Stable concentrated polyaluminum chlorosilicate solutions

Abstract

Novel polyaluminum chlorosilicates (PACSi) and sodium aluminum silicate (SAS) products having improved characteristics useful in the treatment of water and wastewater as compared with polyaluminum chlorides (PAC), are provided herein, as well as new processes for their manufacture, and methods of using PACSi as coagulants and flocculants in the treatment of water and/or wastewater.

Claims

1. A method for producing a sodium aluminum silicate (SAS) composition, the method comprising the steps of: a) preparing a mixture containing: 30-60 wt % of a 50% NaOH, 1.7-6 wt% of a 30% sodium silicate solution, and 5-15 wt % water; b) heating the mixture until the mixture is clear; c) after the mixture is clear, adding 35-50 wt % aluminum oxide trihydrate to the mixture to form a liquid solution; and d) heating the liquid solution until the aluminum oxide trihydrate is dissolved in order to produce the SAS composition having a molar ratio of Si:Al of 0.015-0.08 and a molar ratio of Na.sub.2O:Al.sub.2O.sub.3 of 1.0-1.30.

2. The method of claim 1, wherein the mixture is heated to a boiling temperature of the mixture.

3. The method of claim 1, wherein the mixture is heated when adding the aluminum oxide trihydrate.

4. The method of claim 1, wherein the solution is heated for 1 hour.

5. The method of claim 1, wherein the aluminum oxide trihydrate is added to the mixture such that a resulting aluminum oxide concentration is 20% to 27% Al.sub.2O.sub.3.

6. The method of claim 1, wherein the sodium silicate solution includes 0.9 to 4 wt % SiO.sub.2.

7. A SAS composition produced by the method of claim 1 having a formula:
(Na.sub.2O)a(Al.sub.2O.sub.3)(SiO.sub.2).sub.c (Formula III), wherein: a is 1-1.3 and c is 0.03 -0.15 and Si:Al has a molar ratio of 0.015-0.08 and Na.sub.2O:Al.sub.2O.sub.3 has a molar ratio 1.8-1.30.

8. The SAS composition of claim 7, comprising: a) 20-32 wt % Al.sub.2O.sub.3; b) 12-22 wt % Na.sub.2O; and c) 0.5-1.7 wt % SiO.sub.2.

9. The SAS composition of claim 7, wherein Na.sub.2O:Al.sub.2O.sub.3 has a molar ratio of 1.22-1.30.

10. A method of treating water to remove impurities, the method comprising: producing the SAS composition according to claim 1; and adding the SAS composition to water in order to remove turbidity and/or non-purgeable organic carbon (NPOC) from the water.

11. A method of treating water to remove impurities, the method comprising: producing the SAS composition according to claim 1; mixing a solution of 10 to 30 wt % of the SAS composition with a solution of 70 to 90 wt % comprising basic aluminum chloride (BAC) or aluminum chloride (ACL) to form a second solution; and adding the second solution to water in order to remove turbidity and/or NPOC from the water.

12. The method of treating water according to claim 11, wherein the mixing includes agitating the second solution for 1 hour to 12 hours.

13. The method of treating water according to claim 11, further comprising forming a silicated BAC or a silicated ACL before the mixing, wherein the second solution comprises the solution of 10 to 30 wt % of the SAS composition and the solution of 70 to 90 wt % of the silicated BAC or the silicated ACL.

Description

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Definitions

(1) As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires:

(2) Aluminum chlorohydrate (ACH) is a 50% solution of aluminum chlorohydrate dihydrate having the chemical formula of Al.sub.2(OH).sub.5Cl-2H.sub.2, a concentration of 23-24% aluminum oxide, and a basicity of 80-84%.

(3) Aluminum chloride (ACL) solutions are products of the reaction of aluminum oxide trihydrate and hydrochloric acid. Commercially available solutions of ALC contain 28% aluminum chloride and 0 to 0.5% free hydrochloric acid. Aluminum chloride has the chemical formula of AlCl.sub.3, and is commercially available, for example, from United States Aluminum Company (USALCO), Baltimore, Md.

