WO2019060361A1

WO2019060361A1 - Adsorbent granules for removal of heavy metals and method of making

Info

Publication number: WO2019060361A1
Application number: PCT/US2018/051660
Authority: WO
Inventors: Qian Yang; Minling Liu; Rajiv Banavali
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2017-09-22
Filing date: 2018-09-19
Publication date: 2019-03-28
Anticipated expiration: 2020-03-22
Also published as: CN109529763A

Abstract

Procédé de formation de granulés sensiblement sphériques d'un diamètre souhaité à partir d'une poudre comprenant les étapes qui consistent à mettre en rotation un récipient contenant la poudre et un liquide autour d'un axe longitudinal du récipient tout en faisant tourner le récipient autour d'un axe centrifuge coplanaire avec l'axe longitudinal.A method of forming substantially spherical granules of a desired diameter from a powder comprising the steps of rotating a container containing the powder and a liquid about a longitudinal axis of the container while rotating the container around a coplanar centrifugal axis with the longitudinal axis.

Description

ADSORBENT GRANULES FOR REMOVAL OF HEAVY METALS AND METHOD

OF MAKING

FIELD

[0001] The present invention relates to adsorbent granules for water purification. More specifically, the present invention relates to adsorbent granules for removal of heavy metals from water and methods for making adsorbent granules for removal of heavy metals from water.

BACKGROUND

[0002] Heavy metals, for example, arsenic (As), lead (Pb), cadmium (Cd) and mercury (Hg), may be found in harmful concentrations in some drinking water. The sources of the heavy metals may be naturally occurring or result from industrial pollution. The heavy metals can be removed by a number of techniques including reverse osmosis or distillation. However, these techniques can be costly because they can be energy and resource intensive.

[0003] A less costly method of heavy metal removal can be the filtration of water through a cartridge containing a granular adsorbent that is designed to remove heavy metals. However, such granular adsorbents may not be able to remove heavy metals with great efficiency, resulting in larger and more costly filter cartridges.

SUMMARY

[0004] A method of making a plurality of adsorbent granules includes forming adsorbent granules including a filter material powder, a natural clay powder, and water, and then sintering the adsorbent granules in a stepped sintering process. A composition of adsorbent granules for the removal of heavy metals from water includes a metal oxyhydroxide material, a metal oxide material, a manganese oxide material, and a natural clay binder. The natural clay binder is from 5 wt. % to 20 wt. % of the composition.

[0005] Various embodiments concern a method of making a plurality of adsorbent granules. The method includes forming the plurality of adsorbent granules, and sintering the plurality of adsorbent granules. The adsorbent granules include a filter material powder, a natural clay powder, and water. The sintering of the plurality of adsorbent granules includes heating the plurality of adsorbent granules to a first temperature at a temperature ramp rate and holding at the first temperature for a first hold time, heating the plurality of adsorbent granules to a second temperature at the temperature ramp rate and holding at the second temperature for a second hold time, heating the plurality of adsorbent granules to a third temperature at the temperature ramp rate and holding at the third temperature for a third hold time, and heating the plurality of adsorbent granules to a fourth temperature at the temperature ramp rate and holding at the fourth temperature for a fourth hold time. The first temperature is sufficient to remove free water, but not sufficient to remove adsorbed water. The second temperature is sufficient to remove adsorbed water, but not sufficient to remove crystallization water. The third temperature is sufficient to remove crystallization water, but not sufficient to remove constitutional water. The fourth temperature is sufficient to remove constitutional water. In some embodiments, the natural clay powder is from 5 wt. % to 20 wt. % of the total weight of the filter material powder and the natural clay powder. In some particular embodiments, the natural clay powder is from 10 wt. % to 12 wt. % of the total weight of the filter material powder and the natural clay powder. In some embodiments, the filter material powder includes a metal oxyhydroxide material, a metal oxide material, and a manganese oxide material. In some embodiments, the metal oxyhydroxide material includes iron oxyhydroxide, the metal oxide material includes titanium dioxide, and the manganese oxide material includes manganese sand. In some embodiments, the natural clay powder includes at least one of:

attapulgite, sepiolite and bentonite. In some particular embodiments, the natural clay powder consists of attapulgite, the first temperature is 80°C, the second temperature is 95C°, the third temperature is 125C°, and the fourth temperature is 500°C. In some embodiments, the temperature ramp rate is at least 0.5°C per minute and no greater than 3°C per minute. In some embodiments, the first hold time, the second hold time, the third hold time, and the fourth hold time are each for from 0.2 hours to 2 hours.

