Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
  • C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
  • C02F1/5254—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using magnesium compounds and phosphoric acid for removing ammonia
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/105—Phosphorus compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/12—Halogens or halogen-containing compounds
  • C02F2101/14—Fluorine or fluorine-containing compounds

Definitions

• the calcium sulfate will settle and the excess water will be liberated.
• This liberated water will normally be collected in a system of channels and ponds and recycled to the phosphoric acid production plant for reuse (i.e., washing the calcium sulfate filter cake).
• These channels and ponds also serve as a collection means for other water that is used in and around the phosphoric acid plant, such as for cleaning or washing, fresh water fume scrubbers, and as a collection means for phosphoric acid spills or leaks within the plant. Also, since these channels and ponds are located outside, they collect rain water.
• This method consists of adding a calcium compound (such as CaCO 3 , Ca(OH) 2 or CaO) to the pond water, in two stages, such that the phosphate and other impurities form solid precipitates that settle and are separated from the thus purified water.
• a calcium compound such as CaCO 3 , Ca(OH) 2 or CaO
• This method is described in Francis T. Nielsson, ed., Manual of Fertilizer Processing, Marcel Dekker, Inc. (1987), pp. 480 to 482; G.A. Mooney, et al., Removal of Fluoride and Phosphorus from Phosphoric Acid Wastes with Two Stage Line Treatment, Proceedings of the 33rd Industrial Waste Conference, Purdue Univ. (1978); G.A.
• a fourth problem with this treatment process is that the purified pond water often just barely meets the criteria for discharge and cannot be used as a substitute for the fresh water that would normally be required in a phosphoric acid plant, such as for steam production.
• Reverse osmosis Another general method of water purification is reverse osmosis. This process is based on the application of external pressure on an aqueous salt solution in contact with a semi permeable membrane, such that the applied pressure exceeds the osmotic pressure of the water component of the solution in contact with the membrane. Thus, some of the water is forced through the membrane in the reverse direction, while the other components in the solution (i.e., soluble salts) do not pass through the membrane. This results in a stream of purified water, known as permeate, and a stream of increased salt content, known as the reject or concentrate. Reverse osmosis is well known in the art and is described in Douglas M. Ruthven, ed., Encyclopedia of Separation Technology, Volume 2, pp.
• pond water contaminated phosphoric acid plant pond water
• pond water contaminated phosphoric acid plant pond water
• a first embodiment of the present invention which provides a process for partial purification pre-treatment of pond water comprising the steps of adding a first compound that will react with the fluorides in the pond water and form an essentially insoluble fluoride salt, adding a second compound that is either basic or will form a base when water is present, the cationic portion of said second compound being such that the phosphate salts thereof remain soluble, allowing the precipitates thus formed to settle, decanting or otherwise separating the clarified liquid portion of the mixture, holding the liquid portion of the mixture for a time period sufficient to allow the silicic acid present to decompose into hydrated silicon dioxide, separating the hydrated silicon dioxide and adding an acid to the liquid solution thus obtained, such that the solubility of the ions remaining in solution are increased and are greater than or equal to their concentrations that are expected in the thus treated solution when the solution is concentrated via the removal of essentially pure water.
• a second embodiment of the present invention provides a simplified process for partial purification pre-treatment of pond water-comprising the steps of adding a first basic compound that will cause the precipitation of an essentially insoluble salt containing the majority of the calcium and fluorine in the pond water while allowing the majority of the phosphate to remain in solution (i.e., the phosphate salts of the base are soluble), allowing the precipitates thus formed to settle, decanting or otherwise separating the clarified liquid portion of the mixture, holding the liquid portion of the mixture for a time period sufficient to allow any silicic acid present to decompose into hydrated silicon dioxide, separating the hydrated silicon dioxide and adding an acid to the liquid solution thus obtained, such that the solubility of the ions remaining in solution are increased and are greater than or equal to their concentrations that are expected in the thus treated solution when the solution is concentrated via the removal of essentially pure water.
