WO2000001459A1

WO2000001459A1 - Small diameter water stable zeolite composite useful as an ion exchange material

Info

Publication number: WO2000001459A1
Application number: PCT/US1999/015022
Authority: WO
Inventors: Evan E. Koslow
Original assignee: KX Industries LP
Current assignee: KX Technologies LLC
Priority date: 1998-07-07
Filing date: 1999-07-02
Publication date: 2000-01-13
Anticipated expiration: 2001-01-07

Abstract

The present invention relates to the production of zeolite particle composites that have average diameters in the range of about 10 νm to about 180 νm. These diameter sizes are especially suitable to be used in conjunction with carbon block filters in household potable water applications. The composite particles are produced by mixing 4 to 5 Å commercial zeolite with water and organic or inorganic binders. The particles are then calcined at high temperatures to remove water and organic binders, which results in a water-stable structure. The particles are then ground in a low-shear grinder under extremely precise control to produce high yield of particles with particle sizes that are suitable for use with carbon block purifiers and other composite filter elements.

Description

SMALL DIAMETER WATER STABLE ZEOLITE COMPOSITE USEFUL AS AN ION EXCHANGE MATERIAL

This invention relates to the use of zeolite composites as ion exchange materials. More particularly, it involves forming small diameter zeolite composites with average particle sizes of about 10 μm to about 180 μm utilizing a low shear process. The particles are particularly efficient as ion exchange materials for the removal of heavy metals from solutions.

BACKGROUND OF THE INVENTION

Zeolites have long been used as ion exchange materials. An ion exchanger removes unwanted ions from a solution by transferring the unwanted ions to the ion exchange material and transferring an equivalent number of desired species from the ion exchange material to the solution. When the ion exchange material is full of the unwanted species, it either must be discarded or regenerated by washing the ion exchange material with the desired ion species.

A practical use for ion exchangers is the home water softening industry where the ion exchange material is used to soften water by removing calcium and magnesium and replacing them with a more desired species such as sodium. Another significant area in which ion exchangers are used is the removal of heavy metals from potable water. The contamination of drinking water by heavy metals, especially lead, has become an especially important health issue for the country. The Environmental Protection Agency (EPA) stated that there is no safe threshold level of lead in drinking water and estimates that there is over 100 million people in the United States at risk from some degree of lead poisoning. Sources of lead poisoning include industrial wastes contamination, and lead bearing plumbing.

There are many types of devices that are commercially used to treat drinking water and they can be classified by size. The smaller devices usually remove contaminates after water is poured from the tap, or the devices are installed in the plumbing and remove contaminates before the water exits the tap. These smaller devices usually have a chamber occupied by both activated carbon to remove organic contaminates, and an ion exchange material to remove metal contaminates. Obviously, it is desirable to have an efficient ion exchange material so that more of the container space can be occupied by the activated carbon. Typically, these water treatment devices are designed so that the filter cartridge must be replaced before the ion exchange material is full. This is done to prevent the avalanche effect, which occurs when the ion exchange material exhausts its capacity to absorb the undesired ion species. The avalanche effect is when the concentrated ions in the exhausted ion exchange material are suddenly released into the water. If the ions are lead, then this could lead to a significant health hazard.

Many types of materials can be used as ion exchange materials. As previously mentioned, zeolites have been studied for their potential use in the removal of toxic heavy metals and especially soluble lead. However, natural zeolites often have low theoretical ion exchange capacities, reduced kinetics for adsorption and have limited specificity for lead compared to other non-targeted ions such as iron, magnesium, calcium, and mono-valent alkaline metal ions.

In order to improve upon the natural zeolites, Kuznicki et al. in U.S. Patent Nos. 5,223,022 and 5,071,804 disclose synthetic zeolites consisting of aluminum enriched chabazite as a medium for the reduction of heavy metals and the recovery of precious metals. Compared to natural chabazite, the aluminum-enriched form displayed improved selectivity and capacity. However, this invention was directed for industrial applications and especially the recovery of precious metals where the kinetics are not as critical as in household potable water applications where the total contact time is often as low as two seconds. Since many of the commercial synthetic zeolites crystal sizes are in the order of 1 to 3 μm, they can be agglomerated by mixing with clays and organic binders to produce particles or pellets of larger dimensions. For example, Hertzenburg in U.S. Pat. No 4,613,578 discloses a method of agglomerating zeolite crystals by mixing synthetic zeolite with alkali metal silicates and water. The resulting particles are calcined or baked at temperatures greater than 225°C to form a stable particle. Although the particles made by this process are an improvement over the natural zeolites, their kinetics are still too slow to be used in household potable water applications.