[0006] In some embodiments, the method further includes adding an amount of water to the plurality of adsorbent granules, and sealing the plurality of adsorbent granules within a container for an aging time before sintering the plurality of adsorbent granules. In some particular embodiments, the aging time is from 1 day to 3 days. In some embodiments, the method further includes treating the sintered plurality of adsorbent granules in an acid solution for a treatment time, and rinsing the plurality of adsorbent granules in rinse water until the rinse water has a pH greater than 6.6. In some embodiments, forming the plurality of adsorbent granules includes mixing together the filter material powder, the natural clay powder, and the water to produce a paste, baking the paste to remove at least some of the water to produce a filter material cake, and granulating the filter material cake to form the plurality of adsorbent granules.

[0007] Various embodiments concern a composition of adsorbent granules for the removal of heavy metals from water. Each of the plurality of adsorbent granules includes a metal oxyhydroxide material, a metal oxide material, a manganese oxide material, and a natural clay binder. The natural clay binder is from 5 wt. % to 20 wt. % of the composition. In some embodiments, the natural clay binder includes at least one of: attapulgite, sepiolite and bentonite. In some embodiments, the natural clay binder is from 10 wt. % to 12 wt. % of the composition. In some embodiments, each of the plurality of adsorbent granules further includes a molecular sieve material. In some particular embodiments, a ratio of the metal oxyhydroxide material to the metal oxide material to the manganese oxide material to the molecular sieve material is 0.5-2 to 0.5-2 to 0.5-2 to 0.01 -1 . In some embodiments, each of the plurality of adsorbent granules further includes a pore-forming agent. In some particular embodiments, the pore-forming agent is at least one of: sodium

bicarbonate, sodium carbonate, and calcium carbonate.

[0008] The above mentioned and other features of the invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a graph illustrating the efficiency levels at which various adsorbent granules remove heavy metals from water, and a crush strength of the adsorbent granules as functions of natural clay binder weight percentage, according to embodiments of this disclosure.

[0010] FIG. 2 is graph illustrating a crush strength of adsorbent granules as a function of sintering methods, according to embodiments of this disclosure. DETAILED DESCRIPTION

[0011] Embodiments of this disclosure include adsorbent granules for use in adsorbing heavy metals from water. The adsorbent granules can be made of a combination of adsorbent materials. The synergistic combination of the adsorbent materials in close proximity can result in greater than 95% efficiency in removal of at least some heavy metals. The adsorbent materials can be pulverized into a fine powder, mixed together with a binder, and then formed into adsorbent granules sized for use in, for example, a filter cartridge for household applications. The adsorbent granules held together with the binder can have a crush strength of at least 2 Newtons (N), and in some embodiments, greater than 7 N, to be able to withstand the rigors of manufacturing and handling associated with the fabrication and use of filter cartridges. However, it has been found that the binder itself can interfere with the heavy metal removal efficiency of the adsorbent materials.

[0012] Embodiments of this disclosure employ natural clay binders in quantities sufficient to impart the desired strength to the adsorbent granules, but not so large as to impair the heavy metal removal efficiency of the adsorbent granules. Embodiments of the disclosure include a method for making the adsorbent granules that include sintering the granules in a stepped fashion, as described below. It has been found that adsorbent granules with a relatively small amount of natural clay binder and sintered with the stepped sintering process can be significantly stronger than adsorbent granules sintered in a conventional sintering process. In some embodiments, additional adsorbent granule strength can be achieved by an aging process, as described below. In some embodiments, the heavy metal removal efficiency can be further improved with an acid soak, as described below, following the stepped sintering process.

[0013] Adsorbent granules made according to some embodiments of this disclosure can exhibit heavy metal removal efficiencies greater than 95% and crush strengths greater than 7 N. Adsorbent granules made according to some embodiments of this disclosure can exhibit heavy metal removal efficiencies greater than 99% and crush strengths greater than 13 N.

[0014] In some embodiments, the adsorbent granules can be formed by mixing together a filter material powder, a natural clay powder, and water to produce a paste. The paste can then be baked to remove most of the water to produce a filter material cake. The filter material cake can then be granulated to form the adsorbent granules. Some techniques used for granulating include compaction granulation, centrifugal granulation, melting granulation, spraying granulation, and extrusion pelletizing, as are known in the art.