• a first embodiment of the present invention provides a process for partially purifying contaminated phosphoric acid plant pond water such that the partially purified or pre-treated pond water can be concentrated by the removal of pure water without the formation of precipitated solids or scale that would otherwise impede or render inoperable the concentrating means or apparatus.
• the pre-treated pond water could be processed through a conventional reverse osmosis system comprising one or more stages to obtain a purified water stream and a stream of concentrated pond water.
• pond water is defined as a dilute solution of phosphoric acid, also containing sulfuric acid, silicic acid, fluoride ions, calcium ions, sodium ions, ammonium ions, and other ionic and non-ionic species, that is normally present in and around phosphate fertilizer plants that employ the so-called wet process for the production of phosphoric acid.
• a first compound is added to the pond water that will react with the fluorides in the pond water and form an essentially insoluble fluoride salt.
• Several compounds of this type include magnesium containing compounds, calcium containing compounds, strontium containing compounds and barium containing compounds.
• magnesium containing compounds include magnesium containing compounds, calcium containing compounds, strontium containing compounds and barium containing compounds.
• the calcium containing compounds including calcium carbonate, calcium hydroxide and calcium oxide.
• the quantity of said compound added to the pond water is based on the fluorine concentration in the pond water such that the molar ratio of the cationic portion of the compound to the fluorine in the pond water is within the range of 0.45 to 0.80, or more preferably within the range of 0.50 to 0.70, or still more preferably within the range of 0.55 to 0.65.
• the quantities of fluorine contained in the pond water to be treated were 19 pounds and the compound to be added were calcium oxide
• the quantities of calcium oxide corresponding to the three ranges stated above would be about 25.2 - 44.9 pounds, 28.0 - 39.2 pounds and 30.8 - 36.4 pounds.
• This first compound can be added to the pond, water either in dry form, as a paste or as a liquid slurry, and still be within the scope of the present invention. Furthermore, this first compound can be added to the pond water either on a batch basis or on a continuous basis and still be within the scope of the present invention.
• This first compound is mixed with the pond water for a time period sufficient for the compound to react with the fluorine in the pond water. Typically, this time period will be from 1 minute to 30 minutes, depending on the form in which the compound is added to the pond water and the configuration of the mixing apparatus.
• the mixture can be clarified and the solids formed as a result of reactions of the first compound with the pond water can be removed.
• the solids formed as a result of reactions of the first compound with the pond water are left in the pond water.
• removal of these solids at this point is still considered within the scope of the present invention.
• a second compound is now added to the pond water. If the pond water is being treated on a batch basis and the solids produced as a result of the reactions of the first compound with the pond water are not removed, this second compound can be added in the same vessel. If the pond water is being treated on a continuous basis, the pond water, with or without the reaction products from the first compound addition, must be transferred to a second tank or vessel.
• the second compound must be a strong base or a compound that will form a strong base when water is present.
• the cationic component of the second compound must be such that the phosphate salts formed thereof remain soluble in the pond water. Examples of strongly basic compounds that form soluble phosphate salts include sodium hydroxide and potassium hydroxide.
• the second compound is added to and mixed with the pond water, either in pure form or as a solution, in sufficient quantity to increase the pH of the resulting pond water solution to a value within the range of 4.2 to 8.0, or more preferably within the range of 5.0 to 6.5, or still more preferably within the range of 5.5 to 6.0.
• pure form refers to the physical state of the compound (i.e., a solid for sodium hydroxide or potassium hydroxide, or a gas or pressurized liquid for anhydrous ammonia) and not the chemical purity of the compound. In terms of chemical purity, ordinary technical grade purity is acceptable for both the first compound and the second compound.
• the pH as used above and elsewhere, is defined as the negative power to which 10 must be raised to equal the molar hydrogen ion concentration in solution.
• solid precipitates will form in the solution.
• These solid precipitates are now removed from the solution either by settling the solids and decanting the liquid, centrifuging the solution, filtering the solution, or any other means that will result in a separation of a clear liquid from the solid precipitates.
