CA1048175A - Phillipsite-gismondite for ammonia - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Ammonium ions are selectively removed from aqueous solutions containing alkali and/or alkaline earth cations by cation exchange with natural or synthetic zeolites of the phillipsite-gismodite type, which possess unusual capacity and selectivity for the ammonium ion.

Description

, ~L~4~7 BACKGROUND OF THE INVENTION

- This invention relates to the zeolitic cation exchange of ammonium ions from aqueous solutions containing at least one alkali or alkaline earth cation, and more particularly concerns the selective cation exchange of such solutions with certain natural or synthetic crystalline aluminosilicates. The invention is primarily concerned with the purification of waste waters containing ammonium cations in addition to other alkali or alkaline earth cations.
Ammonia, or the ammonium cation, has long been recognized as a serious pollutant in water. Its presence in municipal waste water and in the effluent from agri-cultural and industrial operations is as harmful as it is pervasive.
It has become apparent that the presence of ammonia in water has far more serious implications than merely serving as an index of recent pollution (see Mercer, B.M. et al., "Ammonia Removal from Agricultural Runoff and Secondary Effluents by Selecti~e Ion Exchange", Pacific Northwest Laboratories (Battelle), December, 1968).
It can be toxic to fish and aquatic life; while a maximum recommended ammonia concentration is 2.5 mg/l, as little as 0.3 to 0.4 mg/l is lethal to trout fry. It can con-tribute to explosive algae growths, ultimately causing eutrophic conditions in lakes. It can restrict waste water renovation and water reuse; since typical municipal

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waste water may contain 30 mg/L NH~, the removal of 90-95 percent would be required for water reuse, but to achieve this by conventional electrodialysis "would be prohibitively costly" ( ) It can have detximental effects on disinfection of water supplies; it reacts with chlorine to form chlora-mines which, while still bactericid~l, are slower acting and less effective. Lastly, ammonia can be corrosive to certain metals and materials of construction, its effect on copper and zinc alloys is well known, and it can also be destructive to concrete made from portland cement.
Cation exchange for ammonia removal, using a variety of cation-active "zeolites", has been studied extensively but has resulted in only limited commercial utilization The permutits (synthetic gel "zeolites"
derived from sodium silicate and aluminum sulate~ and the hydrous gel-type amorphous minerals such as glauconite( ) ("green sand") are effective but suffer from hydrolytic instability, have relatively low exchange capacity7 often have other unsatisfactory regeneration characteristics, and may be difficult to form into useful shapes of accep~able ., .

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(l) Weinberger, L W., et al , "Solving Our Water Problems-Water Renovation and Reuse", New York Academy of Science Meeting, Div. of Engineering, Dec. 8, 1965; quoted in Mercer et al.
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~ 2) Gleason, G.H. et al. 5 Sewage Works Jour. 9 Vol. 5, pp 61-73 (1933); Vol. 6, No. 3, pp. 450-468 (1934).

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physical properties Organic "zeolites",( ) which are sulfonated or carboxylated high polymers, are not selective ; for the ammonium ion, and instead prefer other cations such as calcium;(4) in addition, their use entails excessive ,.
regenerant wastes.(5) Certain of the natural and synthetic crystalline aluminosilicates, which are true zeolites, have been studied for use in the selective cation exchange removal of ammonia.(6) Fundamentally, the problem of selecting a zeolite is to obtain one having both adequate cation exchange capacity and adequate selectivity for the ammonium cation in the presence of alkali and alkaline earth metal cations, which inevitably are present in waste water streams. Some crystalline aluminosilicates possess desirable selectivity characteristics, but relatively low cation exchange capacity in terms of equivalents per unit weight. Conversely, many ` of the commonly available zeolites display satisfactory '

(3) Nesselson, E.J., "Removal of Inorganic Nitrogen from Sewage Effluent", Ph.D Thesis, Univ. of Wisconsin (1954); Poll o; F.X. et al., Hydrocarbon Proce~ , pp 124-

(4) Mercer, B.M. et al., cited above; Chem. AbstractVol. 71, No. 12, ref. 116322b.
; (5) Ibid.

