U.S. patent application number 16/218741 was filed with the patent office on 2019-06-20 for filtering medium for fluid purification.
This patent application is currently assigned to Hoganas AB (Publ). The applicant listed for this patent is Hoganas AB (Publ). Invention is credited to Avinash Gore, Bo Hu, Sydney Luk.
Application Number | 20190184368 16/218741 |
Document ID | / |
Family ID | 45592371 |
Filed Date | 2019-06-20 |
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United States Patent
Application |
20190184368 |
Kind Code |
A1 |
Gore; Avinash ; et
al. |
June 20, 2019 |
FILTERING MEDIUM FOR FLUID PURIFICATION
Abstract
A filtering medium, a method for the production thereof, the use
of said filtering medium and a method for reducing the content of
multiple contaminants simultaneously in fluids by means of said
filtering medium, wherein said filtering medium has or includes at
least one of the following: a mixture (A) containing a major part
of an iron-based powder and a minor part of a silver powder, an
iron-silver powder alloy (B), and an iron-based porous and
permeable composite containing silver (C).
Inventors: |
Gore; Avinash; (Johnstown,
PA) ; Hu; Bo; (Greensburg, PA) ; Luk;
Sydney; (Cherry Hill, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hoganas AB (Publ) |
Hoganas |
|
SE |
|
|
Assignee: |
; Hoganas AB (Publ)
Hoganas
SE
|
Family ID: |
45592371 |
Appl. No.: |
16/218741 |
Filed: |
December 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13984318 |
Oct 17, 2013 |
10173196 |
|
|
PCT/EP2012/052001 |
Feb 7, 2012 |
|
|
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16218741 |
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61441064 |
Feb 9, 2011 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 20/0233 20130101;
B01D 15/20 20130101; B01J 20/28004 20130101; C02F 2101/163
20130101; B01D 2239/0407 20130101; C02F 2101/12 20130101; C02F
2101/20 20130101; C02F 2303/04 20130101; B01J 20/28057 20130101;
C02F 2101/30 20130101; C02F 1/281 20130101; B01J 20/0203 20130101;
C02F 1/705 20130101; B01J 20/2803 20130101; C02F 2101/166 20130101;
C02F 1/288 20130101; B01J 20/02 20130101; B01J 20/0229 20130101;
B01J 20/3078 20130101; B01J 2220/42 20130101; B01D 15/00 20130101;
B01D 39/2034 20130101; C02F 1/505 20130101 |
International
Class: |
B01J 20/02 20060101
B01J020/02; B01D 15/00 20060101 B01D015/00; B01D 15/20 20060101
B01D015/20; B01J 20/28 20060101 B01J020/28; C02F 1/28 20060101
C02F001/28; C02F 1/50 20060101 C02F001/50; B01D 39/20 20060101
B01D039/20; B01J 20/30 20060101 B01J020/30 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 2011 |
SE |
1150100-4 |
Claims
1. A filtering medium for reducing the content of contaminants in
fluids, wherein said filtering medium comprises iron and silver in
a form chosen from at least one of: a mixture (A) comprising a
major part of an atomized iron-based or iron powder and a minor
part of a silver powder, an iron-silver powder alloy (B), and a
silver containing iron-based porous and permeable composite (C);
and wherein said contaminants are selected from the group
consisting of chlorine containing compounds, nitrates, nitrites,
heavy metals, toxic inorganic substances, toxic organic compounds,
microorganisms and/or combinations thereof.
2-20. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 13/984,318, filed on Oct. 17, 2013, which is a
U.S. national stage of International Application No.
PCT/EP2012/052001, filed on Feb. 7, 2012, which claims the benefit
of Provisional Application No. 61/441,064, filed on Feb. 9, 2011
and Swedish Application No. 1150100-4, filed on 9 Feb. 2011. The
entire contents of each of U.S. application Ser. No. 13/984,318,
International Application No. PCT/EP2012/052001, U.S. Provisional
Application No. 61/441,064, and Swedish Application No. 1150100-4
are hereby incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a filtering medium, a
method for the production thereof, use of said filtering medium and
a method for reducing the content of multiple contaminants
simultaneously in fluids by means of said filtering medium.
BACKGROUND
[0003] Toxic inorganic/organic substances in various water sources
have to be reduced below regulated levels before the water goes
into drinking water systems or is released into recipients.
[0004] Nitrate (NO.sub.3.sup.-) is a common inorganic contaminant
found in groundwater in the areas where agriculture activities
occur heavily. Nitrates usually come from fertilizers, used in
farming and gardening in order to provide the plants and shrubs
with nutrients.
[0005] Other contaminants which may be generated from such
activities are phosphates (PO.sub.4.sup.3-) and traces of
pesticides such as atrazine. Accumulation of fertilizers is a
problem as they can go through the soil and contaminate ground
water systems. Both shallow water wells and deep water wells can be
affected.
[0006] Toxic metals such as arsenic (As), chromium (Cr), whereof
its oxidation state +6 (Cr.sup.VI) is regarded as most harmful,
lead (Pb), mercury (Hg), cadmium (Cd), selenium (Se), etc., other
substances as chlorinated hydrocarbons and other organic
substances, sometimes measured as Total Organic Carbon (TOC) are
generated either from natural origins or from industrial or farming
activities.
[0007] Other types of contaminants that may be present in the water
are microorganisms, such as bacteria.