• the solids can be removed as a slurry containing, for example, 50% by weight solids and 50% by weight liquid.
• the suspended solids concentration in the liquid be no greater than 0.5% by weight.
• the clear liquid is now allowed to age.
• the purpose of the aging is to allow silicic acid present in the liquid to decompose into hydrated silicon dioxide.
• the aging time should be at least 2 hours and preferably at least 16 hours. While there is no upper limit to the aging time, and longer aging times have been found to be beneficial, practicality and economics dictate that the maximum aging time would normally be limited to about 10 days or less.
• the hydrated silicon dioxide formed as a result of the aging process must be removed from the liquid. This can be done by any conventional solid liquid separation technique including centrifuging, filtering or settling. Of particular utility is the use of a flocculent, specifically a cationic flocculent, followed by settling of the flocculated silicon dioxide and decantation of the liquid.
• a flocculent specifically a cationic flocculent
• the quantity of flocculent required and the method of addition will depend, among other factors, on the concentration of hydrated silicon dioxide in the liquid and the specific flocculent used. Thus, laboratory tests, by techniques well known in the art, would be required to determine the flocculent addition parameters.
• the acid is added to convert carbonates (for example calcium carbonate) to carbon dioxide such that the carbon dioxide can be removed from the water in the forced draft and vacuum degasifiers.
• carbonates for example calcium carbonate
• the net effect of the acid addition in U.S. Patent No. 5,338,456 is to decrease the solubility of the carbon compounds in solution and not to increase the solubility of the various ions and salts present, as is the purpose of the acid addition in the pond water of the this embodiment of the present invention.
• acids that may be used include sulfuric acid, sulfurous acid, phosphoric acid, hydrochloric acid and nitric acid.
• compounds that may be used that will form an acid when water is present include sulfur trioxide, sulfur dioxide, hydrogen chloride and nitrogen dioxide.
• Acids that should not be used for pH adjustment include hydrofluoric acid and hydroflurosilicic acid.
• the acid or the compound that will form an acid in the presence of water should be added to the liquid in sufficient quantity to decrease the pH of the resulting solution to a value within the range of 2.0 to 4.0, or more preferably within the range of 2.5 to 3.5, or still more preferably within the range of 2.9 to 3.1.
• the liquid solution thus obtained will be essentially clear and stable with respect to post precipitation.
• pure water may now be removed from the liquid solution by any of several methods including reverse osmosis, evaporation, or other means, without the formation of solid precipitates.
• a second embodiment of the present invention provides a simplified process for partially purifying contaminated phosphoric acid plant pond water, when the molar ratio of the calcium plus magnesium to fluorine present in the pond water is greater than or equal to about 0.60, such that the partially purified or pre-treated pond water can be concentrated by the removal of pure water without the formation of precipitated solids or scale that would otherwise impede or render inoperable the concentrating means or apparatus.
• the pre-treated pond water could be processed through a conventional reverse osmosis system comprising one or more stages to obtain a purified water stream and a stream of concentrated pond water.
• pond water is defined as a dilute solution of phosphoric acid, also containing sulfuric acid, silicic acid, fluoride ions, calcium ions, sodium ions, ammonium ions, and other ionic and non-ionic species, that is normally present in and around phosphate fertilizer plants that employ the so-called wet process for the production of phosphoric acid.
• a first compound that is a strong base or that will form a strong base when water is present is added to the pond water.
• the cationic component of this first compound must be such that the phosphate salts formed thereof remain soluble in the pond water.
• strongly basic compounds that form soluble phosphate salts include sodium hydroxide and potassium hydroxide.
• An example of a compound that will form a strong base when water is present and whose phosphate salt is soluble is ammonia.
• Other compounds meeting the above two criteria may also be used and are still considered within the scope of the present invention.
• This first compound is added to and mixed with the pond water either in pure form or as a solution, in sufficient quantity to increase the pH of the resulting pond water solution to a value within the range of 6.0 to 8.0, or more preferably within the range of 6.5 to 7.5.