(4) Basic aluminum chlorides (BAC) are products of the reaction of aluminum oxide trihydrate and hydrochloric acid. The amount of hydrochloric acid is shorted so that there is insufficient chloride to make the neutral salt of aluminum chloride. They can also be made digesting aluminum metal in hydrochloric acid, or aluminum chloride. Basic aluminum chloride of various basicities can be made by blending products of the above two processes. Basic aluminum chloride solutions can be formulated from 8 to 25% Al2O3. Basic aluminum chlorides are of the Formula I: Al.sub.2(OH).sub.(6-x)Cl.sub.x where x=1 to 6, preferably 2 to 6, and are commercially available, for example, from USALCO, Baltimore, Md.

(5) Percent Basicity: Percent basicity is defined as (% OH)(52.91)/(% Al). On a molar level, this may be expressed as ((OH)/(Al))/3 multiplied by 100. Thus, Al.sub.2(OH).sub.2Cl.sub.4 has a basicity of 33%.

(6) Sodium Silicate solution: These are highly alkaline solutions made by dissolving SiO.sub.2 in sodium hydroxide solutions. They can have a weight ratio of 3.22 to 1.80 SiO.sub.2/Na.sub.2O and concentrations of 23 to 34% SiO.sub.2. For the purpose of this invention a weight ratio of 3.22 is ideal (although not required) as it minimizes the amount of sodium hydroxide in the product.

(7) Polyaluminum chlorosilicates: The polyaluminum chlorosilicates of embodiments of the invention have the formula of Formula III: Al(OH).sub.xCl.sub.(3-x-2y)(SiO.sub.2).sub.y, (formula I), in which: x is 1.5 to 2.5; y is 0.003 to 0.1; the ratio of OH:Al is 2.2 to 2.55; wherein the polyaluminum chlorosilicate solution has a basicity of 74% to 84% and a concentration of Al.sub.2O.sub.3 of 10% to 22%.

(8) Sodium aluminate solution: Sodium aluminate solutions are highly alkaline solutions made by reacting aluminum oxide trihydrate with sodium hydroxide solutions, and have a chemical formula of Na.sub.2Al.sub.2O.sub.4. Sodium aluminate solutions are commercially available, for example, from USALCO, Baltimore, Md., at 38%, 43% and 45%, and in different Na.sub.2O/Al.sub.2O.sub.3 mole ratios. It is preferable to use a lower mole ratio such as 1.27 to minimize the amount of sodium chloride in the product of this invention. Solutions would have the chemical formula of Formula II: (Na.sub.2O).sub.a(Al.sub.2O.sub.3)(SiO.sub.2).sub.c in which: a is 1 to 1.3 and y is 0.03 to 0.15.

(9) Sodium aluminum silicate solutions are prepared by dissolving aluminum oxide trihydrate in a sodium hydroxide solution containing sodium silicate. They can have a molar ratio of SiO.sub.2 to Na.sub.2Al.sub.2O.sub.4 of 0.03 to 0.15, a molar ratio of Na.sub.2O to Al.sub.2O.sub.3 of 1.0-1.25 and a concentration of 30 to 55% Na.sub.2Al.sub.2O.sub.4. These compounds have the chemical formula of Formula II: (Na.sub.2O).sub.a(Al.sub.2O.sub.3)(SiO.sub.2).sub.c in which: a is 1 to 1.3 and c is 0.03 to 0.15

Polyaluminum Chlorosilicates

(10) Embodiments of the present invention are directed to concentrated, high basicity polyaluminum chlorosilicate (PACSi) compositions that are temperature stable from 0 to 150 F. for periods up to six months to a about one year. These compositions are highly effective in removing impurities from water and wastewater. They have the ability to remove non-purgeable organic carbon (NPOC) and turbidity from waters with surprising efficiency. The compositions of embodiments of the invention include PACSi having the chemical formula: Al(OH).sub.xCl.sub.(3-x-2y)(SiO.sub.2).sub.y, (Formula I), in which x is 1.5 to 2.5, y is 0.01 to 0.1, and the ratio of OH:Al is 2.2 to 2.55, wherein the composition has a basicity of 74 to 84%, and a concentration of Al.sub.2O.sub.3 of 10 to 22%. A specific PACSi formula of embodiments of the invention is that of Formula IV: Al(OH).sub.2.18Cl.sub.0.78(SiO.sub.2).sub.0.02.

