U.S. patent application number 10/975976 was filed with the patent office on 2005-03-17 for method for removing heavy metals using an adsorbent.
Invention is credited to Vo, Toan Phan.
Application Number | 20050059549 10/975976 |
Document ID | / |
Family ID | 32230751 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050059549 |
Kind Code |
A1 |
Vo, Toan Phan |
March 17, 2005 |
Method for removing heavy metals using an adsorbent
Abstract
A method is presented for removing heavy metal anions from a
fluid or gas medium containing metal anions. The method includes
providing an adsorbent having deposited therein at least one
oxygen-containing compound of at least one metal selected from the
group consisting of iron, copper, and aluminum; and contacting a
portion of the medium with the adsorbent. The oxygen-containing
compound may be incorporated into the carbon by impregnation or
dispersion of a suitable precursor of such a compound. The
precursor may be further treated to yield the oxygen-containing
compound. Such adsorbents are particularly useful for removing
arsenic and/or selenium from the environment and may be used in
treating drinking water sources.
Inventors: |
Vo, Toan Phan; (Niskayuna,
NY) |
Correspondence
Address: |
COHEN & GRIGSBY, P.C.
11 STANWIX STREET
15TH FLOOR
PITTSBURGH
PA
15222
US
|
Family ID: |
32230751 |
Appl. No.: |
10/975976 |
Filed: |
October 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10975976 |
Oct 28, 2004 |
|
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|
09940178 |
Aug 27, 2001 |
|
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Current U.S.
Class: |
502/406 ;
210/660 |
Current CPC
Class: |
B01J 20/02 20130101;
C02F 1/281 20130101; C02F 2101/20 20130101; B01D 2253/10 20130101;
B01J 20/08 20130101; B01J 2220/4893 20130101; B01J 20/3236
20130101; B01J 20/186 20130101; B01J 20/3035 20130101; C02F 2307/06
20130101; B01J 20/2808 20130101; B01J 20/28033 20130101; B01D 53/64
20130101; B01J 20/3071 20130101; B01J 2220/56 20130101; B01J
20/3042 20130101; B01J 2220/485 20130101; C02F 2101/103 20130101;
B01J 20/06 20130101; B01J 20/28019 20130101; B01J 20/28045
20130101; B01J 20/223 20130101; B01J 2220/62 20130101; C02F 1/283
20130101; C02F 1/288 20130101; B01D 2257/60 20130101; B01J 20/3028
20130101; B01J 20/3078 20130101; B01J 20/3204 20130101; B01J 20/20
20130101 |
Class at
Publication: |
502/406 ;
210/660 |
International
Class: |
B01D 015/00 |
Claims
What is claimed is:
1. A method for removing heavy metal anions from a fluid or gas
medium containing metal anions, said method comprising the steps
of: (1) providing an adsorbent comprising a carbon having a BET
surface area greater than about 100 m.sup.2/g and having deposited
therein at least one oxygen-containing compound of at least one
metal selected from the group consisting of iron, copper, and
aluminum; (2) contacting a portion of said medium with said
adsorbent; and (3) obtaining a treated medium having a lower
concentration of said heavy metal than a concentration of said
heavy metal of said medium; wherein said anions contain oxygen; and
said oxygen-containing compound is selected from the group
consisting of oxides, hydroxides, and combinations thereof.
2. A method for removing heavy metal anions from a fluid or gas
medium containing metal anions, said method comprising the steps
of: (1) contacting an adsorbent with a portion of said medium; and
(2) filtering said adsorbent from said medium wherein said
adsorbent comprises a carbon having a BET surface area greater than
about 100 m.sup.2/g and having deposited therein at least one
oxygen-containing compound of at least one metal selected from the
group consisting of iron, copper, and aluminum; wherein said anions
contain oxygen; and said oxygen-containing compound is selected
from the group consisting of oxides, hydroxides, and combinations
thereof.
3. The method according to claim 1, wherein said heavy metal is
selected from the group consisting of arsenic, selenium, and
combinations thereof.