• pure form refers to the physical state of the compound (i.e., a solid for sodium hydroxide or potassium hydroxide, or a gas or pressurized liquid for anhydrous ammonia) and not the chemical purity of the compound. In terms of chemical purity, ordinary technical grade purity is acceptable for both the first compound and the second compound.
• the pH as used above and elsewhere, is defined as the negative power to which 10 must be raised to equal the molar hydrogen ion concentration in solution.
• solid precipitates will form in the solution.
• These solid precipitates are now removed from the solution either by settling the solids and decanting the liquid, centrifuging the solution, filtering the solution, or any other means that will result in a separation of a clear liquid from the solid precipitates.
• the solids can be removed as a slurry containing, for example, 50% by weight solids and 50% by weight liquid.
• the suspended solids concentration in the liquid be no greater than 0.5% by weight.
• the clear liquid is now allowed to age.
• the purpose of the aging is to allow silicic acid present in the liquid to decompose into hydrated silicon dioxide.
• the aging time should be at least 2 hours and preferably at least 16 hours. While there is no upper limit to the aging time, and longer aging times have been found to be beneficial, practicality and economics dictate that the maximum aging time would normally be limited to about 10 days or less. If the initial silicon concentration in the pond water is less than about 120 parts per million, a hydrated silicon dioxide precipitate may not form and the aging and hydrated silicon dioxide separation steps indicated above will not be required.
• the hydrated silicon dioxide formed as a result of the aging process must be removed from the liquid. This can be done by any conventional solid liquid separation technique including centrifuging, filtering or settling. Of particular utility is the use of a flocculent, specifically a cationic flocculent, followed by settling of the flocculated silicon dioxide and decantation of the liquid.
• a flocculent specifically a cationic flocculent
• the quantity of flocculent required and the method of addition will depend, among other factors, on the concentration of hydrated silicon dioxide in the liquid and the specific flocculent used. Thus, laboratory tests, by techniques well known in the art, would be required to determine the flocculent addition parameters.
• Examples of compounds that may be used that will form an acid when water is present include sulfur trioxide, sulfur dioxide, hydrogen chloride and nitrogen dioxide. Other acids, or compounds that will form acids in the presence of water, may be used and are still considered within the scope of the present invention. Acids that should not be used for pH adjustment include hydrofluoric acid and hydroflurosilicic acid. The acid or the compound that will form an acid in the presence of water should be added to the liquid in sufficient quantity to decrease the pH of the resulting solution to a value within the range of 2.0 to 4.0, or more preferably within the range of 2.5 to 3.5, or still more preferably within the range of 2.9 to 3.1.
• liquid solution thus obtained will be essentially clear and stable with respect to post precipitation.
• pure water may now be removed from the liquid solution by any of several methods including reverse osmosis, evaporation, or other means, without the formation of solid precipitates.
• a 1000.3 gram sample of contaminated phosphoric acid plant pond water containing 0.4092% P 2 O 5 , 0.0582% Ca, 0.0445% F, 0.0098% Si and 0.5307% SO 4 was obtained from a commercial wet process phosphoric acid plant pond system.
• 5.52 grams of 50% sodium hydroxide solution was added to and mixed for 7 minutes. After mixing the pH of the above solution was 7.28. The solution was then allowed to stand, whereupon the solids precipitated as a result of the chemical reactions between the sodium hydroxide and pond water settled to form a sludge at the bottom of the container.
• a 3780 gram sample of contaminated phosphoric acid plant pond water containing 1.85% P 2 O 5 , 0.121% Ca, 0.360% F, 0.074% Si and 0.425% SO 4 was obtained from a commercial wet process phosphoric acid plant pond system.
• 17.3 grams of calcium oxide was added and the solution was mixed for about 20 minutes.
• 50% sodium hydroxide solution was added to and mixed with the above solution in the amount of 42.16 grams, which was sufficient to increase the pH to 5.0.
• the solution was then allowed to stand, whereupon the solids precipitated as a result of the chemical reactions between the calcium oxide, sodium hydroxide and pond water settled to form a sludge at the bottom of the container.
