High capacity adsorbent for fluoride ion and oxyanions of phosphorous and arsenic and method for making the same

Abstract

An alumina-based adsorbent and method of making exhibiting high affinity and capacity towards fluoride ions and oxyanions of phosphorus and arsenic in a broad pH range and presence of large excess of competitive ions. Alumina based adsorbent is a mixed oxide of alumina existing in tetra-, penta-, and octahedral coordination at specific ratio, and oxides of polyvalent metals of elements titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof. The alumina based adsorbent may be used for selective removal of fluoride ion and oxyanions of phosphorus and arsenic from drinking water, industrial streams and wastes, in medicine and food industry.

Claims

1. An adsorbent for fluoride ion and oxyanions of arsenic and phosphorus, comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof, wherein content of said alumina in said mixed oxide is from about 20 wt % to about 80 wt % or from about 50 wt % to about 80 wt %, and wherein said mixed oxide contains 50% Al.sub.2O.sub.3 and 50% TiO.sub.2, having 80% Octahedral Al, 15% Pentahedral Al, and 5% Tetrahedral Al.

2. An adsorbent for fluoride ion and oxyanions of arsenic and phosphorus, comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof, wherein content of said alumina in said mixed oxide is from about 20 wt % to about 80 wt % or from about 50 wt % to about 80 wt %, and wherein said mixed oxide contains 50% Al.sub.2O.sub.3 and 50% ZrO.sub.2, having 60% Octahedral Al, 25% Pentahedral Al, and 15% Tetrahedral Al.

3. An adsorbent for fluoride ion and oxyanions of arsenic and phosphorus, comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof, wherein content of said alumina in said mixed oxide is from about 20 wt % to about 80 wt % or from about 50 wt % to about 80 wt %, and wherein said mixed oxide contains 50% Al.sub.2O.sub.3 and 50% Fe.sub.2O.sub.3, having 80% Octahedral Al, 15% Pentahedral Al, and 5% Tetrahedral Al.

4. An adsorbent for fluoride ion and oxyanions of arsenic and phosphorus, comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof, wherein content of said alumina in said mixed oxide is from about 20 wt % to about 80 wt % or from about 50 wt % to about 80 wt %, and wherein said mixed oxide contains 67% Al.sub.2O.sub.3 and 33% TiO.sub.2, having 70% Octahedral Al, 20% Pentahedral Al, and 10% Tetrahedral Al.

5. The adsorbent of the claim 1 wherein said mixed oxide does not show phase segregation and remains amorphous up to 500 C.

6. The adsorbent of the claim 1 wherein said mixed oxide shows adsorption capacity decrease less than 40% after calcination up to 500 C.

7. The adsorbent of the claim 1 wherein said mixed oxide has capacity on fluoride ion from about 40 mg F/g to about 80 mg F/g at pH range from 7 to 6, respectively.

8. The adsorbent of the claim 1 wherein said mixed oxide capacity on fluoride ion does not decrease more than 30% in the presence of competitive ions that are approximately 10 to 100 times in excess, said competitive ions including HCO.sub.3, Cl, NO.sub.3, SO.sub.4, or any combination of thereof.

9. The adsorbent of the claim 1 wherein said mixed oxide capacity on fluoride ion does not decrease more than 40% in the presence of equimolar amounts of phosphate, silicate ions, or any combination of thereof.

10. The adsorbent of the claim 1 wherein said mixed oxide has a higher affinity towards phosphate ions than arsenic ions.

11. The adsorbent of the claim 1 wherein said mixed oxide has separation factor ratio of phosphorus/arsenic from about 1.2 to about 2 in equimolar solutions.

12. The adsorbent of the claim 1 wherein said mixed oxide has an adsorption capacity on PO.sub.4 ions from hemo-dialysate solution at a pH level of about 5 to 6 of at least 160 mg PO.sub.4/g.

13. The adsorbent of the claim 1 wherein said mixed oxide has an adsorption capacity on PO.sub.4 ions from peritoneal dialysate solution at a pH level of about 7 to 8 of at least 100 mg PO.sub.4/g.

14. The adsorbent of claim 1 wherein said mixed oxide is thermally stable, and has an adsorption capacity decrease of less than 40% after calcination.

15. The adsorbent for fluoride ion and oxyanions of arsenic and phosphorus of claim 1, wherein said mixed oxide contains Al(OH).sub.3 having 100% Al Octahedral.

16. The adsorbent of the claim 2 wherein said mixed oxide capacity on fluoride ion does not decrease more than 40% in the presence of equimolar amounts of phosphate, silicate ions, or any combination of thereof.

