SIST EN 12671:2009

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kemikalije, ki se uporabljajo za pripravo pitne vode - Klorov dioksid, proizveden na kraju samemProdukte zur Aufbereitung von Wasser für den menschlichen Gebrauch - Vor Ort erzeugtes ChlordioxidProduits chimiques utilisés pour le traitement de l'eau destinée à la consommation humaine - Dioxyde de chlore obtenu sur siteChemicals used for treatment of water intended for human consumption - Chlorine dioxide generated in situ71.100.80Chemicals for purification of water13.060.20Pitna vodaDrinking waterICS:Ta slovenski standard je istoveten z:EN 12671:2009SIST EN 12671:2009en,fr,de01-maj-2009SIST EN 12671:2009SLOVENSKI
STANDARDSIST EN 12671:20001DGRPHãþD



SIST EN 12671:2009



EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12671January 2009ICS 71.100.80Supersedes EN 12671:2000
English VersionChemicals used for treatment of water intended for humanconsumption - Chlorine dioxide generated in situProduits chimiques utilisés pour le traitement de l'eaudestinée à la consommation humaine - Dioxyde de chloreproduit sur siteProdukte zur Aufbereitung von Wasser für denmenschlichen Gebrauch - Vor Ort erzeugtes ChlordioxidThis European Standard was approved by CEN on 29 November 2008.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre:
Avenue Marnix 17,
B-1000 Brussels© 2009 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12671:2009: ESIST EN 12671:2009



EN 12671:2009 (E) 2 Contents Page Foreword . 3Introduction . 41Scope . 52Normative references . 53Description . 53.1Identification . 53.2Presentation form . 63.3Physical properties . 63.4Chemical properties . 74Purity criteria . 84.1General . 84.2Composition of in-situ generated product . 84.3Impurities and main by-products . 84.4Chemical parameters . 85Test methods . 95.1Sampling . 95.2Determination of chlorine dioxide and chlorite concentrations . 96Labelling - Storage - Distribution system . 126.1Risk and safety labelling according to the EU Directives
...................................................................... 126.2Means of distribution .................................................................................................................................. 136.3Storage, stability .......................................................................................................................................... 14Annex A (informative)
General information on chlorine dioxide . 15A.1Origin . 15A.2Use . 16A.3Spectrometric method for specific determination of CIO2 . 16A.4Determination of chlorite and chlorate ions contents in aqueous chlorine dioxide as produced by the reactors . 19Annex B (normative)
General rules relating to safety. . 21B.1Rules for safe handling and use . 21B.2Emergency procedures . 21Bibliography . 22 SIST EN 12671:2009



EN 12671:2009 (E) 3 Foreword This document (EN 12671:2009) has been prepared by Technical Committee CEN/TC 164 “Water supply”, the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by July 2009, and conflicting national standards shall be withdrawn at the latest by July 2009. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. Significant technical differences between this edition and EN 12671:2000 are as follows: a) deletion of the reference to EU Directive 80/778/EEC of July 15,1980 in order to take into account the latest Directive in force (see [1]); This document supersedes EN 12671:2000. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. SIST EN 12671:2009



EN 12671:2009 (E) 4 Introduction In respect of potential adverse effects on the quality of water intended for human consumption, caused by the product covered by this document: 1) this document provides no information as to whether the product may be used without restriction in any of the Member States of the EU or EFTA; 2) it should be noted that, while awaiting the adoption of verifiable European criteria, existing national regulations concerning the use and/or the characteristics of this product remain in force. NOTE Conformity with this standard does not confer or imply acceptance or approval of the product in any of the Member States of the EU or EFTA. The use of the product covered by this document is subject to regulation or control by National Authorities.
SIST EN 12671:2009



