Method and system for processing raw sodium chloride brine
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SCHWEIZER SALINEN AG
- Filing Date
- 2024-06-27
- Publication Date
- 2026-05-13
Smart Images
Figure EP2024068044_09012025_PF_FP_ABST
Abstract
Description
[0001]PSALI001EP / 25.06.20241 Method and plant for the treatment of sodium chloride crude brine. The present invention relates to a method for the treatment of sodium chloride crude brine and a plant for carrying out the method. The method and the plant can be used for the extraction of evaporated salt. Sodium chloride crude brine (or common salt crude brine, salt crude brine) can be extracted, among other things, by pumping water into underground salt domes or salt deposits, whereby the salt is dissolved to obtain the saturated sodium chloride crude brine. This process is referred to as solution mining, salt leaching, or brine extraction.Depending on the composition of the salt dome or salt deposit, a variety of chemical treatment processes are necessary to remove undesirable secondary components such as sulfate, calcium, and magnesium ions before the treated pure sodium chloride brine can be further processed into solid evaporative salt by evaporation crystallization. The soda-lime process (also called the Schweizerhalle process) is a state-of-the-art process for processing raw sodium chloride brine (DE 140605 C, VON GLENCK KORNMANN & CIE FA, April 3, 1903). In a first step, calcium hydroxide (also known as slaked lime) or calcium oxide (also known as quicklime) is added to the raw sodium chloride brine. If calcium oxide is added, it reacts with water to form calcium hydroxide. The calcium hydroxide causes magnesium ions to be almost completely precipitated as magnesium hydroxide.At the same time, a certain proportion of sulfate ions in the solution are precipitated as poorly soluble calcium sulfate, which leads to a reduction in the calcium and sulfate contents of the solution. In addition, a further proportion of the calcium ions, together with the bicarbonate ions present in the brine, precipitates as calcium carbonate through deprotonation. Thus, after the first stage, a proportion of calcium and a proportion of sulfate ions remain as undesirable secondary components. In a second stage of the soda-lime process, sodium carbonate (also known as soda) is used to almost completely precipitate the remaining calcium ions as calcium carbonate. In contrast to the classic soda-lime process, more recent processes use carbon dioxide in addition to sodium carbonate to precipitate calcium carbonate in the second stage. The carbon dioxide is usually introduced into the reactor as flue gas.Completely replacing sodium carbonate with more economically advantageous flue gas is not possible, as the addition of carbon dioxide would cause the pH of the brine to drop too much, causing precipitated calcium carbonate to be redissolved in the form of calcium bicarbonate. For this reason, only a portion of the basic sodium carbonate can be dispensed with in the second stage. Evaporative crystallization can then be used to produce evaporated salt from the treated brine, leaving a mother liquor rich in dissolved sodium chloride. To avoid losing the sodium chloride in the mother liquor, it is advantageous if at least some or all of the mother liquor can be reused in the first stage. This recycling of the basic mother liquor also means that less sodium carbonate is required in the second stage, which is a further advantage.A disadvantage of these processes is that the sulfate ions cannot be completely removed from the brine in the first stage using calcium oxide or calcium hydroxide due to the high solubility product of calcium sulfate in the raw brine. If the entire mother liquor were repeatedly recycled to the first treatment stage, sulfate ions would accumulate. To prevent the precipitation of sodium sulfate in the crystallizers, a portion of the mother liquor must be discharged each time. In practice, the mother liquor is usually discharged into flowing waters, which leads to a significant increase in chloride ions and other undesirable substances. In addition to this ecological disadvantage, the discharge of mother liquor is also disadvantageous from an economic perspective, since sodium chloride is lost with each discharge.In the current state of the art, various processes are used in the treatment of crude sodium chloride brine to minimize or completely prevent the undesirable accumulation of sulfate ions: Membrane separation methods such as nanofiltration can be used to remove sulfate from the brine. EP 1826179 A1 (ESCO-EUROPEAN SALT COMPANY GMBH, August 29, 2007) and DE 19932955 A1 (SALINEN AUSTRIA, January 25, 2001) describe processes for treating brine in which nanofiltration is performed before evaporative crystallization to obtain a low-sulfate permeate. In addition to selectivity problems with these membranes, such processes require regular cleaning and maintenance, and the membranes must be replaced after a certain period of operation due to age. In addition, the use of membrane