JP2016155128A - PARTICULATE CaCO3 SLURRY INJECTION SYSTEM FOR RECALCIFICATION OF DESALTED WATER AND FRESH WATER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recalcifying water, which is a method capable of adjusting the amount of a mineral to a required value.SOLUTION: A method for recalcifying water includes stages for: (a) providing supply water having carbon dioxide with a concentration of at least 20 mg/l, preferably in the range of 25-100 mg/l, more preferably in the range of 30-60 mg/l; (b) providing aqueous slurry containing particulate calcium carbonate; and (c) combining the supply water in the stage (a) with the aqueous slurry in the stage (b) in order to obtain recalcified water.SELECTED DRAWING: None

Description

The present invention relates to the field of water treatment , and more particularly to a method for remineralization of water and the use of calcium carbonate in such a method.

  Drinking water has been scarce. Even in water-rich countries, not all water sources and reservoirs are suitable for drinking water production, and many water sources are threatened today by rapid deterioration of water quality. The feed water used for drinking purposes was initially primarily surface water and groundwater. However, for environmental and economic reasons, the treatment of seawater, brine, brackish water, wastewater and contaminated effluent is becoming increasingly important.

  Several methods are known for beverage use to recover water from seawater or brackish water, which are very important in dry areas, coastal areas and sea islands, Distillation, electrolysis, and osmosis or reverse osmosis methods are included. The water obtained by such a method is very low in hardness and has a low pH value due to the lack of pH buffer salts and therefore tends to be highly reactive, and if not treated, in a normal pipeline This can cause major corrosion problems during transportation. Furthermore, untreated demineralized water cannot be used directly as a source of drinking water. It is necessary to remineralize the water in order to prevent the dissolution of undesirable substances in the pipeline system, to avoid corrosion of waterworks such as pipes and valves, and to make the water delicious.

  The usual methods used primarily for water remineralization are lime dissolution with carbon dioxide and limestone bed filtration. Other less common remineralization methods include, for example, the addition of hydrated lime and sodium carbonate, the addition of calcium sulfate and sodium bicarbonate, or the addition of calcium chloride and sodium bicarbonate.

The lime method involves the treatment of a lime solution with CO ₂ acidic water, in which case the following reactions are involved.

Ca (OH) ₂ + 2CO ₂ → Ca ²⁺ + 2HCO ₃ ⁻
As can be obtained from the above reaction scheme, for remineralization, two equivalents of CO ₂ are required to convert one equivalent of Ca (OH) ₂ to Ca ²⁺ and bicarbonate. This method relies on the addition of 2 equivalents of CO ₂ to convert basic anionic hydroxyl groups to buffered bicarbonate species. For water remineralization, a calcium hydroxide solution, commonly referred to as lime water, saturated from 0.1 to 0.2% by weight, based on the total weight, is prepared from lime milk (usually at most 5% by weight). The Therefore, a saturator from which lime water is produced must be used, and a large amount of lime water is required to achieve the target level of remineralization. Another disadvantage of this method is that hydrated lime is corrosive and requires proper handling and special equipment. Furthermore, if hydrated lime is added to soft water under inadequate control, there is no buffering property of lime, which can cause an unwanted pH shift.

Limestone bed filtration involves passing soft water through a granular limestone bed that dissolves calcium carbonate in a water stream. By contacting the limestone with CO ₂ acid water, the water is calcified according to the following formula.
CaCO ₃ + CO ₂ + H ₂ O → Ca ²⁺ + 2HCO ₃ ⁻

Unlike the lime method, remineralization requires only one equivalent of CO ₂ stoichiometrically to convert one equivalent of CaCO ₃ to Ca ²⁺ and bicarbonate ions . Furthermore, limestone is not corrosive and does not cause a large pH shift due to the buffering properties of CaCO ₃ .

One further advantage of using calcium carbonate instead of lime is its very low carbon dioxide footprint. 75 kg of CO ₂ is released to produce 1 ton of calcium carbonate, while 750 kg of CO ₂ is released to produce 1 ton of lime. Thus, the use of calcium carbonate instead of lime has several environmental advantages.

  However, the dissolution rate of granular calcium carbonate is slow and a large filter is required for limestone filtration. This increases the footprint of these filters and requires a large plant surface for such a limestone bed filtration system.

  Methods for the remineralization of water using lime milk or a slurry of lime are described in US 7,374,694 and EP 0520826. US 5,914,046 describes a method for reducing the acidity of effluent emissions using a pulsed limestone bed.

  The Applicant has described an unpublished European patent application 101722771. which describes a method for remineralizing demineralized water and fresh water by injecting fine calcium carbonate slurry and gaseous carbon dioxide into the feed water. I know about No. 7.

  However, all of the prior art documents cited above describe methods for remineralization of feed water that do not contain carbon dioxide or contain low concentrations of carbon dioxide prior to the remineralization process. Yes.

However, there are also feed waters with a high or sufficient concentration of carbon dioxide based on the desired level or remineralization prior to the remineralization process. A high or sufficient concentration of carbon dioxide means an amount of CO ₂ in an amount of at least 20 mg per liter of feed water.

  One type of feed water with such a high concentration of carbon dioxide is groundwater sourced from water that has leached through calcareous rocks or due to anaerobic conditions.