[0015] The filter material powder can include a metal oxyhydroxide material, a metal oxide material, and a manganese oxide material. The metal oxyhydroxide material can include, for example, an iron oxyhydroxide (FeO(OH)) or a titanium oxyhydroxide (TiO(OH)). The metal oxide material can include, for example, titanium dioxide (T1O2), ferrous oxide (FeO), or ferric oxide (Fe203). The manganese oxide (MnO) material can be in the form of, for example, a manganese sand material. In some embodiments, the filter material powder can further include a molecular sieve material, such as, for example, activated alumina, or a zeolite, such as zeolite 13X.

[0016] In some embodiments, the weight ratios of the metal oxyhydroxide material to the metal oxide material to the manganese oxide material to the molecular sieve material can range from 0.5-2 to 0.5-2 to 0.5-2 to 0.01-1. In some embodiments, the weight ratios of the metal oxyhydroxide material to the metal oxide material to the manganese oxide material to the molecular sieve material can be 1 to 1 to 1 to 0.6, otherwise expressed as: 1 :1 :1 :0.6.

[0017] In some embodiments, the weight of the metal oxyhydroxide material as a percentage of the total weight of the filter material powder can be as low as 2 wt. %, 5 wt. %, or 10 wt. %, or as high as 30 wt. %, 60 wt. %, or 90 wt. %, or be any weight percentage between any two of the preceding weight percentages. For example, in some embodiments, the weight of the metal oxyhydroxide material as a percentage of the total weight of the filter material powder can range from 2 wt. % to 90 wt.%, 5 wt. % to 60 wt.%, or 10 wt. % to 30 wt.%.

[0018] In some embodiments, the weight of the metal oxide material as a percentage of the total weight of the filter material powder can be as low as 2 wt. %, 5 wt. %, or 10 wt. %, or as high as 30 wt. %, 60 wt. %, or 90 wt. %, or be any weight percentage between any two of the preceding weight percentages. For example, in some embodiments, the weight of the metal oxide material as a percentage of the total weight of the filter material powder can range from 2 wt. % to 90 wt.%, 5 wt. % to 60 wt.%, or 10 wt. % to 30 wt.%.

[0019] In some embodiments, the weight of the manganese oxide material as a percentage of the total weight of the filter material powder can be as 2 wt. %, 5 wt. %, or 10 wt. %, or as high as 30 wt. %, 60 wt. %, or 90 wt. %, or be any weight percentage between any two of the preceding weight percentages. For example, in some embodiments, the weight of the manganese oxide material as a percentage of the total weight of the filter material powder can range from 2 wt. % to 90 wt.%, 5 wt. % to 60 wt.%, or 10 wt. % to 30 wt.%.

[0020] In some embodiments, the weight of the molecular sieve material as a percentage of the total weight of the filter material powder can be as low as 0.5 wt. %, 2 wt. %, or 5 wt. %, or as high as 10 wt. %, 20 wt. %, or 30 wt. %, or be any weight percentage between any two of the preceding weight percentages. For example, in some embodiments, the weight of the molecular sieve material as a percentage of the total weight of the filter material powder can range from 0.5 wt. % to 30 wt.%, 2 wt. % to 20 wt.%, or 5 wt. % to 10 wt.%.

[0021] The metal oxyhydroxide material, the metal oxide material, the manganese oxide material, and the molecular sieve material can each be pulverized to form the filter material powder. As defined herein, the powder is a fine powder having a median powder particle size as small as 0.05 microns (μιη), 0.1 μιη, 0.2 μιη, 0.3 μιη, 0.5 μιη, 1 μιη, or 2 μιη, or as large as 3 μιη, 5 μιη, 10 μιη, 20 μιη, 30 μιη, 50 μιη, or 100 μιη, or between any two of the preceding values. For example, in some embodiments, the median powder particle sized can range from 0.05 μιη to 100 μιη, 0.05 μιη to 2 μιη, 0.3 μιη to 30 μιη, 1 μιη to 50 μιη, 3 μιη to 50 μιη, or 10 μιη to 20 μιη. In some embodiments, the median powder particle size can be about 10 μιη. The median powder particle size can be determined by, for example, a dynamic light scattering system, as is known in the art. In some embodiments, the metal oxyhydroxide material, the metal oxide material, the manganese oxide material, and the molecular sieve material can each be pulverized separately, and then combined to form the filter material powder. In some other embodiments, metal oxyhydroxide material, the metal oxide material, the manganese oxide material, and the molecular sieve material can be combined, and then pulverized together to form the filter material powder.

