Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Reexamination Certificate
1999-09-01
2001-07-24
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
C210S911000, C205S742000, C205S761000
Reexamination Certificate
active
06264845
ABSTRACT:
BACKGROUND OF THE INVENTION
The Field of the Invention
The present invention relates generally to the field of treatment of aqueous solutions including domestic water, surface waters and wastewater using electrolytic means. More specifically, this invention relates to the area of electrolytic chemistry wherein anions and transition metal and post-transition metal cations are removed from aqueous solutions. More particularly, the present invention is directed to methods of augmenting the electrolytic chemistry by introducing nonambient environmental and electrical potential, stresses and influences.
One example of the application of the present invention is the removal of arsenic from potable water or waste water. Arsenic is a well known poison, indeed nearly all compounds containing arsenic are toxic. The presence of even small amounts of arsenic in potable water and slightly higher amounts in wastewater cannot be tolerated. The electrolytic method and apparatus of the present invention can efficiently and cost effectively remove arsenic from aqueous solutions down to a nearly imperceptible trace. The present invention can also be used to remove other contaminants, such as iron, from such solutions to render the water more potable and more palatable.
The Relevant Technology
Various removal methods of heavy metal ions from aqueous solutions are known.
For example, Bouard et al., U.S. Pat. No. 5,425,857 discloses a process and device for the electrolytic generation of arsine.
Brewster, U.S. Pat. No. 5,368,703 discloses a multi-step process and apparatus for removing arsenic from aqueous media. The process utilizes ferrous +2 ions provided by an electrolytic cell in which the +2 ions are added to the aqueous media in a first step. A second step comprises oxidizing conditions generated by the addition of hydrogen peroxide (Fentons Reagent). In the second step, the ferrous +2 ions react with the components of the hydrogen peroxide to form a hydroxide that is oxidized to an oxyferric oxide. Under these conditions, a third reaction occurs in which the arsenic present at a +3 oxidation state is oxidized to a +5 oxidation state. Thereafter, a forth reaction forms a precipitate by which the arsenic oxyacid is adsorbed to the hydroxy ferric oxide and precipitated out.
O'Connor et al., U.S. Pat. No. 5,182,023, discloses a process for treating arsenic-containing aqueous waste using ultra filters to remove solids. It is followed by a chemical treatment to adjust the pH range from about 6 to 8. Then, antiscalents and antifouling material are added. The chemically treated filtrate is then subjected to a reverse osmosis process to result in a permeate stream having less than about 50 parts per billion arsenic.
Gallup, U.S. Pat. No. 5,024,769 discloses a method of treating an aqueous solution containing one or more arsenic compounds in a +3 oxidation state. The method comprises contacting the aqueous solution with a halogenated organic oxidizing agent to convert the +3 arsenic to a +5 oxidation state.
McClintock, U.S. Pat. No. 5,358,643 discloses a treatment method for removing arsenic from water via conditioning the water with one or more additives including an iron salt, an acid, and an oxidant until the water contains more iron than arsenic, is acidic, and has an oxidation-reduction potential of about plus 600 mV. A reagent is then added to the conditioned water until it becomes basic and the water and additives are then reacted in a reaction chamber wherein iron and arsenic are co-precipitated in the form of iron arsenate and iron hydroxide or iron oxide. The treated water is then separated from the precipitate by settling or filtering.
In the article entitled “Use of Electrochemical Iron Generation for Removing Heavy Metals from Contaminated Groundwater” by M. D. Brewster and R. J. Passmore published in the
Environmental Progress
(Vol. 13, No 2) May, 1994 at page 143, the authors discuss an electrochemical iron addition process developed by Andco Environmental Processes, Inc. The process employs electric current and steel electrodes to put ferrous and hydroxyl ions into solution. Once added, the chemistry is manipulated with the addition of various ions to provide coprecipitation and adsorption conditions capable of simultaneously removing a wide variety of heavy metals. For example, hydrogen peroxide was introduced to convert Fe+2 to Fe+3, and arsenite to arsenate. The pH was then adjusted to precipitate and adsorb various heavy metal oxides.
What is needed is a more direct method of precipitating out heavy metals without the necessity of multiple steps, reagents and reactions. These needs could be met by a continuous processing method or flow-through method and a static batch process to remove ions from an aqueous solution by constructing an electrolytic cell with a transition metal or post-transition metal anode and a transition metal, post-transition metal or graphite cathode to electrolytically and directly precipitate out the desired ionic specie for physical removal of the precipitates from the aqueous solution.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention provides methods and apparatus to enhance and augment the efficient removal of anions and transition metal and post-transition metal cations from aqueous solutions. The present invention directly produces a precipitate comprising an adion and an in-migrated anion. The method alleviates the need for multiple steps, additional reagents and the removal problems associated with the prior art devices and methods. Use of the devices and methods of the present invention also reduce the ion concentration left in the treated aqueous solution to significantly less than the prior art methods. Some examples are the removal of arsenic at both the +5 and the +3 oxidation state and the removal of iron.
The present invention also provides a method for determining the amounts of arsenic present in a solution in its trivalent, pentavalent and particulate forms. The present invention also provides a method of producing Iron III hydroxide, aluminum hydroxide and manganese dioxide which can be used as filter media or adsorption media.
The methods of the present invention may employ a batch process or a flow-through process. In the batch process, electrodes contact the solution in a static container wherein a fixed amount of aqueous solution is treated. This method is most appropriate for treating small amounts of solution and for analysis such as the speciation technique of the present invention as described below.
In the flow-through process, a flow of aqueous solution, such as a domestic water supply, is allowed to flow through an electrolytic cell of the present invention wherein the desired contaminants are precipitated to an insoluble form to be removed from the solution downstream by known filtration, settlement or other means.
Whether the process is employed in batch or flow-through, direct precipitation is enhanced by subjecting the process to increased pressure, increased electrical potential, increased flow rate and decreased temperature. Increased pressure is believed to better organize the solvent molecules and to better disorganize the solutes (cations and anions). This allows for an enhanced migration velocity of ions towards their respective electrodes. Increased voltage potential is believed to better control the amount of available iron ion going into solution. Increased flow rate acts to convect away from the surface of anode unwanted anions that would discharge electrons causing undesirable side reactions. Decreased temperature is believed to lessen the mobility of solvent molecules, which when very mobile react at the electrodes, in great abundance, to produce unwanted by-products. These nonambient conditions augment the removal of the target minerals or compounds.
An object of the present invention is to provide an entirely electrolytic method for the treatment of aqueous solutions contaminated with anions and transition metal and post-transition met
Higby Loren P.
Higby Travis P.
Hoey Betsey Morrison
Kirton & McConkie
Krieger Michael F.
Simmons David A.
Watermark Technologies
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