4. The method according to claim 1, wherein said at least one metal
is present at a concentration from about 0.01 to about 50 percent
by weight of said carbon.
5. The method according to claim 1, wherein said adsorbent has a
micropore volume of greater than about 20 cm.sup.3/100 g of
adsorbent.
6. The method according to claim 1, wherein said adsorbent has a
form selected from the group consisting of granule, pellet, sphere,
powder, woven fabric, non-woven fabric, mat, felt, block, and
honeycomb.
7. The method according to claim 1, wherein said adsorbent is
disposed at a point of use.
8. The method according claim 7, wherein said adsorbent is disposed
in a fixed bed or fluidized bed.
9. The method according claim 7, wherein said adsorbent is disposed
in a section of a water supply piping of a house.
10. The method according to claim 8, wherein said fixed bed
comprises a cartridge that is disposed at a water faucet.
11. The method according to claim 10, wherein said cartridge
further comprises at least one adsorbent selected from the group
consisting of zeolites, ion exchange resins, silica gel, alumina,
impregnated carbon and unimpregnated activated carbons.
Description
CROSS REFERENCE
[0001] This application is a divisional of copending U.S. patent
application Ser. No. 09/940,178 (Attorney Docket Number 01-159)
filed on Aug. 27, 2001.
FIELD OF INVENTION
[0002] The present invention relates to methods for removing heavy
metals from a medium adjacent thereto. In particular, the present
invention relates to a method for removing arsenic and/or selenium
from medium adjacent to it using an adsorbent containing at least
one oxygen-containing compound.
BACKGROUND OF THE INVENTION
[0003] It has been known that many heavy metals, such as lead,
arsenic, and selenium, are toxic to humans even at low levels. One
cause for the presence of these heavy metals in the environment has
been increasing industrial activities in the recent past. However,
in some parts of the world, high levels of heavy metals, such as
arsenic, exist naturally in underground water sources because of
natural occurrence of these metals in rock formations. Recent
epidemiological studies on the carcinogenicity of arsenic have
triggered increasing concern about the concentration of arsenic in
drinking water and have prompted reevaluation of the current United
States maximum contaminant level ("MCL") of 50 .mu.g/l for arsenic.
Some recent studies on long-term human exposure show that arsenic
in drinking water can be associated with liver, lung, kidney, and
bladder cancer. Over exposure to selenium has been shown to have
undesired effects on the nervous system and to contribute to the
cause dyspnea, bronchitis, and gastrointestinal disturbance.
[0004] Many experimental techniques have been proposed or tested
for removing arsenic. All of these techniques have achieved varying
degrees of effectiveness when arsenic is first oxidized to As(V).
Coagulation using alum or ferric sulfate has been shown to have an
effect on arsenic levels at a near neutral pH in laboratory and
pilot-plant tests. However, the efficiency of this process
decreases sharply at low or high pHs. Moreover, the coagulant
containing arsenic must be filtered, resulting in additional costs.
Lime softening techniques have been shown to be effective at pH
levels greater than about 10.5; and, therefore, is not likely to be
applicable in drinking water applications. Adsorption treatment
methods using activated alumina or ion exchange have been proposed
and tested on a pilot-plant scale. However, adsorption of arsenic
on alumina is seriously compromised when other ions are present,
such as selenium, fluoride, chloride, and sulfate. The adsorption
process using ion exchange adsorbents can remove arsenic, but
sulfate, total dissolved solids ("TDS"), selenium, fluoride, and
nitrate also compete with arsenic for the ion exchange capacity,
thus decreasing likely effectiveness.
[0005] Therefore, there is a need to provide simple and convenient
materials and methods for removing heavy metals such as arsenic
and/or selenium from the environment that do not have the
disadvantages of the prior-art materials and methods. It is also
desirable to provide convenient materials and methods for removing
arsenic and/or selenium from the environment, which materials and
methods can be made widely available at low cost.