EN 12671:2009 (E) 5 1 Scope This document is applicable to chlorine dioxide generated on site for treatment of water intended for human consumption. It describes the characteristics for chlorine dioxide and specifies the composition and the corresponding test methods for chlorine dioxide. It gives information on its use in water treatment. It also determines the rules relating to safe handling and use of chlorine dioxide generated on site (see Annex B). 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references the latest edition of the referenced document (including any amendments) applies. EN ISO 3696:1995, Water for analytical laboratory use – Specification and test methods (ISO 3696:1987) ISO 3165, Sampling of chemical products for industrial use – Safety in sampling ISO 6206, Chemical products for industrial use – Sampling –Vocabulary 3 Description 3.1 Identification 3.1.1 Chemical name Chlorine dioxide. 3.1.2 Synonym or common name None. 3.1.3 Relative molecular mass 67,46 3.1.4 Empirical formula ClO2 3.1.5 Chemical formula OClO__KK (resonance structure) 3.1.6 CAS Registry Number 1) 10 049 - 04-4
1) Chemical Abstracts Service Registry Number. SIST EN 12671:2009



EN 12671:2009 (E) 6
3.1.7 EINECS reference 2) 233 – 162 - 8 3.2 Presentation form For water treatment, chlorine dioxide is generated in situ as an aqueous solution on or near the site of use and transferred to the site of use. 3.3 Physical properties 3.3.1 Appearance The pure product is an orange gas or liquid, which forms a yellow solution in water. NOTE If the solution becomes red-brown, it is sign of decomposition. 3.3.2 Density Gas: 3,09 g/l, (2,4 g/l relative, air = 1) at 273 K and 101,3 kPa 3). Liquid: 1,64 g/ml at 20 °C. 3.3.3 Solubility in water In Table 1 the solubility values (S) for chlorine dioxide are given in grams per m³ water at a pressure of 101,3 kPa for different temperatures 1: Table 1 –Solubility values Temperature of water °C S value : gasg/mOHg/m323 0 70 ± 0,7 5 (60,3) 10 (53,7) 15 45 20 (42,7) 25 (33) 30 (30,1) 35 26,5 ± 0,8 NOTE 1 S is a ratio, not an absolute value of concentration. NOTE 2 The S values are directly measured values except those in brackets which are extrapolated data. 3.3.4 Vapour pressure The vapour pressure of pure chlorine dioxide as a function of temperature is given in Table 2.
2) European Inventory of Existing Commercial Chemical Substances. 3 ) 100 kPa = 1 bar SIST EN 12671:2009



EN 12671:2009 (E) 7 Table 2 –Vapour pressure of pure chlorine dioxide Temperature [C°] Vapour pressure [kPa]
0 82,3
5 90,4
10 98,8
11 100,5
20 116,5 (extrapolated) 25 125,8 (extrapolated) 30 135,3 (extrapolated) 35 145,1 (extrapolated) 40 155,0 (extrapolated) 3.3.5 Boiling point at 101,3 kPa 4) 11 °C (for pure chlorine dioxide). 3.3.6 Crystallisation point - 59 °C (for pure chlorine dioxide). 3.3.7 Specific heat The specific heat of solutions of chlorine dioxide is very similar to that of pure water. 3.3.8 Viscosity (dynamic) The dynamic viscosity of solutions of chlorine dioxide is very similar to that of pure water. 3.3.9 Critical temperature 153 °C (for pure chlorine dioxide). 3.3.10 Critical pressure Not applicable. 3.3.11 Physical hardness Not applicable. 3.3.12 Dissolution heat The heat of the dissolution in water is – 26,8 kJ/mol (exothermic). 3.4 Chemical properties Chlorine dioxide is a molecule containing an unpaired electron and has the characteristics of a "molecule-free-radical". Relevant Redox potentials of chlorine dioxide and related molecules are (Eo values at 25 °C in volts):
4) 100 kPa = 1 bar SIST EN 12671:2009