[0022] The natural clay powder can include at least one of: attapulgite, sepiolite and bentonite. Each of these natural clay powders can be selected to serve two purposes. Primarily, the natural clay powder can act as a binder to bind together the filter material powder and, once sintered, provide the adsorbent granule with the necessary physical strength, also referred to as the crush strength. Secondarily, by virtue of their composition and structure, these natural clays are believed to have at least some capacity to adsorb heavy metals. This adsorbent quality may improve the overall heavy metal absorption efficiency compared to other binders, such as, for example, silica gel or colloidal silica. However, even the natural clay powders do not adsorb as efficiently as the filter material. Thus, it is desirable to have as little natural clay binder in the adsorbent granules, and still have enough to provide the adsorbent granules with the necessary crush strength.

[0023] The balance between the heavy metal removal efficiency and the crush strength is shown in FIG. 1 . FIG. 1 is a graph illustrating efficiency levels at which various adsorbent granules remove heavy metals from water, and a crush strength of the adsorbent granules as functions of natural clay binder weight percentage, according to embodiments of this disclosure. The filter powder material included iron oxyhydroxide, titanium dioxide, manganese sand, and zeolite 13X in weight ratios of 1 : 1 : 1 :0.6. The filter material powder was divided into four parts and each part combined with attapulgite powder in one of four weight percentages (wt. %) of the total amount of filter material powder and attapulgite powder. Adsorbent granules were formed from the filter material powder, attapulgite powder, and water, as described above, producing four groups of adsorbent granules with respective attapulgite powder weight percentages of: 4.8 wt. %, 8 wt. %, 1 1 wt. %, and 20 wt. %. The adsorbent granules were sintered by heating to 500°C at a rate of 10°C per minute, and holding at 500°C for 1 hour. The adsorbent granules were spherical and about 2 millimeters in diameter.

[0024] Twenty adsorbent granules from each of the four groups were tested for crush strength. The crush strength was measured with a Particle Strength Tester from Dalian Panghui Keji, Ltd., and an arithmetic mean determined for each group. Adsorbent granules from each group were also tested for removal efficiency of arsenic and lead. For each removal efficiency test, a 0.2 g sample of adsorbent granules was placed in 250 milliliters of a test solution containing about 268 parts per billion (ppb) of arsenic and about 333 ppb of lead. The test solution with the granules was shaken for 24 hours at room temperature. The arsenic and lead remaining in the test solution after 24 hours was measured by Inductively Coupled Plasma Mass Spectrometry to determine the percentage of arsenic or lead removed by the adsorbent granules. [0025] The results are shown in FIG. 1 . As shown in FIG. 1 , the removal efficiency of the adsorbent granules decreases with increasing amounts of the attapulgite binder. As also shown in FIG. 1 , the crush strength decreases with decreasing amounts of binder, dropping below 2 N at 4.8 wt. %. FIG. 1 shows that at binder weight percentages from about 10 wt. % to about 12 wt. %, the adsorbent granules exhibit both high strength and high heavy metal removal efficiency. Thus, in some embodiments, the natural clay powder as a weight percentage of the total weight of the filter material powder and the natural clay powder can be as low as 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, 9 wt. % or 10 wt. %, or as high as 12 wt. %, 13 wt. %, 14 wt. %, 16 wt. %, 18 wt. %, or 20 wt. %, or between any two of the preceding weight percentages. For example, in some embodiments, the natural clay powder as a weight percentage of the total weight of the filter material powder and the natural clay powder can be from 5 wt. % to 20 wt. %, 6 wt. % to 18 wt. %, 7 wt. % to 16 wt. %, 8 wt. % to 14 wt. %, 9 wt. % to 13 wt. %, or 10 wt. % to 12 wt. %.

[0026] In some embodiments, the adsorbent granules can further include a pore-forming agent (PFA). The PFA can be mixed in with the water before adding it to the filter material powder and the natural clay powder. In some embodiments, the PFA can include at least one of: sodium bicarbonate (NaHCOs), sodium carbonate (Na2C03), and calcium carbonate (CaCOs).