[0008] A conventional method for killing bacteria is the use of the
chlorination process where chlorine containing chemical substances
is added to the water for disinfection. Chlorine is a highly
efficient disinfectant; however one of the drawbacks with this
process is the remaining chlorine compounds in the water, such as
ClO.sup.- ions which can cause health problems.
[0009] In order to reach acceptable levels of contaminants in
drinking water, several processes are currently used.
[0010] Reverse osmosis is based on the process of osmosis. This
involves the selective movement of water from one side of a
membrane to the other.
[0011] This technique is also very energy consuming.
[0012] The ion exchange process percolates water through bead-like
spherical resin materials (ion-exchange resins). Ions in the water
are exchanged for other ions fixed to the beads. Microorganisms can
attach to the resins, providing a culture medium for rapid
bacterial growth and subsequent pyrogen generation. This technique
has a low initial capital investment but a high long-term
operational cost.
[0013] One of the above techniques is usually applied to target
one, or in some cases two contaminants present in the water. This
means that several techniques often need to be applied following
each other, in a chain process. In order to increase the
efficiency, reducing costs, it would be desirable to purify the
water from several contaminants in one single step. However, today
there are few products available in the market capable of
effectively purifying water from multiple contaminants
simultaneously.
[0014] US patent publication no. 2007/0241063A1 describes a process
for treating water contaminated with a volatile organic compound
with iron powder granules containing iron, carbon and oxygen.
[0015] U.S. Pat. No. 5,534,154 describes a procedure for treating
contaminated water by passing the water containing contaminant in
solution through a permeable body of treatment material comprising
particles of an adsorptive material physically mixed with particles
of metal. The iron metal particles mentioned in the patent are iron
fillings generally in solid granular form. The procedure requires a
negative Eh voltage which in turn demands oxygen exclusion.
[0016] U.S. Pat. No. 6,827,757 describes a magnetite-iron based
composite with very small average particle size of 0.05-10
.mu.m.
[0017] EP 1273371A2 describes an iron powder adapted to remediate
selected media by dehalogenating halogenated hydrocarbons in the
media comprising iron powder particles and inorganic compounds.
Said inorganic compounds should have a very low electric
resistivity, and are preferably selected from the group consisting
of Ca, Ti, V and Cr. Said inorganic compounds should be present on
at least a portion of the surface of each particle.
[0018] WO 2008/129551 discloses a liquid filter medium comprising
carbonaceous material, a water-insoluble metal oxide or hydroxide,
and at least one of chitosan and an ion exchanger.
[0019] U.S. Pat. No. 4,642,192 discloses a method of reducing the
concentration of inorganic chlorine by passing water through a bed
of metal particles, brass. This method shows insignificant effect
on reduction of nitrate.
[0020] U.S. Pat. No. 6,303,039 discloses a formulation comprising
at least two biocide metals and at least one chelating agent,
wherein said formulation dissolves over a period of months or
longer.
[0021] WO 03/076341 describes a system for control of bacterial
growth in water comprising antimicrobial treatment media within a
containment vessel, the treatment media including one or more of
transition metals and transition metal oxides.
[0022] U.S. Pat. No. 6,261,986 provides a method for producing a
pollutant adsorption and degradation article and the article
itself. At least one adsorbent is mixed with at least one pollutant
transforming agent to form a mixture. This mixture is compacted to
form a porous highly permeable article. Zeolites or surface
modified zeolites, SMZ, are proposed as adsorbent and iron powder
or iron in combination with other metals such as silver are
proposed as pollutant transforming agent. Reduction of chromate and
perchloroethylene in water was using the article was
demonstrated.
[0023] U.S. Pat. No. 6,942,807 provides a water filter device and
method which removes heavy metals and organic compounds from raw
water. The device comprises at least one iron filter connected in
series to a sand filter.
[0024] In US 2006/0021946 the use of volcanic rock or recycled
minerals from anthropogenic brick to remove toxic metals from
contaminated aqueous solutions is disclosed. The volcanic rock or
recycled minerals from anthropogenic brick may be combined with
zero valent iron, oxidized iron derivates and activated carbon.
[0025] The published patent application US 2009/0218266 discloses
an ion delivery system, IDS, that comprises a source of metal ions
with biocidal properties and a matrix that immobilizes the source
of ions and provides a sustained release of ions at biocidal
concentrations. Such source may be metal salts, metal particles or
particulate metallic alloy. Silver combined with various metals are
disclosed. The particle size of the metals or alloys being from 5
to 2 000 nm, preferably under 1 000 nm and most preferably between
100-300 nm.
[0026] US 2010/0176044 provides a carbonaceous filtering media for
treating drinking water. In some embodiments the filtering media
contains silver as an antimicrobial component.
[0027] The published application WO2010/019934 provides a process
for removing virus from drinking water comprising filtering
drinking water through a layer of coarse sand and contacting the
drinking water with a composite iron matrix. The composite iron
matrix comprises components containing iron, manganese, cerium,
carbon phosphorous, sulfur, aluminum silicon, chromium, copper and
zinc.
SUMMARY
[0028] It is previously known that silver containing powder can
kill bacteria when the content of silver is greater than certain
percentage but have very little effect on the reduction of nitrate.
It is also previously known that iron containing powders can only
reduce insignificant amounts of nitrate.
