MXPA00000753A - Photo-assisted oxidation of inorganic species in aqueous solutions - Google Patents

Abstract

A method for oxidising an inorganic species in an aqueous solution comprises the steps of:(i) supplying an oxidisable source of sulphur, and oxygen to the solution;and (ii) irradiating the solution with UV light such that both the inorganic and sulphur species are oxidised.

Description

DBE PHOTOASISED OXIDATION INORGANIC SPECIES IN AQUEOUS SOLUTIONS FIELD OF THE INVENTION The present invention relates to a method intended to oxidize inorganic species in aqueous solutions, and more specifically, with the treatment of contaminants for example in drinking water for human use and wastewater from industries and process liquors. However, it will be appreciated that it is possible to employ the invention when it is necessary to oxidize an inorganic species for any reason.

BACKGROUND OF THE INVENTION Dissolved sulfur dioxide or sulfite is usually considered as a reducing agent. In addition, it is known that it is possible to accelerate the oxidation of sulfite by. its exposure to ultraviolet (UV) radiation (Matthews, JH et al, J. Am. Chem. Soc. 1917, 39, 635. Matthews teaches, however, that oxidation is retarded by the presence of trace amounts of different species Likewise, no change in the oxidation state of these species was observed REF: 32668 jria_A ___ ifi_h _._ fc .- 'fji-fíriiÉiMfttf'- ^ tóa? * = ¡j? g ^ * ^^ g éáá There are many sources of drinking water in the world that are contaminated by trace elements, such as arsenic, cyanide, manganese , sulfides and selenium. The standards of the World Health Organization require very low levels of contaminants (example: the limit for arsenic is 10 ppb). The presence of manganese gives rise to "dirty water" problems that can result in dirt on clothes and stains on household appliances when it occurs in concentrations higher than 20 ppb in drinking water. Many wastewater and mineral processing liquors from industry also contain cerium and those from the field of nuclear technology, uranium. As part of the elimination process, chemical oxidants, such as chlorine, ozone and permanganate, are frequently used. However, these oxidants can cause harmful byproducts (for example chloroform) and the presence of residual permanganate can result in discolored water.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method for oxidizing an inorganic species in an aqueous solution, comprising the steps of: (i) supplying an oxidizable source of sulfur and oxygen to the solution and (ii) irradiating the solution with UV light, that the species in question is oxidized. In this invention, oxygen is advantageously used as an oxidizing agent, without having residual contaminating after-effects. The sulfur sources can be selected (for example the sulphite) so that a relatively benign product (for example: a sulphate) is formed in the oxidizing process. Although the final product when using sulfite is a relatively benign dissolved sulfate, it is preferable to use it in reduced form, especially if an ion exchange is then applied to remove the contaminant (such as arsenic). In this case, sulphate dissolved in a dose of not more than 25 mg / liter is preferred, in order to obtain an effective elimination of arsenic (v) (sulfate and arsenic compete for sites in the ion exchange material). ). ^^? ^^ ^^ gg ^ The oxidizable sources of sulfur can be S032", S2032", S 062", S02 (g), aqueous S02 or HSQ. However, the most preferred sources are sulfur dioxide. and sulfite.5 Typically, the process is applied in the treatment of trace amounts of inorganic species, although the process may also have application because of more concentrated amounts of contaminants. or more among arsenic, manganese, vanadium, cerium or iron. Also typically the ultraviolet light employed has a wavelength of about 254 nm. The radiation can be supplied continuously or in pulses. In addition, it is possible to use mercury arc lamps at low, medium or high pressure as a source of UV radiation. It has also been observed that the UV wavelengths of 254 nm from a lamp source were able to conveniently disinfect the water thus treated. Typically, oxygen is sprayed into the aqueous solution in the form of air, although other possible methods of addition exist. As noted above, the solution typically corresponds to a drinking water solution, wastewater from the industry or process liquor, etc.

Typically and if necessary, the pH of the solution can be made to a more or less neutral or basic value.