SUMMARY OF THE INVENTION
[0006] The present invention provides adsorbents and methods for
removing heavy metals that exist as anions from the environment to
acceptable levels. An adsorbent comprises a carbon adsorbent having
at least one oxygen-containing compound incorporated therein
wherein said oxygen-containing compound is of a metal selected from
the group consisting of iron, copper, and aluminum. In one
embodiment of the present invention, the oxygen-containing compound
of a metal is selected from the group consisting of oxides and
hydroxides. In another embodiment of the present invention, the
oxygen-containing compound of a metal is incorporated into the
carbon adsorbent by a method of impregnating or dispersing at least
a compound of said metal in the carbon adsorbent.
[0007] Another embodiment of the present invention provides a
method for producing a carbon adsorbent capable of removing heavy
metals that exist as anions. The method comprises the steps of: (1)
providing a carbon adsorbent; (2) impregnating the adsorbent with
at least one compound of a metal selected from the group consisting
of iron, copper, and aluminum or combinations thereof; and (3)
converting said compound into at least one oxygen-containing
compound. In another embodiment, the method comprises the steps of:
(1) providing a carbonaceous material; (2) mixing at least one
compound of a metal selected from the group consisting of iron,
copper, and aluminum or combinations thereof into the carbonaceous
material to produce a mixture of said carbonaceous material and
said metal; (3) forming the mixture into particles of a
carbonaceous material containing said metal; and (4) converting the
particles of said carbonaceous material containing said metal into
particles of a carbon adsorbent containing said metal.
[0008] Alternatively, a carbon adsorbent of the present invention
for use in removing metal anions from a liquid or gas medium may be
made by: (1) pulverizing a carbonaceous material, a binder, and at
least one compound of a metal selected from the group consisting of
iron, copper, and aluminum or combinations thereof to form a
powdered mixture; (2) compacting said powdered mixture into shaped
objects; and (3) crushing and screening the shaped objects into a
metal-containing particulate material to produce said carbon
adsorbent. Preferably, in step one, the carbonaceous material,
binder and metal compound is pulverized together or, alternatively,
the carbonaceous material, binder and metal compound are pulverized
separately before making the pulverized mixture. Preferably in step
two, the compacting is accomplished by briquetting, pelletizing,
densifying or extruding processes. The method may also have an
additional step four comprising gasifying said metal containing
particulate material to produce said carbon absorbent. In an
embodiment, the gasifying of step four is conducted under an
atmosphere comprising an oxygen-containing gas at a temperature in
a range from about 900.degree. C. to about 1100.degree. C. for a
time sufficient to produce an adsorbent having a BET surface area
of at least 100 m.sup.2/g. The method may also comprise the
additional step of oxidizing said metal-containing particulate
material before the step of gasifying.
[0009] In another preferred embodiment of the present invention the
method for removing heavy metals that exist as anions comprises the
steps of: (1) providing a carbon adsorbent containing a metal
selected from the group consisting of iron, copper, and aluminum;
and (2) contacting said carbon adsorbent containing said metal with
a medium containing the heavy metal anions. In all embodiments, the
medium may be a liquid or gas phase in which the metals exist as
anions. Preferably, the medium is drinking water.
[0010] Other features and advantages of the present invention will
be apparent from a perusal of the following detailed description of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention provides an adsorbent for removing
heavy metal from a medium that comprises a carbon having at least
one oxygen-containing compound of a metal incorporated therein,
wherein said metal is selected from the group consisting of iron,
copper, and aluminum. Some heavy metals such as arsenic and
selenium normally exist in the environment as anions and, thus, are
soluble in water and difficult to be removed therefrom. One theory
why conventional adsorption methods of water treatment using
conventional solid adsorbents (such as activated carbon or alumina)
are not very effective is because the adsorbents typically develop
negative charges on their surfaces when immersed in water.