[0029] The inventors of the present invention have now surprisingly
found that using a combination of silver and iron in powder form, a
significant synergetic and/or catalyst effect can be obtained which
is shown in a surprisingly enhanced capability of killing bacteria
and reducing nitrate and chlorine. Thus such combination can reduce
significant amounts of heavy metals, bacteria, chlorine and nitrate
simultaneously. The synergetic effect can be achieved by optimizing
the combination through choosing the type of iron powder and silver
powder, determining the amount of silver, and the method of
preparing the iron-based filtering medium containing silver.
[0030] The filtering medium according to the present invention may
also be used for reducing other contaminants such as nitrites,
heavy metals, such as As, Cr, especially Cr having the most stable
state at oxidation stage +6, Pb, Hg, toxic organic and inorganic
compounds, other microorganisms or combinations thereof.
[0031] The present invention relates to a filtering medium for
reducing the content of contaminants in fluids, wherein said
filtering medium comprises iron and silver in a form chosen from at
least one of: --a mixture (A) comprising a major part of an
atomized iron-based or iron powder and a minor part of a silver
powder; --an iron-silver powder alloy (B); and--a silver containing
iron-based porous and permeable composite (C); and wherein said
contaminants are selected from the group consisting of chlorine
containing compounds, nitrates, nitrites, heavy metals, toxic
inorganic substances, toxic organic compounds, microorganisms
and/or combinations thereof. The present invention also relates to
a method for reducing the content of contaminants in fluids
comprising the steps of:
[0032] a) providing a filtering medium comprising iron and silver
in a form chosen from at least one of: [0033] a mixture (A)
containing a major part of an iron-based powder and a minor part of
a silver powder, [0034] an iron-silver alloy (B), and [0035] a
silver containing iron-based porous and permeable composite
(C),
[0036] b) bringing one or more contaminated fluid(s) in contact
with the filtering medium to purify said one or more fluid(s),
[0037] c) optionally removing the filtering medium from the
purified one or more fluid(s).
[0038] Further, the present invention relates to a method for the
production of a filtering medium comprising iron and silver in a
form chosen from at least one of: [0039] a mixture (A) containing a
major part of an iron-based powder and a minor part of a silver
powder, [0040] an iron-silver alloy (B), and [0041] a silver
containing iron-based porous and permeable composite (C),
[0042] wherein
[0043] the mixture (A) is obtained by mixing atomized iron powder
with at least essentially pure Ag powder particles; [0044] the
iron-silver alloy (B) is obtained by thermal bonding and/or
alloying iron-based powder particles with silver powder
particles;
[0045] the silver containing iron-based porous and permeable
composite (C) is obtained by subjecting a mixture (A) containing a
major part of an iron-based powder and a minor part of a silver
powder or an iron-silver powder alloy (B), to one or more of the
following steps: compaction, heat treatment and sizing.
[0046] The present invention also relates to use of a filtering
medium in a fluid, preferably a water containing fluid, more
preferably ground water, river water, industrial waste water, civic
waste water, medical waste water and/or surface water for reducing
the content of contaminants selected from the group consisting
chlorine containing compounds, nitrates, nitrites, heavy metals,
toxic inorganic substances, toxic organic compounds, microorganisms
and/or combinations thereof in the fluid.
BRIEF DESCRIPTION OF THE DRAWING
[0047] FIG. 1 shows a schematic drawing of a column test used for
evaluating the performance of the filtering medium according to the
invention.
[0048] FIG. 2 illustrates example of pure silver powder with
100%<60 um
[0049] FIG. 3 is a schematic illustration of thermal bonding and
thermal alloying silver particles to the surface of iron
particles.
DETAILED DESCRIPTION
[0050] The silver particles, the iron or iron-based particles, or
the particles may be characterised by the particle size or the
average particle size. In this context the average particle size
means that 50% by weight has particle sizes above the average
particle size and 50% by weight has particle sizes less than the
average particle size.
[0051] The silver particles may have a purity above 99% and they
may have spherical solid particle shape, and a particle size
between 0.1 to 125 .mu.m, preferably between 1 to 75 .mu.m and most
preferably between 1 to 60 .mu.m, such as 3 to 60 .mu.m.
Mixture (A)
[0052] In one embodiment of the present invention the filtering
medium for treatment of contaminated fluids consists of or
comprises a mixture, (A), containing a major part of an iron-based
powder and a minor part of a silver powder. This mixture is
characterized in that it contains between 0.01-5%, preferably
0.05-1% silver, by weight of the mixture.
[0053] The mixture (A) is typically produced by mixing iron-based
powder particles with silver powder particles in a mixer, until the
silver particles have been homogenously distributed throughout the
mixture. The mixing may be performed in an ordinary mixer, such as
a Z-blade mixer, cone mixer, ribbon mixer or high speed mixer for a
period of time between 0.5 min and 8 hours, preferably 1 minute to
5 hours or 30 min to 3 hours.
[0054] The iron-based powder particles used originates directly
from atomization of molten iron i.e. gas atomization and/or water
atomization of molten iron. Said production process is the most
common powder production routes in the industry today. However, the
iron-based powder particles according to the invention could
originate from other production processes providing particles
similar to those of the processes mentioned above.
[0055] In general, atomized powder particles contain less internal
porosity than particles produced by chemical reduction. The
particle morphology and sizes also varies depending on the
production process. Due to these differences atomized particles
often have higher apparent densities than chemically reduced
particles, such as apparent densities above 2.5 g/cm.sup.3 or
mostly above 2.8 g/cm.sup.3.