EN 12671:2009 (E) 8 HCIO2 + 3H+ + 4e- ⇒ CI- + 2H2O 1,57 CIO2 (dissolved gas) + 1e- ⇒ CIO2- 1,15 CIO3- + 1e- + 2H+ ⇒ ClO2 + H2O 1,15 ClO2 (dissolved liquid) + 1e- ⇒ CIO2- 0,95 CIO2- + 4e-+ 4 H+ ⇒ CI- + 2H2O 0,78 4 Purity criteria 4.1 General This European Standard specifies the minimum purity requirements for chlorine dioxide generated in situ used for the treatment of water intended for human consumption. Limits are given for impurities commonly present in the product. Depending on the raw material and the manufacturing process, other impurities may be present and, if so, this shall be notified to the user and when necessary to relevant authorities. NOTE Users of this product should check the national regulations in order to clarify whether it is of appropriate purity for treatment of water intended for human consumption, taking into account raw water quality, required dosage, contents of other impurities and additives used in the product not stated in this product standard. Limits have been given for impurities and chemical parameters where these are likely to be present in significant quantities from the current production process and raw materials. If the production process or raw materials lead to significant quantities of impurities, by-products or additives being present, this shall be notified to the user. 4.2 Composition of in-situ generated product Chlorine dioxide (ClO2) is produced as aqueous solution on or near the site of use. For safety reasons the aqueous ClO2-solution without intermediate storage in a storage tank (i.e. without headspace) may not exceed a concentration of 20 g/l.
The concentration of the aqueous ClO2 solution with intermediate storage in a storage tank (i.e. with headspace) should not exceed a concentration of 3 g/l, to ensure an adequate distance to the explosion limit (see B.1). 4.3 Impurities and main by-products Impurities and main by-products of the starting products used for the generation (indicated in A.1.1) can be found in the in situ generated product in respective proportional concentrations.
Inadequate design, operation and maintenance of reactors can give rise to the formation of chlorine and traces of chlorate ion and, eventually, the presence of unreacted chlorite, chlorate and/or chlorine (see [5]); for analysis see 5.2 and A.4. 4.4 Chemical parameters Limits of chemical parameters being potentially present in chlorine dioxide solution have been specified in the corresponding EN standards of the starting products (indicated in A.1.1). SIST EN 12671:2009



EN 12671:2009 (E) 9 5 Test methods 5.1 Sampling Sampling of chlorine dioxide solutions shall avoid photochemical decompositions, losses by evaporation of the product and consumption by the glassware and dilution water. Samples shall be taken at the exit of the reactor or from the storage tank with a sampling tube and the analytical procedures started as fast as possible. In order to achieve these objectives the following step by step procedure shall be adopted:  sampling shall be made in accordance with the general requirements given in ISO 3165 and take into account ISO 6206;  all glassware is to be conditioned immediately before sampling, with the solution under investigation and this preliminary rinsing sample is to be discarded;  liquid samples for analytical control shall be introduced directly into the analytical reagent solutions; the sampling device and procedure shall take care that the sample is directly contacted with the analytical reagent without running along the walls of the analytical glassware;  the sample vessels shall be stoppered leaving no -or only a little- a head-space, to store the sample with reagent mixture;  at high concentration of chlorine dioxide (>10 g/l) the samples shall be collected in a vessel, containing water; the analytical result shall be corrected accordingly for the dilution factor;  titration analysis shall best be carried out immediately after sampling plus reaction;  if immediate titration or measurement is not possible, prior to the analytical measurements the sample plus reagent shall be stored in the dark at low temperature about 5° C and contact with ambient air shall be avoided;  if immediate collection and analysis are not possible, sample the reactor effluent in a 250 ml conical flask stored on crushed ice and, by introducing the liquid at the bottom of the flask and fill the flask completely allowing overflow of chlorine dioxide solution. The volume of the samples shall be adjusted in accordance with the analytical procedure described hereafter. 5.2 Determination of chlorine dioxide and chlorite concentrations 5.2.1 General This standard method concerns the determination of chlorine dioxide and chlorite concentrations in stored solution.
NOTE Other oxidizing agents could interfere with the determination. 5.2.2 Principle 5.2.2.1 General Phosphate-buffered iodide is first reacted with the chlorine dioxide sample and titrated at pH 7,2 and subsequently acidified to pH 2 and titration is continued. 5.2.2.2 With iodometry at pH 7,2 ClO2 + l- ⇒ ClO2- +1/2 l2 (1) SIST EN 12671:2009