Processes of Making PACSi

(11) The various embodiments of the invention disclosed herein include a process for producing polyaluminum chlorosilicates by mixing sodium aluminum silicate with a 28% aqueous aluminum chloride solution. The aluminum chloride can be purchased commercially or manufactured by digesting aluminum oxide trihydrate in a hydrochloric acid solution. The sodium aluminum silicate is produced by digesting aluminum oxide trihydrate in a mixture of sodium hydroxide and sodium silicate. The aqueous solution contains 0.9 to 4% SiO.sub.2 and 30 to 45% sodium hydroxide. Aluminum oxide trihydrate is added such that the final aluminum oxide concentration is about 20 to 27% Al.sub.2O.sub.3.

(12) The polyaluminum chlorosilicate can be made either continuously or in batch mode by mixing 10 to 30% sodium aluminum silicate with 70 to 90% aluminum chloride solution. It is important to not exceed 84% basicity during the mixing process to prevent solidification of the product. Since there is no sulfate in the product, there is no need to reduce the temperature to prevent temperature degradation of the product. It may be convenient to mix the solutions under ambient conditions to enhance mixing. Mixing is done using an mechanical agitator such as a magnetic stirrer. After all the ingredients are mixed together the solution is generally agitated to keep the solids suspended until completely dissolved. This process may take one to twelve hours, depending on mixing conditions and temperature. Any colloidal materials remaining can be filtered out to produce a clear solution.

(13) In an alternative process, the polyaluminum chlorosilicate is made with basic aluminum chloride instead of aluminum chloride solution. Basic aluminum chlorides can be formulated at higher concentrations of aluminum oxide than aluminum chloride, and use of the higher concentration enables the polyaluminum chlorosilicates to be formulated at higher concentrations. The higher basicity of the basic aluminum chloride minimizes the amount of sodium silicate that is added. The process is generally the same as making polyaluminum chlorosilicates from aluminum chloride solution. A solution of 10 to 30% sodium aluminum silicate is mixed with 70 to 90% basic aluminum chloride solution. Mixing should be done with enough shear to produce a uniform suspension. After all the ingredients are mixed together the solution should be agitated to keep the solids suspended until completely dissolved. This process will take one to twelve hours depending on mixing conditions, and temperature. Any colloidal materials can be filtered out to produce a clear solution.

(14) Another alternative to the process of making polyaluminum chlorosilicates is the incorporation of sodium silicate into the basic aluminum chloride or aluminum chloride solution. The sodium silicate is diluted to provide an aqueous solution containing 0.2% to 7% SiO.sub.2, followed by addition of 1 to 10% of the sodium silicate solution to an aluminum chloride (ALC) or basic aluminum chloride (BAC) solution. Mixing is not temperature dependent, and can occur at ambient temperatures or whatever temperature is convenient. The mixing is applied until a clear solution is reached. Silicated-aluminum chloride and/or silicated-basic aluminum chloride can be obtained from commercial sources or can be manufactured from commercially available sodium aluminate without requiring the production of sodium aluminum silicate. To produce the polyaluminum silicate, 10 to 30 wt % sodium aluminate solution is mixed with 70 to 90 wt % silicated-aluminum chloride or silicated-basic aluminum chloride. As described above, mixing is done with enough shear to produce a uniform suspension. After all the ingredients are mixed together the solution is agitated generally for one to twelve hours, to keep the solids suspended until completely dissolved. The amount of time needed can vary according to mixing conditions, and temperature. Any colloidal materials can be filtered out to produce a clear solution.

(15) According to another embodiment, 10 to 30% sodium aluminum silicate is mixed with 70% to 90% silicated-basic aluminum chloride or silicated-aluminum chloride. The process for producing the polyaluminum chlorosilicates is the same as described above.