BRIEF DESCRIPTION OF THE DRAWINGS In spite of any other forms that are within the scope of the present invention, the preferred forms thereof are described below, by way of example only, with reference to the accompanying drawings and the following examples, which are not of a limiting nature. . In the drawings: Figure 1 is a graph indicating the increase in arsenic concentration (V) and the respective decrease in sulfite concentration, as a function of lighting time, using a 15W mercury lamp at low Pressure. The corresponding change in the concentration of arsenic (V) in the dark is also plotted. (Initial conditions: 1.7 liters of solution containing 470 ppb of arsenic (III) in the presence of 10 mg / liter of sulfite, in which the pH of the solution was adjusted to 9, using sodium carbonate.) Figure 2 is a graph indicating the increase in arsenic concentrations (V) as a function of the type of illumination, using a lamp of 15, 254 nm. (Initial conditions: 1.7 liters of solution containing an arsenic (III) concentration of approximately 470 ppb, the pH was adjusted to 9 using sodium carbonate, the initial sulfite concentrations ranged from 0 to 12 mg / liter.) 3 is a graph indicating the concentrations of arsenic (V) as a function of the time elapsed when the solutions (of 1.7 liters) containing arsenic (III) at a concentration of 470 ppb were illuminated with a 15 W lamp, 254 nm. and different controlled pH values. A solution of sodium sulfite was added at a dose of 2 mg / liter / minute and air was sprayed at a rate of 2.5 liters per minute. The data is also included without UV illumination (in the dark). Figure 4 corresponds to a graph that shows arsenic (V) concentrations as a function of the time elapsed when a 1.7-liter solution containing arsenic (III) at a concentration of around 20 mg / liter and a pH of 6.5 was illuminated with a lamp of 15, 254 nm. Sulfur dioxide gas was injected at a rate of 0.02 liters per minute and sprayed with air at a rate of 2.5 liters per minute. The data is also displayed without UV illumination (in the dark).

Figure 5 is a graph illustrating arsenic (V) concentrations as a function of the time elapsed when solutions (1.7 liters) containing an arsenic (III) concentration of 470 ppb, at a pH 6.5 level, were illuminated with a lamp of 15 W, 254 nm. A solution of sodium thiosulfate was added at different doses (in mg / liter / minute) and air was sprayed at a rate of 2.5 liters per minute. Data is also included without UV illumination (in the dark). Figure 6 is another graph of arsenic concentrations (V) as a function of the time elapsed when a 1.7 liter solution containing arsenic (III) at a concentration of 470 ppb and a pH was illuminated with a 15, 254 nm lamp. 6.5 A solution of tetrathionate sodium was added at a dose of 2 mg / liter / minute and air was sprayed at the rate of 2.5 liters / minute. The dark data is also displayed, excluding UV illumination. Figure 7 shows a graph of the residual manganese concentrations as a function of the time elapsed when the 1.7 liter solutions with a manganese (II) concentration of around 500 ppb, at a pH of 8.5, were illuminated with a 15 W, 254 nm. A solution of -G * YIG íir _______ffl_rrr ¡j¡3 ^ ^^ & sodium sulfite at a dose of 2 mg / liter / minute and air was sprayed at a rate of 2.5 liters / minute. The oxidized manganese was removed using a 0.025 micron membrane filter. To facilitate the removal of manganese, ferric chloride (6.2 mg Fe / liter) was added in two of the four tests. Data is also displayed without UV illumination (in the dark). Figure 8 is a graph illustrating the residual manganese concentrations as a function of the time elapsed when a 1.7 liter solution containing manganese (II) was illuminated at a concentration of about 20 mg / liter at a pH of 9.5 using a lamp of 15, 254 nm. A solution of sodium sulphite was added at a dose of 80 mg / liter / minute, air being pumped at a rate of 2.5 liters per minute. Next ferric chloride was added at a rate of 6.2 mg Fe / liter, to facilitate the removal of manganese. Data is also included without UV illumination (in the dark). Figure 9 shows a graph with iron (II) concentrations as a function of the time elapsed when a 1.7 liter solution containing iron (II) was illuminated at a concentration of around 20 mg / liter and a pH equal to 2 , illuminating with a lamp of 15, 254 nm. A solution of sodium sulfite was added at a rate of 20 mg / liter / minute and air was sprayed at the rate of 2.5 liters per minute. Data are included with UV light without sulfite and data without UV illumination (in the dark). Figure 10 is a graph showing cerium (IV) concentrations as a function of the time elapsed when a 1.7 liter solution containing cerium (III) at a concentration of 20 mg / liter and a pH value of 6.5, was illuminated with a lamp of 15 W, 254 nm. A solution of sodium sulfite was added at a dose of 20 mg / liter / minute; then air was sprayed at a rate of 2.5 liters per minute. Data are shown with UV illumination but without sulfite, and data without UV illumination (in the dark).

