WO2010101991A1

WO2010101991A1 - Method of removing heavy metal from an aqueous solution

Info

Publication number: WO2010101991A1
Application number: PCT/US2010/026032
Authority: WO
Inventors: Thomas J. Shaniuk; Michael D. Capracotta; Jennifer L. Wade
Original assignee: Basf Se
Priority date: 2009-03-04
Filing date: 2010-03-03
Publication date: 2010-09-10

Abstract

A precipitate for use in removal of heavy metal from an aqueous solution includes a reaction product of an acidic solution and a basic solution. The acidic solution comprises a metal salt and water. The basic solution comprises a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, a Lewis base, and water. The acidic solution is added directly to the basic solution over a period of time of at least 5 minutes thereby forming a reaction mixture that includes the precipitate.

Description

METHOD OF REMOVING HEAVY METAL FROM AN AQUEOUS

SOLUTION

FIELD OF THE INVENTION

[0001] The subject invention generally relates to a method of forming a precipitate. More specifically, the subject invention relates to a method of forming a precipitate for use in removal of heavy metal from aqueous solutions.

DESCRIPTION OF THE RELATED ART

[0002] It is known in the art that ion exchange is a common method of removing heavy metal from aqueous solutions, such as drinking water. It is also known that metal silicates demonstrate significant ion exchange capacity and unique ion selectivity. Some metal silicates such as amorphous titanium silicates are known to be particularly selective towards heavy metal. Due to this selectivity, metal silicates have been incorporated into water filtration devices for a plurality of water systems. Specifically, amorphous titanium silicates are used for removing heavy metal from drinking water.

[0003] Methods of forming metal silicates typically involve acid-base neutralization reactions, wherein the metal silicates are formed as precipitates. These acid-base neutralization reactions involve adding a basic solution directly to an acidic solution, thereby forming metal silicate precipitates there from.

[0004] Other methods of forming amorphous titanium silicates that are known in the art involve use of acid-base neutralization reactions and a porous or impregnable support structure. These methods typically include partially or fully coating the support structure with a basic solution and subsequently partially or fully coating the support structure with an acidic solution to form a substrate-supported amorphous titanium silicate. The amorphous titanium silicate precipitate forms on, and impregnates, the support structure.

[0005] Despite the amounts of heavy metal in aqueous solutions that are removed by known compounds that demonstrate ion exchange capacity, such as amorphous titanium silicates, there remains an opportunity to provide ion-exchangers that maximize the removal of heavy metal from aqueous solutions beyond performance achieved with known compounds. In particular, there remains an opportunity to develop improved precipitates (and methods) that can be used to further maximize removal of heavy metal from aqueous solutions beyond levels achieved by existing precipitates.

SUMMARY OF THE INVENTION

[0006] The subject invention provides a precipitate and a method of forming the precipitate for use in removal of heavy metal from an aqueous solution. The method includes the step of providing an acidic solution. The acidic solution comprises a metal salt and water. The method also includes the step of providing a basic solution. The basic solution comprises a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, a Lewis base, and water. Additionally, the method includes the step of adding the acidic solution directly to the basic solution over a period of time of at least 5 minutes thereby forming a reaction mixture that includes the precipitate. The subject invention also provides a method for removing the heavy metal from the aqueous solution including the step of contacting the aqueous solution with the precipitate. The precipitate comprises a reaction product of the acidic solution and a basic solution. In this invention, the acidic solution is added directly to the basic solution over the period of time of at least 5 minutes as indicated above. [0007] The precipitate formed in accordance with the method of this invention effectively removes heavy metal from aqueous solutions beyond removal achieved by existing precipitates. Effective removal of heavy metal from aqueous solutions is beneficial to both human and livestock health, specifically as it pertains to water used for drinking, sanitation, hygiene, and growing produce. To this end, the precipitate may be incorporated into applications such as water filtration devices including, but not limited to, under-the-tap filters, under-the-counter filters, and whole-building filters.

[0008] The precipitate formed in accordance with the method of this invention effectively removes high amounts of heavy metal from aqueous solutions. Since the precipitate is so effective, much less of the precipitate is required to reduce heavy metal in drinking water to nationally-recognized allowable amounts of heavy metal in water used for drinking, and/or other uses, as compared to precipitates formed through other methods. Using less of the precipitate in water filtration devices reduces the overall volume occupied by the precipitate, thereby allowing manufactures of water filtration devices to create smaller and more portable water filtration devices. Overall cost of manufacturing water filtration devices is also reduced since fewer raw materials are required to produce an at least equally effective, but smaller water filtration device. Alternatively, water filtration devices may remain unchanged but consumer cost may be reduced in that a more effective water filtration device may require replacement less frequently.