  Another type of feed water having a carbon dioxide concentration of at least 20 mg / l can be found, for example, during wastewater treatment of a sewage plant. The reason is that one treatment stage of wastewater consists of desalination of wastewater by using reverse osmosis. However, to prevent or reduce scale formation on the membrane of the reverse osmosis device, an acid, particularly sulfuric acid, is added to the reverse osmosis feed water to lower the pH. Addition of acid in the reverse osmosis feed converts carbonate species in the feed water to free carbon dioxide. The carbon dioxide is not removed by the membrane of the reverse osmosis device and is therefore present in the feed water leaving the osmosis device. However, this excess carbon dioxide present in the feed water must be removed before the lime addition. Currently, the removal of excess carbon dioxide in the feed water is performed by using a decarboxylation tower that is costly, time consuming and energy intensive.

US Pat. No. 7,374,694 European Patent No. 0520826 US Patent 5914046 European Patent Application No. 10172771.7

Thus, in view of the shortcomings of known methods for water remineralization, the object of the present invention is an alternative or alternative for water remineralization with an initial concentration of carbon dioxide of at least 20 mg / l. An improved method is to provide a method wherein the remineralized water has a certain level of remineralization, for example a calcium concentration of 30 to 40 mg / l as CaCO ₃ .

  Another object of the present invention is that it does not require corrosive compounds, thus avoiding the risk of crust formation, eliminating the need for corrosion resistant equipment, and providing a safe environment for people working in the plant. It is to provide a method for remineralization. It would also be desirable to provide a way to reduce operating costs by eliminating environmentally friendly, time consuming, energy and costly process steps.

  Another object of the present invention is to provide a method for remineralization of water in which the amount of mineral can be adjusted to the required value.

  Another object of the present invention is to provide a method for remineralization using limestone, which is possible, for example, or smaller than the lime method, which allows the use of smaller remineralization units. It is to provide a remineralization process that allows the use of volume remineralization compounds. It would also be desirable to provide a method that can operate on a smaller plant surface than limestone bed filtration.

  The foregoing and other objects provide: (a) providing a feed water having a concentration of carbon dioxide of at least 20 mg / l, preferably in the range of 25 to 100 mg / l, more preferably in the range of 30 to 60 mg / l. (B) providing an aqueous slurry comprising fine calcium carbonate, and (c) combining the feed water of step a) with the aqueous slurry of step b) to obtain remineralized water. This is solved by providing a method for the optimization.

  According to another aspect of the present invention, the use of fine calcium carbonate for water remineralization is provided.

  Advantageous embodiments of the invention are defined in the corresponding dependent claims.

  According to one embodiment, the concentration of calcium carbonate in the slurry is 0.05 to 40% by weight, 1 to 25% by weight, 2 to 20% by weight, preferably 3 to 15%, based on the total weight of the slurry. Wt%, most preferably 5 to 10 wt%, or the concentration of calcium carbonate in the slurry is 10 to 40 wt%, 15 to 30 wt%, 20 to 25 wt% based on the total weight of the slurry It is. According to another embodiment, the calcium carbonate has a particle size of 0.1 to 100 μm, 0.5 to 50 μm, 1 to 15 μm, preferably 2 to 10 μm, most preferably 3 to 5 μm, or calcium carbonate Has a particle size of 1 to 50 μm, 2 to 20 μm, preferably 5 to 15 μm, most preferably 8 to 12 μm. According to yet another embodiment, the calcium carbonate is 0.02 to 2.5 wt%, 0.05 to 1.5 wt%, or 0.1 to 0, based on the total weight of the fine calcium carbonate. .6% by weight of HCl insolubles. According to yet another embodiment, the calcium carbonate is ground calcium carbonate, modified calcium carbonate, or precipitated calcium carbonate, or a mixture thereof.

  According to one embodiment, the slurry is a mineral comprising magnesium, potassium or sodium, preferably magnesium carbonate, calcium carbonate, for example magnesium oxide such as dolomite limestone, calcareous dolomite, dolomite or semi-calcined dolomite, calcined dolomite, It further contains magnesium sulfate, potassium bicarbonate, or sodium bicarbonate. According to another embodiment, the slurry is freshly prepared by mixing water and calcium carbonate. According to yet another embodiment, the time between slurry preparation and slurry injection is less than 48 hours, less than 24 hours, less than 12 hours, less than 5 hours, less than 2 hours or less than 1 hour. According to yet another embodiment, the injected slurry meets the microbiological quality requirements set by national drinking water quality guidelines.

  According to one embodiment, the resulting remineralized water has a calcium concentration as calcium carbonate of 15 to 200 mg / l, preferably 50 to 150 mg / l, most preferably 100 to 125 mg / l, or 15 to 100 mg / l. 1, preferably 20 to 80 mg / l, and most preferably 40 to 60 mg / l calcium concentration.

  According to another embodiment, the resulting remineralized water has a magnesium concentration of 5 to 25 mg / l, preferably 5 to 15 mg / l, most preferably 8 to 12 mg / l. According to yet another embodiment, the remineralized water has a turbidity value of less than 5.0 NTU, less than 1.0 NTU, less than 0.5 NTU, or less than 0.3 NTU.

According to another preferred embodiment, the remineralized water has a Langeria saturation index of -2 to 1, preferably -1.9 to 0.9, most preferably -0.9 to 0. According to yet another embodiment, the remineralized water has a soil index SDI _{15 of} less than 5, preferably less than 4, and most preferably less than 3. According to yet another embodiment, the remineralized water has a membrane fouling index MFI _0.45 of less than 4, preferably less than 2.5, and most preferably less than 2.

  According to one embodiment, the feed water is demineralized seawater, brackish water or brine, treated wastewater or natural water, such as groundwater, surface water or rainwater, preferably demineralized seawater, brackish water or brine, treated wastewater or groundwater. .

  According to one embodiment, the remineralized water is blended with the feed water. According to another embodiment, the method further comprises a particle removal step.