MODALITIES OF EXECUTION OF THE INVENTION Preferred forms of the present invention find application in the treatment of drinking water, wastewater and mineral processing liquors. It is possible to appreciate, however, that the invention has wider applications. For the treatment of drinking water, it is convenient to eliminate the oxidizing pollutants, such as arsenic, manganese and sulfur. At least in ^ ..- ^^^^ the preferred forms, the contaminants are oxidized and then removed under neutral or slightly alkaline conditions. In the treatment of wastewater and 5 mineral processing liquors, it is convenient to neutralize and / or eliminate (depending on the final use of water or liquor) species such as arsenic, iron and manganese. In these applications, however, oxidation can take place under acidic, neutral or alkaline conditions. 10 Problems of "dirty water" related to manganese are an important aspect of water quality for the authorities that supply it. It is understood that 40 percent of public water supplies in the United States have concentrations manganese that exceed levels of 10 to 20 ppb. Manganese is also a problem in processed wastes from the milling of uranium ores and in the acid drainage of mines. Manganese is usually present in the mineral that is going to grind or it can be introduced as an oxidant in the form of pyrolusite (Mn02), which is the oxidant used in the leaching of uranium. In the liquors of industrial processes, it is necessary to oxidize different ions of metals as part of the overall processing of the plant.

Next, details of various operating parameters in the preferred processes are described.

Radiant energy source It was possible to observe that any source of radiant energy in the UV region of the electromagnetic spectrum is useful, provided that the radiation has been absorbed by the dissolved sulfur compound that acted as a photoinitiator of the process. Low pressure mercury arc lamps were used for the oxidation of arsenic (III), manganese (II), iron (II), cerium (III) and vanadium (III) dissolved. Typical UV wavelengths of less than 300 nm (preferably around 254 nm) were used.

Choice of the photoabsorbent The dissolved sulfur species absorbed the UV light supplied and were oxidized by the dissolved oxygen. These sulfur species were used (oxidized) during the photochemical reaction. Dissolved sulfur (IV) species derived from the addition of sodium sulfite included S032_, HS03"or H ^ 0, depending on the pH value of the solution. obtained the same species * of dissolved sulfur by dissolving S02 gas in the water, which delivers aqueous S03 which, in turn, becomes sulfurous acid (H2S03) • Sulfuric acid and dissociated in HS03"and S032" in conditions of a higher pH. Dissolved sulfite from sodium sulfite was used for the oxidation of manganese (II). Other partially oxidized sulfur species (sulfur (VI) as in sulphate compounds having completely oxidized sulfur species) obtained in the solution of sodium thiosulfate or tetrathionate sodium were also used as photoabsorbents. In addition, the dissolved sulfite was obtained by spraying sulfur dioxide gas or a mixture of sulfur dioxide gas and air / oxygen / nitrogen in the solution. In this way, the forms of sulfur that could be used included S03 'S02 (g), aqueous S02, HSO3, S2032 and S4062".

Oxidant source Oxygen was the oxidant used in the photochemical oxidation process. It was typically supplied at around 0.2 atmospheres of partial pressure, when aerating the reaction mixture. By way of > jaáb *. ^. Alternatively, oxygen was supplied by spraying a gaseous mixture of sulfur dioxide with air or an oxygen / nitrogen mixture in the solution (or any other compatible gas source). Partial oxygen pressures greater or less than 0.2 atmospheres may also be employed, as appropriate. Lighting was achieved by placing a lamp inside a quartz envelope inside the reaction vessel (alternatively, the light was irradiated from above the solution). The types of lamps used included a high or low pressure mercury arc lamp or a xenon arc lamp. It was possible to observe that when the chosen UV source emitted light at a wavelength of around or below 190 nm, ozone was generated from dissolved oxygen (Ozone is a powerful oxidant that can oxidize arsenic (III) and manganese (II).) For the examples described below, lamps that did not produce ozone were used.

Examples The following are examples of non-limiting nature.