[0056] Iron-based powders produced with H2-reduction usually have
low apparent densities, such as less than 2.0 g/cm.sup.3 or less
than 1.8 g/cm.sup.3.
[0057] Iron-based powders produced with CO-reduction usually have
an apparent density between the two mentioned above, such as
between 1.8 and 2.8 g/cm.sup.3, or between 2.0 and 2.5
g/cm.sup.3.
[0058] In similar fashion there are also differences regarding the
specific surface areas (BET). Atomized powders have low surface
area, such as less than 0.1 m.sup.2/g, CO-reduced powders generally
have surface areas between 0.1 and 0.18 m.sup.2/g, and H2-reduced
powders generally have surface areas above 0.18 m.sup.2/g.
[0059] The differences in the powder particle morphology, density,
porosity, surface area etc., affect the performance of the filter
media according to the invention, and are (for the sake of
simplicity) referenced by specifying the production route in the
present application. However, it is important to point out, that it
is the particle properties and not the production route that affect
the properties of the filter media. Thus, any other technique that
provides iron-based powder particles with properties similar to the
mentioned above should be understood to be included in the
embodiments of the current application.
[0060] Also other types of particles, such as activated carbon,
activated alumina and zeolites, copper powder-may be added before
mixing, rendering the product enhanced properties for reducing
contaminants. The added amount of said other types of particles
should be 0.01-10%, preferably 0.05-8%, more preferably 0.10-5% by
weight of the mixture.
[0061] The iron-based powder may have a content of Fe of 90% or
above, such as 95% or above. The average particle size of the iron
based powder may be between 1 .mu.m and 10 mm, for example between
20 .mu.m and 5 mm, such as between 45 .mu.m and 2 mm, but is not to
be interpreted as limited to these particle sizes. Further, it may
be that maximum 2% the iron based particles may be above 850 .mu.m
and maximum 30% by weight of the iron based particles may be below
45 .mu.m, for example maximum 2% may be above 212 .mu.m and maximum
30% below 45 .mu.m.
[0062] It has surprisingly been shown that only a specified type of
silver particles in combination with the atomized iron-based powder
particles will render the filter medium the desired properties and
performances. In order to fulfill the requirements the silver
particles may have a purity above 99% and they may have spherical
solid particle shape, and a particle size between 0.1 to 125 .mu.m,
preferably between 1 to 75 .mu.m and most preferably between 1 to
60 .mu.m, such as 3 to 60 .mu.m but is not to be interpreted as
limited to these particle ranges. In contrast to known methods and
products, which include silver particles, for reducing contaminants
in fluids, the silver particles used according to the present
invention have a much bigger size and cannot be regarded or defined
as nano-particles. This fact is of great importance since the
negative aspects as regarded to the spreading of nano silver
particles to various recipients can be omitted.
[0063] FIG. 2 shows the particle morphology of a silver powder,
with particle size between 3 and 60 .mu.m.
[0064] In one embodiment iron-based powder with a content of iron
of more than 95% by weight, preferably more than 99% weight, is
mixed with a Fe--Ag alloy, wherein said Fe--Ag alloy consists of
Ag-particles that have been thermal-bonded or thermal-alloyed to
iron particles and said Fe--Ag alloy comprises 0.01-5% by weight of
silver.
[0065] In one embodiment of the present invention the filtering
medium comprises the mixture (A) wherein the mixture comprises:
[0066] 1) atomized iron powder with an average particle size
between 10 mm and 1 .mu.m, and with an Fe-content of at least 90%
by weight of the iron powder and essentially pure Ag powder
particles, with a silver content of at least 99% by weight, and
wherein the mixture (A) contains between 0.01-5% Ag, by weight.
Iron-Silver Powder Alloys (B)
[0067] In one embodiment of the present invention the filtering
medium consists of or comprises iron-silver powder alloy(s).
[0068] The iron-silver powder alloy(s) according to the invention
may have a particle size range between 10 mm and 1 .mu.m,
preferably between 5 mm and 20 .mu.m and most preferably between 2
mm and 45 .mu.m but is not to be interpreted as limited to these
particle sizes. The iron-silver powder alloy(s) may be obtained
from the silver and iron powders according to (A).
[0069] In an embodiment the iron-silver alloy is produced by
thermal bonding and/or thermal alloying, in which case silver
particles are bonded and/or alloyed to the surface of iron-based
particles. The amount of silver in the alloy in this embodiment is
0.01-5%. Said iron based particles originate directly from
atomization of molten iron i.e. gas atomization or water
atomization of molten iron. The silver particles used in the
diffusion bonding process originate from pure Ag.
[0070] In this context, the term "thermal bonding" means that the
silver particles are merely bonded to the surface of the iron-based
particles below 950.degree. C., preferably between 500 and
950.degree. C. and most preferably between 600 and 950.degree. C.
The term "thermal alloying" means that the silver particles are
firmly alloyed to the surface of the iron-based particles above
950.degree. C. preferably between 950 and 1250.degree. C. and most
preferably between 950 and 1200.degree. C., FIG. 3 shows a
schematic illustration of thermal bonding and thermal alloying
silver particles to the surface of iron particles.
[0071] In an alternative embodiment the silver particles are bonded
to the surface of the iron powder through a binder.
Iron-Based Porous and Permeable Composite Containing Silver (C)
[0072] In one embodiment of the present invention the filtering
medium for treatment of contaminated fluids consists of or
comprises an iron-based porous and permeable composite containing
silver.
