Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2002-10-08
2004-10-05
Hopkins, Robert A. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C501S126000, C501S152000
Reexamination Certificate
active
06800204
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A “MICROFICHE APPENDIX”
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a composition of a lanthanum (a rare earth element) concentrate, a process for manufacturing of the composition, and a process for using the composition to remove the toxic forms of selenium and arsenic from water. In particular, the composition uses lanthanum oxides in conjunction with other oxides to form a filtration media that does not dissolve to any great extent in water that it is filtering.
2. Description of the Related Art
The need for potable water is currently being recognized as a high priority for governments worldwide in response to growing populations in areas with limited water supplies. This is particularly true for the United States with projections of continued population growth over the next several decades in its Southwest and Northeast regions. It is these western regions, which have large areas of desert, which by their definition have limited rainfall and corresponding limited water resources. As a result, municipalities of growing population centers in these areas are increasingly tapping into and relying upon large underground aquifers (well water supply) to obtaining the necessary water supply for their growing communities. On the eastern portion of the United States, where there is limited reservoir water supplies, municipalities face the same challenge as new population growth in that area has also pushed the demand for increased aquifer fed water supply.
Although there are concerns regarding the pollution of underground water from mining, refining, manufacturing and other industrial type operations and concerns, toxins, including elements such as arsenic, selenium and other elements are also naturally found in the ground where water aquifers are present and naturally ‘contaminate’ the water percolating through such aquifers. When such toxic elements leach from natural underground deposits into well saturated aquifers, the toxic elements will, over a period of time, spread throughout and dilute into very small minute trace non-hazardous amounts. However, under drought conditions when such aquifers are not fully replenished by natural rain or snow fall, such toxic water-borne elements concentrate into unacceptably dangerous concentrations which are injurious to human heath when ingested.
In other areas, such as India and China, the two most populous countries in the world, naturally occurring underground deposits of arsenic and selenium contaminate the drinking water. In some areas of these countries, the situation is so dire that arsenic and selenium water poisoning has become unavoidable and causes chronic or fatally acute poisoning.
There is also concern by many industrialists, who take great pride in maintaining green and environmentally friendly operations, to properly ensure that any industrial effluent be cleansed of any toxins before being released into the open environment. To meet this challenge, industrialists often meet, then exceed, current and future governmental environmental mandates regulating the waste discharge from industrial concerns. At the same time, in order to remain competitive, industrialists try to find pollution control means that are economic and practical in reclaiming harmful elements from waste discharge that might have any contact with outside bodies of water, both above and below ground.
Of the two contaminates in concern, the element Arsenic (As) is a metal commonly found in nature and can naturally contaminate underground water supplies. It is naturally found in an ionic form (the −3, 0, +3, and +5 oxidation states). This means that when the element has excess or a depletion of its negatively charged electrons (e
−
), the element becomes a charged ion (e.g., As
−3
). When arsenic (As) gains three electrons (3e
−
) in addition to its normal complement of electrons (e
−
), arsenic (As) converts to its −3 oxidation state to become the negatively charged ion form of the element, As
−3
. When arsenic (As) loses five electrons (5e
−
) from its normal complement of electrons (e
−
), this gives arsenic (As) its positive oxidation state or the positive ionic form of As
+5
. Arsenic (As) loses its electrons (e
−
) when it is dissolved into water (H
2
O). At that time, the oxygen (O) from water cleaves off from the hydrogen (H
2
) to form new ionic compounds with the ionic forms of dissolved arsenic. The most common forms of ionic arsenic found in drinking water and wastewater streams being (As
+3
) and (As
+5
). These arsenic ions combine with negatively charged oxygen ions (O
−
) called oxygen anions or oxyanions.
The toxicity of arsenic (As) dissolved in water depends on the arsenic's oxidation in water. Arsenate (As
+5
) is reported to be less toxic that arsenite (As
+3
) and other forms of arsenic based compounds such as methylated arsenic and the like. The level of arsenic (As) in water beyond 0.05 micrograms per liter (ug/l) is known to cause carcinogenic effect in human beings. The United States Environmental Protection Agency (EPA), in monitoring the health and environmental concerns regarding arsenic (As) levels in water, has promulgated a new Maximum Contaminant Level (MCL) of 10 parts-per-billion (ppb) in drinking water (i.e., ten parts of arsenic per billion parts of water). Under federal mandates, any water having higher levels of arsenic (As) than the MCL will be found to be unfit and dangerous for human consumption.
Selenium (Se), the other element of toxic concern, is also a naturally occurring element. In comparison with Arsenic (As), however, selenium (Se) is naturally found in much smaller quantities so as to be considered an essential trace element, which is practically nontoxic. Like arsenic (As), selenium (Se) can be found in an ionic form in water such as selenite, Se
+4
and selenate, Se
+6
where it loses its electrons (e
−
) when it dissolves into water (H
2
O). The oxygen (O) cleaves off from the hydrogen (H) of the water to form a new ionic compound with the selenium (Se). The oxygenated ionic forms of selenium (Se) are selenite (Se
2
O
−2
) and selenate (Se
3
O
−2
), respectively.
In nature, the deficiency of selenium (Se) in some animal diets, such as the longhorn sheep, can cause weakness in the animals'young. On the other extreme, the over accumulation of selenium (Se) in the locoweed, as consumed by cattle, horses and the like, can cause the imbibing animal to exhibit manic characteristics.
It is, however, the presence of various man-made compound forms of selenium (Se) in water that is of the most environmental concern. Selenium (Se) compounds such as hydrogen selenium, selenium sulfide, selenium dioxide (SeO
2
), selenium oxychloride (SeOCl
2
) and the like are extremely toxic and can resemble arsenic (As) poisoning in their physiological reactions.
In order to address these environmental concerns of the presence of Arsenic (As) and Selenium (Se) compounds in aqueous (water) solution, either as naturally occurring in water or as part of the reclamation of such chemicals from industrial waste water or runoff, various techniques have been developed so that water, whatever its source, can be purified of these harmful chemicals to make the water safe for drinking.
The removal of Arsenic (As) from water can be accomplished through chemical precipitation of arsenic (As) though the addition of lime, alum or an iron salt at an appropriate acidity (pH) to the contaminated water. The combination of the Arsenic (As) with lime or salt will cause the arsenic (As) to form a insoluble compound that solidifies or precipitates out of the water for easy removal. Other scientific methods rely on the removal of the ionic form of the element from contaminated water using techniques such as ion exchange, reverse osmosis, electrolysis or distillation. These tech
Harck John F.
Wilkis Stephanie
Winters Ivan
Clear Water Filtration Systems
Hopkins Robert A.
Long John D.
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