Photooxidation of dissolved arsenic (III) A 1700 ml reaction mixture containing 470 μg / liter of As (III) (the typical concentrations in groundwater in areas where arsenic leaching from minerals that are leached was prepared in the following manner contain arsenic in natural form) and 10 mg / liter of dissolved sulfite (S032 ~). The sulfite stock solution was prepared by dissolving sodium sulphite salt in demineralized water; the solution of arsenic acid (As (III)) was obtained by dissolving arsenic trioxide in demineralized hot water. The pH of the reaction mixture was adjusted to 9 by the addition of sodium carbonate (because the groundwater usually has an important carbonate alkalinity). The solution was then aerated through the injection of fine bubbles of air. In the absence of UV illumination, no significant oxidation of As (III) was observed - see Figure 1. When a 15 W mercury lamp was connected at low pressure to illuminate the reaction mixture, oxidation of the Ace rapidly occurred. (III) and S (IV) (Figure 1). The experiments were repeated using different initial concentrations of dissolved sulfite, say, from 0 to 12 mg / liter of dissolved sulfite. As shown in Figure 2, the oxidation rate of As (III) depended more strongly on the initial sulfite concentration, when it was less than 8 mg / liter. Figures 1 and 2 show that both UV light and dissolved sulfite were needed for the photooxidation reaction to occur. Figure 3 indicates that the oxidation rate of arsenic increased with increasing the pH value of the solution. During these tests, the pH of the solution was controlled to the selected value, using an automatic titrator that added sodium hydroxide solution when required. Sodium sulfite was added by continuous injection of a stock solution (17 g / liter of sulfite) at a precisely controlled flow rate using a titrant, in order to deliver a dosage rate of 2 mg / liter this is, 0.2 ml / minute of stock solution was injected into the 1.7 liter reaction mixture. This method of sulfite dosing is more efficient than the procedure described for Figures 1 and 2, in that sodium sulfite was added in a single dose. It also simulates the procedure in which S02 gas is used. Air was sprayed at a rate of 2.5 liters per minute.

Sulfur dioxide gas was used instead of sodium sulfite, as shown in Figure 4. Arsenic (III) was oxidized when bubbles of sulfur dioxide and air were made in the absence of UV illumination (autooxidation process). However, the oxidation rate was accelerated when the reaction mixture was illuminated. It was observed that there was presence of significant concentrations of dissolved sulfite in the reaction mixture, which indicated that an excessive amount of sulfur dioxide had been sprayed. Therefore, there was not a big difference between the results of the experiments "with light" and "in the dark". Sodium thiosulfate can be replaced by sodium sulfite, as illustrated in Figure 5. 15 Similarly, sodium tetrathionate was used as a photoabsorbent, as shown in Figure 6. The determination of the Actinometry using potassium ferrioxalate showed that a maximum of 20 6 Watts of 254 nm radiation produced by a 15 W lamp was absorbed by the reaction mixture. The concentrations of total As and As (III) were determined using atomic absorption spectroscopy with hydride generation. The concentrations of As (V) in the reaction mixture were determined ? itiUiBtitá ^. **** i ____ ¿_Í_ÍÍ__í_ft ___ 7 ** 17 by means of the blue spectrophotometry method with molybdenum (Johnson, D. and Pilson, M., "Analytical Chimica Acta" 68, 289-299, 1972). Sulfite concentrations were also determined spectrophotometrically (Humphrey, R.E., Ward, M.H. and Hinze, W., "Analytical Chemistry", 42, 698-702, 1970).

Photooxidation of dissolved manganese (II) A reaction mixture (1700 ml) containing 500 μg / liter of Mn (II) was tested in the following manner (typical concentrations in surface and groundwater are less than 1 mg / liter) and 10 mg / liter of S032 ~). The sulfite stock solution was prepared by dissolving sodium sulphite salt in demineralized water; the mother solution of Mn (II) was obtained by dissolving MnS04. 4H20 in demineralized water. The pH of the reaction mixture was 6.5 and was aerated by injection of fine bubbles of air. After a 15 W mercury lamp was connected at low pressure to illuminate the reaction mixture for two minutes, it became cloudy due to the appearance of gray and black suspended particles, indicating that an oxide had formed. manganese. A 25 ml sample was taken and its pH adjusted (from 4-5) to 7, using a diluted sodium hydride solution, in order to coagulate the colloidal manganese oxide particles. After 30 minutes, to allow sufficient time for the 5 precipitated gray and black particles to coagulate, the sample was filtered using an Amicon unit equipped with a 0.025 μm membrane. The concentration of Mn dissolved in the filtrate was 22 μg / liter. This indicates that most of the dissolved Mn (II) was oxidized as Mn (III) / Mn (IV) and precipitated as manganese oxide (which is black). When the same procedures were repeated without illumination, the reaction mixture remained clear and colorless. A sample was taken after 30 minutes and subjected to the coagulation and filtration procedure. The concentration of manganese in the filtrate was 505 ppb (see Table 1). Dissolved manganese concentrations were analyzed using ICP-MS, ICP-AES or spectroscopy of atomic absorption with a graphite furnace. The results of one of these procedures are summarized in Table 1.