Therefore, their surfaces tend to repulse the heavy metals anions,
leading to low adsorption capacities for these anions. The present
invention provides carbon adsorbents that overcome this shortcoming
of traditional carbon adsorbents by incorporating at least an
oxygen-containing compound of a metal selected from the group
consisting of iron, copper, and aluminum into a porous carbon. It
is contemplated that these and similar metals having metal oxides
or hydroxides which are stable in liquid phase would work in the
present invention. The carbon adsorbents of the present invention
retain a substantial amount of their microporosity enabling them to
remove heavy metal anions such as arsenic and selenium anions as
well as organic materials from the surrounding medium such as
liquid or gas. In a preferred embodiment, the medium is drinking
water.
[0012] A metal-containing carbon adsorbent of the present invention
is preferably a microporous carbon adsorbent, which has a large
surface area as measured by the Brunauer-Emmett-Teller ("BET")
method and has a substantial micropore volume for pores having
diameter less than about 2 nm. As used herein, "micropore volume"
is the total volume of pores having diameter less than 2 nm.
Suitable carbon adsorbents for use in the present invention are
those having a BET surface area greater than about 100 m.sup.2/g,
preferably greater than about 200 m.sup.2/g, more preferably
greater than about 400 m.sup.2/g, and most preferably greater than
about 600 m.sup.2/g. In general, it is contemplated that the higher
surface areas will capture metal anions and other contaminants,
especially organics. These carbon adsorbents typically have a
micropore volume greater than about 20 cm.sup.3/100 g. Preferably,
the carbon adsorbents have a micropore volume greater than about 30
cm.sup.3/100 g, more preferably greater than about 40 cm.sup.3/100
g, and most preferably greater than about 50 cm.sup.3/100 g.
[0013] Suitable carbon adsorbents for use in the present invention
may be made from any of a variety of starting carbonaceous
materials such as, but not limited to, coals of various ranks such
as anthracite, semianthracite, bituminous, subbituminous, brown
coals, or lignites; nutshell; wood; vegetables such as rice hull or
straw; residues or by-products from petroleum processing; and
natural or synthetic polymeric materials. The carbonaceous material
may be processed into carbon adsorbents by any conventional thermal
or chemical method known in the art before incorporating the metal
therein. They will inherently impart different surface areas and
pore volumes. Generally, for example, lignites can result in carbon
having surface areas about 500-600 m.sup.2/g and, typically,
fiber-based carbons areas are about 1200-1400 m.sup.2/g. Certain
wood-based carbons may have areas in the range of about 200
m.sup.2/g, but tend to have a very large pore volume which is
generally suitable for depositing large amounts of impregnates.
Surface area and pore volume of coal based carbon may also be made
to allow for some control of surface area and pore volumes.
Preferably, the carbon is an activated carbon adsorbent.
Alternatively, at least one metal may be incorporated into the
carbonaceous starting material, then the mixture may be processed
into carbon adsorbents containing one or more of such metals.
[0014] In an embodiment, the carbon adsorbent contains metal at a
concentration of up to about 50% by weight of the carbon.
Preferably, the metal is present at a concentration in the range
from about 1% to about 40% or, more preferably, from about 2% to
about 30% and, more preferably, from about 3% to about 20% by
weight of the carbon.
[0015] In another embodiment of the present invention, a
microporous carbon adsorbent is impregnated with at least one salt
of a metal selected from the group consisting of iron, copper, and
aluminum. Examples of such salts include halides, nitrates,
sulfates, chlorates, carboxylates having from one to five carbon
atoms such as formates, acetates, oxalates, malonates, succinates,
or glutarates of iron, copper, or aluminum. The impregnated salts
are then converted to oxygen-containing compounds of iron, copper,
or aluminum by either thermal decomposition or chemical reaction.
Preferred forms of the oxygen-containing compounds are hydroxides
and oxides.
[0016] The following examples illustrate preferred embodiments of
the present invention.