According to one embodiment, the method comprises (d) measuring parameter values of remineralized water, wherein the parameters are alkalinity, total hardness, conductivity, calcium concentration, pH, remineralized water, A step selected from the group comprising CO ₂ concentration, total soluble solids, and turbidity, (e) comparing the measured parameter value with a predetermined parameter value, and (f) the measured parameter value And providing an amount of the infused slurry based on the difference between the predetermined parameter values. According to another embodiment, the predetermined parameter value is a pH value, which is 5.5 to 9, preferably 7 to 8.5.

  According to one embodiment, the fine calcium carbonate is used for remineralization of water, where the remineralized water is potable water, recreational water such as swimming pool water, industrial water for process applications. Irrigation water, or aquifer or well recharge water.

As used herein, the term “alkalinity (TAC)” is a measure of the ability of a solution to neutralize an acid to the equivalent point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric total amount of base in solution and is defined as mg / l as CaCO ₃ . The alkalinity can be measured by titration.

For the purposes of the present invention, the term “calcium concentration” refers to the total amount of calcium in solution and is defined as mg / l as Ca ²⁺ or CaCO ₃ . The concentration can be measured by titration.

  “Conductivity” in the context of the present invention is used as an indicator of how much water being measured is salt-free, ion-free, or impurity-free, the more pure the water, the lower the conductivity. The conductivity can be measured using a conductivity meter and is determined in μS / cm.

  As used herein, “ground calcium carbonate (GCC)” is calcium carbonate obtained from natural resources including marble, chalk, limestone or dolomite. Calcite is a carbonate mineral and is the most stable polymorph of calcium carbonate. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470 ° C and vaterite is even more unstable. The ground calcium carbonate is processed by grinding, screening and / or wet and / or dry, for example, by cyclone treatment. It is known to those skilled in the art that ground calcium carbonate can contain essentially a certain concentration of magnesium, as is the case with dolomitic calcite.

As used herein, the term “Langeria saturation index (LSI)” describes the tendency of an aqueous liquid to be scale-forming or corrosive, with positive LSIs indicating a tendency to scale and negative LSIs corroding. The characteristics of Therefore, a balanced Langeria saturation index, ie LSI = 0, means that the aqueous liquid is in chemical equilibrium. The LSI is calculated as follows.
LSI = pH-pH _s ,
Here, pH is the actual pH value of the aqueous liquid, and pH _s is the pH value of the aqueous liquid with CaCO ₃ saturation. The pH _s can be estimated as follows.
pH _s = (9.3 + A + B)-(C + D),
Here, A is a numerical index of total soluble solids (TDS) present in the aqueous liquid, B is a numerical index (K) of the temperature of the aqueous liquid, and C is the calcium concentration of the aqueous liquid. Is a numerical index (CaCO ₃ mg / l), and D is a numerical index (CaCO ₃ mg / l) of the alkalinity of the aqueous liquid. The parameters A to D are determined using the following equation:
A = (log ₁₀ (TDS) −1) / 10,
B = -13.12 × log ₁₀ (T + 273) +34.55,
C = log ₁₀ [Ca ²⁺ ] −0.4,
D = log ₁₀ (TAC),
Where TDS is the total soluble solids (mg / l), T is the temperature (° C.), [Ca ²⁺ ] is the calcium concentration of the aqueous liquid (CaCO ₃ mg / l), TAC is the alkalinity (CaCO ₃ mg / l) of an aqueous liquid.

As used herein, the term “soil index (SDI)” refers to the amount of particulate matter in the water and correlates with the soil tendency of reverse osmosis or nanofiltration systems. The SDI can be calculated from, for example, the speed of blockage of the 0.45 μm membrane filter when water passes at a constant applied water pressure of 208.6 kPa. The SDI ₁₅ value is calculated from the rate of occlusion of the 0.45 μm membrane filter when water passes for 15 minutes at a constant applied water pressure of 208.6 kPa. Typically, a spiral reverse osmosis system will require less than 5 SDIs and a hollow fiber reverse osmosis system will require less than 3 SDIs.

  As used in the present invention, the term “Modified Fouling Index (MFI)” refers to the concentration of suspended matter, rather than SDI for predicting the tendency of water to reverse osmosis or nanofiltration membranes. Is also an accurate indicator. The method that can be used to determine the MFI may be the same as for SDI, except that the volume is recorded every 30 seconds over a 15 minute filtration period. The MFI can be obtained from the slope of the linear part of the curve using the figure if t / V is plotted against V (t is the time (in seconds) to collect the volume V (liter). .) An MFI value of <1 corresponds to an SDI value of <about 3, and can be considered low enough to control colloid and particle fouling.

When an ultrafiltration (UF) membrane is used for MFI measurements, the indicator is called MFI-UF, as opposed to MFI _0.45 where 0.45 μm membrane filler is used.

  For the purposes of the present invention, the term “fine particles” refers to a particle size in the micrometer range, for example a particle size of 0.1 to 100 μm. The microparticles can be obtained by techniques based on friction, for example milling or grinding under both wet or dry conditions. However, by any other suitable method, such as precipitation, rapid expansion of supercritical solutions, spray drying, classification or subdivision of naturally occurring sand or mud, water filtration, sol-gel method, spray reaction synthesis, flame synthesis Alternatively, fine particles can be produced by liquid bubble synthesis.