[0073] Said composite can be manufactured into various forms, such
as chip, flake, block or pellet, by subjecting the iron-silver
alloy (B) or the iron-based powder-silver containing mixture (A) to
common powder metallurgical technologies.
[0074] The use of the wording "permeable" as disclosed herein is to
be interpreted as a composite or an iron-based powder body being
constructed so that it is permeated or penetrated, especially by
liquids or gases.
[0075] The use of the wording "porous" as disclosed herein is to be
interpreted as a composite or an iron powder or body being
constructed so that it is admitting the passage of gas or liquid
through pores or interstices.
[0076] Thus, the iron-based porous and permeable composite
containing silver (C) according to the present invention may
comprise silver containing particles located in pores and cavities
of the composite.
[0077] The iron-based powder mixture (A) or the iron-silver alloy
(B) can be subjected to compaction and/or thermal treatment
optionally followed by sizing to produce an iron-based porous and
permeable composite containing silver.
[0078] Compaction is usually performed at pressures below 1000 MPa,
preferably below 600 MPa, e.g. 10-1000 MPa or 20-600 MPa, to
achieve a compacted density of about or less than 7.0 g/cm.sup.3 to
form desired shapes, such as blocks, granules or pellets.
Preferably the compacted density is between 2.5-7.0 g/cm.sup.3,
preferably 4-6 g/cm.sup.3 depending of type of iron-based powder
used.
[0079] Thermal treatment usually involves temperatures below
1200.degree. C., below 1000.degree. C., or below 800.degree. C.,
depending on the types of materials (A) or (B) used, in a reducing
or inert atmosphere. The thermal treatment temperature is usually
above 300.degree. C., preferably above 400.degree. C. Temperature
intervals of interest are especially 300-1200.degree. C.,
400-1200.degree. C., 300-1000.degree. C., 400-1000.degree. C.,
300-800.degree. C., 400-800.degree. C., 300-700.degree. C.,
400-700.degree. C., 300-600.degree. C., 400-600.degree. C.,
300-500.degree. C. and 400-500.degree. C.
[0080] Sizing or gently grinding is usually performed after heat
treatment and/or compaction and may be performed in any suitable
equipment resulting in a particle size between 10 mm and 10 .mu.m,
preferably between 5 mm and 20 .mu.m and most preferably between 2
mm and 45 .mu.m.
Use of the Filtering Medium
[0081] The present invention also relates to the use of the
filtering medium for treatment of contaminated fluids from multiple
contaminants simultaneously, wherein a fluid is allowed to pass
through or be contacted with said filtering medium. The
contaminated fluids are preferably in liquid form. Said fluid may
be a water containing fluid, preferably ground water, river water,
industrial waste water, civic waste water, medical waste water
and/or surface water. Said fluid may be used as drinking water
after purification treatment according to the present invention.
Said contaminants may be selected from the group consisting of
chlorine containing compositions, nitrates, nitrites, heavy metals,
such as As, Pb, Hg, Cd, Se, Cr and hexavalent Cr, other toxic
inorganic substances, toxic organic compounds and/or microorganisms
such as bacteria; or combinations thereof.
Method for Reducing the Content of Multiple Contaminants in
Fluids
[0082] The present invention also relates to a method for reducing
the content of multiple contaminants in fluids which comprises the
steps of obtaining the iron powder-based silver containing mixture
(A) or the iron-silver alloy (B), or the permeable porous composite
(C) as described above and allowing one or more contaminated
fluid(s) to pass through or be contacted with a filtering medium
consisting of or comprising said alloy, or said mixture or said
composite, thus reducing the content of multiple contaminants
simultaneously.
[0083] Said filtering medium can be placed inside a container
connected to the supply system of the fluid to be treated.
[0084] Such containers could be placed serial or parallel and
connected to additional containers containing other known
substances for reducing the content of harmful substances in the
fluid.
[0085] Said filtering medium could also be added to the water to be
cleaned and after a certain time the filtering medium could be
removed or the water could be decanted after which the purified
water can be used.
[0086] The filtering medium according to the invention preferably
has a specific surface area between 0.05 and 50 m.sup.2/g as
measured by BET (Brunauer, Emmett and Teller, 1938).
[0087] A highly surprising synergetic effect is obtained with the
filtering medium according to the invention, when combining a
certain type of silver powder particles with a certain type of iron
powder particles. This synergetic effect is evident by the
remarkably high efficiency for removal of multiple contaminants,
especially the removal of bacteria, chlorine and nitrate.
[0088] An additional advantage with the method for reducing
multiple contaminants simultaneously in fluids according to the
present invention is, in contrast to methods such as conventional
ion exchange, that no hazardous waste is generated by the
method.
[0089] The filtering medium according to the present invention
should have a permeability, expressed as porosity ranging from 11
to 68%, preferably 23-50%, regardless of embodiment.
[0090] One embodiment of the invention is to apply the filtering
medium according to the invention to drinking water treatment,
waste water (municipal and industrial) treatment and/or soil
remediation.
[0091] The generated byproduct, i.e. the used filtering medium
comprising the iron-silver alloy, or the iron powder-based silver
containing mixture, or the porous composite, can be used in other
industries, for instance as raw material for the steel
industry.
