever an oxidative action i5 necessary due to the formation of chlorine dioxides. This can be dead matter of organic, particularly reducing substances, as well as living organisms, su~h as microorganisms, fungi and the like.
Thus, the chlorite solution can be considered in the widest sense ~ 16 ~z~ s as a biocidally active agent with absolute skin compatibility, i.e.
it can be used as an insecticide, fungicide, herbicide, etc. where hitherto commercial sodium chlorite solutions have either proved unsuitable or have only had a limited success. A particular advan-tage of the chlorite solution is that it generally permits a 100%
conversion of the chlorite into chlorine dioxide in a wide pH-range, as well as in an alkaline medium. This contrasts with the prior art chlorite solutions which only lead to the desired 100% conver-sion rate to chlorine dioxide in a pH-range of ~ 3. In addition, the solution of the present invention can be very simply prepared, in that e.g. the acid solution (preferably with a pH~value c 1) is mixed with a concentrated, commercial chloride solution in a volume ratio oE approximately 1:1 until a pH-value just above 7 is obtain-ed.
The invention is further illustrated hereinafter by means of an example:
Example 0.5 g of a 30gO by weight hydrogen peroxide solution is added to 1 litre of water (carbonate hardness:18) with a pH-value of ~O~.
0.91 of a commercial sodium chlorite solution (approximately 300 g of sodium chloride/litre) is added to this solution, accompanied by adequate stirring. The solution has a brown colouring and on exceeding the pH-value of 7 and following the stabilization reac-tion changes to a light, lime green colour. A pH-value of approx-imately 7.5 is obtained in the solution, which gives a 100% conver-sion to chlorine dioxide when treating the water of an indoor swimming pool. Conversion ta~es place so quickly that on the pure water side, chlorite was never detected, although small amounts of chlorine dioxide were found. The water quality is significantly improved. The fresh water additlon per bather can be reduced to 20~.
The aqueous solution prepared in the aforementioned man-ner, inter alia has an excellent action in the treatment of psoria-9iS and hymenomycetes when used in a 0.1 to 0.5~ by weight concen-tration.

":

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a stabilized, modified, aqueous chlorite solution with a peroxy compound content, wherein a weak, acid, aqueous solution of a peroxy compound substantially stable therein, is provided; and an amount of an aqueous solution of a chlorite is added thereto until the pH-value of 7 is exceeded, thereby forming a greenish solution.

2. A process according to claim 1 wherein the weak, acid, aqueous solution of a peroxy compound contains sulphate ions.

3. A process according to claim 1 wherein the peroxy compound used is an inorganic peroxy compound in the form of hydrogen peroxide, a persulphate, percarbonate, perborate or a peroxide of an alkali metal or alkaline earth metal.

4. A process according to claim 1, 2 or 3 wherein the peroxy compound is added in a quantity such that it is present in approximately 0.001 to 0.01 molar concentration in the finished greenish solution.

5. A process according to claim 1, 2 or 3 wherein a commercial aqueous solution of an alkali metal and/or alkaline earth chlorite is used.

6. A process according to claim 1, 2 or 3 wherein a weak, acid, aqueous solution with a pH-value of <1 is initially used.

7. A process according to claim 1, 2 or 3 wherein the process is carried out in an inert gas atmosphere when using water with a low carbonate hardness.

8. A process according to claim 1, 2 or 3 wherein a water-soluble phosphate is added.

9. A process for the preparation of a stabilized, modified, aqueous chlorite solution comprising the steps of:
providing an aqueous acid solution having a pH of less than about 3;
adding a peroxy compound to said aqueous acid solution;
and introducing an aqueous chlorite solution into the acid solution to which said peroxy compound has been added, until the pH of said acid solution exceeds 7 and the solution becomes a greenish color.

10. A stabilized, modified chlorite solution prepared accord-ing to the process of claim 1, 2 or 3.

11. A method of treating swimming pool water, and bath water comprising adding a predetermined amount of a chlorite solution prepared by a process according to claim 1, 2 or 3 directly to the water.