Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-11-12
2001-03-20
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S911000
Reexamination Certificate
active
06203709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the use of alginates in water purification systems. More particularly, the present invention involves using doped alginates to remove oxyanions such as arsenic (V) and selenium (IV) oxyanions from polluted water.
2. Description of Related Art
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference. For convenience, the reference materials are numerically referenced and grouped in the appended bibliography.
Of the many toxic materials that may be present as contaminants in natural waters and wastewaters, a few (specifically arsenic (V), chromium (VI), and selenium (IV) occur as oxyanions. Removal of arsenic is, in particular, an issue of increasing concern. Reevaluation of the current Maximum Contaminant Level (MCL) for arsenic is mandated under the 1996 re-authorization of the Safe Drinking Water Act. A decrease in the current standard (50 &mgr;g/l) would impact the required levels of treatment not only for potable water, but also for hazardous wastewaters and effluents under the Resource Conservation and Recovery Act.
Arsenic is a major contaminant of concern at many Superfund sites (1, 2). Arsenic containing wastestreams are generated in the microelectronics industry due to the use of arsenic in the form of gallium arsenide (GaAs) for the manufacturing of semiconductor devices (4). The average concentration of arsenic in wastewater at facilities which produce GaAs has been estimated to be 2.4 mg/l (5).
For arsenic-contaminated wastestreams, various physical/chemical treatment technologies have been applied for contaminant removal. Arsenic-contaminated water collected during clean up at a former pesticide facility was treated in a full-scale process involving co-precipitation/adsorption with ferric chloride, filtration and carbon adsorption (6).
In pilot-scale studies using electrochemically generated Fe
2+
and hydrogen peroxide, arsenic was efficiently removed from contaminated waters at both a Superfund site and a wood-preserving facility (1). Other processes, such as adsorption onto activated carbon (7, 8) or fly-ash (9) have been tested at bench scale.
Many of these processes generated a significant quantity of sludges or other solid wastes. In some cases, these materials had to be disposed of as hazardous waste. In some applications, selective removal of oxyanions may provide options for more economical treatment of wastestreams. For example, by reducing subsequent sludge disposal costs.
At the bench scale, biosorbents have been tested primarily for removal of heavy metal cations, which are removed preferentially to alkali and alkaline earth metals and anionic species (10). Alginic acid has been shown to be effective at removing many cationic metals from solution including Pb
2+
and Cu
2+
(11), UO
2+
2
(12). Cu
2+
(13), Cu
2+
, Zn
2+
, Cd
2+
, and Ni
2+
, (14), Nd
3+
and Yb
3+
(15), and
226
Ra (16).
Pretreatment or doping of an anionic biosorbent, such as alginic acid, with cations allows (indirect) interaction between the biosorbent and anionic contaminants. Charged polysaccharides, such as sodium alginate, often form hydrogels in the presence of cations (18), the gel characteristic depend on the specific cation. Metal recovery (Co, Cu, As, Fe, Mg, Al, Ca) from an acidic (pH 2-3) cobalt ore leachate with alginic acid has been investigated by Jang et al. (17).
As is apparent from the above, there is a continuing need to provide efficient and economical systems for purifying polluted waters. Such systems are especially needed for removing hazardous oxyanionic pollutants, such as arsenic and selenium oxyanions.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system is provided for removing arsenic (V) and selenium (IV) oxyanions from polluted water utilizing calcium cross-linked alginate which has been further doped with ferric iron. It was discovered that doping calcium alginate with ferric iron produced a sorption media which is effective in sorbing arsenic (V) and selenium (IV) from polluted water. Once the iron-doped calcium alginate is saturated with the pollutants, the doped alginate is dehydrated to form a solid waste. Depending on the pertinent state and/or federal criteria (e.g. total arsenic-content and/or leachability), the dehydrated arsenic-containing alginate solid may be acceptable for disposal as a non-hazardous substance.
Systems for removing arsenate and selenite include a sorption vessel which includes an inlet through which the polluted water is introduced into an oxyanion sorption zone and a purified water outlet through which water having reduced levels of oxyanionic pollutants (i.e., arsenate and selenite) exits the sorption zone. As a feature of the present invention, a sorption media is located within the oxyanion sorption zone. The sorption media includes calcium cross-linked alginate which is further doped with ferric iron, wherein the amount of ferric iron present in the sorption media is between about 0.5 percent and about 4 percent by weight of the wet doped calcium alginate or up to 60% of the dry weight.
The sorption vessel may be used in batch-type processes wherein a given amount of water is introduced into the sorption vessel and agitated therein with a suitable agitator to ensure intimate mixing of the sorption media and polluted water. Once purified, the water is then removed as a batch from the sorption vessel. The sorption vessel may also be operated in a continuous manner wherein polluted water continuously flows into the sorption vessel inlet and purified water continually flowing out of the sorption vessel outlet. As the water passes through the vessel, it intimately contacts the sorption media either as a fixed or fluidized bed. The systems of the present invention may also include a dehydrator for dehydrating the spent sorption media to form a disposable waste product.
The present invention is particularly well suited in situations where an efficient sorption system is required for removing arsenate and selenite that has been introduced into sensitive environments from various human activities, such as mining, smelting, pesticide manufacture and use. In addition, the present invention is well suited for use in treating industrial waste streams to prevent the need to remediate contaminated ground water.
The above described and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5144016 (1992-09-01), Skjak-Braek et al.
patent: 5385741 (1995-01-01), Rinn et al.
patent: 5453201 (1995-09-01), Etzel et al.
patent: 5520819 (1996-05-01), Asahi et al.
patent: 5563186 (1996-10-01), Thompson
patent: 5567451 (1996-10-01), Rinn et al.
patent: 5596084 (1997-01-01), Sanderson et al.
Min, J.H. et al., “Arsenate Sorption by Fe(III)-Doped Alginate Gels,”Wat. Res.vol. 32, No. 5, pp. 1544-1552, 1998.
Min, J.H. et al., “Arsenate, Selenite, and Chromate Sorption by Fe(III)-Doped Alginate Gels,”Advances in Environmental Research, 2 (2) 1998, 207-217.
Jang, L.K. et al., “Recovery of Copper and Cobalt by Biopolymer Gels,”Biotechnology and Bioengineering, vol. 37, pp. 266-273 (1991).
Hering Janet G.
Min Joon H.
California Institute of Technology
Cintins Ivars
Oppenheimer Wolff & Donnelly LLP
LandOfFree
Iron (III)-doped calcium alginate gel sorbents for sorption... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Iron (III)-doped calcium alginate gel sorbents for sorption..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Iron (III)-doped calcium alginate gel sorbents for sorption... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472220