DETAILED DESCRIPTION

[0009] Cleanliness of drinking water is a common concern shared by people and governments around the world. Consumption of drinking water having contaminates, such as heavy metal, could be hazardous to human health. The United States Environmental Protection Agency (hereinafter "the EPA") has provided national standards for drinking water which detail acceptable amounts of contaminates, including heavy metal. A precipitate formed in accordance with the method of the subject invention and used in accordance with this method removes heavy metal from aqueous solutions, such as drinking water. To this end, the precipitate is well suited for use in filtration devices to remove heavy metal from drinking water, thereby providing consumable drinking water having amounts of heavy metals within the national standards provided by the EPA.

[0010] For purposes of this application, the term "precipitate" is further defined as a solid and/or a semisolid compound formed from the addition of an acidic solution directly to a basic solution as described below. Also, the heavy metal typically includes lead, cadmium, zinc, copper, chromium, cobalt, arsenic, mercury, silver, and combinations thereof. The heavy metal may be present in the aqueous solution in the form of heavy metal ions (for example Pb (II), Pb (IV), Hg (II), Cr (III), Co (II), Co (III), Cd (II), Ag (I), As (III), As (V), and the like), and/or compounds containing at least one heavy metal atom (for example, sodium arsenate).

[0011] Typically, the aqueous solution comprises water and the heavy metal. However, it is to be appreciated that the aqueous solution may include other components in addition to the water and the heavy metal. Further, the aqueous solution is typically homogenous. Suitable examples of aqueous solutions include, but are not limited to, water derived from municipal water systems, industrial water systems, waste water systems, inland bodies of water, sea water, well water, any other solution in which water is a solvent, and combinations thereof.

[0012] The method of forming the precipitate comprises the step of providing the acidic solution. Typically, the acidic solution has a pH of less than about 7.0. The acidic solution typically has a pH of less than about 4, and more typically less than about 1.

[0013] Typically, the acidic solution comprises a metal salt and water. While not intending to be bound by any theory, it is believed that the metal salt dissociates to form a first metal intermediate and a salt intermediate. Upon reacting of the acidic solution and the basic solution, the first metal intermediate contributes to form the precipitate and the salt intermediate contributes to form a salt by-product as described in greater detail below.

[0014] In one embodiment, the metal salt of the acidic solution comprises a metal selected from Group IV metals, Group V metals, Group VIII metals, Group XIII metals, and Group XIV metals of the periodic table. Suitable examples of the metal include, but are not limited to, titanium, tin, aluminum, iron, niobium, and zirconium. Alternatively, the metal salt comprises a metal oxide of any of the metals referenced above. Additionally, the metal salt of the acidic solution further comprises a ligand. Typically, the ligand comprises a halogen atom. Suitable halogens may be selected from the group of fluorine, chlorine, bromine, and iodine. Suitable examples of the ligand include, but are not limited to, a chloride ion, a bromide ion, a sulfate ion, a phosphate ion, and a sulfide.

[0015] Suitable examples of the metal salt include, but are not limited to, titanium sulfate, titanium oxychloride, tin chloride, aluminum chloride, iron chloride, niobium chloride, and zirconium chloride. In one embodiment titanium tetrachloride is used to form the metal salt. For example, titanium tetrachloride, when added to water, forms an aqueous solution comprising titanium oxychloride and hydrochloric acid. Under these circumstances, the metal salt is defined as titanium oxychloride and the acidic solution further comprises hydrochloric acid. [0016] The metal salt is typically present in the acidic solution in an amount of from about 5 to about 60, more typically from about 10 to about 50, and most typically from about 33 to about 45, percent by weight based on total weight of the acidic solution.

[0017] In one embodiment, the water in the acidic solution is further defined as deionized water. Deionized water is substantially free of ions which may interfere with the acid-base neutralization reaction provided for herein. Water is typically present in the acidic solution in an amount from about 10 to about 95, more typically from about 10 to about 60, and most typically from about 30 to about 40, percent by weight based on total weight of the acidic solution.

