Patent Application
20080035564
Anion exchange materials have positively charged functional groups. Thus, anionic ligands can easily permeate in and out of anion exchange material without encountering the Donnan co-ion exclusion effect. Examples of anionic ligands include, but are not limited to, arsenates, chromates, oxalates, phosphates, and phthalates. Hydrous metal oxide particles, such as hydrous iron oxide (HFO) particles, dispersed or impregnated within an anion exchange material increase anion sorption capacity. Consequently, hydrous metal oxide loaded anion exchange materials exhibit significantly greater capacity for removing arsenates, arsenites, and other arsenic oxyanions, as well as other anionic ligands, in comparison with cation exchange materials. It will be appreciated by one skilled in the art that the terms dispersed, impregnated, or loaded are used synonymously with reference to hydrous metal oxide particles in or on the sorbent except as otherwise indicated. It will be appreciated that the terms resin, material, beads are used synonymously with reference to the anion exchange sorbent and include embodiments such as membranes, fibers, and fibrous material except as otherwise indicated.
Dispersing hydrous metal oxide particles such as HFO particles poses a challenge due to the positively charged functional groups of the anion exchange material and heretofore has not been successfully achieved. As cations, Fe+2 and Fe+3 are repelled by the positively charged functional groups on anion exchange materials, and hence in most circumstances cannot be directly loaded. Thus, methods for dispersing HFO particles within cation exchange materials are not usually applicable when anion exchange materials serve as the sorbent.
An anion exchange material containing dispersed or impregnated metal oxide particles that have been precipitated from a solution into the sorbent is disclosed. The metal oxide particles include, but are not limited to, HFO particles. A fluid containing a ligand, such as an arsenic compound, arsenite, chromate, molybdate, selenite, phosphate, vanadate, or other ligand, is effectively treated using the HFO loaded anion exchange material to reduce or remove the contaminating ligand or compound from the fluid.
The physical properties of the anion exchange material may add structural integrity to materials that are otherwise friable and weak, such as granular ferric oxide (GFO) and granular ferric hydroxide (GFH). Thus, HFO particles dispersed into anion exchange materials can be synthesized with superior material properties when compared to the granulation or agglomeration of HFO particles. The physical robustness of the HFO-loaded sorbent allows for its use under more demanding conditions (i.e. higher operating pressures, increased flow, etc.). It also permits effective regeneration and reuse of the material, reduces the need for backwashing, and reduces other maintenance problems common in the treatment of streams with hydrous metal oxides that are not supported by substrates. Granular inorganic adsorbents are prone to numerous operational problems due to the low physical strength of the particle aggregates. This leads to a gradual breakdown of the aggregates during routine operations resulting in pressure increases, channeling and generally poor hydraulic flow through the sorbent bed.
An anion exchange sorbent containing hydrous metal oxide particles, such as HFO particles, for selective removal of contaminants or other ligands from fluids is prepared by a sequence of steps. In the inventive method, HFO particles are irreversibly encapsulated within and on the surface of the anion exchange material. However, due to the porous nature of anion exchange resin beads, these HFO particles are still accessible to contaminants (e.g. arsenic) within an aqueous stream contacted with the beads. Turbulence and mechanical stirring did not result in any noticeable loss of HFO particles.
The method may be used with both gel-type anion exchange materials (e.g. Purolite A400, Thermax Tulsion A-23P) and macroporous anion exchange materials (e.g. Purolite A503, Thermax Tulsion A-72 MP and with other positively charged substrates including, but not limited to, membranes, filters, fibers and other materials that are appropriately functionalized to contain anion exchange sites or groups. The anion exchange material may be of the Type I or Type II strong base organic resin type that contains quaternary groups with a positively charged nitrogen atom (e.g. Purolite A-510, Rohm & Haas Amberlite PWA900). Alternatively, the anion exchange material may be a weak base organic resin bead containing primary, secondary, and/or tertiary amine groups (e.g. Purolite A100). If the resin is a bead, the bead may be polystyrene, polystyrene/divinylbenzene, polyacrylic, or other polymeric matrices. The anionic exchange material may also be an inorganic material including, but not limited to, hydrous alumina, hydrous zirconia, hydrous titanic, hydrotalcites, and layered double hydroxides (LDH). Various other anionic exchange material may also be used as known to one skilled in the art. For example, polymeric anion exchange beads exhibit excellent kinetics, hydraulic properties, and durability during fixed bed column runs. In all cases, the dispersed hydrous metal oxide particles in or on the beads, fibers, membranes, etc. serve as active sorbents for the contaminants or targeted ligands.