[0027] In some embodiments, after sintering, the adsorbent granules can be treated in an acid solution. The treatment can include placing the adsorbent granules into the acid solution to soak for a treatment time. After soaking in the acid solution for the treatment time, the adsorbent granules can be rinsed in water until the pH of the rinse water is neutral. As defined herein, neutral pH is a pH greater than 6.6 and less than 7.3. Without wishing to be bound by any theory, it is believed that the sintering process can decrease the quantity of surface hydroxyl groups, which may reduce the ability of the adsorbent granules to remove heavy metal ions. It is believed that the acid treatment increases the quantity of surface hydroxyl groups, restoring the ability of the adsorbent granules to remove heavy metal ions. It is also believed that the acid treatment produces some additional pores on the surface of the adsorbent granules which may further improve the ability of the adsorbent granules to remove heavy metal ions.

[0028] In some embodiments, the acid solution for the post-sintering acid treatment can be a strong acid, for example, hydrochloric acid (HCI), sulfuric acid (H2SC ), or nitric acid (HNO3). In some embodiments, the acid solution can have an acid concentration as low as 0.2 moles per liter (M), 0.3 M, 0.4 M, 0.5 M, or 0.6 M, or as high as 0.7 M, 0.8 M, 0.9 M, 1 M, or 1 .2 M, or an acid concentration between any two of the preceding acid concentrations. For example, in some embodiments, the acid solution can have an acid concentration ranging from 0.2 M to 1 .2 M, 0.3 M to 1 M, 0.4 M to 0.9 M, 0.5 M to 0.8 M, 0.2 M to 1 M, or 0.5 to 1 .2 M.

[0029] In some embodiments, the treatment time for the post-sintering acid treatment can be as short as 0.2 hours, 0.4 hours, 0.6 hours, 0.8 hours, or 1 hour, or as long as 1 .2 hours, 1 .4 hours, 1 .6 hours, 1 .8 hours, or 2 hours, or for any length of time between any two of the preceding times. For example, in some embodiments, the treatment time for the post-sintering acid treatment can range from 0.2 hours to 2 hours, 0.4 hours to 1 .8 hours, 0.6 hours to 1 .6 hours, 0.8 hours to 1 .4 hours, 1 hour to 1 .2 hours, or 0.8 hours to 1 hour.

[0030] As noted above, it has been found that the crush strength of the granules may be further increased with a stepped sintering process, instead of the sintering process described above in reference to FIG. 1 . The stepped sintering process is designed according to a weight loss curve for the binder. The stepped sintering process drives out one of each of four types of water at each of four temperature steps. The four types of water are free water, adsorbed water, crystallization water, and constitutional water. Free water is water held among the adsorbent granules by the forces of capillary action. The adsorbed water is a film of water held on the surface of the adsorbent granules by electrochemical forces. The crystallization water is water trapped with crystals of the adsorbent granules. The constitutional water is water chemically bound to the adsorbent granules. The adsorbed water is driven off at a higher temperature that that necessary to drive of the free water. The crystallization water is driven off at a higher temperature than that necessary to drive off the adsorbed water. The constitutional water is driven off at the highest temperature, higher than that necessary to drive off the crystallization water. Generally, regardless of the natural clay binder used, the free water can be driven off at between 60°C and 100°C, the adsorbed water can be driven off between 90°C and 130°C, the crystallization water can be driven off between 100°C and 300°C, and the constitutional water can be driven off between 300°C and 1000°C. It has been found that for the attapulgite binder, the free water is driven off at 80°C, the adsorbed water is driven off at 95°C, the crystallization water is driven off at 125°C, and the constitutional water is driven off at 500°C.

[0031] The stepped sintering process begins with heating the adsorbent granules to a first temperature that is sufficient to remove the free water and holding at the first temperature for a first hold time. The first temperature is sufficient to remove the free water, but not sufficient to remove the adsorbed water. The next step is heating the adsorbent granules to a second temperature and holding at the second temperature for a second hold time, the second temperature sufficient to remove the adsorbed water, but not sufficient to remove crystallization water. The next step is heating the adsorbent granules to a third temperature and holding at the third temperature for a third hold time, the third temperature sufficient to remove the crystallization water, but not sufficient to remove the constitutional water. The last step of the stepped sintering process is heating the adsorbent granules to a fourth temperature and holding at the fourth temperature for a fourth hold time, the fourth temperature sufficient to remove the constitutional water. Thus, for embodiments including the attapulgite binder, the first temperature can be 80°C, the second temperature can be 95°C, the third temperature can be 125°C, and the fourth temperature can be 500°C.