Throughout this document, the “particle size” of a calcium carbonate product is described by its particle size distribution. The value d _x represents the diameter at which particles having a diameter smaller than d _x are x wt%. This means that a d ₂₀ value is a particle size where 20% by weight of all particles are smaller than that value, and a d ₇₅ value is a particle size where 75% by weight of all particles are smaller than that value. . Thus, d ₅₀ value, the weight median particle size, i.e., 50 wt% of all particulate material, larger or smaller than this particle size. For the purposes of the present invention, the particle size is defined as the weight median particle size d ₅₀ , unless otherwise specified. To determine the weight median particle size d ₅₀ value for particles having a d ₅₀ greater than 0.5 μm, the US company Micromeritics's Sedigraph 5100 device can be used.

As used herein, “precipitated calcium carbonate (PCC)” means by precipitation after reaction of carbon dioxide and lime in an aqueous environment, or by precipitation of calcium and a carbonate source in water, or calcium and carbonate ions, such as CaCl _2. It is a synthetic material generally obtained by precipitation from a solution of Na ₂ CO ₃ . Precipitated calcium carbonate exists in three main crystal forms: calcite, aragonite and vaterite, and there are many different polymorphs (crystal habits) for each of these crystal forms. Calcite is a typical crystal such as Skelno-Hedral (S-PCC), rhombohedral crystal (R-PCC), hexagonal prism, table crystal, colloidal (C-PCC), cubic crystal, prism (P-PCC), etc. It has a trigonal structure with a habit. Aragonite is a typical crystal habit of twin hexagonal prism crystals, as well as slanted prisms, curved blades, steep cones, chisel crystals, branched trees, and obliques with various classifications of coral or worm-like shapes Crystal structure.

Means in the present invention "modified calcium carbonate" is a natural calcium carbonate whose surface is reacted, this is a natural calcium carbonate, and other one acid pK _a is 2.5 or less at 25 ° C. Gaseous CO ₂ formed in situ and / or gaseous CO ₂ derived from an external supply, optionally with at least one aluminum silicate and / or at least one synthetic silica and / or at least one Calcium silicate and / or at least one monovalent salt silicate, such as sodium silicate and / or potassium silicate and / or lithium silicate, and / or at least one aluminum hydroxide and The presence of at least one sodium silicate and / or potassium silicate; Obtainable by a method of reacting under. Additional details regarding the preparation of surface-reacted natural calcium carbonate are disclosed in WO 00/39222 and US 2004/0020410 A1, the contents of these references being included in this patent application with this specification. Yes.

  As used herein, the term “remineralization” refers to the recovery of minerals in water that is free of minerals in an amount sufficient to obtain no minerals or delicious water. Remineralization can be achieved by adding at least calcium carbonate to the water to be treated. In some cases, for example, for health-related benefits or to ensure proper uptake of some major minerals and trace elements, another substance is mixed into the calcium carbonate in the remineralization process and then Can be added to water. According to national guidelines on human health and drinking water quality, remineralized products may contain additional minerals containing magnesium, potassium or sodium, such as magnesium carbonate, magnesium sulfate, potassium bicarbonate, sodium bicarbonate or major Other minerals including trace elements can be included.

  For purposes of the present invention, a “slurry” includes insoluble solids and water, optionally with other additives, and usually contains a large amount of solids and is therefore more viscous and generally higher than the liquid formed therefrom. Density.

  As used herein, the term “total soluble solids (TDS)” is a combination of all inorganic and organic substances contained in a liquid in the form of molecular, ionic or particulate (colloidal sol) suspensions. It is a measure of quantity. In general, the operational definition is that the solid must be small enough to pass through a 2 micrometer sized sieve. Total soluble solids can be estimated using a conductivity meter and is defined in mg / l.

  As used herein, “turbidity” describes the turbidity or turbidity of a fluid caused by individual particles (suspended material) that are generally invisible to the naked eye. Turbidity measurement is an important test of water quality and can be performed using a nephelometer. The unit of turbidity from a calibrated nephelometer used in the present invention is defined as a turbidimetric turbidity unit (NTU).

  The method of the invention for water remineralization has (a) carbon dioxide at a concentration of at least 20 mg / l, preferably in the range of 25 to 100 mg / l, more preferably in the range of 30 to 60 mg / l. Providing the feed water; (b) providing an aqueous slurry comprising fine calcium carbonate; and (c) providing the feed water of step (a) and the aqueous slurry of step (b) to obtain remineralized water. Including the step of combining.

  The feed water to be used in the process of the present invention can be obtained from various water sources. The feed water preferably treated by the method of the present invention is desalinated seawater, brackish water or brine, treated wastewater or groundwater, natural water such as surface water or rainwater, more preferably desalted seawater, brackish water or brine, treated wastewater or groundwater. It is.

According to one embodiment of the present invention, the feed water can be pretreated. Pretreatment may be necessary, for example, when the feed water is obtained from surface water, ground water or rain water. For example, in order to achieve drinking water quality guidelines, water needs to be treated through the use of chemical or physical techniques to remove contaminants such as organic matter and undesirable minerals. For example, ozonation can be used as the first pretreatment stage, followed by coagulation, agglomeration, or decantation as the second pretreatment stage. For example, iron (III) salts such as FeClSO ₄ and FeCl ₃ or aluminum salts such as AlCl ₃ , Al ₂ (SO ₄ ) ₃ and polyaluminum can be used as the flocculant. Agglomerated material can be removed from the feed water by, for example, a sand filter or a multilayer filter. Other water purification methods that can be used to pretreat the feed water are described, for example, in EP 1975310, EP 1982759, EP 1974807, or EP 1974806.

