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Zero valent iron/iron oxide mineral/ferrous iron composite for treatment of a contaminate fluid

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Zero valent iron/iron oxide mineral/ferrous iron composite for treatment of a contaminate fluid


The present inventors have discovered a novel composition, method of making the composition, system, process for treating a fluid containing a contaminant. The fluid may be aqueous. The contaminated fluid may be in the form of a suspension. The treatment reduces the concentration of the contaminant. The reduction in concentration of a contaminant may be sufficient so as to effect remediation of the fluid with respect to the contaminant. The treatment may reduce the concentration of a plurality of contaminants. The present composition, system, and process are robust and flexible. The composition includes zero valent iron, an iron oxide mineral, and ferrous iron. The ferrous iron promotes maintenance of the iron oxide mineral. The iron oxide mineral promotes the activity of the zero valent iron. The process and system may involve multiple stages. A stage may be optimized for treatment with respect to a particular contaminant. The present composition, system, and process are effective for treating a fluid containing one or more of a variety of contaminants such as toxic metals, metalloids, oxyanions, and dissolved silica. It may be applied to treating various aqueous fluids, such as groundwater, subsurface water, and aqueous industrial waste streams.
Related Terms: Iron Oxide

Browse recent The Texas A&m University System patents - College Station, TX, US
Inventor: Yongheng Huang
USPTO Applicaton #: #20120273431 - Class: 210719 (USPTO) - 11/01/12 - Class 210 
Liquid Purification Or Separation > Processes >Making An Insoluble Substance Or Accreting Suspended Constituents >Including Chemical Reduction

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The Patent Description & Claims data below is from USPTO Patent Application 20120273431, Zero valent iron/iron oxide mineral/ferrous iron composite for treatment of a contaminate fluid.

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BACKGROUND

Wastewater treatment is one of the most important and challenging environmental problems associated with coal-based power generation.

Using wet scrubbers to clean flue gas is becoming more popular worldwide in the electrical power industry. In the coming years, hundreds of wet scrubbers will be installed in the US alone. While wet scrubbers can greatly reduce air pollution, toxic metals in the resulting wastewater present a major environmental problem. The industry prepares to invest billions of dollars in the next decade to meet more the ever more stringent environmental regulations; unfortunately, a cost-effective and reliable technology capable of treating such complicated wastewater is still not available.

The compositions of FGD wastewaters vary greatly, depending not only on the types of coal and limestone used but also on the types of scrubber and processes used. Pretreatment method and management practices also affect wastewater characteristics. According to a recent survey by EPR1 (2006), untreated raw FGD wastewater could have TSS in ˜10,000 mg/L but after settlement, it falls to ˜10 mg/L; the pH typically falls in 5.8-7.3; sulfate is in the range of 1,000-6,000 mg/L; nitrate-N at level of 50 mg/L is not uncommon; chloride, alkalinity and acidity vary from hundreds to thousands ppm; selenium exists in various forms, ranging from dozens of ppb to over 5 ppm, among which, selenate could account for about half of total Se; arsenic ranges from a few ppb to hundreds of ppb; mercury ranges from below 1 ppb to dozens of ppb; and boron can be as high as hundreds of ppm.

Treatment of selanate-Se in wastewater is often considered to be one of the most difficult in toxic metal treatments. Selenium is a naturally occurring chemical element in rocks, soils and natural waters. Although Se is an essential micronutrient for plants and animals, it can be toxic at elevated levels and some of Se species may be carcinogenic. The hexavalent selenium is stable in oxic environments and exists as the selenate (SeO42−) anion, which is weakly sorbed by mineral materials and generally soluble. Tetravalent Se is the stable valence state under mildly reducing or anoxic condition (0.26 V<Eh<0.55 V at pH 7). It exists as the selenite (SeO32−) anion, which tends to be bound onto mineral surfaces (e.g., Fe and Mn oxides). Selenate and selenite are more toxic due to their high bioavailability than elemental selenium or metallic selenides.

A biological treatment system, ABMet, has been patented and is being marketed by GE Water.

However, there remains a need for a cost-effective and reliable treatment process for removing toxic pollutants from the wastewater generated by the wet scrubbers operated for flue gas desulfurization in coal-fired power plants.

SUMMARY

The present inventor has developed a chemical treatment process that can cost-effectively treat all major pollutants in the flue gas desulfurization (FGD) wastewater in a single process.

The present inventor developed a fluidized reacting system using a hybrid reactive solid/secondary reagent reactor that can cost-effectively remove many toxic metals from wastewater. The system and process are effective to treat an aqueous suspension. The system uses a reactive solid and a secondary reagent as reactive agents to rapidly reduce selenate to become insoluble selenium species, which are then adsorbed or precipitated along with various of other toxic metals (such as As and Hg, if present) in wastewater onto the iron oxide sludge. The system is particularly effective for removing selenate-Se.

The present process is effective for removing almost all concern toxic metals in an aqueous suspension; in addition, it can remove oxyanion pollutants and metalloids. More particularly, contaminants removable by the present system and process are: most toxic metals such as arsenic, mercury, selenium, cobalt, lead, cadmium, chromium, silver, zinc, nickel, molybdenum, and the like; metalloid pollutants such as boron and the like; many oxyanion pollutants, such as nitrate, bromate, iodate, and periodate, and the like; and the like.

The present system and process use common, non-toxic, and inexpensive chemicals. The present chemical treatment system costs much less to construct and operate than biological treatment systems, which tend to be more complex.

The present system and process are versatile and flexible. The present system and process are more robust and manageable than a biological process when exposed to toxic chemicals or any disturbances and changes in wastewater quality and quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating a single-stage fluidized bed reactor;

FIG. 2 is a flow chart illustrating a three-stage reaction system;

FIG. 3 is a schematic illustrating a single-stage fluidized bed ZVI/FeOx/Fe(II);

FIGS. 4A, 4B are pictures illustrating a bench scale single-stage reactor;

FIGS. 5A, 5B are pictures illustrating an alternative bench scale single-stage reactor;

FIGS. 6A. 6B, 6C are pictures illustrating a bench scale three-stage ZVI/FeOx/Fe(II) fluidized-bed reactor system; and

FIG. 7 shows three panels of pictures illustrating settling of a mixture of Fe0 and magnetite powder rich of surface bound Fe(II); pictures taken after settling for 1 min (left panel), 3 min (middle), and 6 min (right).

DETAILED DESCRIPTION



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Industry Class:
Liquid purification or separation
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stats Patent Info
Application #
US 20120273431 A1
Publish Date
11/01/2012
Document #
13509963
File Date
09/20/2010
USPTO Class
210719
Other USPTO Classes
252178, 210209, 210207, 210201, 210192
International Class
/
Drawings
8


Iron Oxide


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