(16) In yet another embodiment, the polyaluminum chlorosilicates are blended with aluminum chlorohydrate solutions. This blending results in a lower salt concentration, which adds stability and shelf life of the product, and also increased basicity and concentration of the products that is not attainable by processes that use sodium aluminum silicate or sodium aluminate.

(17) The procedures described above produce PACSi having a concentration of at least 10% Al.sub.2O.sub.3, preferably 10-22%, and a basicity greater than 74% (preferably 74-84%). The PACSi is used to treat water, for example, by adding PASCi to raw water or wastewater to coagulate and remove impurities. Typically, the PACSi is mixed into raw water at dosage of 5 to 100 mg/L. The water is generally rapidly mixed with the PACSi and then is slowly mixed for several minutes. Mixing is then stopped and the impurities that have been attracted to the PACS and are allowed to settle to the bottom of the water. The supernatant can then be filtered and proceeds through the rest of the treatment process. PACSi can be used in wastewater treatment to remove phosphorous and/or impurities.

(18) Most typically, the PACSi solution will be added to raw water or wastewater to coagulate and remove impurities. The water is generally rapidly mixed with the PACSi and then is slowly mixed for several minutes. Mixing is then stopped and the impurities that have been attracted to the PACSi and are allowed to settle to the bottom of the water. The supernatant is then filtered and proceeds through the rest of the treatment process. PACSi can be used in wastewater treatment to remove phosphorous and/or impurities. When used for this, 50 to 300 mg of PACSi is typically used per liter of wastewater.

Advantages of PACSi

(19) Sulfated PACS are widely used as flocculants in water treatment. They react quickly in water, form large flocs and settle rapidly. They are highly efficient in treating highly turbid water conditions but fail to remove NPOC as efficiently as aluminum chlorohydrate. The drawback is that the sulfated PACSs have a limited shelf life and degrade quickly at temperatures above 84 F. This makes PACS products unsuitable for areas where the temperature will degrade the product or where there is a need for greater NPOC removal. Aluminum chlorohydrate works effectively in removing NPOC, but does not work effectively in removing turbidity from high turbidity waters, or when the temperature of the water falls below 40 F. The aluminum chlorohydrate solutions freeze at temperatures above 0 F.

(20) High basicity PACSi of the present invention are highly effective as flocculants in water treatment. The PACSi products described herein produce fast large flocs in water at all temperatures, do not decompose at elevated temperatures, and have a shelf life of about 6 months to a year. The PACSi products remove more NPOC than the sulfated PACSs and equal or exceed the removal of NPOC by aluminum chlorohydrate.

(21) The PACSi products described herein are unique and provide advantages for water treatment efficiency over sulfate polyaluminum chlorides. As described above, the PACSi products maintain their stability for more than 6 months. As shown in Example 7, a PACSi product disclosed herein maintained its turbidity at than 50 ntu during that 6 month period, and even after 10 months, and as well after 10 weeks exposure to a temperature of 110 F. (See Table 2). The American Water Works Association publishes a standard for Liquid Polyaluminum Chloride. The current standard is ANSI/AWWA B408-10. The Standard requires that solutions of polyaluminum chloride have a turbidity of less than 50 ntu.

(22) The following non-limiting Examples are provided to demonstrate methods of production and use of the PACSi molecules disclosed herein.

EXAMPLES

Example 1

Production of Sodium Aluminum Silicate (SAS)

(23) Sodium aluminum silicate: In a 600 milliliter glass beaker 317 grams of 50% sodium hydroxide was added along with 34 grams of sodium silicate solution having 28.7% SiO.sub.2 and a weight ratio of 3.22 SiO.sub.2/Na.sub.2O and 78 grams of water. The solution was heated to boiling, at which time 273 grams of aluminum oxide trihydrate was added. The solution was maintained at boiling for a period of one hour. The solution was then cooled to room temperature. This process produced a 1.4% sodium aluminum silicate solution (SAS) having 25.5% Al.sub.2O.sub.3, 18.4% Na.sub.2O, a Na.sub.2O to Al.sub.2O.sub.3 mole ratio of 1.22, and a Si:Al molar ratio of 0.05 and solution.