EXAMPLE 1
[0017] Preparation of an Iron-Impregnated Carbon Adsorbent:
[0018] 4.6 ml of an aqueous ferric chloride solution (having a
concentration of 100g ferric chloride in 40 ml water) was diluted
with 40.3 g of deionized water. This solution was poured slowly
into 50.0 g of oven-dried 12.times.30 mesh (U.S. sieve series)
coconut shell-based PCB.TM. activated carbon (Calgon Carbon
Corporation, Pittsburgh, Pa.) contained in a pyrex glass dish.
PCB.TM. activated carbon has a BET surface area of about 1050
m.sup.2/g and a micropore volume of about 60 cm.sup.3/100 g. The
impregnated carbon was stirred thoroughly while the solution was
being poured into the carbon. The wet impregnated carbon was dried
in an oven at 105.degree. C. for 2 hours based on the amount of
ferric chloride solution used for the impregnation. The dried
impregnated carbon had an iron content of about 7.9% by weight of
the carbon. The dried impregnated carbon was taken out of the oven
and cooled down in a hood. A KOH solution was prepared by
dissolving 12.47 g of KOH pellets in 60.02 g deionized water. The
KOH solution was poured into the dried impregnated carbon. This
amount of KOH was enough to completely wet the impregnated carbon
without leaving an excess solution. The wet KOH-treated carbon was
transferred into a 2000-ml beaker and the beaker was filled with
deionized water. The water from the beaker was decanted and fresh
deionized was added to wash potassium chloride from the impregnated
carbon. This process of washing was repeated until the pH of the
solution was about 7, as indicated by pH paper. The wet carbon was
then dried in an oven at 105.degree. C. overnight. It was expected
that the iron in the carbon would be in the form of ferric
hydroxide. The dried ferric hydroxide-impregnated carbon was
pulverized in a titanium vial containing tungsten abrading balls
for testing of the removal of heavy metal anions. This impregnated
carbon was identified as "3224-31-1."
[0019] Testing of Arsenic Removal:
[0020] An aqueous arsenic solution having an arsenic concentration
of about 100 parts per billion ("ppb") by weight was prepared for
testing by diluting into deionized water an appropriate amount of
an arsenic standard solution of arsenic trioxide in 10% (by weight)
nitric acid.
[0021] Polyethylene bottles having a nominal volume of 500 ml and
magnetic stirring bars were cleaned with dilute nitric acid
solution and dried. An appropriate amount of the pulverized
impregnated carbon adsorbent 3224-31-1, as disclosed above, was put
into a cleaned and dried polyethylene bottle containing a magnetic
stirring bar. An amount of about 500 g of the arsenic solution
prepared as disclosed above was put into the bottle. The bottle was
then put on a multi-position stirring plate and the stirring
continued for about 24 hours. At the end of the 24-hour period, a
sample of the solution in the bottle was taken and filtered. The
residual concentration of arsenic in the solution was analyzed by
ICP/MS method. Many such bottles were prepared during the same
experiment, each had a different amount of pulverized carbon
adsorbent. In addition, a control bottle was also prepared in which
no carbon adsorbent was added. The results of this testing are
shown in Table IA below. The limit of detection for this method of
analysis was 0.3 ppb. This carbon could reduce the level of arsenic
to less than detection limit with a small dose of the carbon.
1TABLE 1A Amount pH of Carbon Residual As (measured with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3208-17B 0 83.8
4 3208-17F 0.0249 19.8 4 3208-17G 0.0496 1.25 4.1 3208-17A 0.0998
<0.3 4.2
[0022] Testing of this carbon was conducted with another aqueous
arsenic solution having a targeted concentration of about 300 ppb
similarly prepared. The results are shown in Table 1B.
2TABLE 1B Amount pH of Carbon Residual As (measured with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3208-37A-6 0 331
3.4 3208-37A-2 0.05 171 3.4 3208-37A-3 0.10 54.4 No data 3208-37A-4
0.20 5.5 No data
[0023] Although a coconut shell-based carbon was used in this
example it is understood that other activated carbons may be
equally applicable for the present invention. An economically
attractive carbon for the present invention is one made from
bituminous coal in a steam gasification process. For example,
activated carbons suitable for the present invention may be those
made from wood chips in a chemical activation process employing
phosphoric acid, or those made from phosphoric acid treatment of
petroleum residue, or activated carbons made from gasification of
carbonized polymeric materials, such as those derived from phenolic
resins or polyesters. Activated carbons suitable for the present
invention may have the form of powder, granule, sphere, pellet,
honeycomb, woven or nonwoven fiber, mat, or felt.
