Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Patent
1996-04-22
1997-11-18
Tung, T.
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
20415744, 2041582, 4231503, 423 87, 423304, 210763, 210758, 210906, 210912, 588237, 588247, B01D 1100, C02F 168, A62D 300
Patent
active
056883781
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/AU94/00649, filed Oct. 24, 1994.
TECHNICAL FIELD
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.
BACKGROUND ART
Within the above-mentioned industries, there are many impurity bearing aqueous streams. For example streams containing arsenic in the trivalent (+3) oxidation state are found. Known methods of arsenic removal from arsenic-bearing waters include adsorption processes using metal-hydroxide co-precipitation or ion-exchange media, and arsenic precipitation as ferric- or calcium-compounds. When arsenic is in the dissolved state, it is most efficiently removed from aqueous solutions by the above methods when it is present in the pentavalent (arsenate) form. Consequently, there is a need to convert arsenic(III) to arsenic(V) in order to achieve effective arsenic removal from solution. Furthermore, trivalent (arsenite) compounds have been reported to be fifty times more toxic than the corresponding pentavalent arsenate forms. (In this specification, and in accordance with the IUPAC convention, reference to the terms "arsenic(III)" or "As(III)" will include all arsenite species in which the arsenic is present in the trivalent oxidation state, and reference to the terms "arsenic(V)" or "As(V)" will include all arsenate species in which the arsenic is present in the pentavalent oxidation state. Similar reasoning applies to the oxidation states for all other species disclosed.)
Arsenic(III) compounds in solution can be oxidised to arsenic(V) by dissolved oxygen in ambient conditions only at an extremely slow rate. Hence, 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. In many cases these oxidants represent the major cost item of the water treatment process.
Furthermore, many of the published methods for the oxidation of arsenic(III) to arsenic(V) have been complex, costly or inappropriate for application on a large or industrial scale. Many of the reagents used in the oxidation treatment are expensive, as are some of the sources of ionising radiation. Alternatively, the conversion of arsenic(III) to arsenic(V) has not been sufficiently fast enough. Other complexities include the need for special equipment due to operating parameters such as high pressure, and elevated temperature, the use of electrolysis techniques etc. Clearly, it would be advantageous if a cheaper means was provided for oxidizing arsenic using a method which can be used at room temperature and low pressure without the need for special equipment and complex operation.
DESCRIPTION OF THE INVENTION
In a first aspect, the present invention provides a method for the oxidation of As(III) in solution comprising the steps of: of increasing the rate of As(III) oxidation when exposed to UV radiation; and
Preferably the photoabsorber is a metal-containing dissolved or solid species, which in one form of the invention can be a dissolved cation 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.
Preferably 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 ph
REFERENCES:
patent: 3819516 (1974-06-01), Murchison et al.
WPIDS abstract of DD 292893 (Mock et al.), Aug. 14, 1991.
Emett Maree Therese
Khoe Ging Hauw
Robins Robert G.
CRC for Waste Management & Pollution Control
Noguerda Alex
Tung T.
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