EN 12671:2009 (E) 10 and Cl2 + 2 l- ⇒ l2 + 2Cl- (2) 5.2.2.3 Subsequent iodometry at pH 2 ClO2- + 4 I- + 4 H+ ⇒ Cl- + 2 H2O + 2 I2 (3) The ratio of equivalents titrated at pH 7,2 and pH 2 shall be 1 to 4 within a deviation of less than 3 % and indicate at least 97 % of the expected yield. If not appropriate, adjustments and an additional control as given in 5.2.2.4 can be made, and more selective controls made occasionally according to the methods described in A.3 and A.4. 5.2.2.4 Chlorite determination Determination of chlorite concentration after degassing of a separate sample followed by iodometry at pH 2 (reaction is as in 5.2.2.3 and measure only the chlorite concentration of the sample). The degassing procedure is given in A.4.1. 5.2.3 Reagents All reagents shall be of a recognized analytical grade and the water used shall conform to grade 3 in accordance with EN ISO 3696:1995. 5.2.3.1 Sodium thiosulfate standard volumetric solution c(Na2S2O3) = 0,1 mol/l. 5.2.3.2 Phosphate buffer of pH = 7,2
Dissolve in 1l of water, 28,2 g of sodium dihydrogen phosphate (NaH2PO4 . 2H2O) and 100 g monohydrogen phosphate (Na2HPO4 . 12H2O). NOTE If necessary, precise adjustment of the pH value can be done with aliquots of sodium hydroxide (NaOH) or phosphoric acid (H3PO4). 5.2.3.3 Sulfuric acid c(H2SO4) = 6 mol/l. 5.2.3.4 Potassium iodate (KlO3) powdered. 5.2.3.5 Hydrochloric acid standard volumetric solution c(HCl) = 0,1 mol/l or sulfuric acid c(H2SO4) = 0,5 mol/l. 5.2.3.6 Potassium iodide, (Kl) crystalline. 5.2.3.7 Zinc iodide (ZnI2)-starch indicator. Disperse 4 g starch into a small quantity of water. Add the dispersion to a solution of 20 g zinc chloride (ZnCl2) in 100 ml of water. The solution is boiled until the volume has been reduced to 100 ml and finally diluted to 1 l while adding 2 g of ZnI2. NOTE An alternative starch indicator is soluble starch 5 g + ZnCl2 4 g + salicylic acid 1,25 g; disperse the starch in a small volume of water. Dissolve ZnCl2 and salicylic acid in 500 ml water, boil and, while boiling, add the starch dispersion. Continue boiling for 5 min and finally dilute to 1 l. 5.2.3.8 Standardization of sodium thiosulfate solution 5.2.3.8.1 Reactions 5KI + 5H+ ⇒ 5Hl + 5K+
(4) SIST EN 12671:2009