EXAMPLE 2
[0024] The same oven-dried PCB.TM. carbon was impregnated with
ferric chloride to achieve a ferric ion loading of about 15.8% by
weight of the carbon using the same manufacturing method as in
Example 1. An arsenic solution having a targeted concentration of
about 1 part per million ("ppm") was prepared from the arsenic
trioxide standard solution as above. The results of this experiment
are shown in Table 2. This carbon could remove a very high level of
arsenic (841 ppb) to less than detection limit with only a small
dose of the carbon.
3TABLE 2 Amount pH of Carbon Residual As (measured with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3246-18M 0 841
6.4 3246-18O 0.50 <0.3 6.3 3246-18Q 2.50 <0.3 No data
EXAMPLE 3
[0025] Preparation of Iron (II) Impregnated Carbon Adsorbent:
[0026] An iron (II) impregnated activated carbon was prepared
similarly to the process disclosed in Example 1, except a ferrous
chloride solution was prepared for impregnation, instead of ferric
chloride. 1.778 g of FeCl.sub.2.4H.sub.2O was dissolved into 40.0 g
of deionized water. The ferrous chloride solution was impregnated
into 50.0 g of oven-dried 12.times.30 mesh PCB.TM. activated
carbon. The dried impregnated carbon had a nominal iron (II)
loading of about 1% by weight. The dried impregnated carbon was
reacted with a KOH solution consisting essentially of 1.27 g of KOH
pellet dissolved in 70.16 g of deionized water. The washed and
dried impregnated carbon was pulverized as above and labeled as
"3224-32-1" for testing.
[0027] Testing for Arsenic Removal:
[0028] The arsenic solution and the method of testing were similar
to those disclosed in Example 1. The results of the testing are
shown in Table 3.
4TABLE 3 Amount of pH (measured Carbon Residual As with a Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3208-18F 0 348
3.4 3208-18A 0.0253 307 No data 3208-18B 0.0500 279 No data
3208-18C 0.1001 211 3.4 3208-18D 0.2000 116 No data 3208-18E 0.5002
8.2 3.8
EXAMPLE 4
[0029] Oven-dried 12.times.30 PCB.TM. activated carbon was
impregnated with aluminum chloride in the same manner as disclosed
in Example 1. The aluminum chloride solution was prepared by
dissolving 89.48 g of AlCl.sub.3.6H.sub.2O in 80.0 g of deionized
water. The solution was impregnated into 100 g of oven-dried
12.times.30 PCB.TM. activated carbon. Thus, the impregnated carbon
has an aluminum loading of about 10% by weight of the carbon. The
aluminum chloride-impregnated carbon was reacted with a solution
containing 63.17 g KOH in 120 g deionized water. The steps of
washing, drying, and pulverizing were the same as those of Example
1. An arsenic solution having a targeted As concentration of about
1 ppm was prepared for testing. The arsenic removal testing was the
same as that disclosed in Example 1 except different amounts of
impregnated carbon were used. The results are shown in Table 4.