Generally, an anion ion exchange material is contacted for a period of between one and eight hours with a solution of metal salt dissolved in an organic solvent. The resulting metal salt-loaded ion exchange material is collected (e.g., by filtration) and dried at a temperature less than about 150° C. The dried metal-loaded anion exchange material is added to a solution of base (about 1%w/v to about 20%w/v) and stirred for about one hour; the base may be sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, or other alkali. The metal-loaded material is filtered and washed to remove any displaced metal hydroxide and residual base, and is dried at ambient temperature (e.g., about 19° C. to about 25° C. or between about 19° C. up to about 150° C. depending upon the chemical and physical characteristics of the anion exchange material). The process may be repeated many times, for example, to further load hydrous metal oxide-loaded anion exchange material.
The metal loaded on the anion-exchange material is in the form of a hydrous metal oxide or metal hydroxide. The metal may be salts of iron, copper, zinc, nickel, manganese, titanium, zirconium, yttrium, lanthanum (and lanthanides), scandium, yttrium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, indium, thallium, germanium, tin, lead, antimony, bismuth, actinium or actinides. In one embodiment, iron salts may be iron (III) sulfate, iron (III) chloride, iron (III) nitrate, iron (III) acetate and/or other soluble iron (III) salts. The organic solvent in which the metal is in solution may be methanol, ethanol, propanol, acetone or other organic solvent in which the metal salt may be soluble.
The method and composition will be further appreciated with respect to the following non-limiting examples.
Anion exchange resin (Purolite A500P) (69.2 g in 100 mL) was contacted with 800 mL of 7%w/v FeCl3 in methanol for six hours and forty minutes to result in iron-loaded resin. The resin was filtered and air dried overnight at ambient temperature. The dried iron-loaded resin was contacted with fresh 7%w/v FeCl3 in methanol for four hours (second loading). This resin was filtered and air dried at ambient temperature. This dried iron-loaded resin was contacted with fresh 7%w/v FeCl3 in methanol for four hours (third loading), filtered, and air dried at ambient temperature. This iron-loaded resin was contacted with 0.5%w/v NaOH and stirred for about one hour to precipitate the HFO particles. This solution was filtered and the iron-loaded resin was washed with tap or distilled water, filtered, and dried at ambient temperature. The resulting resin beads were a dark brown/reddish color.
The resulting iron-loaded resin was used to remove arsenic from synthetic water that had been spiked with 3 ppm arsenic (as As(V)). The results are shown in
Anion exchange resin (34.7 g in 50 mL) (Purolite A400) was contacted with 400 mL of 7%w/v FeCl3 in methanol for four hours to result in iron-loaded resin. The resin was dried under vacuum and then contacted with about 400 mL of 10%w/v NaOH for about one hour with stirring to precipitate the HFO particles. Any unbound HFO, evidenced as brown iron floc, was decanted. This iron-loaded resin was filtered and rinsed four times with about 400 mL tap or deionized water, and the resulting black resin was vacuum filtered and dried overnight at ambient temperature. The iron-loaded resin was then added to a fresh 7%w/v FeCl3 in methanol (about 400 mL) and stirred for about 4.5 hours (second loading). This resin was filtered and dried overnight as above, and then contacted with about 400 mL 10%w/v NaOH to precipitate the HFO particles. The residual iron floc was decanted. This solution was stirred for one hour and then washed four times with about 400 mL water. After drying at ambient temperature overnight, this resin was contacted with fresh 7%w/v FeCl3 methanol (third loading). After stirring for about four hours, this resin was vacuum dried and washed with about 400 mL of 10%w/v NaOH to precipitate the HFO particles. The resin was then filtered and washed four times with about 400 mL water and dried at about 20° C. to about 25° C.
Samples of resin after each FeCl3 loading cycle were taken and analyzed for iron content (mg of iron per gram of dried resin), as shown in Table 1.
