Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1996-08-26
2001-07-03
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S695000, C210S709000, C210S717000, C210S726000, C210S738000, C210S748080, C210S912000, C205S750000
Reexamination Certificate
active
06254783
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and process for the removal of contaminants such as heavy or light metals from waste water, particularly such that are discharged from various processing operations and particularly to a method which incorporates magnetic, electrolytic and chemical techniques.
PRIOR ART AND INFORMATION DISCLOSURE
There have been many attempts at the removal of light and heavy metals from aqueous solutions. These attempts include electrowhinning, reverse osmosis, electrophoresis, hydroxide precipitation, radical pH shifting, and direct chemical replacement reaction systems. All of these systems are effective only within very narrow and restrictive process specifications and parameters. The presence of very high large or vey small contaminant levels, the presence of large calcium levels or high pH conditions together with multivalent or multiple contaminants can completely defeat the effectiveness and applicability of the processes.
Techniques disclosed in the patent literature can generally be classified into five groups: electrolytic; hydroxide precipitation; oxidation state modification; low voltage electrolysis high voltage electrolysis.
U.S. Pat. No. 3,901,781 to Passino et al discloses pretreatment of water utilizing ion exchange followed by a dialysis process. Ion exchange resins are expensive and must be periodically reconditioned.
U.S. Pat. No. 4,006,067 to Gussack discloses a process for changing the oxidation state of a dissolved ionic species using porous electrodes. Porous electrodes are subject to degradation by accumulation of scum in pores.
U.S. Pat. No. 4,011,151 to Ho et al discloses a process for purifying water in two steps. In the first step, the electrolysis is effected by dipping an iron anode and a carbon cathode in the waste water, filtering the water, adjusting the pH to 14 by electrolysis with a carbon anode and an aluminum electrode.
U.S. Pat. No. 4,054,516 to Iziumi et al discloses the use of blowing air into the solution to create a foam to carry off precipitates. This approach is not readily adaptable to processing large quantities of water.
U.S. Pat. No. 4,121,991 to Miller et al discloses an electrolytic treatment of water using abrasion of the anode surface with precipitates to clean the electrode surface. This method would be expensive to implement.
U.S. Pat. No. 4,132,622 to Kenny discloses a bi-polar cell having a large surface area.
U.S. Pat. No. 4,123,339 to Gale et al discloses a plurality of closely spaced parallel electrodes. A hydrochloric acid cleaning system is used to keep the iron electrodes free from oxides coating. Removal of the chloride ions requires an additional step.
U.S. Pat. No. 4,338,178 to Vyacheslav et al discloses a nozzle which, together with gas formed on the surface of the electrode carry the sludge away from the electrodes.
U.S. Pat. No. 4,566,975 to Ailgulia discloses hydroxide coprecipitation. This approach requires the additional steps of removing and disposing of the precipitating agent.
U.S. Pat. No. 4,655,895 to Feofanov et al discloses dissolving a metal anode in the presence of a nonsoluble cathode and precipitating nonsoluble inorganic and organic impurities., the electrodes being alternately brought into contact with the air, oxygen and liquor being treated. The patent clearly states that calcium is a problem and requires a preprocessing step not disclosed. A magnetic field is positioned to remove iron particles.
U.S. Pat. No. 4,676,878 to Chez discloses hydrolysis of water using a large field.
U.S. Pat. No. 4,810,344 to Okazaki discloses a plurality of electrolysis vessels, each having an anode and cathode and an electrolysis diaphragm partitioning the space between them with an alkaline water discharge conduit connected to the cathode side and an acidic discharge conduit connected to the anode side of the diaphragm. A magnetic supply unit may be disposed to the vessels to exert a magnetic effect. A diaphragm tends to have a limited life in the field.
U.S. Pat. No. 5,045,214 to Walker discloses coprecipitating non-volatile contaminants with a carrier precipitate formed in situ in the solution. This system is essentially a batch process and requires long treatment times. The primary drawback of this type of system is that, as contaminant levels decrease, the law of “Mass Action” predicts a slowing of the reactions that take place in these batch processes.
For example, the data presented shows a final concentration of Se to be 22 mg/l of water with significantly greater than the levels permitted by the present EPA Water Standard for Se allowance which is 0.05 mg/l.
The processes disclosed in the cited art are not as efficient as the present invention for decontaminating the solutions having the wide range of contaminant concentrations and conditions for which the present invention is targeted nor are they practical for use in reducing pollutant ion concentrations down to the very low levels required for most solution disposal purposes.
In some instances even very low levels of contaminating materials can be a significant problem. Certain metals can cause severe damage to animal life. It is well known that the selenium levels in water entering Kesterson reservoir has had a devastating effect on wildlife living in the wetlands.
The most plentiful ionic species of metallic selenium in aqueous solution is a +4 valent ion, a strong reducing agent that readily combines with oxygen to form SeO
2
, a colorless solid that is readily soluble in water.
The ineffectiveness of the cited art for dealkalinizing highly concentrated solutions can be explained by considering the nature of hydrolysis.
Hydrolysis of water is the disassociation of the water molecule into ions.
The disassociation is given by:
H
2
O - - - 2H
+
+(OH)
−
for “cation” hydrolysis:
M
+
+H
2
O=M(OH)+H
+
and for “anion” hydrolysis,
X
−
+H
2
O=HX+(OH)
−
While most metals and metalloids will readily form hydrated oxides and hydroxides that, in the presence of a high pH environment, precipitate out of solution, many of these “high pH precipitates” become highly water soluble upon lowering the pH level and, in doing so, recontaminate the treated water solution.
The best known example of ion state modification occurs in electroplating processes where a metal is removed from the anode and enters solution by removing an electron (oxidation) and then deposited on the cathode by combining with an electron supplied by the cathode (reduction). The electroplating process is dramatic illustration of the dependence of the solubility of an atom on the ion state. Ion state modification has been overlooked in the cited art with a consequent limitation on the effectiveness of the processes of the present art such as discussed in the BACKGROUND of this specification.
OBJECTS
Accordingly, it is an object of this invention to remove contaminating heavy and light metal ions from waste water and particularly to provide an efficient process for removing large concentrations of calcium and magnesium such as are found in desert waters in brines created from operations used in processing olives.
It is a particular object of this invention to remove from water impurities such as selenium and arsenic (metallic and non metallic forms) which pose a hazard even when present in small concentrations.
In comparison with prior methods of treatment of spent processing solutions, it is an object that the method and apparatus of the present invention be less complex in terms of required steps and additives required and consequently less costly.
SUMMARY
This invention is directed toward a process of steps including putting the solution through “ion state modification” chambers where ions that would normally and naturally form soluble hydroxides are converted to species that form insoluble hydroxides.
Exemplary steps of the method include:
preparation of a treatment solution containing a high concentration of hydroxyl ions;
mixing the waste water with the treatment fluid prefer
Overton James M.
Wurzburger Stephen R.
Morrison Betsey J.
Simmons David A.
Smith Robert Samuel
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