5TABLE 4 Amount of pH (measured Carbon Residual As with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3246-18A 0 851
5.6 3246-18C 0.51 333 7.6 3246-18E 2.50 4.84 No data 3246-18F 5.00
4.19 No data
EXAMPLE 5
[0030] Preparation of Carbon Adsorbent Containing Ferric Oxide:
[0031] 3.7325 g of Fe(NO.sub.3).sub.3.9H.sub.2O was dissolved into
37.70 g of deionized water. This solution was poured over a 50.02 g
of oven dried 12.times.30 mesh PCB.TM. carbon in a glass dish. The
impregnated carbon was mixed thoroughly and then dried in an oven
at 105.degree. C. for 3 hours. The dried impregnated carbon was
charged into a quartz tube having an inner diameter of about 2.54
cm. The carbon was retained in place by a piece of glass wool at
each end. The quartz tube was inserted in a horizontal tube furnace
and heated from ambient temperature to about 300.degree. C. in 30
minutes, then held at that temperature for about 20 hours. The
temperature was subsequently increased to 500.degree. C. in about
20 minutes and held for an additional 3 hours. The heating was
conducted under a flow of nitrogen at substantially ambient
pressure at about 300 cm.sup.3/minute. The tube with the carbon
still inside was cooled down under nitrogen flow to ambient
temperature. It was expected that ferric nitrate decomposed to
ferric oxide under this treatment condition. A representative
sample of the ferric oxide-loaded carbon was pulverized as
described in Example 1 above for testing. The results of the
testing are shown in Table 5. The results show that arsenic was
removed even at low doses of carbon.
6TABLE 5 Amount of pH (measured Carbon Residual As with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3208-19F 0 326
No data 3208-19A 0.010 317 No data 3208-19B 0.026 299 No data
3208-19C 0.050 271 No data 3208-19D 0.100 222 No data 3208-19E
0.200 131 No data
EXAMPLE 6
[0032] Preparation of Carbon Adsorbent Containing Iron (III):
[0033] Meadow River bituminous coal (a bituminous coal from West
Virginia, U.S.A.) was pulverized with 4% (by weight of the coal)
coal tar pitch and 10% (by weight of the coal) Fe.sub.3O.sub.4
powder so that at least 90% of the pulverized material passed
through 325 mesh screen (U.S. sieve series). Alternatively, the
coal, pitch binder, and the iron powder may be pulverized
separately and then mixed together after pulverization. The powder
mixture was compacted in a Fitzpatrick roll press at about 1.5 MPa
into elongated briquettes of about 1cm wide, about 0.5 cm thick,
and about 3-4 cm long. Other briquette shapes and sizes also may be
used. The mixture also may be extruded into pellets instead of the
above pressing to briquettes. The compaction pressure may be
appropriately chosen for the particular coal used. It may be higher
or lower than the pressure disclosed above, but typically is in the
range from about 8 MPa to about 16 MPa. The briquettes were crushed
and screened to produced particles having a mesh size of about
6.times.14. The produced particles were oxidized under an excess
flow of air in an indirectly heated rotary kiln, the temperature of
which was increased from ambient to about 250.degree. C. at a rate
of 45.degree. C. per hour, and then from 250.degree. C. to about
450.degree. C. at a rate of 60.degree. C. per hour. Other oxidizing
gases also may be used, such as a mixture of oxygen and air or an
inert gas, which mixture has an oxygen concentration greater than
about 21% by volume, or a combustion product from a combustor
containing oxygen, steam, and other gases. The resulting oxidized
iron-containing coal particulate material was gasified in steam at
925-950.degree. C. for about 40-45 minutes to produce an
iron-containing porous carbon adsorbent of the present invention.
The step of gasifying the carbon precursor, such as this coal
particulate, in an oxidizing atmosphere is usually termed
"activation." It should be understood that the activation
temperature and time are chosen to be appropriate for the type of
coal, the compaction technique, the type of activation furnace used
in the process of manufacture, and the desired microporosity of the
activated product. Generally, higher-rank coals and higher
compaction would require a higher temperature and/or a longer time.
A longer activation time produces a more porous activated carbon.
Activation furnace types that provide a very intimate contact
between the solid and the gas phase and a well-mixed solid therein
usually require a shorter activation time. Activation temperature
is typically in the range from about 900.degree. C. to about
1100.degree. C., and activation time is typically in the range from
about 10 minutes to about 10 hours. In addition to steam, other
oxygen-containing gases may also be present. The steps of oxidizing
the coal particles and of gasifying the oxidized coal particles
were carried out in this example in a rotary kiln. However, other
types of furnaces or kilns may also be used in which an intimate
contact between the solid and the gas phase can be maintained.