The breakthrough curve for arsenic, using the resin containing about 190 mg iron/g resin (dry weight) after three cycles of iron chloride and sodium hydroxide contact, is shown in
A gel-type anion exchange resin (Purolite A400) (34.7 g in 50 mL) was contacted for about four hours with 400 mL 14%w/v FeCl3 in methanol. The resin was dried under vacuum and contacted with about 400 mL 10%w/v NaOH for about one hour. The resin was filtered and rinsed four times with about 400 mL tap or distilled water. The resulting black resin beads were vacuum filtered and dried overnight at ambient temperature. The iron-loaded resin was added to fresh 14%w/v FeCl3 in methanol (about 400 mL) (second loading) and stirred for about four hours. The resin was filtered and contacted with about 400 mL of 10%w/v NaOH to precipitate the HFO particles. The iron floc was decanted. The solution was stirred for about one hour, filtered, and washed four times with about 400 mL of water. This iron-loaded resin was filtered and dried at ambient temperature.
Samples of resin after each FeCl3 loading cycle were taken and analyzed for iron content, as shown in Table 2.
An isotherm demonstrating the capacity for As(V) for the final product is shown in
A macroporous strong base anion exchange resin (Purolite A500P) (67 g in 100 mL) was stirred in 7%w/v FeCl3 in methanol for about six hours. The resin turned bright yellow immediately after contact with FeCl3. Samples of resin were taken for iron analysis after two hours, four hours, and six hours. After six hours, the resin was dried at room temperature (about 20° C. to about 25° C.).
No increase in iron loading was observed after two hours contact with FeCl3, indicating rapid reaction kinetics. The results are shown in Table 3A.
Fe-loaded resin from the first FeCl3 cycle was again contacted with 7%w/v FeCl3 in methanol for about four hours (second loading), filtered, and dried at room temperature.
This resin was split into two parts: one part was neutralized with 2%w/v NaOH, the other part was neutralized with 10%w/v NaOH. More loose iron floc was formed in the resin treated with 2%w/v NaOH upon washing than in the resin treated with 10%w/v NaOH. This indicated that more iron was lost from the resin when neutralized with 2%w/v NaOH than when neutralized with 10% W/v NaOH.
Both iron-loaded resins were filtered and dried at ambient temperature for about eighteen hours. The resin neutralized with 2%w/v NaOH was reddish-brown, while the resin neutralized with 10%w/v NaOH was darker brown and contained about 25% more iron. The results are shown in Table 3B.
The rate of arsenic uptake of the iron-loaded resin neutralized with 10% NaOH is shown in
A macroporous strong base anion exchange resin (Purolite A500P) (33.5 g in 50 mL) was stirred in 400 mL of 14%w/v FeCl3 in methanol for about four hours. The bright yellow resin beads were filtered from the solution and contacted for about one hour with about 400 mL of 10% W/v NaOH with stirring. The resin beads were filtered and washed four times with about 400 mL of tap or distilled water until the water was clear. The resin beads were vacuum dried using a Buchner funnel and dried at room temperature overnight. The resulting iron-loaded resin beads were a brown-red color. These iron-loaded resin beads were then contacted with fresh 14%w/v FeCl3 in methanol and stirred for about 4.5 hours (second loading). These resin beads were filtered and contacted with about 400 mL of 10%w/v NaOH to precipitate the HFO particles. The iron floc was decanted. The solution was stirred for about one hour, filtered, and then washed four times with about 400 mL water and dried overnight at room temperature. These resin beads were then contacted with fresh 14%w/v FeCl3 in methanol (third loading). After stirring for four hours, these resin beads were vacuum dried and contacted with about 400 mL of 10%w/v NaOH to precipitate the HFO particles. These resin beads were washed four times with about 400 mL water and dried at room temperature.
The iron content of the resin beads after each FeCl3 loading cycle is shown in Table 4.
A strong base anion exchange resin (Purolite A500P) (33.5 g in 50 mL) was stirred in 400 mL of 21%w/v FeCl3 in methanol for about four hours. After filtering the bright yellow resin beads from the solution, the resin beads were contacted with about 400 mL of 10%w/v NaOH to precipitate the HFO particles and stirred for about one hour. The resin beads were filtered and washed four times with about 400 mL of tap or distilled water until the water was clear. These resin beads were vacuumed dried and dried at room temperature (about 19° C. to about 25° C.) overnight. The resulting iron-loaded resin beads were reddish-brown, with an iron content of about 105 mg/g resin (dry weight).