  According to another exemplary embodiment of the present invention, seawater or brackish water is first pumped from the sea by uptake of the ocean or near surface water, such as a well, and then screened, settled or removed sand, etc. Physical pre-processing is performed. Depending on the water quality required, further processing steps such as coagulation and agglomeration may be necessary to reduce potential fouling on the membrane. The pretreated seawater or brackish water can then be distilled using, for example, multistage flash, multi-effect distillation, or using membrane filtration such as ultrafiltration or reverse osmosis, to leave residual particulates and dissolved material Can be removed.

  The remineralization of the feed water is an aqueous solution comprising fine calcium carbonate with feed water having a concentration of carbon dioxide of at least 20 mg / l, preferably in the range of 25 to 100 mg / l, more preferably in the range of 30 to 60 mg / l. Caused by combining with slurry. The combination of the feed water and the aqueous slurry can be performed by a general method known to those skilled in the art, for example, by injecting an aqueous slurry containing fine calcium carbonate into the feed water.

  The aqueous slurry combined with the feed water contains fine calcium carbonate. According to one embodiment, the concentration of calcium carbonate in the slurry is 0.05 to 40% by weight, 1 to 25% by weight, 2 to 20% by weight, 3 to 15% by weight, based on the total weight of the slurry. Or 5 to 10% by weight. According to another embodiment, the concentration of calcium carbonate in the slurry is 10 to 40 wt%, 15 to 30 wt%, or 20 to 25 wt%, based on the total weight of the slurry.

  Fine calcium carbonate has a particle size in the micrometer range. According to one embodiment, the fine calcium has a particle size of 0.1 to 100 μm, 0.5 to 50 μm, 1 to 15 μm, 2 to 10 μm or 3 to 5 μm, or the calcium carbonate is 1 to 50 μm, It has a particle size of 2 to 20 μm, preferably 5 to 15 μm, most preferably 8 to 12 μm.

  Examples of suitable calcium carbonate are ground calcium carbonate, modified calcium carbonate or precipitated calcium carbonate, or mixtures thereof. Natural ground calcium carbonate (GCC) may be characterized by, for example, one or more of marble, limestone, chalk, and / or dolomite. Precipitated calcium carbonate (PCC) may be characterized by one or more of aragonite-type, vaterite-type and / or calcite-type mineralogical crystal forms. Aragonite is generally acicular, while vaterite belongs to the hexagonal crystal system. Calcite can form skelnohedral, prismatic, spherical, and rhombohedral shapes. Modified calcium carbonate, with modification of the surface and / or internal structure, can characterize natural ground or precipitated calcium carbonate, for example, calcium carbonate is a hydrophobic surface such as, for example, aliphatic carboxylic acids or siloxanes It can be treated or coated with a treating agent. Calcium carbonate can be treated or coated to become a cation or anion using, for example, polyacrylate or polydadmac.

  According to one embodiment of the invention, the fine calcium carbonate is ground calcium carbonate (GCC). According to a preferred embodiment, the fine calcium carbonate is ground calcium carbonate having a particle size of 3 to 5 μm, or 8 to 12 μm.

  According to another embodiment of the present invention, the fine calcium carbonate is 0.02 to 2.5 wt%, 0.05 to 1.5 wt%, or 0.005%, based on the total weight of the fine calcium carbonate. Contains 1 to 0.6 wt% HCl insolubles. Preferably, the HCl insoluble content of the fine calcium carbonate does not exceed 0.6% by weight, based on the total weight of the fine calcium carbonate. The HCl insoluble matter may be a mineral such as quartz, silicate or mica.

  In addition to the fine calcium carbonate, the slurry can further comprise fine minerals. According to one embodiment, the slurry comprises finely divided magnesium carbonate, calcium carbonate, such as dolomite limestone, calcareous dolomite, dolomite or semi-calcined dolomite; magnesium oxide such as calcined dolomite, magnesium sulfate, potassium bicarbonate, sodium bicarbonate Or other minerals containing major trace elements can be included.

  According to one embodiment of the present invention, the slurry is freshly prepared by mixing water and fine calcium carbonate. In-situ preparation of the slurry is preferred because the premixed slurry may require the addition of another agent, such as a stabilizer or biocide, which may be an unwanted compound in the remineralized water. There is a case. According to one preferred embodiment of the present invention, the time between slurry preparation and slurry injection is short enough to prevent bacterial growth in the slurry. According to one exemplary embodiment, the time between slurry preparation and slurry injection is less than 48 hours, less than 24 hours, less than 12 hours, less than 5 hours, less than 2 hours or less than 1 hour. According to another embodiment of the present invention, the infused slurry meets the microbiological quality requirements set by national drinking water quality guidelines.

  The slurry can be prepared, for example, using a mixer such as a mechanical stirrer for dilute slurries, or using a special powder liquid mixing device for higher concentration slurries. . Depending on the concentration of the slurry to be prepared, the mixing time may be 0.5 to 30 minutes, 1 to 20 minutes, 2 to 10 minutes, or 3 to 5 minutes. According to one embodiment of the present invention, the slurry is prepared using a mixer, where the mixer can simultaneously mix and dispense the slurry.

  The water used to prepare the slurry can be, for example, distilled water, feed water or industrial water.

  According to one embodiment, a slurry containing fine calcium carbonate is injected directly into the feed water stream. For example, the slurry can be injected into the feed water stream at a controlled rate by a pump in communication with the slurry storage vessel. Preferably, the slurry can be injected into the feed water stream at a rate of 1 to 10 liters per cubic meter of feed water, depending on the slurry concentration. According to another embodiment, the slurry comprising fine calcium carbonate is mixed with the feed water in the reaction chamber using, for example, a mixer such as a mechanical stirrer. According to yet another embodiment, the slurry is injected into a tank that receives the entire flow of feed water.