17. The adsorbent of claim 2 wherein said mixed oxide is thermally stable, and has an adsorption capacity decrease of less than 40% after calcination.

18. The adsorbent for fluoride ion and oxyanions of arsenic and phosphorus of claim 2, wherein said mixed oxide contains Al(OH).sub.3 having 100% Al Octahedral.

19. The adsorbent of the claim 3 wherein said mixed oxide does not show phase segregation and remains amorphous up to 500 C.

20. The adsorbent of the claim 3 wherein said mixed oxide shows adsorption capacity decrease less than 40% after calcination up to 500 C.

21. The adsorbent of the claim 3 wherein said mixed oxide has capacity on fluoride ion from about 40 mg F/g to about 80 mg F/g at pH range from 7 to 6, respectively.

22. The adsorbent for fluoride ion and oxyanions of arsenic and phosphorus of claim 3, wherein said mixed oxide contains Al(OH).sub.3 having 100% Al Octahedral.

23. The adsorbent of the claim 4 wherein said mixed oxide has a higher affinity towards phosphate ions than arsenic ions.

24. The adsorbent of the claim 4 wherein said mixed oxide has separation factor ratio of phosphorus/arsenic from about 1.2 to about 2 in equimolar solutions.

25. The adsorbent of the claim 4 wherein said mixed oxide has an adsorption capacity on PO.sub.4 ions from hemo-dialysate solution at a pH level of about 5 to 6 of at least 160 mg PO.sub.4/g.

26. The adsorbent of the claim 4 wherein said mixed oxide has an adsorption capacity on PO.sub.4 ions from peritoneal dialysate solution at a pH level of about 7 to 8 of at least 100 mg PO.sub.4/g.

27. The adsorbent for fluoride ion and oxyanions of arsenic and phosphorus of claim 4, wherein said mixed oxide contains Al(OH).sub.3 having 100% Al Octahedral.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 graphs P/A separation factors calculated from adsorption capacities on As and P as a function of equilibrium pH on hydrous titanium oxide, hydrated ferric oxide, aluminum hydroxide, and the mixed oxide 33.4% TiO.sub.2-66.6% Al.sub.2O.sub.3 from Example 3; and

(3) FIG. 2 graphs Fluoride breakthrough curves as a function of Bed Volume for the alumina based mixed oxide made in Example 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(4) In describing the preferred embodiment of the present invention, reference will be made herein to FIGS. 1-2 of the drawings in which like numerals refer to like features of the invention.

(5) The deficiencies of the prior art as discussed above can be alleviated or overcome by the adsorbent of the present invention. The present invention is directed to a high capacity mixed oxide adsorbent comprising alumina that exists in tetra-, penta-, and octahedral coordination, and a polyvalent metal oxide selected from the group of titanium, zirconium, tin, cerium, lanthanum, iron, or any combination thereof, that can be used for simultaneous selective removal of fluoride ion and oxyanions of phosphorus, arsenic(V) and arsenic(III) from different aqueous streams.

(6) Mixed oxide adsorbent is an amorphous material that contains from about 20 wt % up to about 80 wt % of alumina, or preferably from about 50% to about 80% of alumina, in which aluminum exists in octahedral, pentahedral, and tetrahedral coordination, wherein the amount of pentahedrally coordinated aluminum is from about 10% to about 30%, and tetrahedrally coordinated aluminum is from about 5% to about 15%.

(7) The unexpected result of the present invention is a strong synergism between all elements in the mixed oxide composition resulting in a significant increase of media adsorption capacity towards fluoride ion and oxyanions of phosphorus and arsenic in comparison with alumina hydroxide or activated alumina (on the order of twice to six times greater), as well as with other individual polyvalent metal oxides tested under similar conditions. Aluminum hydroxides are able to adsorb arsenic(V) and have no affinity towards arsenic(III), and alumina-based mixed oxides of present invention are able to remove both arsenic(V) and arsenic(III) species with a significant capacity increase only for arsenic(V).

(8) There appears to be little synergistic affect towards other oxyanions like silicate, chromate, sulfate, and the like. The proposed mixed oxide has capacity on fluoride ion from about 40 mg F/g up to about 80 mg F/g at a pH range of approximately 7 to 6, respectively. Advantageously, the adsorbent's capacity on the fluoride ion does not decrease more than 30% in the presence of competitive ions that are approximately 10 to approximately 100 times in excess. The competitive ions typically include HCO.sub.3, Cl, NO.sub.3, SO.sub.4, or any such combination, and do not decrease more than 40% in the presence of equimolar amounts of phosphate, silicate ions, or their combination.