Example 2

Production of Polyaluminum Chlorosilicate (PACSi)

(24) Polyaluminum chlorosilicate: In a 600 milliliter glass beaker was placed 291 grams of basic aluminum chloride solution having 10.75% Al.sub.2O.sub.3 and a basicity of 0.22%. Into this solution was mixed 128 grams of the sodium aluminum silicate solution of Example 1 and 31 grams of water. The solutions were mixed until homogeneous, generating a white suspension, and reaching a temperature of 126 F. After 12 hours the solution was filtered, yielding a polyaluminum chlorosilicate of 13.7% Al.sub.2O.sub.3, 81.2% Basic and 0.4% SiO.sub.2.

Example 3

Production of Polyaluminum Chlorosilicate (PACSi)

(25) Polyaluminum chlorosilicate: Into a 150 milliliter beaker was placed 4.5 grams of sodium silicate solution containing 28.7% SiO.sub.2 and 8.9% Na.sub.2O. This solution was mixed with 24.5 g of water to form a clear 4.5% SiO.sub.2 solution. Into a 600 milliliter glass beaker was placed 295 grams of basic aluminum chloride containing 10.75% Al.sub.2O.sub.3 and having a basicity of 0.22%. An amount of 28.9 grams of the dilute sodium silicate solution (4.5% SiO.sub.2) was added, and the resulting solution was mixed with 126 grams of the sodium aluminum silicate (SAS) solution of example 1. The solution was mixed until homogeneous, generating a white suspension, and reaching a temperature of 126 F. After 12 hours the solution was filtered and yielded a polyaluminum chlorosilicate (PACSi) of 14.0% Al.sub.2O.sub.3, 82.6% Basic and 0.7% SiO.sub.2.

Example 4

Production of Polyaluminum Chlorosilicate (PACSi) with SAS

(26) Polyaluminum chlorosilicate: In a 250 ml beaker, 160 grams of the PACSi of Example 2 was blended with 40 grams of a 50% solution of aluminum chlorohydrate (ACH), This yielded a 15.7% Al.sub.2O.sub.3 polyaluminum chlorosilicate solution with a basicity of 82%, 0.38% SiO.sub.2, and a Si:Al ratio of 0.02.

Example 5

Production of Polyaluminum Chlorosilicate (PACSi) with SAS

(27) Polyaluminum chlorosilicate: In a 250 ml beaker 140 grams of the PACSi of Example 2 was blended with 60 grams of ACH. This yielded a 16.7% Al.sub.2O.sub.3 polyaluminum chlorosilicate solution with a basicity of 82%, 0.38% SiO.sub.2, and a Si:Al ratio of 0.019.

Example 6

Water Jar Testing to Compare Performance of PACS and PACSi

(28) Jar testing was performed on water obtained from the Occoquan Reservoir to compare the performance of Sulfated PACS versus PACSi. Table 1 below demonstrates improved removal of turbidity and NPOCs by PACSi described herein versus PACS. At same alumina dosage, PACSi (Jars 3-6) showed double the percentage of turbidity removal and of NPOC removal as compared with PACS (Jars 1 and 2). The PACSi samples removed more turbidity and nonpurgeable organic carbon (NPOC) than DP-2500, a commercially available sulfated PACS, available from USALCO, Baltimore, Md.

(29) TABLE-US-00001 TABLE 1 Performance of PACS versus PACSi Jar #1 Jar #2 Jar #3 Jar #4 Jar #5 Jar #6 Product DP-2500 DP-2500 Example 2 Example 2 Example 3 Example 3 PACS PACS PACSi PACSi PACSi PACSi Dosage microliters 47 94 42 83 42 83 Dosage mg/L 30 60 27 54 27 54 Dosage mg/L Al.sub.2O.sub.3 3.75 7.5 3.78 7.56 3.78 7.56 Turbidity NTU 0.925 0.675 0.724 0.514 0.743 0.43 % Turbidity Removal .sup.16% .sup.39% .sup.34% .sup.53% .sup.32% .sup.61% NPOC mg/L 3.319 3.148 2.97 2.456 2.7 2.444 % NPOC Removal 13.5% 18.0% 22.6% 36.0% 29.7% 36.3%