(63 Review articles by Sherry on the ion exchange properties of zeolites appear ~s Chapter 3 of Marinsky, "Ion Exchange", Vol. 2 (M. Dekker, N.Y. 1969), and as Paper 28 of "Molecular Sieve Zeolites-I", Advances in Chemistry Series 101 tA.C.S. 19713. See also Papers Nos. 30, 31, 32, 35, and 38 of Advances...101.

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capacity, but their selectivity or preference for the ammonium cation is less than that of the mineral zeolites.
` It is~ accordingly, an object of the invention to provide a method for the zeolitic cation exchange re-moval of ammonium ions from an aqueous solution utilizing .
a zeolite possessing both high cation exchange capacity ` and excellent selectivity for t~e ammonium ion in the presence of one or more alkali or alkaline earth metal cations; and which zeolite has the necessary advantageous characteristics of rapid rate of exchange, ease and completene~s of regeneration, stability to both the exchange solution and regenerant solutions, capability of functioning over a comparatively broad range of acidities and alkalinities, long service life, and relatively low economic cost.
'.': ;' SUMMARY OF THE INVENTION
Briefly, in accordance with the invention, ;- ammonium ions are removed from aqueous solutions contain-; ing one or more alkali or alkaline earth cations by ef-fecting the removal with natural or synthetic zeolitic crystalline aluminosilicates of the phillipsit~-gismondite type. Even when used ln impure form, these zeolites have `
unusual capacity and selectivity for the ammonium cation ' in the presence of interferlng alkali and alkaline earth - metal ions.
For reasons which are not yet clear, the phillipsite-gismondite type zeolites best exhlbit their .. . . . . .

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!'.," superiority for the selective removal of ammonia ln dy-^i~" namic, or flow, systems, where they retain their selec-~: tivity for unusually long durations (Example 1). In batch tests, in which the zeolite is stirred with a solution containing mixed cations~ their selectivity : is adequate but not so outstanding Thus, while in batch cation exchange tests phillipsite is superior to clinoptilolite but inferior to zeolite F, in dynamic tests it displays more than twice the capacity of clinoptilolite and is quite superior to zeolite F (Example II). It is hypothesized that particularly cyclically regenerative systems, flow systems, expose the zeolite to conditions ' ' in which they are able to take up large amounts of alkaline ; earth cations. Perhaps the phillipsite-gismondite type .
- zeolites are relatively free o~ cation sites in the zeolite structure which can be irreversibly occupied by alkaline earth cations.
- The phillipsite-gismondite family of zeolites are those natural (mineral) and synthetic zeolites which have generally similar framework structures, and con-sPquently similar X-ray diffraction patterns, but which may have diEferent overall crystal symmetry and chemical composition (e.g. Si/Al distribution3 cation type and content9 water content~ etc.). See the definitive artlcle by Beard, "Linde Type B Zeolites and Related Mineral and Synthetic Phases," in "Molecular Sieve Zeolites--I"~
Advances in Chemistry Series No. lOl, p. 237 (1971).