(9) Alumina based mixed oxide has higher affinity towards phosphate ion over arsenic ions with a separation factor for phosphorus/arsenic from approximately 1.2 to about 2 in equimolar solutions. Individual polyvalent metal oxides do not show preferences in uptake of these ions, and may preferably remove arsenic ions, like hydrous titanium oxide. The measured alumina based adsorbent capacity on the PO.sub.4 ion from hemo-dialysate solution at a pH level of about 5-6 is at least 160 mg PO.sub.4/g, and at least 100 mg PO.sub.4/g from a peritoneal dialysate solution at a pH level of about 7-8, which makes it an efficient phosphate scavenger in such applications as, for example, artificial kidney devices.

(10) Another advantage of the present invention is that mixed oxide is a thermally stable adsorbent and has an adsorption capacity decrease of less than 40% (after calcination at 450 C. for 2 hours).

(11) In another embodiment of the present invention, a method of making the aforementioned alumina-based mixed oxides is taught. The method requires a reaction between a solution or a slurry containing an aluminum compound, a polyvalent metal compound, and a base solution in the pH range of approximately 4 to about 10, ageing freshly formed precipitate in mother-liquor (a residual liquid resulting from the crystallization and remaining after the substances that readily or regularly crystallize have been removed) at the pH level of precipitation, washing the precipitate with water, and subsequently drying precipitate.

(12) Specific to the method of forming the aluminum compound, a water soluble compound is chosen, preferably including aluminum sulfate, aluminum chloride, aluminum nitrate, and combinations thereof, or aluminum oxide pseudo-sol. The polyvalent metal compound preferably comprises water soluble nitrates, chlorides, sulfates of titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof, or sol of titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof. Additionally, polyvalent metal compound may comprise nano sized titanium, zirconium, tin, cerium, lanthanum, iron oxides, or combinations thereof.

(13) Another feature of the method of the present invention is that precipitation may be carried out at a constant pH level, which is kept in the range of 4-10 under batch or continuous flow conditions by using base chosen from alkali hydroxides, ammonium hydroxide, alkali carbonates, ammonium carbonate, and combinations thereof.

(14) The precipitation may be carried at a pH level changing from acidic to about 4-10 under batch conditions by the addition of a base reagent chosen from alkali hydroxides, ammonium hydroxide, alkali carbonates, ammonium carbonate, or combinations thereof.

(15) On the final stage freshly formed alumina based mixed oxide precipitate is aged in mother-liquor at the pH level of precipitation at ambient or elevated temperature for 1-3 hours and then dried.

(16) The present invention is described more specifically by reference to the following exemplary embodiments, which are not intended to limit the invention described in the appended claims.

EXAMPLE 1

(17) In a first exemplary embodiment, preparation of a metal containing solution of the present invention involves mixing 130.6 g of Al.sub.2(SO.sub.4)3*18H.sub.2O, 133 g of a 15.0 wt % titanyl sulfate solution (on TiO2), and 400 g of deionized water. Metal containing solution and 25 wt % solution of NaOH are added simultaneously into a 2 L glass beaker filled with 800 mL of water with the use of a peristaltic pump at a predetermined flow rate which allows for a constant pH level of 5 in the reaction mixture, the pH level being constant throughout the precipitation process. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration and washed with deionized water. The wet cake is then dried at 100 C. in air for approximately 18 hours. The dry adsorbent contains 50% Al.sub.2O.sub.3 and 50% TiO.sub.2.

EXAMPLE 2

(18) In a second exemplary embodiment, preparation of the metal containing solution comprises mixing 130.6 g of Al.sub.2(SO.sub.4)3*18H.sub.2O, 133 g of a 15.0 wt % titanyl sulfate solution (on TiO.sub.2), and 400 g of deionized water. The metal containing solution and 25 wt % solution of NaOH are then added simultaneously into a 2 L glass beaker filled with 800 mL of water with the use of peristaltic pump at a predetermined flow rate that maintains a constant pH level at about 9 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 1 hour and then the aged precipitate is separated from mother-liquor by filtration and washed with deionized water. The wet cake is dried at 100 C. in air for 18 hours. The resultant dry adsorbent contains 50% Al.sub.2O.sub.3 and 50% TiO.sub.2.