As an alternative to natural and synthetic zeolite crystals, there have been numerous proposals to use amorphous metal silicate gels as ion exchange materials which are formed by precipitating hydrous metal oxides, or by co-gelation of certain metal salts with silica or phosphate ions. It is generally believed that the kinetics for metal silicate gels are too slow for potable water applications. However, Dodwell et al. disclose in U.S. Patent 5,053,139 that specific compositions of amorphous titanium and tin silicates have surprising fast kinetics that can be used for tap water ion exchange devices.

The problem with the metal oxide gels is that they have low mechanical strength. For example, it has often been experienced that when the particles are placed in an aqueous solution and vigorously stirred, the metal-oxide gel particles become finer and are difficult to separate from the aqueous solution. Likewise, when the metal oxide gels are deployed in a packed column, it is hard to prepare particles having a predetermined size. Even if such particles can be prepared, the particles become finer during contact with the aqueous solution and it becomes difficult to keep the particles from migrating into solution.

One solution that has been used to overcome the mechanical problem with the metal oxide gels is to have the gels coated on a support material which is typically activated carbon or another ion exchange material. Weller in U.S. Pat No. 4,692,431, Maglio et al in U.S. Pat. No 5,277,931 and Fujita et al. in U.S. Pat. No. 4, 178,270 disclose attaching the metal oxides to support materials. The problem with these methods is that the attachments often reduce the surface area of both the metal oxides and the support material, which reduces both the capacity of the materials and the kinetics of their respective reactions. These methods also significantly increase the cost of manufacturing water purification devices.

Thus one object of the present invention is to provide ion exchange material having reaction kinetics that are suitable for household potable water applications. Another object of the present invention is to provide ion exchange materials that have high mechanical strength and that can be incorporated into carbon block water purifiers.

Still another object of the present invention is to provide a method for producing the ion exchange material with the proper diameter, which can be used in conjunction with carbon block purifiers so that the ion exchange material will not migrate out into solution.

SUMMARY OF THE INVENTION The present invention relates to the production of zeolite particle composites that have average diameters in the range of about 10 μm to 180 μm. These diameters are especially suitable for the production of carbon block filters used in household potable water applications.

The composite particles are produced by mixing 4 to 5 A commercial zeolite with water and organic or inorganic binders. The particles are then calcined at high temperatures to remove water and organic binder, which results in a water- stable structure. The particles are then ground in a low-shear grinder under extremely precise control to produce a high yield of product with particle sizes that are suitable for use with carbon block purifiers and other composite filter elements.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the use of zeolites that are used as ion exchange materials primarily in household water purification applications. A wide variety of synthetic and natural zeolites may be used. A typical zeolite is a inorganic aluminosilicate material with ion exchangeable cations and loosely held water molecules as shown in formulas I and II below:

Na_x [(AlO₂)x (SiO₂)y] zH₂O Formula I

Ca_x [(AlO₂)χ (SiO₂)_y] zH₂O Formula II wherein x, y and z are integers; and x is between about land 2; y is between about

2 and 12; and Z is between about 0 and 10.

Other cations may be used depending on the application and the desired ion species that is to be transferred into solution. There are a wide variety of zeolites that are commercially available such as

3 A, 4A, 5 A, 10X, 13X, ZSM, etc. These are common names of commercial grade zeolites such that the numbers correspond roughly to the size of the unit crystal cell in angstroms. However, these zeolites are typically too small to be utilized in carbon block purifiers used in household applications. Particles significantly smaller than 10 μm can not be efficiently retained within the carbon block structure or produce exceedingly high back pressure.

In order to increase the size of these commercial zeolites, they are sometimes mixed with a binder and water to form agglomerates. The binders can be an inorganic binder such as clay, a synthetic alkali metal silicate which is discussed in Hertzenburg, (U.S. Pat No. 4.613,578), and which is incorporated herein by reference, or an organic binder. The resulting slurry can be tumbled in a revolving container, disk pelletized, or when suitably diluted sprayed to form particles in a range between 8 to about 80 mesh. The resulting material is calcined at temperatures typically in the range between about 225°C to 525°C to remove the water and organic binder. After calcination, the composite material is water stable. The inventors have discovered that these composite materials are far too large for use in a carbon block structure for household water purification because the kinetics of adsorption are far too slow. The inventors have determined that the size of the composite material should be in the range of between about 10 μm to about 180 μm, preferably in the range of between about 10 μm to 150 μm, more preferably in the range of between about 20 to 100 μm and most preferably in the range of between about 30 to 50 μm.