[0092] In a preferred embodiment a filtering medium for reducing
the content of multiple contaminants in fluids simultaneously
comprises a mixture (A) containing a major part of an iron-based
powder and a minor part of a silver based powder, wherein said
mixture consists of: [0093] atomized iron powder with an average
particles size between 10 .mu.m and 150 .mu.m in size, and with an
Fe-content of at least 90% by weight of the iron powder [0094]
Essentially pure Ag powder particles with Ag-content of at least
99% by weight, in a sufficient amount to ensure that the
composition contains above 0.25 up to 1% of Ag, by weight of the
mixture.
[0095] In an another preferred embodiment a filtering medium for
reducing the content of multiple contaminants in fluids
simultaneously comprises an iron-silver powder alloy (B) having an
average particle size between 40 and 150 micrometers produced
through thermal bonding of silver particles to the surface of iron
particles.
[0096] The iron particles being atomized iron powder with an
average particles size between 10 .mu.m and 150 .mu.m in size, and
with an Fe-content of at least 90% by weight of the iron powder and
the silver particles being essentially pure Ag powder particles
with Ag-content of at least 99% by weight. The content of Ag being
above 0.25 up to 1% by weight of the iron-silver alloy.
[0097] In an another preferred embodiment a filtering medium for
reducing the content of multiple contaminants in fluids
simultaneously comprises an iron-silver powder alloy (B) having an
average particle size between 40 and 150 micrometers produced
through thermal alloying in which case silver particles are alloyed
to the surface of iron particles.
[0098] The iron particles being atomized iron powder with an
average particles size between 10 .mu.m and 150 .mu.m in size, and
with an Fe-content of at least 90% by weight of the iron powder and
the silver particles being essentially pure Ag powder particles
with Ag-content of at least 99% by weight. The content of Ag being
above 0.1 up to 1% by weight of the iron-silver alloy.
EXAMPLES
[0099] Various powder materials according to table 1, showing their
properties, was used in the following examples.
TABLE-US-00001 TABLE 1 properties of iron and copper containing
powders used in the examples. Materials AD, PD, Porosity SSA,
Particle size Powder sample type ID % Ag % Fe g/cm.sup.3 g/cm.sup.3
% m.sup.2/kg distribution pure iron H-reduced A 0 >96 1.22 6.48
17.7 225 80% > 105 um C-reduced B 0 >97 2.45 7.23 8.1 100 80%
< 105 um Atomized C 0 >98 2.95 7.83 0.5 50 80% < 105 um
pure silver Ultrafine I >99 0 1.6 10.5 0 800 100% < 3 um Fine
J >99 0 2.3 10.5 0 550 100% > 0.1 um 80% > 3 um 100% <
60 um coarse K >99 0 3.4 10.5 0 210 80% > 45 um 100% < 125
um
Apparent Density (AD):
[0100] The density when powder is in the loose state without
agitation. It is measured by Hall flowmeter which consist of a
funnel and measuring cup, where the powder passes through the
funnel and flows into the cup. (ASTM B 212 and ASTM B 417)
Particle Size Distribution (PSD):
[0101] Particle size distribution data as expressed by the weight
percentage of powder retained on each of a series of sieves of
decreasing size (increasing mesh). (ASTM B 214)
Particle Density (PD):
[0102] The particle mass per unit volume of particle, including the
inside closed pores. It is measured by pycnometer method that
measures the liquid volume increase found upon adding the powder
into a liquid.
Specific Surface Area (SSA):
[0103] The external powder area per unit weight of powder as
measured by gas absorption (BET method).
% Fe and % Ag:
[0104] The content of iron and silver elements in the powder. It is
determined by a inductively coupled plasma mass spectrometry
(ICP-MS method)
Test Methods
[0105] The following analytical and testing methods for evaluation
of the capability for reducing contaminants in water was used in
the examples:
Bacteria (E-Coli Test):
[0106] 100 g of powder medium, except for the silver powders which
were added in 0.5 g, was added to 250 ml water containing standard
E. Coli bacteria and mixed by shaking for 10 min. After the powder
medium settled, 100 ml treated water was taken for bacteria
Presence/Absence test. One packet of reagent (IDEXX Laboratories)
was added to the water sample in a sterile, non-fluorescing vessel
and mixed by shaking and incubate at 35.degree. C. for 24 h. The
results was read at 24 h by placing a 6 W, 365 nm UV light within 5
inches of the sample. If yellow color, the test was negative (no
bacteria exist). If blue fluorescence was observed, the presence of
E. coli was confirmed. (USA National Environmental Methods Index
68585-22-2)
Chlorine Reduction:
[0107] 100 g powder medium, except for silver powders which were
added in 0.5 g, was added in 250 ml water containing .sup..about.5
mg/L ClO.sup.- by the addition of bleach solution with
.sup..about.6% sodium hypochlorite). The medium was mixed with the
water by stirred gently for 30 min. The amount of chlorine in raw
and treated water were determined by spectrophotometer (Hach
DR5000) and the percentage of chlorine reduction was
calculated.
Nitrate Reduction:
[0108] 100 g powder medium, except for the silver powders which
were added in 0.5 g, was added to 250 ml groundwater containing
.sup..about.20 mg/L-N nitrate (Martinsberg, Pa., USA). The medium
was mixed with the water by gently stirring for 24 hours. The
amount of nitrate in raw and treated water was determined by
spectrophotometer (Hach DR5000) and the percentage of nitrate
reduction was calculated.