Suitable furnaces or kilns are fluidized-bed kilns, belt furnaces,
and Herreshoff furnaces. A representative sample of this adsorbent
was pulverized in titanium vials using tungsten balls as disclosed
above for testing.
[0034] Testing for Arsenic Removal:
[0035] An arsenic solution was prepared similarly to that of
Example 1, except the targeted As concentration was 1 ppm. The
testing procedure was similar to that described in Example 1. The
results of the testing are shown in Table 6.
7TABLE 6 Amount of pH (measured Carbon Residual As with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) 3246-18G 0 837
5.9 3246-18I 0.5 685 6.4 3246-18K 2.5 20 No data 3246-18L 5.0 21.7
No data
EXAMPLE 7
[0036] Testing for Selenium Removal
[0037] The carbon of Example 1 was tested for selenium removal. A
solution containing selenium was prepared as follows.
[0038] An aqueous selenium solution having a selenium concentration
of about 300 parts per billion by weight was prepared for testing
by diluting into Milli-Q water an appropriate amount of a 1000 ppm
selenium standard reference solution. The reference solution was
purchased from Fisher Scientific and is commonly used as the
standard solution for atomic absorption spectroscopy.
[0039] The method of testing was similar to that described in
Example 1. The results of the testing are shown in Table 7.
8TABLE 7 Amount of pH (measured Carbon Residual Se with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) Control 1 0 273
No data 3224-31-1B 0.10 39.3 6.1 3224-31-1C 0.25 15.5 6.2
3224-31-1D 0.50 9.7 6.4 3224-31-1E 1.00 8.1 6.6
EXAMPLE 8
[0040] Testing for Selenium Removal
[0041] The carbon of Example 5 was tested for selenium removal. The
solution containing selenium was prepared as described in Example
7.
[0042] The method of testing was similar to that described in
Example 1. The results of the testing are shown in Table 8.
9TABLE 8 Amount of pH (measured Carbon Residual Se with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) Control 3 0 289
No data 3129-28F-2 0.10 15.6 6.1 3129-28F-3 0.25 6.2 6.2 3129-28F-4
0.50 6.2 6.4 3129-28F-5 1.01 3.3 6.6
EXAMPLE 9
[0043] Testing for Selenium Removal
[0044] The carbon of Example 4 was tested for selenium removal. A
solution containing selenium was prepared to have a target selenium
concentration of about 300 ppb by diluting a selenium atomic
absorption standard solution containing 100 ppm selenium dioxide in
water.
[0045] The method of testing was similar to that described in
Example 1. The results of the testing are shown in Table 9.
10TABLE 9 Amount of pH (measured Carbon Residual Se with Bottle
Number Adsorbent (g) Concentration (ppb) pH meter) Control 2 0 295
No data 3246-14B-2 0.11 23.7 6.2 3246-14B-3 0.26 4.7 6.2 3246-14B-4
0.50 2.2 6.3 3246-14B-5 1.00 1.1 6.4
[0046] The adsorbents of the present invention may be used to
remove heavy metal anions from a medium adjacent thereto in many
arrangements. Granular particles of the adsorbents of the present
invention may be installed in a fixed bed or a fluidized bed.
Granular adsorbents are particularly suitable to be packaged in
small cartridges for installation at the point of use. An adsorbent
in powder form may be injected into a stirred tank and then removed
by filtration or settling. Adsorbents in fiber form may be inserted
in a section of the water supply piping. Furthermore, in certain
circumstances, it may be advantageous to include at least one other
type of adsorbents in a treatment of the medium. Such other types
of adsorbents are, for example, zeolites, ion exchange resins,
silica gel, alumina, and unimpregnated activated carbons.
[0047] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations, equivalents, or improvements therein may be
made by those skilled in the art, and are still within the scope of
the invention as defined in the appended claims.
* * * * *