EN 12671:2009 (E) 11 KlO3 + H+ ⇒ HlO3 + K+ (5) HlO3 + 5Hl ⇒ 3I2 + 3H2O (6) 3I2 + 6S2O32- ⇒ 6I- + 3S4O62- (7) 5.2.3.8.2 Determination Add 0,05 g of potassium iodate (5.2.3.4), 0,5 g of potassium iodide (5.2.3.6) into 50 ml water and a further 50 ml water in a conical flask. After mixing, add 10 ml acid standard volumetric solution (5.2.3.5). Titrate the liberated iodine immediately with the sodium thiosulfate solution (5.2.3.2) until the solution is pale yellow.
Add 0,5 ml of starch indicator (5.2.3.7) and titrate to the end point, i.e. the disappearance of the blue-black colour. Record the volume Vt of the sodium thiosulfate solution added. 5.2.3.8.3 Calculation The concentration, ct, expressed in moles per litre, of the sodium thiosulfate solution is given by the following equation: tatVVcc×= (8) where ca is the concentration, in moles per litre, of the acid (5.2.3.5); V is the volume, in millilitres, of the acid (5.2.3.5); Vt is the volume, in millilitres, of the sodium thiosulfate solution used. 5.2.4 Apparatus Ordinary laboratory apparatus:  all glassware shall be dark brown to protect against photodecomposition;  wash all glassware with a dilute solution (approximately 1 g/l) of chlorine dioxide and rinse with water; the glassware used for the determinations of chlorine dioxide and related oxidants shall be reserved for this specific use and kept maintained separately. 5.2.5 Procedure Prepare sets of three conical flasks of 250 ml immediately before the sampling: take 80 ml of water, followed by 20 ml buffer solution (5.2.3.2) and approximately 1 g of potassium iodide (5.2.3.6). Use immediately or keep in the dark if immediate use is not possible. Introduce a volume (Vs) of chlorine dioxide solution which (presumably) contains between 3 mg and 10 mg of ClO2. Titration of sample under conditions of 5.2.2.2 gives a volume V1 of the sodium thiosulfate standard volumetric solution (5.2.3.1). After this first titration add 5 ml of the sulfuric acid (5.2.3.3) and after shaking the titration is continued to give an additional volume V2 of the sodium thiosulfate standard volumetric solution (5.2.3.1).
SIST EN 12671:2009



EN 12671:2009 (E) 12 5.2.6 Expression of results 5.2.6.1 Calculation The concentration of chlorine dioxide (Cs) expressed in milligrams per litre is given by the following equation: sV
,
c) V(V Cs
××××+=5000156721 (9) where V1 is the volume in millilitres, of the sodium thiosulfate standard volumetric solution (5.2.3.1) used for the titration at pH 7,2; V2 is the volume in millilitres, of the sodium thiosulfate standard volumetric solution (5.2.3.1) used for the titration at pH 2; Vs is the volume in millilitres, of the test portion of chlorine dioxide; c is the actual concentration, expressed in moles per litre, of the sodium thiosulfate standard volumetric solution (5.2.3.1). It is first to be verified that 4 x V1 = V2 with acceptable accuracy of 3 %. If not, the results are rejected and the whole procedure shall be repeated, and/or, action shall be taken as indicated in 5.2.2. 5.2.6.2 Precision Repeatability: 20 mg/l. 6 Labelling - Storage - Distribution system 6.1 Risk and safety labelling according to the EU Directives 5) Labelling requirements in Table 3 shall apply to chlorine dioxide solution at the date of publication of this document.
5 ) See [2]. SIST EN 12671:2009



EN 12671:2009 (E) 13 Table 3 – Risk and safety labelling Water solutions 2,5 % <= C < 3 %0,3 % <= C < 2,5 %Symbols and indications of danger Xi - Irritant N - Dangerous for the environment Xi - Irritant
Nature of special risks R36 - Irritating to eyes R50 - Very toxic to aquatic organisms R36 - Irritating to eyes
Safety advice S1/2 - Keep locked up and out of reach of children. S23 - Do not breathe fumes/vapours. S26 - In case of contact with eyes,rinse immediately with plenty of water and seek medical advice. S28 - After contact with skin, wash immediately with plenty of water. S36/37/39 - Wear suitable protective clothing, gloves and eye/face protection. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible). S61 - Avoid release to the environment. Refer to special instructions/Safety data sheets. S1/2 - Keep locked up and out of reach of children. S23 - Do not breathe fumes/vapours. S26 - In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S28 - After contact with skin, wash immediately with plenty of water. S36/37/39 - Wear suitable protective clothing, gloves and eye/face protection. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).
WARNING! – Even solutions of chlorine dioxide at concentrations < 0,3 % can cause harmful gas emissions. Therefore safety measures have to be followed accordingly (see Annex B).
NOTE Annex I of the Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances and its amendments and adaptations in the European Union contains a list of substances classified by the EU. Substances not in this Annex I should be classified on the basis of their intrinsic properties according to the criteria in the Directive by the person responsible for the marketing of the substance. 6.2 Means of distribution For local short time storage of diluted solutions (e.g. less than 3 g/l, for less than 30 min, at pH value in the range of 2,0 to 5,5 in operational conditions) and, also for generating equipment, appropriate materials are: dark brown glass and borosilicate glassware, polyvinylchlorid (PVC), cross-linked HD-polyethylene, polyfluorocarbons. "Chromium steels" and stainless steels are less suited for contact with chlorine dioxide. Rubber and general plastics materials shall be proven specifically for resistance to chlorine dioxide. SIST EN 12671:2009