EXAMPLE 3

(19) In a third exemplary embodiment, preparation of a metal containing solution comprises mixing 94.5 g of AlCl.sub.3*6H.sub.2O, 66.5 g of a 15.0 wt % titanyl sulfate solution (on TiO.sub.2), and 400 g of deionized water. NaOH at 25 wt % solution is slowly added to a beaker with the metal containing solution until the pH level reaches 7. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 3 hours and then the aged precipitate is separated from mother-liquor by filtration and washed with deionized water. The wet cake was dried at 100 C. in air for 18 hours. The dry adsorbent contains approximately 66.6% Al.sub.2O.sub.3 and 33.4% TiO.sub.2.

EXAMPLE 4

(20) In a fourth exemplary embodiment, preparation of a metal containing solution comprises mixing 147 g of Al(NO.sub.3)3*9H.sub.2O, 10 g of anatase TiO.sub.2, and 400 g of deionized water. NaOH at 25 wt % solution is slowly added to a beaker with metal containing solution until a pH level of approximately 7 is reached. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 3 hours, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is then dried at 100 C. in air for 18 hours. The dry adsorbent contains approximately 66.6% Al.sub.2O.sub.3 and 33.4% TiO.sub.2.

EXAMPLE 5

(21) In a fifth exemplary embodiment, the preparation of a metal containing solution comprises mixing 100 g of 20% aluminum hydroxide pseudo-solution, 10 g of rutile TiO.sub.2 and 300 g of deionized water. A 25 wt % solution of NaOH is added slowly to a beaker with the metal containing solution until the pH level reaches approximately 7. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 3 hours, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is dried at 100 C. in air for 18 hours. The dry adsorbent contains 66.6% Al.sub.2O.sub.3 and 33.4% TiO.sub.2.

EXAMPLE 6

(22) In a sixth exemplary embodiment, the preparation of a metal containing solution comprises mixing 130.6 g of Al.sub.2(SO.sub.4)3*18H.sub.2O, 100 g of a 20 wt % ZrOCl.sub.2 solution (on ZrO.sub.2), and 400 g of deionized water. The metal containing solution and 25 wt % solution of NaOH are added simultaneously into a 2 L glass beaker filled with 800 mL of water with the use of peristaltic pump at a predetermined flow rate to maintain a constant pH level of 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina zirconia mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is dried at 100 C. in air for 18 hours. The dry adsorbent contains 50% Al.sub.2O.sub.3 and 50% ZrO.sub.2.

EXAMPLE 7

(23) In a seventh exemplary embodiment, a preparation of metal containing solution comprises mixing 130.6 g of Al.sub.2(SO.sub.4)3*18H.sub.2O, 100 g of a 20 wt % La(NO.sub.3)3 (on La.sub.2O.sub.3) solution, and 400 g of deionized water. The metal containing solution and 25 wt % solution of NaOH are added simultaneously into a 2 L glass beaker filled with 800 mL of water with the use of peristaltic pump at a predetermined flow rate to maintain a constant pH level of 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina lanthanum mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is dried at 100 C. in air for 18 hours. The dry adsorbent contains 50% Al.sub.2O.sub.3 and 50% La.sub.2O.sub.3.

EXAMPLE 8

(24) In an eighth exemplary embodiment, the preparation of a metal containing solution comprises mixing 130.6 g of Al.sub.2(SO.sub.4)3*18H.sub.2O, 67.5 g of FeCl.sub.3*6H.sub.2O, and 400 g of deionized water. The metal containing solution and 25 wt % solution of NaOH is added simultaneously into a 2 L glass beaker filled with 800 mL, of water with the use of peristaltic pump at a predetermined flow rate maintaining a constant pH level of approximately 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina iron mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is dried at 100 C. in air for 18 hours. The dry adsorbent contains 50% Al.sub.2O.sub.3 and 50% Fe.sub.2O.sub.3.

EXAMPLE 9

(25) The Al-27 MAS NNW spectra of freshly prepared alumina hydroxide and alumina based mixed oxides have been recorded on a Bruker Avance III 400 MHz spectrometer.

(26) TABLE-US-00001 Octahedral Pentahedral Sample Al, % Al, % Tetrahedral Al, % Al(OH).sub.3 100 0 0 50% Al.sub.2O.sub.350% TiO.sub.2 80 15 5 Example 2 50% Al.sub.2O.sub.350% ZrO.sub.2 60 25 15 Example 6 50% Al.sub.2O.sub.350% Fe.sub.2O.sub.3 80 15 5 Example 8 67% Al.sub.2O.sub.333% TiO.sub.2 70 70 10 Example 3

EXAMPLE 10

(27) Adsorption experiments have been carried out under batch conditions with a contact time 18 hours. The following test solutions were used in the adsorption experiments: a) Fluoride ion10 ppm F+2 mM NaHCO.sub.3+2 mM Na.sub.2SO.sub.4, pH=6; b) Phosphate ion0.83 ppm P+2 mM NaHCO.sub.3, pH=8; and c) Arsenate ion2 ppm As+2 mM NaHCO.sub.3, pH=8.