[0018] Typically, the acidic solution is provided as an aqueous solution. In one embodiment, the acidic solution which is already aqueous may be combined with additional water. Under these circumstances, order of addition is unimportant; however, typically the aqueous, acidic solution is typically added to the additional water. It is also to be appreciated that the aqueous, acidic solution and the additional water may be combined simultaneously. In another embodiment, the aqueous, acidic solution and the additional water are combined in a first vessel. In this embodiment, the first vessel may further comprise a mixer and a mixing blade, as generally understood in the art. Typically, the aqueous, acidic solution and the additional water are mixed until homogenous. Typically, the acidic solution is maintained within a temperature range of from about 20 degrees Celsius to about 50 degrees Celsius, which may require external heating/cooling of the acidic solution. [0019] The method of forming the precipitate further comprises the step of providing the basic solution. Typically, the basic solution has a pH of greater than about 7.0 as generally understood in the art. More typically, the basic solution typically has a pH of from about 10 to about 14, and most typically from about 12 to about 13. Typically, the basic solution comprises a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof; a Lewis base; and water. [0020] In one embodiment, the metal compound is further defined as an alkali metal silicate. One suitable example of the alkali metal silicate is sodium silicate. Typically, the metal compound is provided in an aqueous solution prior to addition to the basic solution. Under these circumstances, the aqueous solution comprising the metal compound is typically added to the basic solution in an amount of from about 1 to about 20, more typically from about 1 to about 15, and most typically from about 4 to about 10, percent by weight based on total weight of the basic solution. [0021] In one embodiment, the Lewis base is further defined as a metal hydroxide. The metal hydroxide may be further defined as an alkali metal hydroxide. Suitable examples of the alkali metal hydroxide include, but are not limited to, sodium hydroxide and potassium hydroxide. Typically, the Lewis base is provided in an aqueous solution prior to addition to the basic solution. Under these circumstances, the aqueous solution comprising the Lewis base is typically added to the basic solution in an amount of from about 1 to about 30, more typically from about 5 to about 20, and most typically from about 5 to about 15, percent by weight based on total weight of the basic solution.

[0022] In one embodiment, the water in the basic solution is, like the water in the acidic solution, deionized water. Water is typically added to the basic solution in an amount of from about 50 to about 95, more typically from about 60 to about 95, and most typically from about 75 to about 95, percent by weight based on total weight of the basic solution. [0023] To provide the basic solution, the metal compound, the Lewis base, and water are combined. Order of addition is unimportant; however, the metal compound and the Lewis base are typically added to the water. It is to be appreciated that the water, the metal compound, and the Lewis base may be added simultaneously. In one embodiment, the metal compound, the Lewis base, and water are combined in a second vessel. In this embodiment, the second vessel may further comprise a mixer and a mixing blade, as generally understood in the art. Typically, the basic solution is mixed until homogenous. In one embodiment, the basic solution is maintained within a temperature range of from about 20 degrees Celsius to about 50 degrees Celsius, which may require external heating/cooling of the basic solution. [0024] In one embodiment, while not intending to be bound by any theory, it is believed that the metal compound, e.g., the metal silicate, and the Lewis base, e.g., the metal hydroxide, dissociate in water to form a metal ion, a hydroxyl ion, and a silicate intermediate. In this embodiment, the silicate intermediate contributes to form the precipitate and the metal ion contributes to form the salt by-product as described in greater detail below. In another embodiment, it is believed that the metal compound, e.g., the metal carbonate, and the Lewis base, e.g., the metal hydroxide, dissociate in water to form a metal ion, a hydroxyl ion, and a carbonate intermediate. In this embodiment, the carbonate intermediate contributes to form the precipitate and the metal ion contributes to form the salt by-product as described in greater detail below. [0025] The method of forming the precipitate further comprises the step of adding the acidic solution directly to the basic solution. Typically, the acidic solution is added directly to the basic solution in an amount of from about 5 to about 70, more typically from about 5 to about 60, and most typically from about 5 to about 15, percent by weight based on total weight of the acidic and basic solutions combined. [0026] The basic solution is typically utilized in an amount of from about 30 to about 95, more typically from about 40 to about 95, and most typically from about 80 to about 95, percent by weight based on total weight of the acidic and basic solutions combined.

