Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G28/00—Compounds of arsenic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/122—Incoherent waves
  • B01J19/123—Ultraviolet light
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/30—Treatment of water, waste water, or sewage by irradiation
  • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/74—Treatment of water, waste water, or sewage by oxidation with air
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W10/00—Technologies for wastewater treatment
  • Y02W10/30—Wastewater or sewage treatment systems using renewable energies
  • Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S210/00—Liquid purification or separation
  • Y10S210/902—Materials removed
  • Y10S210/906—Phosphorus containing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S210/00—Liquid purification or separation
  • Y10S210/902—Materials removed
  • Y10S210/911—Cumulative poison
  • Y10S210/912—Heavy metal

Definitions

• the present invention relates to methods and processes for the photoassisted oxidation of dissolved species including arsenic, iron, phosphorus and sulphur. Particularly, though not exclusively, the invention relates to the treatment of process liquors, waters and waste waters, for example, liquors generated by industries such as the mineral processing and chemical industries and as found in ground waters, in geothermal waters, in leachates from coal fly ash piles, and in acid drainage arising from pyritic heaps resulting from the past practices employed in mining metallic ores, etc.
• Arsenic(III) compounds in solution can be oxidised to arsenic(V) by dissolved oxygen in ambient conditions only at an extremely slow rate.
• stronger oxidants such as chlorine, hydrogen peroxide, and ozone are usually used to convert arsenic(III) to arsenic(V) as part of the arsenic-removal process.
• these oxidants represent the major cost item of the water treatment process.
• the present invention provides a method for the oxidation of As (III) in solution comprising the steps of:
• the photoabsorber is a metal-containing dissolved or solid species, which in one form of the invention can be a dissolved cationic species.
• the wavelength(s) of the UV radiation are typically selected such that during irradiation the photoabsorber causes a chemical reaction that increases the rate of oxidation of As (III) by the oxidant relative to a rate where the photoabsorber is absent from the solution.
• the UV radiation can be sourced eg. from all types of mercury lamps and from sunlight.
• the oxidation is that of As (III) to As (V) .
• At least preferred forms of the first aspect of the present invention can provide a photoassisted (or photo- enhanced) oxidation process which may enable the more expensive oxidation processes to be replaced by a simple procedure which can be operated at ambient conditions.
• expensive chemicals such as hydrogen peroxide, chlorine and ozone may not be required and the process can be used to oxidise, for example, arsenic (III) species in industrial waste waters, process liquors, leachates, dissolved arsenic trioxide from flue dust, and contaminated ground water intended for municipal water supply.
• the process can also be used for the treatment of geo-thermal/spring waters which often contain arsenic (III) species in solution.
• the photoabsorber can be a photo catalyst such as a dissolved species or a solid which absorbs light. Changes in the oxidation state of the photoabsorber may be acceptable in some applications.
• the photoabsorber is iro (II) and/or iron(III) species, but in addition or independently can also be one or more of Al(III) , Cr(III) , Cu(II) , Ce(III) etc as appropriate.
• the oxygen can be supplied as pure oxygen or air. Both can be used at pressures greater than 1 atmosphere.
• arsenic (III) when arsenic (III) is oxidised to arsenic (V) , it is considerably easier to remove arsenic from solution.
• Preferred methods are precipitation and adsorption processes.
• the present invention provides a process for removal of As (III) from solution comprising the steps of:
• step (c) allowing precipitation/co-precipitation of the subsequently oxidised As (III) and the photoabsorber, if necessary, by adjusting the pH of the solution from (b) to cause said precipitation/co-precipitation.
• the wavelength (s) of the electromagnetic radiation are selected such that during irradiation the photoabsorber causes a chemical reaction that increases the rate of oxidation of As (III) by the oxidant relative to a rate where the photoabsorber is absent from the solution.
• the pH is adjusted to be greater than about 3.
• the photoabsorber is one or more of Fe(II) , Fe(III) , or Al(III) .
• the pH is adjusted to be greater than about 5.
• the pH is adjusted by adding lime, sodium hydroxide or other base to the solution.
• Electromagnetic radiation of wavelengths in the UV and/or visible light bands is preferably used in the second aspect, although it is most preferred that UV radiation is used.
• a low, medium or high pressure mercury arc lamp can be used as the source of UV radiation.
• UV radiation from a laser source can be used.
• the process of the second aspect also enables the use of sunlight as a source of electromagnetic radiation.
• the oxidant is oxygen, which can be supplied as pure oxygen or air.
• radiation including specific radiant energy at wavelengths of about 254nm and/or 190nm is preferably used, although for the second aspect other wavelengths extending into the visible region of the solar spectrum may also be used.
• the electromagnetic radiation can be supplied continuously or in pulses.