Multiple Contaminant Reduction Efficiency (MCRE):
[0109] In order to compare the efficiency of the tested filter
medium an index was calculated according to the following
formula:
MCRE=(% Bacteria reduction+% Chlorine reduction+% Nitrate
reduction)/3
wherein the % Bacteria reduction is either 0 or 100. The MCRE is
intended to quantify the efficiency of multiple contaminant
simultaneous reduction, and is expressed in %, thus 100 is the
highest level of efficiency.
[0110] The value is intended purely for comparison purposes, since
in practice, one contaminant may be of more importance to remove
than another.
Example 1 (Comparative)
[0111] As reference examples, the powder samples according to Table
1 were tested individually for their ability of reducing bacteria,
chlorine and nitrate. The tests were performed according to the
earlier described testing methods. Table 2 shows powder samples
used and the results.
TABLE-US-00002 TABLE 2 Bac- Nitrate teria Chlorine reduc- Powder Ag
killer reduction tion MCRE sample Type ID % % % % % pure iron
H-reduced A 0 0 98 6 35 C-reduced B 0 0 100 14 38 atomized C 0 0 68
11 26 pure silver ultrafine I 100 0 33 2 11 fine J 100 100 44 1 48
coarse K 100 0 39 2 14
[0112] For pure iron powder by itself, bacteria is not killed, have
a small reduction rate (6-14%) in nitrate removal but can greatly
reduce the chlorine (68-100%). Their MCRE is between 26-38.
[0113] For pure silver powder by itself, almost no reduction for
nitrate, can partly reduce the chlorine and surprisingly even
though they have similar particle shape in the three grades of
silver powders selected in this invention, only the silver powder
with 100%<60 um can completely kill the bacteria and its MCRE is
48.
[0114] Therefore, the following examples will use the fine silver
powder (100%<60 um) to demonstrate the synergetic and catalyst
effect to iron. The iron powder according to the invention used in
the following examples was an atomized iron powder following the
particle size specification maximum 2% above 212 .mu.m and maximum
30% less than 45 .mu.m.
Example 2
[0115] Mixtures of a major part of an iron-based powder and a minor
part of a silver based powder were prepared. As reference examples
pure reduced and pure atomized powders were used. The mixtures were
evaluated for their removal efficiency with respect to bacteria,
chlorine and nitrate. The removal efficiency was calculated as
MCRE. The mixtures were evaluated according to the testing
methods.
TABLE-US-00003 TABLE 3 Bacteria Chlorine Nitrate Ag killer
reduction reduction MCRE Category sample ID % % % % % Pure iron
H-reduced A 0 0 98 6 35 (comparative) Pure iron CO-reduced B 0 0
100 14 38 (comparative) Pure iron atomized C 0 0 68 11 26
(comparative) silver containing Atomized, mix CJ1 0.25 0 56 12 23
silver containing Atomized, mix CJ2 0.5 100 76 15 64 silver
containing Atomized, mix CJ2 1 100 65 17 61 silver containing
H-reduced, mix AJ1 0.5 0 36 2 13 (comparative) silver containing
H-reduced, mix AJ1 1 0 30 4 11 (comparative) silver containing
CO-reduced, mix BJ1 0.5 0 98 16 38 (comparative) silver containing
CO-reduced, mix BJ1 1 0 84 15 33 (comparative)
[0116] The table 3 shows that pure iron powder by itself cannot
kill bacteria and have an insignificant effect of the reduction of
nitrate. When fine silver powder is mixed in pure iron powder, a
synergetic and/or catalyst effect for can be seen with silver
containing atomized powder in bacteria killing, chlorine and
nitrate reduction. The content of silver must be >0.25% by
weight for obtaining a satisfactory bacteria killing effect. The
MCRE value is 64 when the silver is added with 0.5% by weight. A
content of silver >1% by weight is not considered to be
cost-effective since the performance is not improved. For example
the content of silver may be between 0.25 and 1% by weight, such as
between 0.25 and 0.5% by weight. It is clear from table 3 that
silver containing material performs better as compared to pure iron
and that it may be preferred with atomized iron combined with
silver as compared to H or CO reduced iron combined with
silver.
[0117] For silver containing H-reduced and CO-reduced iron powder,
however, no synergetic effect is observed even when the silver is
added with 1%.
Example 3
[0118] Filtering medium containing thermally bonded iron-silver
alloy powder particles according to the invention were used. The
alloy particles were prepared through a thermal bonding process
performed at 900.degree. C. for 30 minutes in an 75% H.sub.2 and
25% N.sub.2 atmosphere.
[0119] As reference examples pure reduced and pure atomized powders
were used. The alloy particles were evaluated for their removal
efficiency with respect to bacteria, chlorine and nitrate according
to the testing methods. The combined removal efficiency was
calculated as MCRE.
TABLE-US-00004 TABLE 4 Bacteria Chlorine Nitrate Ag killer
reduction reduction MCRE Category sample ID % % % % % pure iron
H-reduced A 0 0 98 6 35 (comparative) pure iron CO-reduced B 0 0
100 14 38 (comparative) pure iron atomized C 0 0 68 11 26
(comparative) silver containing Atomized, CJ3 0.25 0 100 67 56
thermal bond silver containing Atomized, CJ4 0.5 100 99 60 86
thermal bond silver containing H-reduced, AJ2 0.5 0 45 30 25
(comparative) thermal bond silver containing CO-reduced, BJ2 0.5 0
84 28 37 (comparative) thermal bond
[0120] The table shows pure iron powder by itself cannot kill
bacteria and have an insignificant effect of the reduction of
nitrate. When the silver is thermal bonded to atomized iron powder,
a much greater synergetic and/or catalyst effect can be achieved
compared to the mix of iron with the same amount of silver (Table
3). The MCRE increases from 64 to 86 with 0.5% silver addition. The
content of silver must be >0.25% by weight for obtaining a
satisfactory bacteria killing effect. For example the content of
silver may be between 0.25 and 1% by weight, such as between 0.25
and 0.5% by weight.