[0027] The basic solution is typically mixed continuously and simultaneously as the acidic solution is added directly to the basic solution. The term "directly", as used in this context, refers to adding the acidic solution to the basic solution without an intermediate step or process. For example, adding the basic solution to a substance and then adding the acidic solution to the substance including the basic solution is not directly adding the acidic solution to the basic solution in the context of this application. For purposes of this application, the step of adding the acidic solution directly to the basic solution is further defined as adding the acidic solution to the basic solution in the absence of a porous support, also referred to as a carrier, which typically functions in the art to support the precipitate. Examples of a porous support include, but are not limited to, diatomaceous earth, e.g. kieselguhr, dehydrated aluminas, chromias, porous silicas and aluminas, gamma alumina, charcoal, activated carbon, and equivalents thereof. The step of adding the acidic solution directly to the basic solution may also be conducted in the absence of any support for the precipitate whatsoever, porous or not.

[0028] The acidic solution is typically added directly to the basic solution over a period of time of from at least 5 to about 400, more typically from about 60 to about 240, and most typically from about 100 to about 160, minutes. However, it should be appreciated that the period of time may be over about 400 minutes. [0029] In one embodiment, the acidic solution is added directly to the basic solution at a constant flow rate. In one embodiment, the constant flow rate is typically from about 0.25 to about 20, more typically from about 0.45 to about 1.60, and most typically from about 0.60 to about 1.00, percent of the acidic solution based on total weight of the acidic solution per minute.

[0030] When the acidic solution is added directly to the basic solution, the acid-base neutralization reaction begins, thereby forming a reaction mixture. In particular, the first metal intermediate from the acidic solution reacts with the silicate intermediate and/or the carbonate intermediate from the basic solution and the salt intermediate reacts with the metal ion, thereby forming the precipitate and salt by-product, respectively. During the acid-base neutralization reaction, the reaction mixture may comprise the first metal intermediate and the salt intermediate from the acidic solution; the silicate intermediate and/or the carbonate intermediate, the metal ion, and the hydroxyl ion from the basic solution; water; a gas by-product; the salt byproduct; and the precipitate formed in accordance with the method of the subject invention.

[0031] It should be appreciated that the reaction mixture may vary in pH as long as the acid-base neutralization reaction continues. In one embodiment, addition of the acidic solution directly to the basic solution is terminated once the reaction mixture has a pH within a range of from about 6.0 to about 9.0, more typically from about 6.5 to about 8.5, most typically from about 7.5 to about 8.5. In another embodiment, the pH of the reaction mixture may be controlled or adjusted by adding diluted hydrochloric acid or any other acid or by adding diluted sodium hydroxide. [0032] In one embodiment, the reaction mixture is maintained within a temperature range of from about 20 degrees Celsius to about 50 degrees Celsius, which may require external heating/cooling of the reaction mixture. [0033] In one embodiment, after formation of the precipitate, the reaction mixture including the precipitate is filtered and the precipitate is isolated as a filtrand. Any filter that captures the precipitate may be used to this end. In one embodiment, the precipitate is washed with deionized water until conductivity of the wash water is less than or equal to about 500, more typically less than about 400, and most typically less than about 300, mS/cm. The precipitate may also be dried. Typically, the precipitate is dried at about 120 degrees Celsius. In one embodiment, the precipitate is formed into particles of consistent size and shape. For example, the precipitate may be powderized by various mechanical processes.

[0034] In one embodiment, when the basic solution includes the metal silicate, the precipitate comprises a second metal silicate different from the metal silicate provided in the basic solution. In this embodiment, one suitable example of the precipitate is titanium silicate, which is typically amorphous titanium silicate. If the precipitate is an amorphous titanium silicate, the precipitate typically has a titanium-to-silicate molar ratio of from about 1:5 to about 2:1 and more typically from about 1:2 to about 1:1. Other suitable examples of the precipitate include, but are not limited to, tin silicate, aluminum silicate, iron silicate, niobium silicate, and zirconium silicate. In another embodiment, when the basic solution includes the metal carbonate, the precipitate comprises a second metal carbonate different from the metal carbonate provided in the basic solution.