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~ -6-~ 8~L75 These zeolites include the minerals phillipsite, harmotome, and gismondite (gismondine), and the synthetic zeolites "P" (Linde Zeolite B), ZK-l9, and W.
: The zeolites of the i~nvention are all within the "Phillipsite Group" classiication of Meier (Conference on Molecular Sieves, Soc. Chem. Ind., London, 10, 1968) and within Group 1 of Breck (Breck "Molecular Sieve Zeolites--I", Advances in Chemistry Series No. 101, page 1 ~1971)), and are based on structures composed of single rings of 4 alumina or silica tetrahedra w~ich are inter-linked by 8-tetrahedra rings According to Meier's des-.
ignation of the directions in which the one distinguishableoxygen atom in a tetrahedron points from the rings (in which "~' is upward and "D" is downward), the sequence of tetrahedra around the 4-rings is always UUDD; around the 8-ring in phillipsite and in harmotome it is UDDDDDD, and in gismondite it is UUUUDDDD. The 8-rings form apertures through the frameworks which establish the molecular sieving character of these zeolites; in phillipsi~e and harmotome the apertures are parallel to the ~lall, "b", and "c"
crystallographic axes, while in gismondite they are parallel to both "a" and "c" directions. The synthetic zeolltes ZK-lg and W are reported to ha~e the phillipsite-harmotome structure; the various "P" zeolites (Linde Zeolite B) are a series of synthetic zeolite phases which have been re-ferred to as "phillipsite-like", "harmotome-like", or "gismondine-like", based on the similarities of their , ~: `

X-ray powder patterns to those of the respective minerals (see the above Beard article). Structures of the synthetic zeolites have not as yet been fully elucidated.
;~The phillipsite-gismondite type aluminosillcate - zeolites are more fully definled in the table below, which .~includes literature references believed to contain the most accurate information on their structures, as presently known.

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- EXAMPLE I

This Example demonstrates the effectiveness of a z201ite of the invention--potassium exchanged phillips-ite--in comparison with other zeolites to effect the selective removal of NH4~ in a flow system.

To evaluate the zeolltes for NH4 exchange capacity from a mixed cation solution ln a dynamic system, a common procedure was adopted w~ich is a modification of a procedure used by Mercer and Amcs.(7) The method is a column technique employing a glass column one inch i.d. and twelve inches long. The zeolite was packed to height of ten inches for the start of each run. Flow direction for the secondary effluent was downflow while regeneration was always upflow. After regeneration the bed was washed downflow with a hot (ab. 80C) salt so-lution untll a pH below 9 was achieved in the effluent.
All zeolites were treated with essentially the same syn-thetic secondary effluent which had the following com-position:

(7) B.W. Mercer, L.L. Amesg C.J. Touhill, W.J. Van Slyke, R.B. Dean; Journal Water Pollution Con-trol Federation, Part 2, "Ammonia Removal from Secondary Effluents by Selective Ion Exchange", February 1970.

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` NH4~ as N 15 mg/l Na~ 51 mg/l ., K~ 11 mg/l Ca~ 56 mg/l .,f ~ ' , Mg+~ 28 mg/l i:, `. Each t~nk of freshly prepared secondary effluent was ~nalyzed for the exact NH4+ content, variation were extremely small between tanks.

A flow rate of 20 bed volumes ~bv) per hour was employed for samples during loading (i.e. ammoni~
exchange); the regeneration flow rate was 10 bv/hr.
All loadings and regenerations were performed at room temperature, the only exception being washing of the ~eds after regeneration with the solution at ~bout 80C.
The effluent was sampled during the NH4 removal cycle at intervals of every hour and analyzed for NH4~ content; during regeneration, samples were taken ~t half hour intervals. To analyæe for NH4~ content in the effluent samples, a boric acid modifiad Kjeldahl method was used, Cyclio evaluation of all samples is b~sed on 10% NH4 breakthrough of the bed, i.e. the NH4~ content ~ of the effluent is 10% of the NH4 influent concentration.
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` The 10% NH4~ breakthrough is equal to 1.5 mg/l; this ; is the maximum NH4~ content ~llowed by most states :~.
which presently h~ve laws pertaining to NH4~ content of weter.