• a 226 gallon sample (1,917 pounds) of pond water containing 1 61% P O , 0 119% Ca, 0 470% F, 0 084% Si, 0 440% SO 4 , and 0 230% Na was used for this test
• 17 64 pounds of calcium oxide was added and the solution was mixed for about 30 minutes
• 50% sodium hydroxide solution was added to and mixed with the above solution, in the amount of 21 34 pounds, which was sufficient to increase the pH to 5 6
• the solution was then allowed to stand, whereupon the solids, precipitated as a result of the chemical reactions between the calcium oxide, sodium hydroxide and pond water, settled to form a sludge at the bottom of the container
• about 206 gallons of clear liquid was decanted from the reaction tank into a second tank After correcting for the volume of clear liquid not removed from the reaction tank, the remaining sludge amounted to 3.54% by volume of the initial 226 gallons of pond water The clear liquid was then allowed to age for an additional 36
• the first flocculent designated 1018C
• the second flocculent designated 81 IE
• Both flocculants were produced by Arr-Maz Products, LP
• the solution was allowed to stand for about 1 hour and then about 170 gallons of clear liquid was decanted from the second tank into a third tank After correcting for the volume of clear liquid not removed from the second tank, the remaining silicon dioxide sludge amounted to 7.28% by volume based on the initial volume of 226 gallons of pond water.
• the pH of the resulting 170 gallons of clear liquid was then adjusted to a value of 3.0 via the addition of 2.44 pounds of 97.35% sulfuric acid.
• Laboratory analysis of a sample of the solution at this point indicated that it contained 1.17% P O 5 , 0.0102% Ca, 0.0114% F, 0.0070% Si, 0.482% Na and 0.530% SO 4 .
• the total quantity of sludge produced by the partial purification process of the this embodiment of the present invention was 10.82% by volume of the starting pond water or 24.45 gallons.
• the first stage reverse osmosis module contained a conventional sand filter, a 5-micron cartridge filter, a feed tank, a 5-HP positive displacement high-pressure pump and a single membrane element.
• the membrane element used in the first stage module was a seawater element with the U.S. Filter designation SW2530.
• the operating conditions for the first stage reverse osmosis module were an inlet pressure of 850 psi (pounds per square inch), a temperature of 102° F. and a permeate recovery of about 80.6% by volume.
• the first stage reverse osmosis module produced about 137 gallons of purified permeate and about 33 gallons of reject or concentrate.
• Laboratory analysis of the permeate indicated that it contained 0.0036% P O 5 , 0.0017% Ca, 0.0045% F, 0.0005% Si, 0.0572% Na and 0.0115% SO 4 .
• Laboratory analysis of the reject stream indicated that it contained 5.65% P 2 O 5 , 0.0429% Ca, 0.0379% F, 0.0369% Si, 2.144% Na and 2.830% SO 4 .
• the 137 gallons of permeate obtained from the first stage reverse osmosis module were mixed with about 0.55 pounds of 50% sodium hydroxide to raise the pH to a value of about 9. This solution was then fed to the second stage reverse osmosis module.
• the second stage reverse osmosis module contained essentially the same components as the first stage reverse osmosis module with the exception of the sand filter.
• the membrane element used in the second stage module was a brackish water element with the U.S. Filter designation BW2530.
• the operating conditions for the second stage reverse osmosis module were an inlet pressure of 195 psi (pounds per square inch), a temperature of 85° F. and a permeate recovery of about 94.5% by volume.
• the second stage reverse osmosis module produced about 130 gallons of permeate and about 6.8 gallons of reject or concentrate.
• Laboratory analysis of the permeate from the second stage module indicated that it contained 0.00005% P 2 O 5 , ⁇ 0.00001% Ca, 0.00008% F, 0.0001% Si, 0.0008% Na and ⁇ 0.0001% SO 4 .
• Laboratory analysis of the reject stream indicated that it contained 0.0680% P 2 O 5 , 0.00002% Ca, 0.0515% F, 0.0028% Si, 0.1370% Na and 0.0300% SO 4 .