• a continuous supply should be used because the oxidation reaction stops or slows when the electromagnetic irradiation is stopped whereas a pulse supply is preferably used when the oxidation reaction continues or accelerates for a period after the electromagnetic irradiation is stopped.
• a preferred operating pH for arsenic oxidation in the first and second aspects is a pH of less than 4. At low pH, the iron can be present in solution in its di- and tri-valent states.
• iron(III) is often used as an oxidant in hydrometallurgical processes, eg. the heap leaching of pyritic ores and the acid leaching of uranium ores. Since the rate of oxidation of iron(II) to iron(III) by, for example, dissolved oxygen in a low pH (acid) solution is very slow, oxidants such as peroxide, hypochlorite and other oxychloride species have been used. However, these species have attendant handling and environmental problems (eg. in disposal, storage etc) and are often costly.
• the present invention provides a method for oxidising Fe(II) to Fe(III) in a solution having acid pH comprising the steps of: (a) supplying to the solution an oxidant, and a substance which is different to Fe(II) and which is both capable of being oxidised and increasing the rate of reaction of Fe(II) to Fe(III) when subject to UV radiation, relative to a rate in which the substance is absent from the solution; and (b) irradiating the resulting solution from (a) with UV radiation.
• the pH of the solution is about 3.5 or less.
• the substance is As (III) , P(III) , S(IV), Ce(III) or Mn(II) .
• the oxidation of Fe(II) to Fe(III) is cheaper than existing techniques and generally environmentally more acceptable.
• the wavelengths of UV radiation used can be selected as appropriate for the substance supplied.
• P(III) When the substance is P(III) , it is preferred that P(III) is oxidised to P (V) so that the Fe(III) is then precipitated as a ferric phosphate.
• the oxidant includes oxygen, which can be supplied as pure oxygen or air.
• the method of the first aspect includes the steps of arsenic (III) oxidation in the presence of oxygen, a photoabsorber and UV radiation.
• the present invention provides a method for the oxidation of phosphorus (III) and/or sulphur (IV) in solution comprising the steps of:
• the method of the fourth aspect has many of the advantages associated with the first aspect of the invention.
• the wavelength (s) of the UV radiation are typically selected such that during irradiation the photoabsorber causes a chemical reaction that increases the rate of said oxidation by oxygen relative to a rate in which the photoabsorber is absent from the solution.
• the photoabsorber can be one or more of iron (II) , iron(III) , Al (III) , Cr(III) , Cu(II) , Ce(III) , etc as appropriate.
• the UV radiation wavelengths can be selected as for the first aspect. It is also preferred that the oxygen is supplied as either pure oxygen or air.
• Figure 1 depicts the changes in the concentrations of arsenic (V) , iron(II) and dissolved oxygen(DO) as a function of time when a low-pressure mercury lamp (254 nm) was turned on, off and on again while the solution was deoxygenated and re-oxygenated.
• Initial concentrations As (III) 50 mg/L, Fe(II) 74 mg/L, pH 1, chloride medium, for the reaction of Example 1;
• Figure 2 depicts the concentrations of dissolved arsenic (V) , iron(II) and oxygen(DO) as a function of irradiation time.
• Initial conditions of the aerated solution As (III) 52.7 mg/L, Fe(III) 74 mg/L, pH 1, chloride medium, for the reaction of Example 2;
• Figure 3 depicts the concentrations of dissolved arsenic (V) as a function of time for different solution pHs.
• Initial conditions of the aerated solution As (III) 52.7 mg/L, Fe(III) 74 mg/L, chloride medium, for the reactions of Example 3;
• Figure 4 depicts the concentrations of arsenic (V) as a function of time when aerated solutions containing low concentrations of AS (III) were irradiated with UV light (254 nm or 350 nm) .
• Initial concentrations As (III) 5 mg/L, Fe(II) 74 mg/L, for
• Figure 5 depicts the concentrations of arsenic (V) and iron(II) as a function of solar irradiation time.
• Figure 6 depicts the concentrations of dissolved arsenic (V) as a function of irradiation time for different photoabsorbers.
• Initial conditions As (III) 50 mg/L, mole ratios of the photoabsorber/arsenic (III) 5/1 for Cr(III) , 110/1 for Al (III) , 4/1 for Cu(II) and 1.6/1 for Ce(III); pH 1, chloride medium, 254 nm UV irradiation, air sparging, for the reactions of Example
• Figure 7 depicts the concentration of arsenic (V) as a function of UV irradiation time using a high pressure mercury lamp.
• Initial conditions A (Fe/As 2/1, pH 2) , B (Fe/As 1/2, pH 2), C (Fe/As 2/1, pH 3), D (Fe/As 4/1, pH 1) .