Example 7

Water Jar Testing to Compare Performance of PACS and PACSi

(30) Samples of stored and heat-stressed sulfated polyaluminum chlorides (PACS) were compared to PACSi products described herein with respect to each product's stability and efficacy under conditions of long term storage and heat exposure. Stable turbidity of polyaluminum chloride products is defined by the AWA having a turbidity value of less than 50 ntu. As shown in Table 2 below, the product turbidity of the tested PACs varied with temperature and storage time, showing unacceptable turbidity for PACs at 4 months and 6 weeks of storage, and at 110 F. In contrast, turbidity of the novel PACSi disclosed herein, remained stable and acceptable, despite long storage and exposure to heat, and were as effective in removing turbidity and NPOC from water. PACs stored for 6 weeks and exposed to high temperatures had the highest PAC turbidity of all samples, and actually increased the turbidity of the treated water rather than removing turbidity (Jar 3).

(31) TABLE-US-00002 TABLE 2 Degradation by Heat and Storage of PACs versus PACSi Jar #1 Jar #2 Jar #3 Jar #4 Jar #5 Jar #6 Product DP-2500 DP 2500 DP 2500 Example 4 Example 4 Example 5 Fresh 4 6 weeks 2.5 10 weeks 10 months at 110 F. months at 110 F. months Product Turbidity NTU 2.7 90 408 5.8 16.1 3.9 Dosage microliters 22.5 22.5 22.5 17 17 16.5 Dosage mg/L 29 29 29 22 22 22 Dosage mg/L Al.sub.2O.sub.3 3.55 3.55 3.55 3.55 3.55 3.55 Turbidity NTU 1.86 1.97 7.88 1.27 1.37 1.1 % Turbidity Removal 73% 72% 13% 82% 80% 84%

Example 8

Jar Testing of Antigua Water to Compare ACL and PACSi

(32) Jar testing was performed on water obtained from Antigua to compare the performance of Aluminum Chlorohydrate versus PACSi. The water is naturally high in turbidity and organics. The chart below demonstrates the differences in performance: The settled turbidity was much higher in treatments with ACH than in treatments with PACSi at equal alumina dosages. The % NPOC removal was slightly better in the PACSi samples than the ACH, also at equal alumina dosages.

(33) TABLE-US-00003 TABLE 3 Degradation by Heat and Age of PACs versus PACSi Jar #1 Jar #2 Jar #3 Jar #4 Jar #5 Jar #6 Product ACH ACH ACH Example 5 Example 5 Example 5 Dosage microliters 15.25 16 17 22.5 23.5 25 Dosage mg/L 20.3 22.6 24.6 29.2 32.5 35.1 Dosage mg/L Al.sub.2O.sub.3 4.8 5.3 5.8 4.7 5.2 5.7 Turbidity NTU 5.37 2.72 2.07 1.76 1.65 1.63 % Turbidity Removal 94.6% 97.3% 97.9% 98.2% 98.3% 98.4% NPOC mg/L 6.4 6.25 6.29 6.39 6.20 6.20 % NPOC Removal 28.7% 30.4% 30.0% 28.8% 31.0% 31.0%

Example 9

(34) The following chart demonstrates the freezing issue of aluminum chlorohydrate. The PACSi compositions produced in Examples 2-5 do not freeze at temperatures of 0 F. or higher. In contrast the polyaluminum chlorosulfate PACS, DelPAC2020, as well as ACH showed signs of freezing, whereas the more concentrated PACS DelPAC2500 did not freeze at 0 F. DelPAC 2020 and 2500 are commercially available sulfate polyaluminum chlorides.

(35) TABLE-US-00004 TABLE 4 Freezing Point of PACs versus PACSi Product Freezing Point Example 2 <0 F. Example 3 <0 F. Example 4 <0 F. Example 5 <0 F. ACH 22 F. DelPAC 2500 <0 F. DelPAC 2020 Partial at 0 F.