processes increases energy consumption.As an alternative to membrane separation methods for removing sulfate ions from sodium chloride brine, ion exchange processes are available, as used, for example, in US 4556463 A (BAYER AG, PSALI001EP / 25.06.20244 03.12.1985). In the process described, a diluted sidestream of the brine is passed through a weakly basic, styrene- or acrylate-based ion exchanger to remove the sulfate ions from the solution. However, ion exchange resins must be regularly regenerated to maintain their efficiency, which requires ecological and economic expenditure. Furthermore, ion exchange resins can become clogged, especially in high-throughput applications such as those commonly found in industrial salt processing.Just as the preceding processes, reverse osmosis and electrocoagulation are unsuitable for removing sulfate ions and other contaminants in industrial salt processing because, among other things, they produce large amounts of waste and require a lot of energy. The object of the present invention is therefore to overcome at least some, if not all, of the disadvantages of the prior art systems and methods. In particular, the object of the invention is to reduce the sulfate ion concentration in the sodium chloride brine so that the mother liquor can be largely or even completely reused in the brine processing after evaporative crystallization. The resulting reduction or even prevention of mother liquor discharge into flowing waters is associated with significant ecological and economic advantages, as described above. This object is achieved by a process for processing crude sodium chloride brine.The process is used in particular for the production of evaporated salt. The processing of the crude sodium chloride brine takes place by precipitation of magnesium hydroxide, calcium carbonate, and a first portion of calcium sulfate by adding calcium oxide and / or calcium hydroxide in a first stage, PSALI001EP / 25.06.20245, and precipitation of calcium carbonate by adding sodium carbonate and flue gas comprising carbon dioxide in a second stage. The process is characterized in that the precipitated calcium carbonate from the second stage is converted into calcium chloride and carbon dioxide by adding hydrochloric acid in a secondary stage. The process is further characterized in that the converted calcium chloride is used to precipitate a second portion of calcium sulfate in the first stage. The converted carbon dioxide is also used to precipitate calcium carbonate in the second stage.The supernatant from the second stage is obtained as purified pure sodium chloride brine. Within the scope of the present invention, the processing of crude sodium chloride brine comprises steps that lead to the purification of the crude brine to pure brine. However, subsequent steps can also be assigned to the processing. These steps include evaporative crystallization and the recycling of individual isolated components, the mother liquor, or a portion thereof, to a preceding process step. Within the scope of the present invention, the term "or" is to be understood as an exclusive disjunction. "A or B" states that exactly one of the two statements is true (if the disjunction is true). In the salt industry, the term "crude sodium chloride brine" refers to an aqueous solution containing sodium chloride (NaCl) – also known as table salt – as its main component.It also typically contains dissolved ions, such as magnesium, calcium, sulfates, and others, which can be considered impurities. If such impurities are partially or completely removed from the brine, the raw brine becomes a "pure sodium chloride brine," which can be further processed by evaporation crystallization. Evaporated salt is high-purity sodium chloride (purity > 99.9%), which is obtained by evaporating pure sodium chloride brine, often under heat. It is used in food and / or industry. The regulatory requirements regarding the purity criteria of table salt are regulated in the Codex Alimentarius CXS 150-1985 (version: 2012) of the Food and Agriculture Organization of the United Nations (FAO) and Regulation (EU) 2023 / 915 on maximum levels for certain contaminants in foodstuffs.Further requirements for evaporated salt for industrial applications are DIN EN 973:2009-12 (as of December 2009; Products for treatment of water intended for human consumption – Sodium chloride for regenerating ion exchangers), DIN EN 14805:2022-11 (as of November 2022; Products for treatment of water intended for human consumption – Sodium chloride for the electrochemical generation of chlorine on-site using membrane-free processes), and DIN EN 16370:2022-12 (as of December 2022; Products for treatment of water intended for human consumption – Sodium chloride for the electrochemical generation of chlorine on-site using membrane cells). For the purposes of this invention, a "stage" is understood to be a specific phase or section of an overall process. Each stage includes a specific step or series of steps performed to produce the desired end product. One stage of the inventive Ver-PSALI001EP / 25.06.20247 process is carried out in at least one reaction vessel designated for this purpose (preferably is carried out in a reaction vessel designated for this purpose), with the reaction vessels of the individual stages being connected to one another by piping so that products and by-products can be transferred from the reaction vessel of one stage to the reaction vessel of another stage. Products and by-products of a higher-numbered stage can also be transferred to the reaction vessels of lower-numbered stages. The designations "first stage" and "second stage" do not exclude the possibility of further process steps being carried out between these stages or in parallel. Furthermore, these designations do not necessarily imply that no further process steps follow the last numerically named stage.The solids precipitated in the process according to the invention can be present as anhydrates and / or as hydrates, preferably as hemihydrates, as monohydrates, as dihydrates, or as a combination thereof. The substances and / or mixtures added in the present invention can be added in one portion, in several portions over a certain period of time, or continuously over a certain period of time. In the first step of the process according to the invention, calcium oxide is added to the crude sodium chloride brine, forming hydroxide ions: CaO. (s) + H2O (l) ^ Ca2+ ( aq) + 2 OH- ( aq)(1) Instead of calcium oxide, calcium hydroxide can also be added directly in the first stage according to the process of the invention.PSALI001EP / 25.06.20248 Due to the high hydroxide ion concentration, the hydrogen carbonate contained in the sodium chloride crude brine is completely deprotonated and converted into carbonate: HCO- - 2 3(aq) + OH(aq) ^ CO - 3(aq) + H2O(l) (2) Due to the high pH value, magnesium ions are completely precipitated as magnesium hydroxide: Mg 2+ (aq) + 2 OH- ( aq) ^Mg(OH) 2(s) ↓ (3) Due to the high calcium excess, the hydrogen carbonate contained in the brine precipitates as calcium carbonate: CO32- ( aq) + Ca2+ ( aq) ^ CaCO 3(s) ↓ (4) The sulfate ions contained in the sodium chloride crude brine are partially precipitated as calcium sulfate dihydrate: Ca 2+ (aq) + SO42- ( aq) + 2 H2O (l) ^ CaSO4·2 H2O (s) ↓ (5)However, complete precipitation of calcium sulfate dihydrate in the brine cannot be achieved using calcium oxide and / or calcium hydroxide alone. Due to the solubility product for calcium sulfate dihydrate in crude sodium chloride brine (which corresponds approximately to a saturated aqueous sodium chloride solution), a maximum possible reduction to a mass concentration of approximately 3.1 g / l results. If no additional substances were added in the first stage, the removal of sulfate ions from the crude sodium chloride brine would therefore only be partially possible. To further reduce the sulfate ion concentration, the calcium chloride obtained from the secondary stage according to the invention is added to precipitate the second portion of calcium sulfate: Na2SO4 4(aq) + CaCl 2(s) + 2 H2O (l) ^ 2 NaCl (aq) + CaSO4·2 H2O (s)↓ (6) Due to the high pH value, any iron ions present are also completely precipitated as Fe(OH)3. The solids precipitating during the process are separated from the liquid supernatant. PSALI001EP / 25.06.20249 The supernatant from the first stage according to the invention, which is transferred to the reaction vessel of the second stage, has a significantly lower sulfate ion concentration than without this addition due to the addition of calcium chloride from the secondary stage. The supernatant is also essentially free of magnesium ions, but still contains calcium ions. In the second stage of the process according to the invention, the remaining calcium ions are precipitated as calcium carbonate using carbon dioxide and sodium carbonate: Ca 2+ (aq) + 2 OH- ( aq) + CO 2(g) ^ CaCO 3(s) ↓ + H2O (l) (7) Na2CO 3(s) ^ 2 Na (aq) + + CO32- ( aq) (8) Ca 2+ (aq)+ CO32- ( aq) ^ CaCO 3(s) ↓ (9)The carbon dioxide used in the second stage is added partly from carbon dioxide-containing flue gas; partly from the carbon dioxide produced in the secondary stage according to the invention. If required, sufficient in-situ formed carbon dioxide is available, so that an exogenous carbon dioxide source such as flue gas could even be dispensed with entirely. As already described above, the addition of cheaper carbon dioxide alone would lower the pH of the brine too much. Therefore, sodium carbonate is also used to precipitate calcium carbonate in the second stage. The supernatant from the second stage according to the invention, i.e. the processed pure sodium chloride brine, is thus essentially free of calcium, magnesium, and sulfate ions.In this context, the term "essentially free from" means that the ion concentration is so low that the mother liquor after the evaporative crystallization following the second stage can be reused in the first stage of the inventive process without mother liquor rejection, without the corresponding ions significantly accumulating in the brine. The calcium carbonate precipitated in the second stage is separated from the supernatant of the second stage and reacted with hydrochloric acid in the secondary stage: CaCO3. 