(28) Commercial adsorbents, such as those from GFO (Bayer), MetSorb (Graver Technologies) and activated alumina AA400, have been used for a comparison study.

(29) TABLE-US-00002 TABLE I Ion Exchange Capacities (IEC) of Test Ions on Alumina Based Mixed Oxides Sorbent IEC-F, mg/g IEC-PO.sub.4, mg/g IEC-AsO.sub.4, mg/g Example 1 75 55 65 Example 2 70 55 70 Example 3 70 50 60 Example 4 65 50 60 Example 5 65 50 60 Example 6 75 55 70 Example 7 80 60 65 Example 8 65 50 65 GFO, Granular 10 12 20 Ferric Oxide MetSorb TiO.sub.2 12 10.5 17 Activated Alumina 15 7 7 AA400

EXAMPLE 11

(30) Adsorption experiments have been carried out under batch conditions with a contact time 18 hours. The following equimolar test solutions were used in adsorption experiments: a) Phosphate ion0.83 ppm P+2 mM NaHCO.sub.3, pH=8; and b) Arsenate ion2 ppm As+2 mM NaHCO.sub.3, pH=8

(31) Adsorption capacities on As and P as a function of equilibrium pH on hydrous titanium oxide, hydrated ferric oxide, aluminum hydroxide, and mixed oxide 33.4% TiO.sub.2-66.6% Al.sub.2O.sub.3 from Example 3 have been determined and P/As separation factors have been calculated from experimental data according to formula:
SF=IECP/IEC-As(at fixed pH),
and presented in FIG. 1. As seen Fe.sub.2O.sub.3 and Al.sub.2O.sub.3 do not show selectivity to AsO.sub.4 or PO.sub.4 in the pH range 6-10, whereas anatase TiO.sub.2 exhibits affinity towards AsO.sub.4 at a pH level of greater than or equal to 7. Alumina based mixed TiO.sub.2Al.sub.2O.sub.3 shows distinct affinity towards phosphate ion over arsenate ion in the tested pH range. The separation factor P/As for this media increases with an increase of equilibrium pH reaching a value of 1.5 at a pH=8, and 1.9 at a pH=9.7.

EXAMPLE 12

(32) The alumina based mixed oxide made in Example 3 (66.6% Al.sub.2O.sub.3-33.4% TiO.sub.2, particle size 45-75 m) and activated alumina 400G (particle size 45-75 m) were tested for fluoride ion removal from tap water spiked with 6.2 ppm F and pH=7.5 under column conditions. In both cases two grams of adsorbent were placed in a glass column with inner diameter 8 mm and test solution was passed through an adsorbent bed with flow rate 80 BV/hr. Fluoride breakthrough curves are presented in FIG. 2. As seen, alumina-based adsorbent from Example 3 (purifies 3.300 BV) outperform the benchmark activated alumina 400G (purifies 500 BV) before breakthrough (1.5 ppm F) more than 6 times.

EXAMPLE 13

(33) The effect of competitive ions on fluoride ion sorption on mixed oxide of Example 1 is shown in the Table II. Initial concentration of fluoride ion in all test solutions was 10 ppm and contact time was 18 hours.

(34) TABLE-US-00003 TABLE II Effect of Competitive Ions on Fluoride Ion Sorption on Alumina-Titania Mixed Oxide Competitive ion Ion Excess, times IEC-F, mg/g 75 HCO.sub.3 5 65 Cl 50 70 SO.sub.4 25 65 SiO.sub.3 4 45 PO.sub.4 1 45

EXAMPLE 14

(35) Effect of thermal treatment on AsO.sub.4 ion sorption on mixed oxide of Example 1 is shown in the Table III. The arsenic test solution contained 2 ppm As(V), pH=8. The fluoride test solution contained 10 ppm F in tap water, pH=7.5. The contact time was 18 hours.

(36) TABLE-US-00004 TABLE III Effect of Thermal Treatment on AsO.sub.4 and F Ion Uptake by Alumina-Titania Adsorbent IEC 100 C., IEC 250 C., IEC 350 C., Ion mg/g mg/g mg/g IEC 450 C., mg/g AsO.sub.4 75 65 60 50 F 25 21 19 18

(37) While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.