Table 1: Concentration of residual manganese in water after filtration (in parts per billion) Initial concentration 511 ppb After 2 minutes of illumination at a pH of 6.5 in the presence of 10 mg / liter of sulphite 22 ppb After 30 minutes without illumination 505 ppb 10 Photooxidation of other dissolved compounds The above procedure can also be used in the photooxidation of dissolved compounds such as Se (IV), CN ", Fe (II), Ni (II), V (IV), U (IV) and Ce III.) Oxidation can be demonstrated by making a reaction mixture containing a concentration of one or more of these compounds. Dissolved sulfur species may obtained from the stock solution, which can be prepared by dissolving either the equivalent sodium or the calcium salt in water. Then, we proceed to divide the mixture into three portions for a set of three tests, namely: 1. Without UV illumination. An amount is added to the first portion of the reaction mixture. suitable sulphite or sulfide taken from a concentrated stock solution. The mixture is aerated with a mixture of nitrogen and oxygen with a known partial pressure of oxygen. The speciation of the oxidation state of the target substance and the sulfur at different time intervals was used to determine the reaction rate. 2. The second portion of the reaction mixture is aerated with the same gas mixture of oxygen and nitrogen that was used in Test 1 and illuminated without the addition of a sulfur compound. 3. The last portion is aerated with the same sulfite or sulfur addition used in Test 1 and the light was switched on to start the experiment. The oxidation rate was determined as indicated above for As (III) and Mn (II). It is possible to achieve illumination by placing a lamp either inside a shell inside the reaction vessel or so that the light is radiated from above. The types of lamps used may include a high or low pressure mercury arc lamp, a xenon arc lamp or a blue fluorescent black light tube.

It should be noted that the oxidation rate of the target substance in Test 3 is greater than in Tests 1 or 2.

Procedures for experiments using sulfur dioxide gas The photooxidation reaction can occur equally well when a sulfur dioxide gas is used in place of the sulfite salt. To demonstrate this, it is possible to perform a set of three tests for each target substance, as in the preceding section. The reaction mixture can be sprayed with a fine stream of gas bubbles. The partial pressure of oxygen, sulfur dioxide and nitrogen can be varied independently in the gas stream from 0 to 100%.

Test A. Sulfur dioxide is added to the gas stream of oxygen and nitrogen at a known partial pressure, in the absence of any illumination, and the rate of oxidation is determined by specifying the oxidation state of the target substance after different time intervals . t t y y y y y Prueba Prueba Prueba Test B. The container is designed so that the second portion of the reaction mixture has been illuminated with light from a lamp in the absence of sulfur dioxide. The slow rate of background oxidation (if any) is determined by spraying the target substance for the oxidation state at different time intervals. Test C The third portion of the reaction mixture was placed in the reaction vessel. Sulfur dioxide was added to the gas stream and the lamp was connected at the same time, to mark the beginning of the experiment. The partial pressure of the sulfur dioxide is the same as in Test A and the source of illumination and intensity of the lamp were equal to those of Test B. The oxidation rate of the target substance in Test C would be higher than in the case of Tests A or B. The pH of the reaction mixture and the addition of the sodium sulfite solution were controlled using automatic titrators, as described above.