The important aspect of this invention is that the composite material is reduced in size by a low shear grinding process so that the zeolite-binder matrix remains essentially intact. This invention defines low shear grinding as a method where particles are subjected to compressive stress sufficient to cause fracture of the particles and where shear, involving the transverse application of force, is minimized. For example, a roll crusher provides significant compressive force and minimal shear, while a disk mill applies significant shear and very little compressive force. The concept, according to the present invention, is to cause the particles to fracture without further disintegration of the resulting particle. It is important to minimize the frictional forces that will cause the shearing of the zeolite-binder bonds. Rubbing, tumbling, ball milling and attrition milling would be inappropriate.

The present inventors have discovered that high shear grinding results in a disruption of the zeolite-binder bonds, which leads to a high volume of small particles and a low yield of particle sizes in the preferred range. As mentioned previously, these small particles can not be efficiently maintained in the carbon block material

Any suitable low shear grinding process can be used to grind the particles to the preferred diameter sizes in the range between about 10 μm to 180 μm. The preferred low shear grinding method uses a one or more stage, two roll mill such as a crackulizer manufactured by Modern Process Equipment. The gap between the rollers is reduced for each stage of the grinding process so that the size of the particles become gradually smaller as they sequentially progress through the stages. The final average particle size will depend on the feed rate, input particle size, hardness of the particles, rotation speed and the gap settings. The particle size can be measured using a conventional sieving machine or an ultrasonic sieving machine. This low shear grinding process does not disrupt the zeolite-binder bonds and produces a high yield of particles in the preferred size range. The commercial zeolites have been shown to have potentially large adsorption capacities and a high specificity for lead and other toxic heavy metals. Although adsorption isotherm data shows that zeolites with 3A structure have poor adsorption for lead, the 4A and 5A zeolite crystals have high adsorption capacity and specificity for lead. The present inventors have discovered that when 4A and 5A zeolites, whose sizes are in the 1 to 3 μm range, are agglomerated, calcined and ground using a low shear process, they are especially suitable to the removal of lead as is shown below.

This invention is explained in further detail with reference to the following examples, which are not by way of limitation, but by way of illustration.

Example 1 Preparation of lead solution

A 100 ppm lead solution was made in a 2 liter glass volumetric flask by diluting 0.0622 grams of lead nitrate with sufficient deionized water to make 2 liters of solution. The flask was agitated to assure a homogenous solution. The pH of the solution was approximately 7, and the solution temperature was kept at room temperature at approximately 68-72°F. The solution was stored in a dark storage area to prevent photochemical degradation.

Example 2 Preparation of zeolite material

The agglomerated zeolite material was a non-commercial product obtained from PQ Corporation. The starting zeolite was 4 A molecular sieve material, which was agglomerated by mixing with bentonite clay. Particle size after agglomeration and prior to grinding was 8 x 30 mesh. Small samples were ground my hand using a laboratory mortar and pestle. The particles were crushed using an up and down motion to avoid excess shear. Particle size after grinding was approximately -200 mesh or less than 75 μm.

Example 3 Lead solution concentration vs. time procedure

The procedure for measuring the lead solution concentration vs. time is shown below. In a polypropylene jar, 0.100 grams of ion exchange material prepared as described in example 2and 100 ml of 100 ppm lead solution prepared according to example 1 were admixed and agitated using a standard laboratory shaker. Samples were extracted every 15 minutes using a syringe and filtered with a 0.2 μm membrane syringe filter to eliminate any residual particulates. The clean filtrate was analyzed for lead using a graphite boat atomic adsorption (AA) spectrometer manufactured by Perkin-Elmer. Serial dilution was used to obtain accurate A A measurements.

Examples 4 to 8 Lead solution concentration vs. time utilizing low shear ground zeolite

Table 1 below shows the lead solution concentration vs. time for the zeolite ion exchange material prepared and measured according to examples 1 , 2 and 3.

