TREATMENT OF WATER

Abstract

Provided is a method of treating water comprising bringing water that contains dissolved chromium (VI) into contact with an anion exchange composition comprising (a) polymeric beads having covalently bound amine groups, and (b) tin (II) oxide.

Claims

1. A method of treating water comprising bringing water that contains dissolved chromium (VI) into contact with an anion exchange composition comprising (a) polymeric beads having covalently bound amine groups, and (b) tin (II) oxide.

2. The method of claim 1, wherein the polymeric beads comprise polymer that comprises polymerized units of styrenic monomer.

3. The method of claim 1, wherein the polymeric beads comprise polymer that comprises polymerized units of one or more monofunctional vinyl monomers and polymerized units of one or more multifunctional vinyl monomers.

4. The method of claim 1, wherein the tin(II) oxide is present in an amount such that the amount of elemental tin is 0.5% to 20% by weight based on the weight of the composition.

5. The method of claim 1, wherein chromium (VI) is present in the water in the form of HCrO.sub.4.sup., CrO.sub.4.sup.2, Cr.sub.2O.sub.7.sup.2, or a mixture thereof.

6. The method of claim 1, wherein chromium (VI), is present in an amount, characterized as elemental chromium, based on the weight of the water, of 0.01 to 100 ppm.

7. The method of claim 1, wherein a ratio of total weight of the polymeric beads to total weight of the chromium (VI) is 450:1 or higher.

Description

EXAMPLE 1

Loading of Tin onto Resins

[0062] Loading of tin onto resins was performed as follows. Resin was centrifuged to remove bulk water to give moist resin. 1 L of resin was mixed with 2 L of stock solution. The mixture was agitated for 4 hours, then decanted. A small sample of resin was removed for analysis. Remaining resin was mixed with 1.5 L of an aqueous solution of 1.0N NaOH. The mixture was agitated for approximately 14 hours, then decanted. The resin was washed thoroughly with DI water.

[0063] The tin content of resin was measured using inductively coupled plasma (ICP) emission spectroscopy. The detection limit of tin was 5 ppm by weight. Resin samples were tested at three stages: before exposure to the stock solution (the Cl or free base stage), immediately after exposure to the stock solution (the SnCl2 or SnCl4 stage), and the resin after decanting from the NaOH solution (the NaOH stage). The amount of tin is reported as the weight of elemental tin as a percentage of the total weight of the resin (i.e., the total weight of the collection of polymeric beads). The results were as follows:

TABLE-US-00003 Example stock Type Resin solution stage Tin wt % preparative SBA-MP none Cl ND preparative SBA-MP Sn(II) SnCl.sub.2 0.3 working SBA-MP Sn(II) NaOH 4.4 comparative SBA-MP Sn(IV) SnCl.sub.4 4.5 comparative SBA-MP Sn(IV) NaOH 5.6 comparative SAC-gel-C none free base ND comparative SAC-gel-C Sn(II) SnCl.sub.2 4.3 comparative SAC-gel-C Sn(II) NaOH 2.9

[0064] In the above table, the material made with SBA-MP, treated with Sn(II) stock solution, and also treated with NaOH solution, is the only material that is a working example of the composition of the present invention. The other materials shown are either preparative, representing intermediate steps on the path to making the working example, or are comparative examples. Materials that use Sn(IV) or that use SAC resins fall outside the scope of the present invention.

[0065] The SAC resin took up less tin from the stock solution than did the SBA resins. Also, in the SAC resin, the amount of tin dropped as a result of the NaOH treatment. It is considered that the SAC-gel-C resin in its final stage has far less tin(II) oxide than the SBA-MP resin in its final stage.

[0066] Three resins were studied by visual observation and by optical microscopy: (1) SBA-MP, with tin (II) oxide, after the NaOH stage; (2) SBA-MP, with tin (IV) oxide, after the NaOH state, and (3) SBA-MP, with no tin treatment. For each resin, 5 g of the respective resin was placed in a 60 mL bottle with 50 mL of a chrome oxide (CrO3) solution of concentration 0.25 g/50 mL, and the pH was adjusted to 7.2 using NaOH. Each resin/CrO3 solution was placed on a shaker bath and agitated for 72 hr at room temperature (approximately 23 C.). The resin was allowed to settle, the excess liquid was decanted to a waste container, and the resin was visually inspected. Both the resin/Sn (II) hybrid and the resin control showed no signs of metal precipitant outside of the resin beads, while the resin/Sn (IV) hybrid showed significant dark, granular insoluble precipitant at the bottom of the resin. The three resins were also examined by optical microscopy. In the tin-free sample and the tin (II) oxide sample, no particles other than the polymeric beads were observed. In the tin (IV) oxide sample, many external particles outside of the polymeric beads were visible; these external particles were identified as tin (IV) oxide, and the external particles covered approximately 80% of the field of view. It is considered that observation of the resins and the microscopic images shows that the tin(II) oxide forms within the polymeric beads or directly on the surface of the beads, while the tin(IV) oxide has a much greater tendency to form particles in the interstitial spaces between the polymeric beads.