• the pretreatment process of the this embodiment of the present invention allowed the recovery of about 72.1% by volume of the initial pond water as essentially pure water in the second stage reverse osmosis permeate stream and the recovery of about 68.5%o of the P 2 O 5 in the initial pond water as an economically valuable solids free solution in the first stage reverse osmosis reject stream.
• a 206 gallon sample (1,718 pounds) of pond water containing 1.57% P 2 O 5 , 0.111% Ca, 0.500% F, 0.094% Si, 0.460% SO 4 , and 0.230% Na was used for this test.
• 19.82 pounds of calcium oxide was added and the solution was mixed for about 30 minutes.
• anhydrous ammonia was injected below the liquid surface and mixed with the above solution in the amount of 3.19 pounds, which was sufficient to increase the pH to 5.6.
• the solution was then allowed to stand, whereupon the solids precipitated as a result of the chemical reactions between the calcium oxide, anhydrous ammonia and pond water settled to form a sludge at the bottom of the container.
• Both flocculants were produced by Arr-Maz Products, LP.
• the solution was then allowed to stand for about 1 hour and then about 120 gallons of clear liquid were decanted from the second tank into a third tank. After correcting for the volume of clear liquid not removed from the second tank, the remaining silicon dioxide sludge amounted to 13.3% by volume based on the initial volume of 206 gallons of pond water.
• the pH of the resulting 120 gallons of clear liquid was then adjusted to a value of 3.0 via the addition of 1.62 pounds of 97.35% sulfuric acid.
• the system components and membrane elements were the same as were used in Example 2, above.
• the operating conditions for the first stage reverse osmosis module were an inlet pressure of 390- 675 psi (varied during the test), a temperature of about 103°F. and a permeate recovery of 71%) to 80.5% (varied as a function of inlet pressure) by volume.
• the first stage reverse osmosis module produced a total volume, at all test conditions run, of about 96.6 gallons of purified permeate and about 23.4 gallons of reject or concentrate.
• the 96.6 gallons of permeate obtained from the first stage reverse osmosis module were mixed with about 0.39 pounds of 50%> sodium hydroxide to raise the pH to a value of about 9. This solution was then fed to the second stage reverse osmosis module.
• the operating conditions for the second stage reverse osmosis module were an inlet pressure of 150 psi (pounds per square inch), a temperature of 90° F. and a permeate recovery of about 85.5% by volume.
• the second stage reverse osmosis module produced about 82.7 gallons of permeate and about 13.9 gallons of reject or concentrate.
• the pretreatment process of the this embodiment of the present invention allowed the recovery of about 64.4% by volume of the initial pond water as essentially pure water in the second stage reverse osmosis permeate stream and the recovery of about 70.8%) of the P 2 O 5 in the initial pond water as an economically valuable solids free solution in the first stage reverse osmosis reject stream.
• a 3000 gram sample (2950 milliliters) of pond water containing 1.84% P 2 O 5 , 0.1072%) Ca, 0.310% F and 0.460% SO 4 was used for this test.
• 48.2 grams of Ca(OH) 2 was added to obtain a pH of 5.31.
• the solids produced as a result of the reactions between the pond water and Ca(OH) 2 were then allowed to settle for 16 hours.
• Additional Ca(OH) 2 in the amount of 30.0 grams, was then added to the clear liquid to obtain a pH of 11.8.

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• 2002
  • 2002-10-22 EP EP02782203A patent/EP1438264A1/en not_active Withdrawn
  • 2002-10-22 IL IL16138502A patent/IL161385A0/xx unknown
  • 2002-10-22 WO PCT/US2002/033775 patent/WO2003035557A1/en not_active Ceased
  • 2002-10-22 BR BR0213525-6A patent/BR0213525A/pt not_active Application Discontinuation
  • 2002-10-22 CA CA002463361A patent/CA2463361A1/en not_active Abandoned
  • 2002-10-22 CN CN02825904.1A patent/CN1608034A/zh active Pending
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