[0032] In some embodiments, the first hold time, the second hold time, the third hold time, and the fourth hold time are the same length of time. In other embodiments, the first hold time, the second hold time, the third hold time, and the fourth hold time are not all the same length of time. In some embodiments, the first hold time, the second hold time, the third hold time, and the fourth hold time are each as short as 0.2 hours, 0.4 hours, 0.6 hours, 0.8 hours, or 1 hour, or as long as 1 .2 hours, 1 .4 hours, 1 .6 hours, 1 .8 hours, or 2 hours, or for any length of time between any two of the preceding times. For example, in some embodiments, the first hold time, the second hold time, the third hold time, and the fourth hold time each range from 0.2 hours to 2 hours, 0.4 hours to 1 .8 hours, 0.6 hours to 1 .6 hours, 0.8 hours to 1 .4 hours, 1 hour to 1 .2 hours, or 0.8 hours to 1 hour. Without wishing to be bound by any theory, it is believed that the stepped sintering process allows water between and within the adsorbent granules to be slowly driven out of the granules, producing a compact structure within the adsorbent granules.

[0033] In some embodiments, the heating to the first temperature, the second temperature, the third temperature, and the fourth temperature can be done at a temperature ramp rate as low as 0.5°C per minute (/min.), 1 °C/min., or 1 .5°C/min., or as high as 2°C/min., 2.5°C/min., or 3°C/min., or at any temperature ramp rate between any two of the preceding temperature ramp rates. For example, in some embodiments, the heating to the first temperature, the second temperature, the third temperature, and the fourth temperature can be done at a temperature ramp rate ranging from 0.5°C/min. to 3°C/min., 1 °C/min. to 2.5°C/min., 1 ^eC/min. to 3°C/min., or 1 .5°C/min. to 2°C/min.

[0034] As noted above, in some embodiments, the crush strength of the adsorbent granules may be further increased with an accelerated aging process. The accelerated aging process takes place after the adsorbent granules are formed, but before they are sintered. Water is sprayed onto the surface of the adsorbent granules and the adsorbent granules are sealed in a container. The adsorbent granules remain sealed within the container for aging time to increase the strength of the adsorbent granules. Without wishing to be bound by any theory, it is believed that the aging process permits water to be uniformly distributed throughout each of the adsorbent granules, and that such uniformity reduces the number of defects after sintering. It is further believed that the addition of the water to the adsorbent granules prior to sealing the container reduces the aging time required, thus accelerating the aging. In some embodiments, the aging time can be for as short as 1 day, 1 .5 days, or 2 days, or as long as 2.5 days, 3 days, or for any length of time between any two of the preceding lengths of time. For example, in some

embodiments, the aging time can range from 1 day to 3 days, 1 .5 days to 2.5 days, or 2 days to 3 days.

[0035] FIG. 2 is graph illustrating the crush strength of four groups of adsorbent granules as a function of the sintering processes and composition, according to embodiments of this disclosure. The four groups of adsorbent granules were prepared with 1 1 wt. % attapulgite binder, with one of the four groups further including a pore-forming agent (PFA), as described above in reference to FIG. 1 . The four groups were aged for 2 days, as described above. A first of the four groups of aged adsorbent granules was sintered by heating to 500°C at a temperature ramp rate of 10°C per minute, and holding at 500°C for 1 hour, as was done for the adsorbent granules of FIG. 1 . A second of the four groups of aged granules was sintered in the same way as the first group, except that the temperature ramp rate was reduced to 3°C per minute. The third and fourth groups, including the group with the PFA, were sintered with the stepped sintering process described above, with a first temperature of 80°C, a second temperature of 95°C, a third temperature of 125°C, and a fourth temperature can be 500°C. The ramp rate for the stepped sintering process was 3°C per minute. The first hold time, the second hold time, the third hold time, and the fourth hold time for the stepped sintering process were each the same length of time, 1 hour. After sintering, the adsorbent granules were treated in an acid solution, as described above. Detailed descriptions of the making of the third and fourth groups are provided below as Examples 1 and 2, respectively.

[0036] Adsorbent granules from each of the four groups were tested for crush strength and removal efficiency of arsenic and lead, as described above in reference to FIG. 1 . The test results are shown in FIG. 2. As shown in FIG. 2, the stepped sintering significantly increased the crush strength of the adsorbent granules.

Further, both of the stepped sintering groups retained excellent heavy removal efficiency. Adsorbent granules of the third group removed 99.4% of the arsenic and 97.9% of the lead. Adsorbent granules of the fourth group removed 96% of the arsenic and 99.9% of the lead.

