Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-01-21
2001-03-06
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S807000, C210S911000
Reexamination Certificate
active
06197204
ABSTRACT:
The present invention relates to the removal of arsenic contaminants from fluids and, more particularly, to a method of treating water with zinc oxide to remove arsenic contaminants from the water.
Raw water may contain undesirable levels of toxic arsenic contaminants. These waters may include for example, industrial, agricultural and/or mining waste waters, as well as natural water sources, and the arsenic may be present in the water due to natural environmental conditions, pollutants or both. Substantial reduction or removal of arsenic contaminants is desirable where the water is to be returned to the environment in as clean as possible form or is to be used as potable water.
Dissolved arsenic in water is primarily arsenates (+5) and arsenites(+3). The arsenates include HAsO
4
2−
, H
2
AsO
4
−
, and H
3
AsO
4
, while the arsenites are H
2
AsO
3
−
and H
3
AsO
3
. In the past dissolved arsenic has been adsorbed by several materials, including ferric hydroxide [Fe(OH)
3
] and aluminum oxide [Al
2
O
3
] with the arsenates being more strongly sorbed than the arsenites. Dissolved arsenic also has been removed by passing the water containing the arsenic through a particulate metal alloy bed of copper and zinc as disclosed in my U.S. Pat. No. 5,275,737.
It has been discovered in the present invention that contact of the water containing arsenic contaminants with zinc oxide is also effective in the removal of arsenic from the water, and the zinc oxide exhibits a greater affinity for arsenites than the other oxides previously employed in arsenic removal.
Accordingly, in one principal aspect of the present invention, a method for reducing the concentration of arsenic in a liquid comprises contacting the liquid containing the arsenic with zinc oxide.
In another principal aspect of the present invention, the liquid is water.
In still another principal aspect of the present invention, the arsenic includes arsenates and/or arsenites.
In still another principal aspect of the present invention, the liquid containing the arsenic is flowed through a bed of the zinc oxide to reduce the concentration of the arsenic.
In still another principal aspect of the present invention the zinc oxide is a finely divided particulate.
In the present invention the liquid containing the arsenic contaminants including arsenates and/or arsenites is contacted with the zinc oxide. The zinc oxide is preferably in a finely divided form and preferably in particulate form. The zinc oxide is also preferably treated to maximize the surface area for contact. The zinc oxide also preferably comprises a bed through which the arsenic containing water is passed.
REFERENCES:
patent: 4954330 (1990-09-01), Ziegenhain
patent: 5268091 (1993-12-01), Boitiaux et al.
patent: 5603836 (1997-02-01), Wollrich
patent: 6106726 (2000-08-01), Fujita et al.
patent: 412862 (1999-01-01), None
patent: 403076789 (1991-04-01), None
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Hoey Betsey Morrison
KDF Fluid Treatment, Inc.
Simmons David A.
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