[0035] Surface area of the precipitate formed in accordance with the method of the subject invention is significantly less than surface area of existing precipitates. Nevertheless, it was surprisingly found that the precipitate of this invention maximizes removal of heavy metal in aqueous solutions beyond performance achieved with known precipitates. Generally, an opposite result would be expected; that is, decreasing surface area of the precipitate would be expected to decrease removal of heavy metal in aqueous solutions by the precipitate. Maximized removal of heavy metal is achieved even when compared to precipitates formed from the very same reactants but with the basic solution added to the acidic solution instead of the acidic solution added to the basic solution as with this invention. In one embodiment the precipitate has a surface area of from about 140 to about 250, more typically from about 180 to about 240, and most typically from about 225 to about 240 m /g. Conversely, precipitates formed from an opposite order of addition, as described above, have surface areas of about 310m²/g.

[0036] The precipitate formed in accordance with the method of the subject invention is typically porous. The precipitate typically defines a plurality of pores each presenting a diameter of from about 0.002 to about 0.5 microns as measured using mercury porosimetry. Further, the precipitate typically presents a total pore volume of from about 0.10 to about 0.80 and more typically from about 0.25 to about 0.75 mL/g as measured using mercury porosimetry. It is believed that the porosity of the precipitate contributes, in part, to the maximized removal of heavy metal in aqueous solutions. Also, the precipitate typically has a tapped bulk density of from about 0.50 to about 1.25, and more typically from about 0.75 to about 1.10, and most typically from about 0.80 to about 1.00 g/cc. It is believed, in part, that the bulk density of the precipitate is influenced by the pH of the reaction mixture once the step of adding the acidic solution directly to the basic solution is terminated.

[0037] While not intending to be bound to any theory, it is believed that adding the acidic solution directly to the basic solution and maximizing the period of time over which the acidic solution is added directly to the basic solution, therefore increasing time the acid-base neutralization reaction takes place in a basic environment, results in formation of the precipitate for effective removal of heavy metal from aqueous solutions beyond removal achieved by existing precipitates. The time the acid-base neutralization reaction takes place in a basic environment is further maximized by terminating the addition of the acidic solution directly to the basic solution when the reaction mixture has a basic pH. Even though the precipitate is formed from the very same reactants as existing precipitates, it is believed that allowing the acid-base neutralization reaction to take place in the basic environment, and for the specified period of time, contributes to favorable modifications of the chemical structure of the precipitate over the existing precipitates. Possible modifications of the chemical structure of the precipitate include formation of chemical bonds at angles and/or orientations different from the chemical bonds present in existing precipitates. It is further believed that the differing chemical bond angles and/or orientations may create and/or expose additional active sites on the surface of the precipitate, thereby increasing capacity for removing heavy metal from aqueous solutions. An active site an atom or group of atoms that make up part of or all of the precipitate and which have a charge. Active sites may bind particular ions depending both on the charge of the ion and the charge of the active site. It is believed that the precipitate comprises active sites each having a negative charge, which attract and bind cations. Examples of cations include heavy metal ions as referenced above.

[0038] The subject invention further provides a method for removing a heavy metal from an aqueous solution. This method comprises the step of contacting the aqueous solution comprising the heavy metal with the precipitate thereby removing the heavy metal from the aqueous solution. As described above, the precipitate comprises the reaction product of the acidic solution added directly to the basic solution over a period of time of at least 5 minutes. [0039] Preferably, the step of contacting is further defined as flowing the aqueous solution comprising the heavy metal through a filtration device. A suitable example of a filtration device is a packed bed having the precipitate encased in a structure which retains the precipitate. The packed bed has an inlet and an outlet that allows the aqueous solution comprising the heavy metal to enter the packed bed through the inlet, contact the precipitate, and exit the through the outlet. However, it should be appreciated that a number of other devices may be used to effectuate a similar result as known in the art.

[0040] The step of contacting the precipitate with the aqueous solution comprising the heavy metal typically reduces the heavy metal in the aqueous solution in an amount of about greater than 20 to about 50 and more typically from about 30 to about 40, percent by weight based on the total weight of the precipitate.

[0041] In one embodiment, the precipitate is used alone for removing the heavy metal from the aqueous solution. Alternatively, the precipitate may be used in combination with other water filtration methods and/or water filtration devices for use in removing heavy metal or an impurity other than heavy metal from aqueous solutions as understood in the art. For example, in one embodiment, the filtration device further comprises activated carbon for removing impurities other than the heavy metal from the aqueous solution. As is understood in the art, activated carbon is a form of carbon that has been manufactured to be highly porous and thus has a large surface area available for adsorption. For example, activated carbon may have a surface area of about or greater than 500 m²/g .