[0121] However, no such significant synergetic and/or catalyst
effect is achieved in the silver thermal-bonded in H-reduced and
CO-reduced iron powders.
Example 4
[0122] Filtering medium containing thermally alloyed iron-silver
powder particles according to the invention were prepared. The
alloy particles were prepared through a thermal alloying process
performed at 1120.degree. C. for 30 minutes in an 75% H.sub.2 and
25% N.sub.2 atmosphere As reference examples pure reduced and pure
atomized powders were used. The mixtures were evaluated for their
removal efficiency with respect to bacteria, chlorine and nitrate
according to the testing methods. The removal efficiency was
calculated as MCRE.
TABLE-US-00005 TABLE 5 Bacteria Chlorine Nitrate Ag killer
reduction reduction MCRE Category sample ID % % % % % Pure iron
H-reduced A 0 0 98 6 35 (comparative) Pure iron CO-reduced B 0 0
100 14 38 (comparative) Pure iron atomized C 0 0 68 11 26
(comparative) silver containing Atomized, CJ5 0.1 0 96 45 47
thermal-alloy silver containing Atomized, CJ6 0.25 100 95 68 88
thermal-alloy silver containing Atomized, CJ7 0.5 100 90 67 86
thermal-alloy silver containing H-reduced, AJ3 0.5 0 55 40 32
(comparative) thermal-alloy silver containing CO-reduced, BJ3 0.5 0
76 35 37 (comparative) thermal-alloy
[0123] The table shows pure iron powder by itself cannot kill
bacteria and have an insignificant effect of the reduction of
nitrate. When the silver is thermal-alloyed to atomized iron
powder, a similar synergetic and/or catalyst effect can be achieved
with a half of silver addition compared to the silver
thermal-bonded iron powder (Table 4). The MCRE increases from 64
obtained with the iron-silver mix to 88 with the 0.25% silver
thermal-alloyed iron powder. The content of silver can be reduced
to a half of amount for bacteria killing compared to the
iron-silver mix and silver thermal-bonded iron powder but it must
be >0.1% by weight for obtaining a satisfactory bacteria killing
effect. For example the content of silver may be between 0.1 and 1%
by weight, such as between 0.1 and 0.5% by weight.
[0124] However, no such significant synergetic and/or catalyst
effect is achieved in the silver thermal alloyed in H-reduced and
CO-reduced iron powders.
Example 5
[0125] A sample of natural occurring water, ground water from
Martinsburg, Pa., USA, was used. Table 6 shows the properties of
the ground water sample. The sample was spiked with E-coli
bacteria, arsenic hexavalent chromium (Cr VI) and chlorine (5 mg/L
ClO- by adding bleach solution with .sup..about.6% sodium
hypochlorite). Table 6 shows the properties of the ground water
sample.
TABLE-US-00006 TABLE 6 Nitrate[mg/l] (as N) 20.2 pH 7.27 Alkalinity
[mg/l] 158 Acidity [mg/l] <1.0 Total hardness [mg/l] 168
Conductivity [uS/cm] 350
[0126] The test was performed by pumping the water into a column
having a test material, as shown in FIG. 1. The empty bed contact
time, EBCT, was 30 minutes. The effluent water was analyzed with
regards to contaminants after certain time intervals. The content
of contaminants at 0 hours is equal to the content in the
non-treated water (influent). 100 g filter medium consisting of
atomized iron powder thermal-alloyed with 0.5% silver was used.
[0127] The concentrations of different contaminants in the water
(effluent) passing the column after various time intervals are
shown in table 7.
TABLE-US-00007 TABLE 7 Nitrate Arsenic Hex-Cr (VI) Chlorine E-coli
bacteria (N) % % Cr VI % (Cl2) % Yes+ % Hours mg/l reduction mg/l
reduction mg/l reduction mg/l reduction No- reduction 0 20.2 0 1.12
0 0.51 0 5.3 0 + 0 2 17.3 14.4 0.01 99.1 0.011 97.8 0.01 99.8 - 100
4 15.4 23.8 0.005 99.6 0.011 97.8 0.01 99.8 - 100 6 13.5 33.2 0.002
99.8 0.01 98.0 0.01 99.8 - 100 12 9.2 54.5 0.001 99.9 0.011 97.8
0.01 99.8 - 100 24 6.1 69.8 0.001 99.9 0.012 97.6 0.01 99.8 - 100
28 6.0 70.3 0.001 99.9 0.009 98.2 0.01 99.8 - 100 30 5.9 70.8 0.002
99.8 0.014 97.3 0.01 99.8 100 32 6.6 67.3 0.001 99.9 0.007 98.6
0.01 99.8 - 100 48 5.1 74.8 0.001 99.9 0.01 98.0 0.01 99.8 -
100
[0128] As can be seen in table 7, the filter medium according to
the invention effectively removes multiple contaminants in the
water, in this case arsenic, hexavalent chromium, chlorine,
nitrates and E-coli bacteria.
* * * * *