EN 12671:2009 (E) 14 6.3 Storage, stability In aqueous solution, at dilutions between 0,5 g/l and 2 g/l, when stored in the dark, chlorine dioxide is stable for several hours. Exposure to direct sunlight and heat shall be avoided. It is generally recommended to limit the local storage to less than 30 min. SIST EN 12671:2009



EN 12671:2009 (E) 15 Annex A
(informative)
General information on chlorine dioxide A.1 Origin A.1.1 Raw materials Chlorine dioxide is produced from raw materials which fulfil the requirements as specified by the following standards:  Chlorine for water treatment: EN 937;  Sodium hypochlorite for water treatment: EN 901;  Hydrochloric acid for water treatment: EN 939;  Sulfuric acid for water treatment: EN 899;  Sodium chlorite for water treatment: EN 938;  Sodium peroxodisulfate for water treatment: EN 12926;  Potassium peroxomonosulfate for water treatment: EN 12678;  Sodium chlorate for water treatment: EN 15028;  Hydrogen Peroxide for water treatment: EN 902. A.1.2 Manufacturing process Numerous reactions to produce chlorine dioxide have been described and operated. For the scale of production required for water treatment, the main reactions are: NaClO3
+
½ H2SO4
+
½ H2O2
⇒
ClO2
+
½ O2
+
½ Na2SO4
+
H2O (A.1)
2 NaClO2 + Cl2 ⇒ 2 ClO2 + 2 NaCl (A.2) NOTE 1 Acidified hypochlorite can be used as an alternative source of chlorine. and 5 NaClO2 + 4 HCl ⇒ 4 ClO2 + 5 NaCl + 2H2O (A.3) an alternative reaction is: 2 NaClO2 + Na2S2O8 ⇒ 2ClO2 + 2 Na2SO4 (A.4) All reactions are operated under controlled conditions and concentrations with process water in closed reactors. Present available reactor designs according to the stoichiometry given above enable to produce chlorine dioxide solutions with a yield of 90 % and higher. Residual impurities are traces of chlorate for reaction (A.1) and chlorine SIST EN 12671:2009



EN 12671:2009 (E) 16 and chlorite for reactions (A.2-A.4). The formation of chlorate for reactions (A.2)-(A.4) is avoided by adequate reactor design, operating and pH control. More details are given in [4] and [5]. A.2 Use A.2.1 Function Chlorine dioxide is widely used in water treatment for oxidation and disinfection purpose, particularly post-disinfection giving an active residual concentration (see [3], [4], [5], [8], [9] and [10]). In water treatment the reactions of chlorine dioxide are most often initiated by a free radical addition mechanism on the electrophylic site of the target molecule followed by transpositions and complementary oxidation reactions. Most encountered reaction products are carboxylic acids and transiently aldehydes, ketones and quinones. Part of the chlorine dioxide that is consumed is transformed into chlorite, i.e. between 40 % and 80 %, depending on the quality of the water. A.2.2 Form in which it is used
Chlorine dioxide is generated as an aqueous solution. Working solutions concentrations are typically in the range of 0, 5 g/l to 2 g/l ClO2 preferably less than 1 g/l. The pH value of the working solutions should be in the range of 2-4 for reactions (A.1) and pH 5,5-8,0 for reactions (A.2)-(A.4). To ensure proper pH stability, the pH should be measured within 30 minutes. Irradiation by sunlight of the stock solutions should be avoided. A.2.3 Treatment dose Treatment
...