[0042] The impurity other than the heavy metal in the aqueous solution may also include volatile by-products, such as carbon containing compounds, particularly halocarbons. Specific examples of impurities other than heavy metals include, but are not limited to, volatile chlorination by-products such as trihalomethanes (for example; chloroform, bromoform, bromodichloromethane, and chlorodibromomethane), bromate, chlorite, haloacetic acids, chloramines, and the like, and volatile organic byproducts such as benzene, halobenzenes, acrylamide, carbontetrachloride, bromodichloromethane, chlorodibromomethane, dichloroethylene, dichloromethane, halopropanes, dioxin, alkylbenzenes, PCBs, toluene, xylenes, vinyl chloride, styrene, and the like.

[0043] The following examples, as presented herein, are intended to illustrate and not limit the subject invention.

EXAMPLES

[0044] Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and Hl- H2 are formed according to the subject invention. Specifically, an acidic solution is provided that comprises a metal salt and water. A basic solution is also provided and comprises a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, a Lewis base, and water. The acidic solution is then added directly to the basic solution over a period of time of at least 5 minutes forming a reaction mixture. Comparative Example 1 is not formed according to the subject invention. Comparative Example 1 is formed by providing a basic solution and an acidic solution. The basic solution comprises a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, a Lewis base, and water. The acidic solution comprises a metal salt and water. The basic solution is then added directly to the acidic solution over a period of time of about 25 minutes forming a reaction mixture.

[0045] For Comparative Example 1 and Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, and E1-E5, the acidic solution is provided by combining and mixing deionized water and aqueous titanium oxychloride. For Inventive Examples F1-F2, G, and H1-H2, the acidic solution is prepared by providing aqueous titanium oxychloride. The percent by weight of each of deionized water, titanium oxychloride, and hydrochloric acid based on the total weight of the acidic solution is set forth in Table 1 below for Comparative Example 1 and Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2.

Table 1:

[0046] For Comparative Example 1 and Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2, the basic solution is provided by combining and mixing deionized water, sodium hydroxide solution, and sodium silicate solution. The percent by weight of each of deionized water, sodium hydroxide solution, and sodium silicate solution based on the total weight of the basic solution is set forth in Table 2 below for Comparative Example 1 and Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2.

Table 2:

[0047] For Comparative Example 1, the basic solution is added directly to and mixed with the acidic solution over the period of time of 25 minutes. For Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2, the acidic solution is added directly to and mixed with the basic solution over the period of time of at least 5 minutes. The percent by weight of each of the acidic solution and the basic solution based on the total weight of the acidic and basic solutions combined is set forth in Table 3 below for Comparative Example 1 and Inventive Examples Al- A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2. Table 3:

[0048] Inventive Examples A1-A5 are lab scale production models formed over various periods of time and use similar amounts and similar ratios of raw materials as compared to amounts and ratios of raw materials used in Comparative Example 1. [0049] Inventive Examples B1-B2 are lab scale production models formed over various periods of time and use various amounts and various ratios of raw materials as compared to amounts and ratios of raw materials used in Comparative Example 1. [0050] Inventive Examples C1-C2 are pilot plant scale production models formed over various periods of time and use increased amounts but similar ratios of raw materials as compared to amounts and ratios of raw materials used in Comparative Example 1.

[0051] Inventive Examples D1-D2 are pilot plant scale production models formed over various periods of time and use increased amounts but similar ratios of raw materials as compared to amounts and ratios of raw materials used in Comparative Example 1.

[0052] Inventive Examples E1-E5 are commercial scale production models formed over various periods of time and use increased amounts but similar ratios of raw materials as compared to amounts and ratios of raw materials used in Comparative Example 1.

[0053] Inventive Examples F1-F2 are lab scale production models formed over one period of time and use similar amounts of raw materials but a concentrated acidic solution and a diluted basic solution compared to amounts and ratios of raw materials used in Comparative Example 1.

[0054] Inventive Examples G is a pilot plant scale production model formed over one period of time and uses an increased amount of raw materials and a concentrated acidic solution and a diluted basic solution compared to amounts and ratios of raw materials used in Comparative Example 1.