  According to one embodiment of the present invention, only a portion of the feed water is remineralized by pouring the slurry, and then the remineralized water is blended with the untreated feed water. In some cases, only a portion of the feed water is remineralized to a high calcium carbonate concentration compared to the final target value, and then the remineralized water is blended with the untreated feed water.

  According to another embodiment, the treated water or a portion of the treated water is filtered, for example by ultrafiltration, to further reduce the turbidity level of the remineralized water.

  According to one embodiment of the invention, the slurry is injected in an amount such that complete dissolution of the calcium carbonate is achieved.

The amount of calcium carbonate injected into the feed water is selected in such a way as to produce the desired quality of water. For example, the quality of remineralized water can be evaluated by the Langeria saturation index (LSI). According to one embodiment, the remineralized water has a Langeria saturation index of -2 to 1, preferably -1.9 to 0.9, most preferably -0.9 to 0. According to another embodiment, the remineralized water has a soil index SDI _{15 of} less than 5, preferably less than 4, most preferably less than 3. According to yet another embodiment, the remineralized water has a membrane fouling index MFI _0.45 of less than 4, preferably less than 2.5, and most preferably less than 2. The evaluation can be performed, for example, by continuously measuring the pH of the treated feed water. Depending on the remineralization system, the pH of the treatment pH is, for example, in the treatment water stream, in the reaction chamber (where the slurry and feed water are mixed) or for remineralization water. It can be measured in a storage tank. According to one embodiment of the invention, the pH is measured 30 minutes, 20 minutes, 10 minutes, 5 minutes or 2 minutes after the remineralization stage. The measurement of the pH value can be carried out at room temperature, ie about 20 ° C.

According to one exemplary embodiment of the present invention, the amount of infused slurry is controlled by detecting the pH value of the treated feed water. On the other hand, the amount of infused slurry is controlled by detecting parameters such as alkalinity, total hardness, conductivity, CO ₂ concentration, pH, calcium concentration, total soluble solids and turbidity. According to one embodiment, the method of the present invention measures (d) a parameter value of remineralized water, wherein the parameters are alkalinity, total hardness, conductivity, calcium concentration, a step selected from the group comprising pH, CO ₂ concentration, total soluble solids, or turbidity, (e) comparing the measured parameter value with a predetermined parameter value, and (f) the measured parameter The method further includes providing an injection slurry in an amount based on the difference between the value and the predetermined parameter value.

  According to one embodiment, the predetermined parameter value is a pH value, where the pH value is 5.5 to 9, preferably 7 to 8.5.

FIG. 2 shows a scheme of an apparatus that can be used to carry out the method of the present invention. Feed water flows from the tank (1) to the pipeline (2). The inlet (4) is located downstream of the pipeline (2), through which slurry containing fine calcium carbonate is injected into the feed water stream from the slurry storage tank (6). The slurry is prepared in situ by mixing the water obtained from the tank (1) via the pipe (10) and the fine calcium carbonate obtained from the storage container (12) using a suitable mixer (8). Is done. The pH of the remineralized water can be measured downstream of the slurry inlet (10) on the sample point (14). According to one embodiment, the feedwater flow rates are 20000 and 500000 m ³ per day.

  The method of the present invention can be used to produce drinking water, recreational water such as swimming pool water, industrial water for process applications, irrigation water, or aquifer or well recharge water.

According to one embodiment, the carbon dioxide and calcium carbonate concentrations in the remineralized water meet the drinking water quality requirements set by national guidelines. According to one embodiment, remineralization Kamizu obtained by the method of the present invention, 15 to 200 mg / l as CaCO _3, preferably 150 mg / l from 50 as CaCO _3, and most preferably from 100 as CaCO ₃ 125 mg / or a calcium concentration of 15 to 100 mg / l, preferably 20 to 80 mg / l, most preferably 40 to 60 mg / l. If the slurry further comprises a magnesium salt such as magnesium carbonate or magnesium sulfate, the remineralized water obtained by the method of the present invention is from 5 to 25 mg / l, preferably from 5 to 15 mg / l, most preferably from 8 It can have a magnesium concentration of 12 mg / l.

  According to one embodiment of the invention, the remineralized water has a turbidity of less than 5.0 NTU, less than 1.0 NTU, less than 0.5 NTU, or less than 0.3 NTU.

  According to one exemplary embodiment of the present invention, the remineralized water has an LSI of −0.9 to +0.0, a calcium concentration of 15 to 200 mg / l, a magnesium concentration of 5 to 25 mg / l, 20 as CaCO 3. And an alkalinity between 100 mg / l, a pH between 7 and 8.5, and a turbidity of less than 1.0 NTU.

  According to one embodiment of the invention, the particle removal step is performed after remineralization, for example, to reduce the turbidity level of remineralized water. For example, a particle removal step can be performed prior to slurry injection to reduce the turbidity level of the feed water or a portion of the feed water. According to one embodiment, a sedimentation step is performed. For example, feed water and / or remineralized water can be sent to a finer or storage tank to further reduce the turbidity level of the water. According to another embodiment, the particles can be removed by decantation. Alternatively, at least a portion of the feed water and / or remineralized water can be filtered, for example, by ultrafiltration to further reduce the turbidity level of the water.

  The invention will be described in detail by the following examples.

Measuring method:
The concentration of carbon dioxide contained in the feed water sample to be CO ₂ measurements used was determined by the use of titration. The principle of this method is in the fact that CO ₂ reacts with sodium carbonate or sodium hydroxide to form sodium bicarbonate (NaHCO ₃ ). Completion of the reaction is indicated by potentiometry or by the pink color characteristic of phenolphthalein indicators at an equivalent pH of 8.3.