3(s) + 2 HCl (l) ^ CaCl 2(aq) + H2O (l) + CO 2(g) (10)The resulting calcium chloride and carbon dioxide are used, as described above, in the first stage to precipitate calcium sulfate and in the second stage to precipitate calcium carbonate, respectively. It has been shown that the process according to the invention can minimize or even completely prevent the discharge of mother liquor into flowing waters after evaporative crystallization. If the sulfate ions were not essentially completely removed from the brine, a large portion of mother liquor would have to be discharged in each case to avoid an accumulation of sulfate ions. This prevents the negative ecological impacts that can arise from increased amounts of sodium chloride and other undesirable substances (e.g., sulfate ions) in flowing waters.Furthermore, the process according to the invention offers the advantage that the sodium chloride contained in the mother liquor remains economically usable, since sodium chloride brine is a finite raw material. In an alternative process, commercially available calcium chloride could be added in the first stage. In contrast, the process according to the invention has the advantage that the calcium carbonate byproduct from stage 2 can be reused if it is converted to calcium chloride with hydrochloric acid. In addition, carbon dioxide is produced, which PSALI001EP / 25.06.202411 significantly reduces the flue gas requirement in stage 2 or even makes it completely obsolete. A lower flue gas requirement or even the elimination of flue gas reduces the use of fossil fuels.One advantage of the increased recirculation of the mother liquor is that a higher sodium sulfate concentration (as well as an increased sodium chloride concentration) is present in stage 1 of the inventive process. The higher the sodium sulfate concentration and sodium chloride concentration, the higher the solubility of calcium oxide. Therefore, a comparatively high hydroxide concentration (approx. 34 mmol / l) can be achieved with the inventive process. This increased alkalinity of the brine further reduces the demand for calcium oxide in the first stage and sodium carbonate in the second stage in the inventive process, since the excess of these substances can be drastically reduced. It has been shown that the resulting savings for sodium carbonate are approximately 40%.A further positive effect of the present process is that the use of calcium chloride in the first stage results in the formation of additional sodium chloride, which can be crystallized (equation 6). Furthermore, it has been shown that the increased molar concentration of sodium chloride has a negative effect on the solubility of calcium sulfate dihydrate, improving its precipitation. In a preferred embodiment of the process according to the invention, the supernatant from the first stage has a hydroxide concentration of at least 20 mmol / l, preferably at least 25 mmol / l, more preferably at least 30 mmol / l, and most preferably at least 34 mmol / l. PSALI001EP / 25.06.202412 The content "mmol / l" refers to the number of hydroxide ions in mmol per liter of the supernatant from the first stage. The hydroxide ion content is measured by potentiometric titration using hydrochloric acid as the titrator.As described above, the increased mother liquor recirculation results in an increased sodium sulfate concentration in the sodium chloride brine, which in turn increases the solubility of calcium oxide. This reduces the calcium oxide requirement in the first stage, since this reactant can no longer be added in excess. The increased basicity of the brine also reduces the sodium carbonate requirement in the second stage. In a further preferred embodiment, the supernatant from the first stage is essentially completely used in the second stage. In this context, the term "essentially completely" means that at least 95%, preferably at least 97%, most preferably at least 99% of the supernatant from the first stage is used in the second stage.It is therefore not necessary to laboriously divide the sodium chloride brine to be treated into several portions or streams and to process the individual portions or streams in different sub-steps and then to combine them again later. In a further preferred embodiment of the process according to the invention, the magnesium ion content in the sodium chloride pure brine is less than 0.10 mg / kg, preferably less than 0.05 mg / kg. Most preferably, the sodium chloride pure brine is substantially free of magnesium ions. In a further preferred embodiment of the process according to the invention, the calcium ion content in the sodium chloride pure brine is less than 15.0 mg / kg, preferably less than 5.0 mg / kg. Most preferably, the sodium chloride pure brine is substantially free of calcium ions.In a further preferred embodiment of the process according to the invention, the sulfate ion content in the pure sodium chloride brine is less than 10.5 g / kg, preferably less than 8.5 g / kg. Most preferably, the pure sodium chloride brine is essentially free of sulfate ions. A combination of the three embodiments regarding the ion contents in the pure sodium chloride brine is also possible. The content specifications "mg / kg" and "g / kg" refer to the mass of the corresponding ion per kilogram of brine. The calcium, magnesium, and sulfate ion contents are measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) according to the test standard "EUsalt / AS 015-2015" (as of 2015). In this context, the term "essentially free from" means that, when the test standard is correctly applied, no ions of the corresponding element are detected.PSALI001EP / 25.06.202414 The process according to the invention leads to the described comparatively low contents of calcium, magnesium, and sulfate ions in the pure sodium chloride brine. This enables the recycling of a large part or all of the mother liquor after evaporative crystallization. In a further preferred embodiment of the process according to the invention, in a third stage, sodium chloride as a solid and a mother liquor are produced from the pure sodium chloride brine in an evaporative crystallization. During evaporative crystallization, the pure sodium chloride brine is heated to evaporate water, whereby sodium chloride crystallizes into a solid. This can take place, for example, in an evaporation tank or in an evaporation pan. After crystallization, the solid sodium chloride is separated from the remaining solution, the mother liquor.The mother liquor is a saturated sodium chloride solution, which may contain other ions in solution. In a preferred embodiment of the process according to the invention, the content of magnesium ions in the mother liquor is less than 0.10 mg / kg, preferably less than 0.05 mg / kg. Most preferably, the mother liquor is substantially free of magnesium ions. In a further preferred embodiment of the process according to the invention, the content of calcium ions in the mother liquor is less than 15 mg / kg, preferably less than 5 mg / kg. Most preferably, the mother liquor is substantially free of calcium ions.PSALI001EP / 25.06.202415 In another preferred embodiment of the process according to the invention, the content of sulfate ions in the mother liquor is less than 35.0 g / kg, preferably less than 24.0 g / kg. Most preferably, the mother liquor is substantially free of sulfate ions.A combination of the three embodiments regarding the ion contents in the mother liquor is also possible. The definitions of the content specifications "mg / kg" and "g / kg", the test standard for measuring the ion contents, and the definition of the term "essentially free from," which were mentioned above, apply equally here. The process according to the invention leads to the described comparatively low contents of calcium, magnesium, and sulfate ions in the mother liquor. This enables the recycling of a large portion or all of the mother liquor. In a further preferred embodiment of the process according to the invention, at least 80%, preferably at least 90%, even more preferably at least 95%, of the mother liquor from the evaporative crystallization is added in the first stage as mother liquor recycling. This leads to the advantages already mentioned above.In particular, this reduces the contamination of flowing waters by sodium chloride and sulfate. Furthermore, the recycling of the mother liquor in the first stage of the process according to the invention increases the sodium sulfate concentration, which ultimately reduces the demand for calcium oxide and sodium carbonate.PSALI001EP / 25.06.202416 In a preferred embodiment of the process according to the invention, a maximum of 1.5 kg, preferably a maximum of 1.0 kg, and most preferably a maximum of 0.5 kg of sodium carbonate is added in the second stage per kilogram of hydrochloric acid added in the secondary stage. If the process within the scope of the present invention is carried out in batch operation (batch process), these mass ratios refer to the amounts added per batch. In continuous or semi-continuous processes, these mass ratios refer to the amount added per unit time.In a further preferred embodiment of the process according to the invention, for each kilogram of hydrochloric acid added in the secondary stage, not more than 1.0 kg, preferably not more than 0.5 kg, even more preferably not more than 0.2 kg, and most preferably no carbon dioxide at all is added as a component of flue gas in the second stage. This refers only to the carbon dioxide that is fed into the process via flue gas; not the carbon dioxide that is produced in the secondary stage. It has been shown that with the process according to the invention, the flue gas requirement can be significantly reduced, or that even no flue gas needs to be used at all to supply carbon dioxide. In a further preferred embodiment of the process according to the invention, the precipitated calcium sulfate from the first stage is converted into calcium chloride and sulfuric acid by adding hydrochloric acid in a second