The oxidation of manganese was evidenced by the appearance of suspended particles of gray and black colors, indicating the formation of an insoluble oxide of manganese (III) or (IV). Preliminary measurements using paramagnetic electron resonance spectroscopy confirmed that the dissolved Mn (II) concentration decreased with the elapsed lighting time. The precipitated manganese particles were removed using an Amicon unit equipped with a 0.025 micron membrane filter. As shown in Figure 7, the addition of ferric chloride solution to deliver a concentration of about 6 mg Fe / liter in the reaction mixture improved the removal of manganese from the solution. Residual manganese concentrations were analyzed using ICP-MS, ICP-AES or atomic absorption spectroscopy with a graphite furnace. As shown in Figure 7, at a pH of 8.5, the rate of manganese removal from the solution was accelerated by illuminating the reaction mixture using the UV light of a low pressure mercury lamp. Oxidation of a more concentrated solution of Mn (II) at a pH of 9.5 is described in Figure 8. Then the dosage of sulfite at 80 mg / liter / minute to respond for the initial concentration of Mn (II) of 20 mg per liter.

Photooxidation of iron (II) dissolved in acidic conditions The oxidation of iron (II) was followed by periodic measurements of the concentration of dissolved iron (II) in the reaction mixture. This was determined by spectrophotometry, using the ferrozine reagent (Stookey, "Analytical Chemistry", Vol. 42, No. 7, 1970). Figure 9 shows iron (II) concentrations as a function of the time elapsed when a 1.7 liter solution containing iron (II) was illuminated at a concentration of about 20 mg / liter at a pH of 2, using a 15 W, 254 nm. The sodium sulfite solution was added at a rate of 20 mg / liter / minute; air was sprayed at a rate of 2.5 liters per minute. Data on oxidation with UV illumination but without sulfite indicated that the oxidation of Fe (II) by dissolved oxygen was accelerated by UV illumination. This was due to the fact that dissolved Fe (II), which is 254 nm, photoinitiated and maintained the oxidation reaction. He ^ j ^^^ Ü ^ ^^ iron (II) dissolved oxidized in the presence of dissolved sulfite and oxygen, without UV illumination (in the dark) - what is known as autooxidation reaction.

Photooxidation of the cerium (III) The oxidation of the cerium (III) was followed by the measurement of the concentration of the cerium (IV) in solution, using a volumetric titration method (Vogel, AI, "A Textbook of Quantitative Inorganic Analysis", Third Edition, Longmans, 1961, p.318). Data taken from three tests with UV illumination and sulfite dosing; with UV illumination but without dosage of sulfite, and without UV illumination but with dosage of sulfite are included in Figure 10. As shown in said Figure, unlike the case of iron (II), the autooxidation reaction (in the dark) ) was not enough to oxidize the dissolved cerium (III). However, like iron (II), dissolved cerium (III) absorbed UV light at 254 nm and photoinitiated the oxidation reaction. The photooxidation reaction was clearly accelerated by the addition of 20 mg / liter of sulfite per minute.

Although the invention has been described with reference to a number of preferred embodiments, it will be appreciated that it can be executed in many other ways. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. s_

Claims (9)

RE IVINDICATIONS Having described the invention as above, the content of the following claims is claimed as property:

1. Method for oxidizing an inorganic species in an aqueous solution, characterized in that it comprises the steps of: (i) supplying an oxidizable source of sulfur and oxygen to the solution and (ii) irradiating the solution with ultraviolet (UV) light in order to oxidize the species.

2. Method according to claim 1, characterized in that the oxidizable source of sulfur can be: S032", S02 (g), aqueous S02, HS03", S2032", S4062".

3. Method according to claim 1 or 2, characterized in that the inorganic species is present in the aqueous solution in trace amounts.

4. Method according to any of the preceding claims, characterized in that the inorganic species is arsenic, manganese, vanadium, cerium and / or iron.

^ Hi: ____ 3g? _s__ £ _i- 5. Method according to any of the preceding claims, characterized in that the wavelength of the UV light is less than 300 nm.

6. Method according to any of the preceding claims, characterized in that the dissolved oxygen is derived from the air.

7. Method of compliance with any of 10 claims 1 to 6, characterized in that the dissolved oxygen is derived from a gas source having a partial pressure of the oxygen of about 0. 2 atmospheres

8. Method according to any of the preceding claims, characterized in that the aqueous solution can be potable water, industrial wastewater or a liquor from an industrial process. 20

9. Method designed to oxidize inorganic species in an aqueous solution, substantially in the manner described in this application with reference to the Examples. 25 ^ H? ^ ^^^ eM ^ í - ^ _. ^. ^^ -, ^. , _______-_ M_ *. * •! -__- .- .. -.- ^