• Initial As (III) concentration 250 mg/L in all cases, as set forth in Example 7; - 8A -
• Figure 8 depicts the photoassisted oxidation of 51.5 mg/L of dissolved arsenic(III) in the presence of 72.2 mg/L of iron(II) in sulphate medium (aerated) using 254 nm lamp, followed by the addition of extra iron and lime to remove the arsenic(V) from solution, being an iron co- precipitation process, for the reaction of Example 8;
• Figure 9 depicts the concentrations of iron(II) and phosphorus (V) as a function of time when a solution of 74 mg/L Fe(II) and 20.5 mg/L (P(III) was aerated and irradiated with 254 nm UV light; chloride medium, pH 1, for the reaction of Examples 9 and 10;
• Figure 10 depicts the changes in dissolved iron(II) concentration, in the presence of S(IV), as a function of irradiation time.
• a 254 nm low-pressure mercury lamp was used to irradiate the air-sparged solution.
• Initial conditions Fe(II) 74 mg/L, S(IV) 20 mg/L, pH 1.5; sulphate medium, for the reaction of Examples 9 and 10;
• Figure 11 depicts the changes in dissolved iron(II) concentration, in the presence of Mn(II), as a function of irradiation time.
• a 254 nm low-pressure mercury lamp was used to irradiate the air-sparged solution.
• Figure 12 depicts the changes in dissolved iron(II) concentration, in the presence of Ce(III), as a function of irradiation time.
• a 254 nm low-pressure mercury lamp was used to irradiate the air-sparged solution.
• Initial conditions Fe(II) 108 mg/L, Ce(III) 50 mg/L, pH 1.5; sulphate medium, for the reaction of Example 9.
• any artificial source of radiant energy in the UV region of the electromagnetic spectrum can be used, provided that the radiation is absorbed by the photoabsorber (or photoactive substance) present.
• Low and high pressure mercury arc lamps were used.
• blac light blue, visible fluorescent tubes and sunlight were also investigated.
• Low pressure Hg arc lamps emit more than 90% of their radiant energy at a fine 254nm line. Light of this wavelength is strongly absorbed by aqueous ferrous ions and ferric ions. It was noted that commercial applications for water disinfection and UV oxidation of dissolved organics use similar low pressure lamps because they are the most efficient at converting electrical to radiant energy (up to 50% conversion efficiency) .
• oxygen is the oxidant during the photoassisted oxidation process.
• Oxygen was supplied at 0.2 atmosphere partial pressure by aerating the reaction mixture. Higher partial pressures were achieved by varying the oxygen/nitrogen ratio in the oxygen- nitrogen gas mixture at 1 atmosphere.
• the reaction mixture pH has a significant effect on the reaction rate and, as indicated above, on the speciation of the photoabsorber.
• Fe(II) species are stable at pH less than about 3 in the presence of dissolved oxygen.
• reaction rates were dependent on the photon flux when other factors such as dissolved oxygen were not limiting. No reactions of significant rate were observed in the absence of irradiation.
• a reaction mixture (575ml) containing 74mg/L Fe(II) as chloride and 50mg/L As (III) was prepared as follows: the Fe(II) stock solution was obtained by dissolving iron metal powder in HC1 solution, the arsenious acid (As(III)) stock solution was obtained by dissolving arsenic trioxide in heated, filtered, demineralised water. The pH of the reaction mixture was adjusted to 1 with the addition of HC1. The reaction mixture was de- oxygenated by bubbling nitrogen and irradiated with light from a 15W Low Pressure Hg lamp (LP Hg lamp) . As indicated in Figure 1, where changes in concentrations of As (V) and Fe(II) are shown as a function of irradiation time, no oxidation of As(III) was observed at this stage.
• LP Hg lamp 15W Low Pressure Hg lamp
• Actinometry determination using potassium ferrioxalate showed that 2 Watts of 254nm radiation produced by the 15W LP Hg lamp was absorbed by the solution.
• Total concentrations of Fe, As and other elements were determined using ICP-AES spectroscopy.
• ppb concentrations of total As and As (III) atomic - 12 - absorption spectroscopy with hydride generation was used.
• mg/L levels of As (V) the molybdenum blue spectrophotometric method was used (Johnson D and Pilson M, Anal. Chim. Acta, 58 (1972), 289-299); Fe(II) was determined using a colorimetry method described by Stookey (Anal Chem 42 (1970), 779-781).
• reaction mixtures each (575ml) containing 74 mg/L Fe(III) as sulphate (ferric sulphate) and 50mg/L As(III), were prepared at several pH values (pH 1, 3, 6 and 11) and aerated with air. When the solution was above pH 5, carbon dioxide-free air was used in order to achieve constant pH readings.