  The feed water titration was performed at 25 ° C. using a Mettler Toledo M 416.

  A three-point calibration of the instrument (by the segment method) was initially performed using a commercial buffer solution (from Mettler Toledo) having pH values of 4.01, 7.00 and 9.21.

  The pH of a 100 ml sample of feed water was then measured as a function of the amount of titrant used to reach the pH 8 endpoint. In this measurement, the titrant was a 0.01 mol / l sodium hydroxide solution.

From the amount of titrant needed to reach the end point of pH 8.3, and using the following equation (I), the amount of CO ₂ can be easily calculated.

ここで：
Ａ＝ｍｌ滴定剤、Ｎ＝ＮａＯＨの規定度、およびｂ＝ｍｌ試料。

here:
A = ml titrant, N = normality of NaOH, and b = ml sample.

Formula (I), "Standard Methods for the Examination of Water & Wastewater, 21 st Edition, 2005, prepared and published jointly by the American Public Health Association, American Water Works Association, Water Environment Federation, publication office American Public Health Association 800 I Street, NW, Washington, DC 20001-3710, Centennial Edition ", pages 4-28 to 4-34, chapter 4500C It described ₂ carbon dioxide. Then, the amount of CO ₂ as shown in the present invention can be derived that refers to the free amount of CO ₂ in water.

BET specific surface area BET specific surface area (also referred to as SSA) was determined according to ISO 9277 using Tristar II 3020 sold by the company MICROMERITICS ™.

Particle size distribution (mass% of particles with diameter <X μm) and particulate matter (weight median particle diameter (d ₅₀ ) of d ₅₀ (μm))
Sedigraph ™ 5100
The weight median particle diameter and particle diameter mass distribution of the particulate material was determined by sedimentation, ie, analysis of sedimentation behavior in a gravitational field. The measurement is performed using a Sedigraph ™ 5100 sold by the company MICROMERITICS ™.

Methods and equipment are known to those skilled in the art and are generally used to determine the particle size of fillers and pigments. Samples were prepared by adding an amount of product corresponding to 4 g of dry PCC to 60 ml of a 0.1 wt% aqueous Na ₄ P ₂ O ₇ solution. The sample was dispersed for 3 minutes using a high speed stirrer (Polytron PT 3000/3100, 15,000 rpm). It was then exposed to ultrasound for 15 minutes using an ultrasonic bath before being added to the Sedigraph mixing chamber.

Weight solids of material in suspension (wt%)
The weight solids (also referred to as material solids) was determined by dividing the weight of the solid material by the total weight of the aqueous suspension.

  The weight of the solid material was determined by weighing the solid material obtained by evaporating the aqueous phase of the suspension and drying the resulting material to a constant weight.

The fine product used to prepare the slurry of the present invention is composed of a number of fine carbonate stones.
Marble calcium carbonate, HCl insoluble matter 1.5% by weight, Bathurst, from Australia, d ₅₀ = 2.8 μm (sample A),
Marble calcium carbonate, 0.1% by weight insoluble in HCl, from Salses, France, two different particle sizes, d ₅₀ = 5.5 μm (sample D), d ₅₀ = 3.5 μm (sample E),
Calcium lime carbonate, HCl insoluble content 0.7% by weight, Superior, Arizona (Sample F: d ₅₀ = 3.5 μm),
Marble calcium carbonate, HCl insoluble content 1.0% by weight, Lucerne Valley, California (Sample J: d ₅₀ = 2.0 μm)
Calcium lime carbonate, HCl insoluble content 0.1% by weight, Organ, France (Sample K: d ₅₀ = 3.0 μm)

  Table 1 outlines the various products used during the remineralization test.

Membrane fouling index (MFI) and Langeria saturation index (LSI) during remineralization of RO water:
The permeate produced by the desalting process is corrosive to concrete and metals due to its low pH and LSI value. If the permeate does not stabilize, it permeates calcium from unprotected concrete in storage tanks, wells, and corrodes ductile iron pipes lined with cement mortar commonly used for water distribution. In most advanced water and wastewater treatment facilities, the permeate is stabilized by the addition of chemicals such as lime.

  However, administration of post-treatment chemicals can result in high turbidity (> 0.2 NTU) and increased fines concentration (high modified fouling index, eg, 2-15 unit range) in the final treated water. Yes, thereby increasing the possibility of fouling of the injection well.

  For indirect beverage use and injection into barrier wells for seawater intrusion control, the permeate turbidity is <0.2 NTU units and the modified fouling index (MFI) is <2.0 units It is done.

  The feed water used for the remineralization test of this example was obtained from the reverse osmosis desalination process of two different sewage plants (Plant 1 and Plant 2) and had the following parameters:

The RO permeate remineralization test is intended to increase the hardness of RO water, for example, with a target of 0.8 mg / L as CaCO ₃ and a maximum of about 50 mg / L as CaCO ₃ , a 2 liter cubic jars (cubic jars). ).

Various types of fine calcium carbonate (Samples A, D, E, F, J and K) were tested for MFI and LSI analysis. The solid content of the CaCO ₃ slurry was 3.5% by weight, based on the weight of the fine calcium carbonate. Appropriate doses of CaCO ₃ slurry were added to achieve the desired water quality. The stabilized final water should meet the following quality requirements.

After adding the CaCO ₃ slurry, the sample was stirred for 4 hours, and the sample was collected at 10, 20, 30, 60, 120, and 240 minutes. Turbidity, pH, total alkalinity, and calcium hardness were measured at individual sampling times. The equilibration time was determined as the time when the turbidity was stable. After reaching the equilibrium time, LSI was calculated and MFI was measured.