EXAMPLES

Example 1

[0037] Adsorbent granules were prepared by pulverizing 40 g of a filter material mixture including iron oxyhydroxide, titanium dioxide, manganese sand, and zeolite 13X in weight ratios of 1 : 1 : 1 :0.6. The filter material mixture was pulverized to a median powder particle size of 10 μιη to form the filter material powder. 5 g of attapulgite clay was dispersed in 25 g of water and then well mixed with the filter material powder to form a paste. The paste was baked at a temperature of 130°C until about 18 g of water was removed to produce a filter material cake. The filter material cake was then broken up and granulated in a centrifugal mixer

(Speedmixer™ DAC 150.1 FVZ-K from FlacTek Inc., Landrum, South Carolina, U.S.) at 3,000 RPM for several minutes to form spherical adsorbent granules. The adsorbent granules were placed in a container and sprayed with no more than about 5 g of water. The container was sealed. The adsorbent granules remained in the sealed container for 2 days for accelerated aging.

[0038] After the accelerated aging, the adsorbent granules were sintered in a stepped sintering process. The adsorbent granules were heated to 80°C at a temperature ramp rate of 3°C/min. and held at 80°C for 1 hour, then heated to 95°C at a temperature ramp rate of 3°C/min. and held at 95°C for 1 hour, then heated to 120°C at a temperature ramp rate of 3°C/min. and held at 120°C for 1 hour, and then heated to 500°C at a temperature ramp rate of 3°C/min. and held at 500°C for 1 hour. After being allowed to cool, the adsorbent granules were soaked in an acid solution of hydrochloric acid at a concentration of 0.5 M for 1 hour. After soaking in the acid solution, the granules were rinsed by water until the pH of the rinse water was neutral.

[0039] The resulting adsorbent granules were about 2 mm in diameter and contained about 1 1 .1 wt. % of attapulgite binder. The adsorbent granules were tested for crush strength, as described above. The adsorbent granules were found to have a crush strength of about 8.6 N.

[0040] The adsorbent granules were also tested for removal efficiency of arsenic and lead. A 0.2 g sample of adsorbent granules was placed in 250 milliliters of a test solution containing about 268 parts per billion (ppb) of arsenic and about 333 ppb of lead. The test solution with the granules was shaken for 24 hours at room temperature. The arsenic and lead remaining in the test solution after 24 hours was measured as described above to determine the percentage of arsenic and lead removed by the adsorbent granules. The adsorbent granules were found to have a heavy metal removal efficiency of about 99.4% for arsenic and about 97.9% for lead.

Example 2

[0041] Adsorbent granules were prepared by pulverizing 40 g of a filter material mixture including iron oxyhydroxide, titanium dioxide, manganese sand, and zeolite 13X in weight ratios of 1 : 1 : 1 :0.6. The filter material mixture was pulverized to a median powder particle size of 10 μιη to form the filter material powder. 4 g of sodium carbonate 5 g was dissolved in 25 g of water. 5 g of attapulgite clay was dispersed in the sodium carbonate/water solution in a centrifugal mixer

(Speedmixer™ DAC 150.1 FVZ-K from FlacTek Inc., Landrum, South Carolina, U.S.) at 3,000 RPM for 30 seconds to form a suspension. The filter material powder was added to the suspension and combined in the centrifugal mixer until a paste was formed. The paste was baked at a temperature of 130°C until about 19 g of water was removed to produce a filter material cake. The filter material cake was then broken up and granulated in the centrifugal mixer at 3,000 RPM for several minutes to form spherical adsorbent granules. The adsorbent granules were placed in a container and sprayed with no more than about 5 g of water. The container was sealed. The adsorbent granules remained in the sealed container for 2 days for accelerated aging.

[0042] After the accelerated aging, the adsorbent granules were sintered in a stepped sintering process. The adsorbent granules were heated to 80°C at a temperature ramp rate of 3°C/min. and held at 80°C for 1 hour, then heated to 95°C at a temperature ramp rate of 3°C/min. and held at 95°C for 1 hour, then heated to 120°C at a temperature ramp rate of 3°C/min. and held at 120°C for 1 hour, and then heated to 500°C at a temperature ramp rate of 3°C/min. and held at 500°C for 1 hour. After being allowed to cool, the adsorbent granules were soaked in an acid solution of hydrochloric acid at a concentration of 1 M for 2 hours. After soaking in the acid solution, the granules were rinsed by water until the pH of the rinse water was neutral.

[0043] The resulting adsorbent granules were about 2 mm in diameter and contained about 10.2 wt. % of attapulgite binder. The adsorbent granules were tested for crush strength, as described above. The adsorbent granules were found to have a crush strength of about 13.5 N.