• the initial dissolved As (III) in all the reaction mixtures was oxidised to As (V) only after they were irradiated with the 15W LP Hg lamp ( Figure 3) . This indicates that the reaction proceeds in the presence of sulphate (chloride was used in previous examples) and in alkaline as well as in neutral and acid conditions.
• reaction mixtures were prepared with 5mg/L As (III) and 74mg/L Fe(II).
• the first mixture was of pH 2 with sulphate as the anion.
• concentrations of Fe(II), As (III) and H + in this solution would be similar to those found in some acid mine drainage effluents arising from heaps of mining wastes containing arsenopyrite. - 13 -
• the second mixture was of pH 1 with chloride as the anion. Both mixtures were irradiated using the low pressure mercury arc lamp as above.
• results from optimisation/screening experiments show that the photoassisted reactions favour the oxidation of arsenic(III) in preference to reductants which are usually present in acid drainage waters such as ferrous species. These species, together with partially oxidised sulphur species, represent an extra chlorine- or peroxide-demand in conventional oxidation processes.
• a third reaction mixture (750ml) , containing 74mg/L Fe(III), a l/l sulphate to chloride anion ratio, and of pH 3, was irradiated with light from a 20W blacklight blue (BLB) fluorescent tube. Actinometry determination using ferrioxalate showed that the solution absorbed 2.9W of light assuming the band of wavelengths are evenly distributed around 350nm. Complete oxidation of the arsenic(III) initially present in the reaction mixtures was achieved in 10 minutes.
• Figure 6 shows the progress of oxidation of arsenite (50mg/L) where other metals were used as the photoabsorber in place of iron. In the absence of irradiation, these species will not oxidise arsenite.
• the molar metal:As ratio was 1.6, 5, 110 and 4 for Ce(III), Cr(III) , Al(III) and Cu(II) respectively.
• the pH was 1 and chloride was the accompanying anion.
• the low pressure mercury lamp was used.
• Metals such as divalent Mn, Ni and Zn do not absorb ultraviolet light at 254nm.
• Sulphur(IV) as sulphite also did not significantly affect the rate. Heavy metals such as nickel chromium zinc manganese and copper were not found to reduce the rate. The reaction is faster if chloride or perchlorate electrolyte is used in plate of sulphate. Carbonate introduced by aerating alkaline solutions has no observable effect on the reaction rate. Calcium and magnesium do not interfere with the reaction so wastes previously stored as calcium arsenite may be successfully treated.
• Fe (III) -sulphate alternatively, Fe (II) -chloride or used pickle solution from the steel industry can also be used because at pH> 3.5 Fe(II) is oxidised to Fe(III) by dissolved oxygen in aerated solution) to give an Fe-to-As mole ratio of about - 16 -
• this aspect of the invention is versatile, in that it can be used to rapidly achieve complete oxidation of arsenic in solutions with either high or low initial arsenic(III) concentrations.
• the projected commercial applications of this invention are:
• Iron(III) in acid solution is commonly used as an oxidant for use in hydrometallurgical processes, for example the oxidative leaching of uranium ores and heap leaching of ores.
• oxidants such as peroxide- or chlorine-compounds are used for the re-oxidation of iron(II) in the leaching circuit.
• the photoassisted - 19 - oxidation of iron) II) by dissolved oxygen can be used as an alterative to these oxidants.
• Oxidation of phosphorus(III) and sulphur(IV) Dissolved iron is a common impurity in hydrometallurgical process liquors. If it is present as Fe(II) in acid solution, the addition of P(III), say as phosphorous acid or its salt, and irradiation using UV lamps or sunlight can precipitate out the iron impurity as ferric phosphate.
• Sulphur(IV) as sulphurous acid (dissolved S0 2 gas) or its salt can be used as an adjunct (like phosphorous species) in the photoassisted oxidation of Fe(II) in acid solution.
• this aspect of the invention can be used to treat/process effluents, waters or process liquors by converting the sulphurous species to sulphate. Uncontrolled oxidation of partially oxidised sulphur species in the environment can result in the lowering of pH with the attendant problems of heavy metal immobilisation.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
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• Life Sciences & Earth Sciences (AREA)
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• Environmental & Geological Engineering (AREA)
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• Electromagnetism (AREA)
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• Removal Of Specific Substances (AREA)
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• Physical Or Chemical Processes And Apparatus (AREA)
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• 1994
  • 1994-10-24 WO PCT/AU1994/000649 patent/WO1995011195A1/en not_active Ceased
  • 1994-10-24 EP EP94930874A patent/EP0729436B1/en not_active Expired - Lifetime
  • 1994-10-24 US US08/633,810 patent/US5688378A/en not_active Expired - Fee Related
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• 2000
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