EXAMPLE 1

[0016] Preparation of an Iron-Impregnated Carbon Adsorbent:

[0017] 4.6 ml of an aqueous ferric chloride solution (having a concentration of 100 g 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 12×30 mesh (U.S. sieve series) coconut shell-based PCB™ activated carbon (Calgon Carbon Corporation, Pittsburgh, Pa.) contained in a pyrex glass dish. PCB™ activated carbon has a BET surface area of about 1050 m ² /g and a micropore volume of about 60 cm 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° 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° 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.”

[0018] Testing of Arsenic Removal:

[0019] 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.

[0020] 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 1A 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. 1

[0021] 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. 2

[0022] 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

[0023] The same oven-dried PCB™ 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. 3

EXAMPLE 3

[0024] Preparation of Iron (II) Impregnated Carbon Adsorbent:

[0025] 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 ₂ .4H ₂ O was dissolved into 40.0 g of deionized water. The ferrous chloride solution was impregnated into 50.0 g of oven-dried 12×30 mesh PCB™ 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.

[0026] Testing for Arsenic Removal:

[0027] 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. 4

EXAMPLE 4

[0028] Oven-dried 12×30 PCB™ 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 ₃ .6H ₂ O in 80.0 g of deionized water. The solution was impregnated into 100 g of oven-dried 12×30 PCB™ 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. 5

EXAMPLE 5

[0029] Preparation of Carbon Adsorbent Containing Ferric Oxide:

[0030] 3.7325 g of Fe(NO ₃ ) ₃ .9H ₂ O was dissolved into 37.70 g of deionized water. This solution was poured over a 50.02 g of oven dried 12×30 mesh PCB™ carbon in a glass dish. The impregnated carbon was mixed thoroughly and then dried in an oven at 105° 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° C. in 30 minutes, then held at that temperature for about 20 hours. The temperature was subsequently increased to 500° 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 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. 6

EXAMPLE 6

[0031] Preparation of Carbon Adsorbent Containing Iron (III):

[0032] 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 ₃ O 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 1 cm 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 6×14. 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° C. at a rate of 45° C. per hour, and then from 250° C. to about 450° C. at a rate of 60° 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° 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° C. to about 1100° 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.

[0033] Testing for Arsenic Removal:

[0034] 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. 7

EXAMPLE 7

[0035] Testing for Selenium Removal

[0036] The carbon of Example 1 was tested for selenium removal. A solution containing selenium was prepared as follows.

[0037] 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.

[0038] The method of testing was similar to that described in Example 1. The results of the testing are shown in Table 7. 8

EXAMPLE 8

[0039] Testing for Selenium Removal

[0040] The carbon of Example 5 was tested for selenium removal. The solution containing selenium was prepared as described in Example 7.

[0041] The method of testing was similar to that described in Example 1. The results of the testing are shown in Table 8. 9

EXAMPLE 9

[0042] Testing for Selenium Removal

[0043] 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.

[0044] The method of testing was similar to that described in Example 1. The results of the testing are shown in Table 9. 10

[0045] 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.

[0046] 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.