[0055] Inventive Examples H1-H2 are commercial scale production models formed over one period of time and use increased amounts of raw materials and a concentrated acidic solution and a diluted basic solution compared to amounts and ratios of raw materials used in Comparative Example 1.

[0056] Aqueous titanium oxychloride is commercially available from Cristal Global. [0057] Sodium silicate solution is commercially available as N Clear ®. [0058] Deionized water and sodium hydroxide are commercially available from a variety of chemical suppliers.

[0059] For Comparative Example 1, the reaction mixture is filtered and washed with deionized water. Filtrand is dried at 120 degrees Celsius and powderized. For Inventive Examples A1-A5, B1-B2, C1-C2, and E1-E5 each reaction mixture is filtered and washed with deionized water. Filtrand is dried at 120 degrees Celsius and powderized. For Inventive Example Dl the reaction mixture is filtered and washed with deionized water. Filtrand is dried at 110 degrees Celsius and powderized. For Inventive Example D2 the reaction mixture is filtered and washed with deionized water. Filtrand is dried at 350 degrees Celsius and powderized. For Inventive Examples F1-F2 each reaction mixture is filtered and washed with deionized water. Filtrand is dried at 107 degrees Celsius and powderized. For Inventive Example G the reaction mixture is filtered and washed with deionized water. Filtrand is dried at 300 degrees Celsius and powderized. For Inventive Examples H1-H2 each reaction mixture is filtered and washed with deionized water. Filtrand is dried at 130 degrees Celsius and powderized. Table 4:

Percent removal of lead by weight based on total weight of the precipitate used. [0060] After formation, Comparative Example 1 and each Inventive Example A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2, are characterized to determine lead removal by the precipitates of these Examples, which is set forth above in Table 4. The Comparative and Inventive Examples are measured and weighed so that a known amount of each is provided. Each known amount of the Comparative and Inventive Examples is contacted with separate aqueous solutions comprising from about 970 to about 1000 ppm lead each. Subsequently, each aqueous solution is measured to determine amount of lead remaining. Amount of lead remaining for each aqueous solution is subtracted from the initial amount of lead in each aqueous solution prior to contact with the Comparative and Inventive Examples. The difference is used to determine how much lead was removed from each aqueous solution by contact with the precipitate of the respective Comparative and Inventive Examples. Amount of lead removed for each Comparative and Inventive Example is divided respectively by the known weight of the precipitate of the Comparative and Inventive Example used to contact the aqueous solution comprising from about 970 to about 1000 ppm lead. A resulting quotient is multiplied by 100 to represent percent removal of lead by weight based on the total weight of the precipitate of the Comparative or Inventive Example used.

[0061] Additionally, after formation, the precipitates of Comparative Example 1 and each Inventive Example A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, and H1-H2 are characterized to determine average surface area, which is also set forth in Table 4. A Micromeritics TriStar instrument and a standard ASTM method for surface area determination are used to calculate surface area of the precipitate of each Comparative and Inventive Example. [0062] As set forth in Table 4, lead removal by the precipitates of Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, F1-F2, G, and H1-H2 is substantially increased over Comparative Example 1. At a minimum, the precipitates of the Inventive Examples formed according to the subject invention demonstrate increased lead removal of 17% as compared to the precipitate of Comparative Example 1. The precipitates formed according to the subject invention on average demonstrate increased lead removal of about 73% as compared to the precipitate of Comparative Example 1. Specifically, the precipitates of Inventive Examples A1-A5, B1-B2, Cl- C2, D1-D2, E1-E5, F1-F2, G, and H1-H2 effectively reduce heavy metal in aqueous solutions at a rate significantly increased over prior art precipitate of Comparative Example 1. More specifically, Inventive Examples F1-F2, G, and H1-H2 formed using a concentrated acidic solution on average demonstrate increased lead removal of about 94% as compared to the precipitate of Comparative Example 1. [0063] As set forth in Table 4, surface area of the precipitates of Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, and H1-H2 is surprisingly lower than the precipitate of Comparative Example 1. However, as outlined above, the precipitates of Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, and H1-H2 maximize removal of lead in aqueous solutions beyond performance achieved by the precipitate of Comparative Example 1. The precipitates of Inventive Examples A1-A5, B1-B2, C1-C2, D1-D2, E1-E5, and H1-H2 demonstrate a surface area of about Vi to about ³A the surface area of the precipitate of Comparative Example 1.