EXAMPLE 2

Treating Water

[0067] In various experiments, an amount of resin (see below) was placed in a 1000 mL Erlenmeyer flask with 1000 mL of a Feed solution. The mixture was stirred continuously, and the chromium content of the water was tested after 3 days and after 8 days. Chromium was studied using ICP, reported in units of microgram of chromium per gram of water (g/g). The detection limit was 0.05 g/g. Results were as follows:

TABLE-US-00004 0.75 g of resin/Feed A Stock Cr 3 days Cr 8 days Resin Solution Stage (g/g) (g/g) none none none 1.21 1.27 SAC-gel-C none free base 0.07 0.08 SAC-gel-C Sn(II) NaOH ND 0.11 SBA-MP none Cl 0.15 ND SBA-MP Sn(II) SnCl.sub.2 0.17 ND SBA-MP Sn(II) NaOH ND ND PCA none ND 0.06
The working example of the present invention in the above table is SBA-MP/Sn(II)/NaOH. This example had the best chromium-removal performance, especially at 8 days.

TABLE-US-00005 Resin SBA-MP/Feed B amount of Stock Cr 3 days Cr 8 days Resin Solution Stage (g/g) (g/g) none non 4.71 3.90 0.25 g none Cl 1.22 1.09 0.50 g none Cl 0.78 0.86 1.00 g none Cl 0.54 0.57 0.25 g Sn(II) NaOH 1.42 1.12 0.50 g Sn(II) NaOH 0.54 0.69 1.00 g Sn(II) NaOH 0.34 0.28 0.25 g Sn(IV) NaOH 1.22 1.15 0.50 g Sn(IV) NaOH 0.75 0.64 1.00 g Sn(IV) NaOH 0.32 0.28
In the above table, the working examples of the present invention are the three samples with Sn(II). These samples remove chromium well.

EXAMPLE 3

Further Loading of Resin

[0068] Resin was loaded with tin as follows. Resin was loaded as in Example 1 above except that 1 L of resin was mixed with 1 L of stock solution in each sample. The equilibrium water content and the tin content were measured by the methods described above, and the results were as follows.

TABLE-US-00006 Example stock Type Resin solution stage EQ-water Tin wt % preparative SBA-MP none Cl 74.5% ND working SBA-MP Sn(II) NaOH 74.4% 11.0 preparative WBA-MP none free base 61.6% ND working WBA-MP Sn(II) NaOH 47.0% 18.4 preparative SBA-gel none Cl 45.0% ND working SBA-gel Sn(II) NaOH 45.0% 6.7

[0069] All three of the anion exchange resins tested showed acceptable ability to be loaded with tin(II) oxide.

EXAMPLE 4

Further Treating of Water

[0070] Resins were tested for uptake of chromium (VI) as in Example 2 above. Resins were centrifuged and decanted to remove free water. Then 0.50 g of resin was mixed with 1000 mL of feed solution. Then the chromium content of the water was tested, as above, and reported as micrograms of chromium per gram of water. Results from testing with Feed C were as follows:

TABLE-US-00007 0.50 g of resin/Feed C Ex. Stock Cr 3 days Cr 8 days Type Resin Solution Stage (g/g) (g/g) comparative none none 5.5 5.2 comparative SBA-MP none Cl 1.3 1.5 working SBA-MP Sn(II) NaOH 1.0 1.2 comparative WBA-MP none free base 1.7 1.4 working WBA-MP Sn(II) NaOH 1.2 1.0 comparative SBA-gel none Cl ND ND working SBA-gel Sn(II) NaOH ND ND

[0071] In all three of the anion exchange resins tested, the tin-loaded resin performed well and performed better than the same resin without tin.

[0072] Additionally, 0.50 grams of resin was tested with 1000 mL of Feed D solution using the method described above. The chromium content of the water was tested, as above, and reported as micrograms of chromium per gram of water. The results were as follows:

TABLE-US-00008 0.50 g of resin/Feed D Ex. Stock Cr 3 days Cr 8 days Type Resin Solution Stage (g/g) (g/g) comparative none none 14 14 comparative SBA-MP none Cl 5.9 5.7 working SBA-MP Sn(II) NaOH 5.8 5.6 comparative WBA-MP none free base 11 12 working WBA-MP Sn(II) NaOH 9.4 9.1 comparative SBA-gel none Cl 2.1 2.0 working SBA-gel Sn(II) NaOH 1.9 1.8

[0073] In all three of the anion exchange resins tested, the tin-loaded resin performed well and performed better than the same resin without tin.