secondary stage.The reacted calcium chloride and sulfuric acid are used to precipitate calcium sulfate in the first stage. CaSO. 4(s) + 2 HCl (l) ^ CaCl 2(aq) + H2OSO 4(aq) ↓ (11) CaCl 2(aq) + Na2SO 4(s) ^ 2 NaCl (aq) + CaSO 4(s)↓ (13) By adding hydrochloric acid to the precipitate from the first stage, calcium chloride and sulfuric acid are formed. Both can be added back to the first stage. The sulfuric acid has a neutralizing effect and more sodium chloride is formed from the sodium already present in the brine and the added chloride. Because the sludge from the first stage is reused, it does not need to be neutralized. Furthermore, by adding this process solution to the first stage, heavy metals dissolved in the first stage can be precipitated as hydroxides. This object is further achieved by a plant for carrying out the process according to the invention. The plant comprises a first container for carrying out the first stage of the process. It also comprises a second container for carrying out the second stage of the process. Furthermore, it comprises a third container for carrying out the secondary stage of the process.Additionally, it comprises first piping for transferring calcium chloride from the third vessel to the first vessel; and second piping for transferring carbon dioxide from the third vessel to the second vessel.PSALI001EP / 25.06.202418 The first piping and the second piping are arranged such that a controlled amount of calcium chloride and carbon dioxide can each be transferred from the secondary stage vessel at a controlled flow rate into a respective vessel provided for this purpose. The first piping is connected to the third vessel at the lower half, preferably at the lower quarter, more preferably at the lower apex, so that the solid calcium chloride can be removed therefrom. The second piping is connected to the third vessel at the upper half, preferably at the upper quarter, most preferably at the upper eighth, so that the gaseous carbon dioxide can be removed therefrom.The plant according to the invention makes it possible to carry out the process according to the invention by reusing the calcium chloride and carbon dioxide produced in the secondary stage from the calcium carbonate by-product of the second stage. The same advantages mentioned above apply to the plant as to the process. In a preferred embodiment of the plant according to the invention, at least 18 kg, preferably at least 90 kg, even more preferably at least 180 kg, most preferably at least 230 kg of calcium chloride can be transferred per hour through the first piping. In a further preferred embodiment of the plant according to the invention, at least 7 kg, preferably at least 35 kg, even more preferably at least 70 kg, most preferably at least 90 kg of carbon dioxide can be transferred per hour through the second piping.PSALI001EP / 25.06.202419 In a further preferred embodiment, the plant has a control device which is configured such that in the second stage, when used as intended, only so much flue gas is added that the sum of the added quantities of carbon dioxide from the secondary stage and carbon dioxide from the flue gas corresponds to the carbon dioxide requirement of the second stage. In a batch process, the carbon dioxide requirement is the quantity (mass or number of particles), and in a continuous process, the flow rate (volume per time, mass per time or number of particles per time) of carbon dioxide that can be added in the second stage without lowering the pH so much that the precipitated calcium ions go back into solution. As described above, the pH of the brine in this stage is largely determined by the added carbon dioxide and the added sodium carbonate.A value below this amount or flow rate can also be set for the carbon dioxide requirement. In a preferred embodiment, the first container, the second container, the third container, or a combination of containers of the system according to the invention is equipped with a stirring device. In a further preferred embodiment, the first piping and / or the second piping is / are equipped with a valve for regulating the mass flow and / or volume flow. The mass flow is the mass of a substance that flows through a specific cross-sectional area per unit of time. It is typically measured in kilograms per hour (kg / h) or other masses per unit of time. PSALI001EP / 25.06.202420 The volume flow is the volume of a substance that flows through a specific cross-sectional area per unit of time.It is typically measured in cubic meters per hour (m³ / h) or other volumes per unit of time. In another preferred embodiment, the first piping and / or the second piping is / are equipped with a pump for regulating the mass flow and / or volume flow. The invention will now be described using specific exemplary embodiments. These embodiments are not intended to limit the essence of the invention in any way, but rather serve to facilitate understanding of the invention. Fig. 1: Flow diagram of a plant according to the invention for processing raw sodium chloride brine to pure sodium chloride