Table 2 shows the remineralization of two different RO waters after adding about 50 mg / L as CaCO ₃ using a 3.5 wt% CaCO ₃ slurry based on the weight of fine calcium carbonate. The different results obtained are shown.

  As shown in Table 2, the use of a fine calcium carbonate product for remineralization of RO water has a water quality requirement for pH, total alkalinity, calcium hardness, and MFI for all tests performed. Satisfied. The fine calcium carbonate product produced turbidity levels between 0.5 NTU and 1.7 NTU, and LSI values between -1.85 and -0.88. Based on turbidity measurements over time, the equilibration time required for dissolution of the calcium carbonate product was about 120 minutes.

Claims (22)

a) providing a feed water having a concentration of carbon dioxide of at least 20 mg / l, preferably in the range of 25 to 100 mg / l, more preferably in the range of 30 to 60 mg / l;
b) providing an aqueous slurry comprising fine calcium carbonate; and c) combining the feed water of step a) with the aqueous slurry of step b) to obtain remineralized water. Way for.   The calcium carbonate concentration in the slurry is from 0.05 to 40% by weight, from 1 to 25% by weight, from 2 to 20% by weight, preferably from 3 to 15% by weight, most preferably from 5 to 5%, based on the total weight of the slurry. 3 or 10 wt%, or the calcium carbonate concentration in the slurry is 10 to 40 wt%, 15 to 30 wt%, or 20 to 25 wt%, based on the total weight of the slurry. The method described in 1.   The calcium carbonate has a particle size of 0.1 to 100 μm, 0.5 to 50 μm, 1 to 15 μm, preferably 2 to 10 μm, most preferably 3 to 5 μm, or the calcium carbonate is 1 to 50 μm, 2 to 3. A method according to claim 1 or claim 2 having a particle size of 20 [mu] m, preferably 5 to 15 [mu] m, most preferably 8 to 12 [mu] m.   HCl insolubles of 0.02 to 2.5%, 0.05 to 1.5%, or 0.1 to 0.6% by weight of calcium carbonate, based on the total weight of the fine calcium carbonate The method according to claim 1, comprising:   The method according to any one of claims 1 to 4, wherein the calcium carbonate is ground calcium carbonate, modified calcium carbonate, or precipitated calcium carbonate, or a mixture thereof.   The slurry is a mineral containing magnesium, potassium or sodium, preferably magnesium carbonate, calcium carbonate, magnesium oxide such as dolomite limestone, calcareous dolomite, dolomite or semi-calcined dolomite, calcined dolomite, magnesium sulfate, potassium bicarbonate, Or the method in any one of Claim 1 to 5 which further contains sodium hydrogencarbonate.   The method according to any one of claims 1 to 6, wherein the slurry is freshly prepared by mixing water and calcium carbonate.   The method of claim 6, wherein the time between slurry preparation and slurry injection is less than 48 hours, less than 24 hours, less than 12 hours, less than 5 hours, less than 2 hours or less than 1 hour.   9. A method according to any preceding claim, wherein the infused slurry meets the microbiological quality requirements set by national drinking water quality guidelines.   The resulting remineralized water has a calcium concentration as calcium carbonate of 15 to 200 mg / l, preferably 50 to 150 mg / l, most preferably 100 to 125 mg / l, or 15 to 100 mg / l, preferably 20 to 80 mg. 10. A method according to any of claims 1 to 9, having a calcium concentration of / l, most preferably 40 to 60 mg / l.   The method according to any of claims 6 to 10, wherein the remineralized water obtained has a magnesium concentration of 5 to 25 mg / l, preferably 5 to 15 mg / l, most preferably 8 to 12 mg / l.   12. A method according to any preceding claim, wherein the remineralized water has a turbidity value of less than 5.0 NTU, less than 1.0 NTU, less than 0.5 NTU, or less than 0.3 NTU.   13. A method according to any of claims 1 to 12, wherein the remineralized water has a Langeria saturation index of -2 to 1, preferably -1.9 to 0.9, most preferably -0.9 to 0. . 14. A method according to any preceding claim, wherein the remineralized water has a soil index SDI _{15 of} less than 5, preferably less than 4, most preferably less than 3. 15. A method according to any of claims 1 to 14, wherein the remineralized water has a membrane fouling index MFI _0.45 of less than 4, preferably less than 2.5, most preferably less than 2.   16. Any of claims 1 to 15, wherein the feed water is demineralized seawater, brackish water or brine, treated wastewater or natural water, for example groundwater surface water or rainwater, preferably demineralized seawater, brackish water or brine, treated wastewater or groundwater. The method of crab.   17. A method according to any preceding claim, wherein the remineralized water is blended with the feed water.   18. A method according to any of claims 1 to 17, wherein the method further comprises a particle removal step. The method is
d) measuring the parameter values of the remineralized water, wherein the parameters are selected from the group comprising alkalinity, conductivity, calcium concentration, pH, total soluble solids, and turbidity of the remineralized water Stage,
The method further comprises: e) comparing the measured parameter value with a predetermined parameter value; and f) providing an amount of injected slurry based on the difference between the measured parameter value and the predetermined parameter value. 18. The method according to any one of 18.   20. The method according to claim 19, wherein the predetermined parameter value is a pH value and the pH value is 5.5 to 9, preferably 7 to 8.5.   Use of fine calcium carbonate for water remineralization.   The remineralized water is selected from drinking water, recreational water such as swimming pool water, industrial water for process applications, irrigation water, or aquifer or well recharge water. use.

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