Isotherms demonstrating performance capacity for As(V) for the gel type resin loaded with 7% FeCl3 as prepared in Example 2 and macroporous resin loaded with 14% FeCl3 as prepared in Example 5, with iron contents of 190 mg/g resin and 310 mg/g resin, respectively, are shown in
Two liters of strong base anion exchange resin (Thermax A-23P) fines (about 150 μm to about 300 μm diameter) were contacted with 16 L of 14%w/v FeCl3 in methanol for about two hours. Excess methanol was decanted and the resin was allowed to drain to remove any excess fluid. The iron-loaded resin was dried for about thirty minutes in flowing air at room temperature before being added to 16 L of 10%w/v NaOH in deionized water. The mixture was shaken for about one hour, the solution decanted, and the resin washed with tap or distilled water until free from unbound iron floc. This resin was dried at room temperature for about forty-five minutes and contacted with 14%w/v FeCl3 in methanol for about two hours (second loading). The product was filtered, contacted with 10%w/v NaOH for about one hour to precipitate the HFO particles, washed to remove iron floc and to reduce the pH, and dried. The final product was analyzed with the results shown in Table 5.
Tap water from Northborough, Mass. was spiked with arsenic (as arsenate) to a concentration of about 50 ppb and the pH adjusted to 7.5 with hydrochloric acid. This water was then passed through an 8 mL column of HFO-impregnated gel-type anion exchange resin (Purolite A400) with an empty bed contact time (EBCT) of two minutes. The effluent was then periodically analyzed for arsenic. After 40,000 BVs of water, the arsenic content of the water was still below 10 ppb indicating a high arsenic selectivity.
Two different samples of Smopex® synthetic polymer anion exchange fibers (Smoptech, Turku Finland) were impregnated with hydrous iron oxide (14% FeCl3) and 10%w/v NaOH using the inventive method previously described. Smopex® is the trademark for synthetic fibers for the recovery of metals from waste solutions and solutions from industrial and commercial processing. The characteristics of the fibers are shown in the following table (Table 6).
The Smopex®-103 fibers had 101 mg iron/g dry product. The Smopex®-105 fibers had 217 mg iron/g dry product.
Each of the HFO-impregnated fiber samples described above was evaluated for arsenic removal from synthetic water using a column technique. Synthetic water spiked with 300 ppb arsenic(V) at pH 6.5 was passed through an 8 mL column of the fibers with an empty bed contact time of about 12 seconds. The arsenic concentration in the effluent was measured. The column was stopped at the end of each working day and restarted the following morning.
Results are shown in
Resin beads impregnated with manganese dioxide were prepared. Twenty-five mL of a gel-type strong base anion exchange resin (Dow, SBR-P) was shaken for one hour with 75 mL of a solution of 13% manganese (II) chloride (MnCl2) in methanol. After one hour, the beads were filtered, dried on a Buchner funnel for fifteen minutes, and then added to 75 mL of a 7.5% solution of sodium hydroxide (NaOH) in deionized water. The mixture was stirred for about thirty minutes, the beads decanted and washed with water to remove any unbound manganese dioxide, and placed on a Buchner flask to remove any surface moisture. The process was repeated to add further MnO2 to the beads. After completing the second NaOH wash, the manganese dioxide-impregnated beads were washed with water to remove any unbound MnO2, followed by 200 mL of a 5% sodium chloride solution that had been sparged with carbon dioxide to convert the base resin to the chloride form and remove any residual hydroxide. The final product had a manganese content of 94 mg per gram of dried resin.
Beads impregnated with zirconia are prepared. Fifty mL of a gel-type strong base anion exchange resin (Purolite, A400) is shaken for about two hours with 200 mL of a solution of 5% zirconium tetrachloride (ZrCl4) in ethanol. After two hours, the beads are filtered, dried on a Buchner funnel for fifteen minutes, and then added to 200 mL of a 10% solution of sodium hydroxide (NaOH) in deionized water. The mixture is stirred for thirty minutes, the beads decanted and washed with water to remove any unbound hydrous zirconia (ZrO2xH2O) and placed on a Buchner flask to remove any surface moisture. The process is repeated to add further zirconia to the beads. After completion of the second NaOH wash, the zirconia-impregnated beads are placed in a column and 200 mL of a 5% sodium chloride solution is passed through to convert the base resin to the chloride form and remove any residual hydroxide.
Other variations and embodiments of the invention will also be apparent to one of ordinary skill in the art from the above description and examples. Thus, the foregoing embodiments are not to be construed as limiting the scope of this invention.