[0064] The lead removal results and the surface area results also demonstrate that the method of forming the precipitate may be used to replace the prior art method, resulting in a more efficient precipitate that may be used to reduce size and cost of water filtration devices. [0065] Many modifications and variations of the subject invention are possible in light of the above teachings. The subject invention may be practiced otherwise than as specifically described within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method of forming a precipitate for use in removal of heavy metal from an aqueous solution, said method comprising the steps of:

A. providing an acidic solution, the acidic solution comprising;

(i) a metal salt, and (ii) water;

B. providing a basic solution, the basic solution comprising;

(i) a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, (ii) a Lewis base, and (iii) water; and

C. adding the acidic solution directly to the basic solution over a period of time of at least 5 minutes thereby forming a reaction mixture that includes the precipitate.

2. A method as set forth in claim 1 wherein the step of adding the acidic solution directly to the basic solution is further defined as adding the acidic solution to the basic solution in the absence of a porous support.

3. A method as set forth in claim 1 wherein the period of time ranges from about 5 minutes to about 400 minutes.

4. A method as set forth in claim 3 wherein the period of time ranges from about 60 minutes to about 240 minutes.

5. A method as set forth in claim 4 wherein the period of time ranges from about 100 minutes to about 160 minutes.

6. A method as set forth in claim 1 wherein the step of adding is terminated when the reaction mixture has a pH of from about 6 to about 9.

7. A method as set forth in claim 1 wherein the acid solution comprises the metal salt in an amount of from about 33 to about 45 percent by weight based on total weight of the acidic solution.

8. A method as set forth in claim 1 wherein the acidic solution is added directly to the basic solution at a constant flow rate.

9. A method as set forth in claim 1 further comprising the step of mixing the basic solution simultaneously as the acidic solution is added directly to the basic solution.

10. A method as set forth in claim 1 further comprising the step of isolating the precipitate.

11. A method as set forth in claim 1 wherein the metal salt includes a metal selected from Group IV metals, Group V metals, Group VIII metals, Group XIII metals, and Group XIV metals of the periodic table.

12. A method as set forth in claim 11 wherein the metal is further defined as titanium.

13. A method as set forth in claim 1 wherein the metal salt includes a ligand.

14. A method as set forth in claim 13 wherein the ligand comprises a halogen atom.

15. A method as set forth in claim 1 wherein the metal salt is further defined as titanium oxychloride.

16. A method as set forth in claim 1 wherein the metal compound is further defined as an alkali metal silicate.

17. A method as set forth in claim 1 wherein the Lewis base is further defined as a metal hydroxide.

18. A method as set forth in claim 1 wherein the precipitate is further defined as an amorphous titanium silicate.

19. A method as set forth in claim 1 wherein the heavy metal is selected from the group of lead, cadmium, zinc, copper, chromium, cobalt, arsenic, mercury, silver, and combinations thereof.

20. A method as set forth in claim 1 wherein the precipitate has a surface area of from about 140 to about 250 m²/g.

21. A method as set forth in claim 1 wherein the precipitate has a tapped bulk density of from about 0.50 to about 1.25 g/cc.

22. A precipitate formed in accordance with the method set forth in claim 1.

23. A method for removing a heavy metal from an aqueous solution, said method comprising the step of contacting the aqueous solution with a precipitate thereby removing the heavy metal from the aqueous solution, wherein the precipitate comprises the reaction product of an acidic solution added directly to a basic solution over a period of time of at least 5 minutes, the acidic solution comprising a metal salt and water, and the basic solution comprising a metal compound selected from the group of metal silicates, metal carbonates, and combinations thereof, a Lewis base, and water.

24. A method as set forth in claim 23 wherein the step of contacting is further defined as flowing the aqueous solution comprising the heavy metal through a packed bed comprising the precipitate.

25. A method as set forth in claim 24 wherein the precipitate removes the heavy metal from the aqueous solution in an amount of from about greater than 20% to about 50% by weight based on the total weight of the precipitate.

26. A method as set forth in claim 25 wherein the precipitate removes the heavy metal from the aqueous solution in an amount of from about 30% to about 40% by weight based on the total weight of the precipitate.

27. A method as set forth in claim 24 wherein the packed bed further comprises activated carbon for removing an impurity other than the heavy metal from the aqueous solution.