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EXAMPLE II

This Example demonstrates the determination of maximum and competitive ammonium ion exchange capacities of a series of zeolites, including phillipsite and zeolite W of the invention.
The maximum ~4~ exchange capacities ~"h"
in the following Table~ were measured by the following procedure:
1) Treat a 5 g. sample (as is wt.) with 3 batch exchanges (at room emperature) a~ follows:
;~ a~ Shake in 500 ml. of 4N NH4cl for 1/2 hour for the first and second exchanges, and 1 hour for the , third exch~nge; and b) Centrifuge and decant between exch~nges.
2) After the third exchange, wash sample by sha~ing in 500 ml. distilled water for 1/2 hourg cen-trifuge, and decant.
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3) Dry sample at 100C until dry enough to handle easily.
4) Determine the LOI (at 1000C) on 0.2-0.3 g.
of dried sample by standard procedure.

5) Accurately weigh out (to four places) 0.15 g. ignited weight of dried sample and determine its NH4~ content by Kjeldahl titration using 0.02525N HCl.

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6) The NH~ exchange levels ~re sta~ed as milliequivalents of NH4~ per gram ~1000C ignited wt.) of zeolite after NH4~ exchange: meq. NH4+~g. ign. wt.

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Maximum ammonlum exchange capacities are also expressed on the basis o meq~tgm~ of the potassium form ('1X" in table) by dividLng "h" by (1 -~ 0.0471h).
Since the maximum theoretical NH4+ capacity (Xmax) is easily calculated, the effective zeolite purlty ("% 'Pure"~) is 100 times the ratio X/Xmax~

The competitive cation NH4 exchange capacities were measured as follows:
1) Mi~ 5.0 g. (dry wt.) sample into 250 ml.
of the following solution:

_alt Meq./l NH4cl 70 NaCl 85 KCl 50 CaC12 5 2) Shake on a wrist-action shaker.
3) Take 10 ml. aliquot samples after 1/2 hr.
and 2 hrs. shaking (each 10 ml. sample was centrifuged and any solid residue from the 1/2 hr. sample was quickly rinsed back into the exchange solution using a minimum amount of water), 4) Determine the NH4~ content o~ the 10 ml.

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; samples by Kjeldahl titratLon using 0.02525N HCl.
5) Calculate the NH4+ exchange level of the zeolite sample at 1/2 hr. ("Bl") and 2 hrs. (I'B2 ) by difference, i.e. by assuming that all of the N~I4~

removed from the solution was exchanged on the zeolite.
;-~ 6) The NH4+ exchange levels are stated ~s - milliequivalents of NH4+ per gram (dry wt.) of starting zeolite before NH~ exchange: meq. NH4+/g dry wt. spl.

-~ The quantities Bl/X and B2/X are then calculated, and represent a measure of the fraction of the ammonium-exchangeable sites occupied by ammonium - ions under the defined mixed cation exchange conditions.
Lastly, the quantities BlXmaX/X and B2Xmax/X

are calculated. These represent ammonium ion exchange capacity per unit weight of zeolite, and accordingly are independent of zeolite purity.

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~ ~8 ~7 5 Thus, it is apparent that -there has been provided, in accordance with the invention, an ammonia removal process that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific em-bodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description.
Accordingly, it is intended to embrace all such alter-natives, modifications, and variations as fall within the spirit and broad scope of the spp6nded cl6ims.

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Claims (8)

WHAT IS CLAIMED IS:

1. In the removal by zeolitic cation exchange of ammonium ions from an aqueous solution containing at least one alkali or alkaline earth cation, the improve-ment comprising: effecting said removal with a phillipsite-gismondite type zeolite.

2. Process of claim 1 wherein said zeolite has the structure of phillipsite.

3. Process of claim 1 wherein said zeolite has the structure of harmotome.

4. Process of claim 1 wherein said zeolite has the structure of gismondite.

5. Process of claim 1 wherein said zeolite has the structure of zeolite P.

6. Process of claim 1 wherein said zeolite has the structure of zeolite W.

7. Process of claim 1 wherein said zeolite has the structure of zeolite ZK-19.

8. Process of claim 1 wherein said aqueous solution is a municipal waste-water secondary effluent.