[0044] The adsorbent granules were also tested for removal efficiency of arsenic and lead. A 0.2 g sample of adsorbent granules was placed in 250 milliliters of a test solution containing about 268 parts per billion (ppb) of arsenic, about 333 ppb of lead, and about 258 ppb of cadmium. The test solution with the granules was shaken for 24 hours at room temperature. The arsenic, lead, and cadmium remaining in the test solution after 24 hours was measured as described above to determine the percentage of arsenic, lead, and cadmium removed by the adsorbent granules. The adsorbent granules were found to have a heavy metal removal efficiency of about 96.0% for arsenic, about 99.9% for lead, and about 98.1 % for cadmium.

[0045] While this invention has been described as relative to exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims

CLAIMS What is claimed is:

1 . A composition of adsorbent granules for the removal of heavy metals from water, each of the plurality of adsorbent granules comprising:

a metal oxyhydroxide material;

a metal oxide material;

a manganese oxide material; and

a natural clay binder, wherein the natural clay binder is from 5 wt. % to 20 wt.

% of the composition.

2. The composition of claim 1 , wherein the natural clay binder includes at least one of: attapulgite, sepiolite and bentonite.

3. The composition of claim 1 , wherein each of the plurality of adsorbent granules further includes a molecular sieve material, and a ratio of the metal oxyhydroxide material to the metal oxide material to the manganese oxide material to the molecular sieve material is 0.5-2 to 0.5-2 to 0.5-2 to 0.01 -1 .

4. The composition of claim 1 , wherein each of the plurality of adsorbent granules further includes a pore-forming agent.

5. A method of making a plurality of adsorbent granules, the method comprising: forming the plurality of adsorbent granules, the adsorbent granules including a filter material powder, a natural clay powder, and water; and sintering the plurality of adsorbent granules, the sintering including:

heating the plurality of adsorbent granules to a first temperature at a temperature ramp rate and holding at the first temperature for a first hold time, the first temperature sufficient to remove free water, but not sufficient to remove adsorbed water;

heating the plurality of adsorbent granules to a second temperature at the temperature ramp rate and holding at the second temperature for a second hold time, the second temperature sufficient to remove adsorbed water, but not sufficient to remove crystallization water;

heating the plurality of adsorbent granules to a third temperature at the temperature ramp rate and holding at the third temperature for a third hold time, the third temperature sufficient to remove crystallization water, but not sufficient to remove constitutional water; and

heating the plurality of adsorbent granules to a fourth temperature at the temperature ramp rate and holding at the fourth temperature for a fourth hold time, the fourth temperature sufficient to remove constitutional water.

6. The method of claim 5, wherein the natural clay powder is from 5 wt. % to 20 wt. % of a total weight of the filter material powder and the natural clay powder.

7. The method of claim 5, wherein the filter material powder includes:

a metal oxyhydroxide material;

a metal oxide material; and

a manganese oxide material.

8. The method of claim 7, wherein the metal oxyhydroxide material includes iron oxyhydroxide, the metal oxide material includes titanium dioxide, and the

manganese oxide material includes manganese sand.

9. The method of claim 5, wherein the natural clay powder includes at least one of: attapulgite, sepiolite and bentonite.

10. The method of claim 9, wherein the natural clay powder consists of attapulgite, the first temperature is 80°C, the second temperature is 95C°, the third temperature is 125C°, and the fourth temperature is 500°C.

1 1 . The method of claim 5, wherein the temperature ramp rate is at least 0.5°C per minute and no greater than 3°C per minute.

12. The method of claim 5, wherein the first hold time, the second hold time, the third hold time, and the fourth hold time are each for from 0.2 hours to 2 hours.

13. The method of claim 5, further including:

adding an amount of water to the plurality of adsorbent granules; and sealing the plurality of adsorbent granules within a container for an aging time before sintering the plurality of adsorbent granules, wherein the aging time is from 1 day to 3 days.

14. The method of claim 5, further including:

treating the sintered plurality of adsorbent granules in an acid solution for a treatment time; and

rinsing the plurality of adsorbent granules in rinse water until the rinse water has a pH greater than 6.6.

15. The method of claim 5, wherein forming the plurality of adsorbent granules includes:

mixing together the filter material powder, the natural clay powder, and the water to produce a paste;

baking the paste to remove at least some of the water to produce a filter material cake; and

granulating the filter material cake to form the plurality of adsorbent granules.