Table 1

Lead solution concentration (ppb) vs. time for zeolite ion exchange material

Example 0 min 15 30 45 60 75 90 105 min min min min min min min

4 100000 3080 328 697 42 43 26 28

5 100000 4508 328 108 59 43 44 31

6 100000 1562 185 75 134 42 254 42

7 100000 7224 118 37 19 53 5 5

8 100000 3550 328 572 23 5 0 10

Comparatiive ex;amples ' 9-11 Lead solution concentration vs. time for commercial lead ion exchange materials.

Table 2 below shows results of lead solution concentration vs. time for two commercial ion exchange materials used for the reduction of lead. Comparative examples 9 and 10 are results from ion exchange material Alusil 70® sold by Selecto Scientific, Inc., and comparative example 1 1 was the result using the ion exchange material ATS® from Englehard Corporation. They are both based on gel technology and are manufactured with gel sizes averaging 30 to 50 μm. They are commonly incorporated into carbon block filters for household lead removal applications. The procedure in example 3 was used in obtaining the data in comparative examples 9 to 11.

Table 2 Lead solution concentration (ppb) vs. time for commercial ion exchange material

Example 0 15 30 45 60 75 90 105 120 mm min mm min mm min min min min

9 Alusil 100000 2526 2194 1295 562 328 344 ^"242^"" 180

70®

10 100000 8484 9090 8394 6832 5738 2500 * *

Alusil

70®

11 100000 7496 5098 4462 1562 1186 246 194 *

ATS®

* - Not measured

The superiority of the zeolite ion exchange material is shown by comparing examples 4-8 with examples 9-11. The zeolite ion exchange material shows improved kinetics by the faster decrease in lead concentration. The zeolite material, according to the present invention, reduced the lead concentration to an average of less than 300 ppb in 30 minutes, while the commercial ion exchange materials only reduced lead concentrations to an average of about 5400 ppb in 30 minutes.

Also, the data appears to show that this unique zeolite material has an improved adsorption capacity and equilibrium for lead than the commercial lead removal products. The zeolite material consistently reduced the lead concentration during extended contact times to less than 50 ppm, while the commercial ion exchange materials had difficulty reducing the lead level to less than 200 ppm.

Claims

What is claimed is:

1. Ion exchange water stable particles comprising zeolite wherein said particles have an average particle size between about 10 μm to 180 μm.

2. The particles of claim 1 wherein the average particle size is between about 10 to 150 μm.

3. The particles of claim 1 wherein the average particle size is between about 20 to 100 μm.

4. The particles of claim 1 wherein the average particle size is between about 30 to 50 μm.

5. The particles of claim 1 wherein said particles are formed by the following steps:

(a) introducing the zeolite particles into a means for grinding; and

(b) grinding the particles, wherein the average final particle size is between about 10 μm to 180 μm.

6. The particles of claim 1 wherein the zeolite is at least one zeolite selected from the group consisting of: 4A and 5A zeolites.

7. A process for preparing zeolite ion exchange composite particles comprising the steps of:

(a) introducing the zeolite ion exchange composite particles into a means for low shear grinding; and;

(b) grinding said zeolite ion exchange composite particles wherein the average final particle size is between about 10 μm to 180 μm.

8. The process of claim 7 wherein said means for grinding is a two roll mill having at least one stage.

9. The process of claim 7 wherein the average zeolite ion exchange composite particle size is between about 10 to 150 μm.

10. The process of claim 7 wherein the average zeolite ion exchange composite particle size is between about 20 to 100 μm.

11. The process of claim 7 wherein the average zeolite ion exchange composite particle size is between about 30 to 50 μm.

12. The process of claim 7 wherein said zeolite ion exchange composite particle is formed by the steps of: (a) mixing zeolite, binder and water to form a composite; and

(b) baking said composite at temperatures greater than 225°C.

13. The process of claim 7 wherein said binder is at least one binder selected from the group consisting of: organic binders and inorganic binders.

14. A carbon block filter comprising activated carbon and ion exchange water stable particles comprising zeolite wherein the particles have an average particle size between about 10 μm to 180 μm.

15. A system for purifying water comprises contacting said water with ion exchange water stable particles, said particles comprising zeolite and having an average particle size between about 10 μm to 180 μm.

16. A process for the removal of heavy metals from a solution comprising the step of contacting the solution with ion exchange water stable particles comprising zeolite wherein the particles have an average particle size between about 10 μm to 180 μm.

17. The process of claim 16 where the heavy metal is lead.