brine; Fig. 2: Maximum possible hydroxide ion concentration in sodium chloride brine as a function of the sodium sulfate concentration; Fig. 3: Flow diagram comprising the mass and volume flows in the brine processing process. In Fig.Figure 1 shows a flow diagram of a plant for carrying out the process according to the invention in batch operation. The plant comprises several vessels (B), which in this exemplary embodiment are reactors in the chemical industry. A stirring device (R)PSALI001EP / 25.06.202421 is installed in certain vessels (B). The piping (VR) shown as arrows indicates the flow direction between the individual vessels (B) and is equipped with valves (V) and pumps (P). The arrows in Figure 1, which are interrupted when crossing another arrow, are not to be understood as interrupted piping (VR). This representation is merely intended to facilitate understanding of the figure.The mother liquor (ML) from evaporative crystallization (VK) is stored in a mother liquor tank (MLT) and added to the sodium chloride crude brine (RoS) in the first stage (S1) together with the calcium oxide, the filtrate (F), and the calcium chloride from the secondary stage (N). After the reaction has taken place, the precipitated magnesium hydroxide, calcium carbonate, and calcium sulfate are separated from the supernatant as first-stage sludge (SS1). The first-stage sludge (SS1) undergoes clarifying filtration, and the resulting filtrate (F) is added to a subsequent batch in the first stage (S1). The supernatant from the first stage (S1) is fed into the tank (B) for the second stage (S2), and sodium carbonate, flue gas (RG) comprising carbon dioxide, and carbon dioxide from the secondary stage (N) are added.The precipitated calcium carbonate is transferred to tank (B) for the secondary stage (N), and the supernatant from the second stage (S2) is used as pure sodium chloride brine (ReS) for evaporative crystallization (VK). Hydrochloric acid is added to the calcium carbonate in tank (B) of the secondary stage (N) to produce calcium chloride and carbon dioxide. The calcium chloride is transferred to tank (B)PSALI001EP / 25.06.202422 of the first stage (S1), and the carbon dioxide is transferred to tank (B) of the second stage (S2). The chemical composition and other physical properties of the crude sodium chloride brine (RoS) are shown in Table 1.Table 1: Chemical (β: mass concentration (mass of species per volume of brine); w: mass fraction (mass of species per mass of brine); c: molar concentration (amount of species per volume of brine)) and physical (ρ: density) parameters of the sodium chloride crude brine (RoS) used in the inventive process and in the comparative processes. Parameter Unit RoS β(SO4. 2– ) g / l 3.06 w(SO4 2– ) g / kg 2.54 β(Ca 2+ ) g / l 1.31 w(Ca 2+ ) g / kg 1.09 β(Br – ) mg / l 7.7 w(Br – ) mg / kg 6.4 β(K + ) mg / l 21.1 w(K + ) mg / kg 17.5 β(Mg 2+ ) mg / l 26.8 w(Mg 2+ ) mg / kg 22.3 β(HCO3 – ) mg / l 95.3 w(HCO3 – ) mg / kg 79.2 c(OH –) mol / l 5.8E-08 β(NaCl) g / l 305.00 c(NaCl) mol / l 5.22 pH value 6.7 pOH value 7.3 ρ(RoS) g / ml 1.203PSALI001EP / 25.06.202423 If this crude sodium chloride brine (RoS) is treated using the process according to the invention, as described above, essentially the entire mother liquor (ML) can be transferred back to stage 1 (S1) after evaporative crystallization (VK) without sulfate ions accumulating in the brine. Because the entire mother liquor (ML) can be recycled, the brine has a higher sodium sulfate concentration (approx. 17 g / l). In addition, by recycling the sodium chloride-containing mother liquor, the sodium chloride concentration of the first-stage mixture is increased to approximately 318 g / l. Figure 2 shows that at an increased sodium sulfate concentration of approximately 17 g / l, the solubility of calcium oxide is increased to such an extent that hydroxide concentrations of approximately 34 mmol / l are possible. This was already described above.This leads, among other things, to less calcium oxide and sodium carbonate being required in the process, which is shown in Table 2 using the required volume flow rates (Q) and mass flow rates (q) of the individual species when multiple batches are produced in succession. Furthermore, in the present exemplary embodiment, the entire carbon dioxide requirement of the second stage (S2) can be covered by the carbon dioxide produced in the secondary stage (N). Thus, no flue gas needs to be used. Fig. 3 shows the mass flow rates (q) and volume flow rates (Q) of the individual stages (stage 1, S1; stage 2, S2; secondary stage, N; evaporative crystallization, VK). In the comparative processes shown in Table 2, sodium chloride crude brines (RoS) with the same chemical and physical properties can be processed.A first comparison process (Comparison 1) corresponds to the soda-lime process described above, with additional carbon dioxide in the form of flue gas (RG) being used in the second stage (S2). However, the precipitated calcium carbonate from the second stage (S2) is not converted into calcium chloride and carbon dioxide and reused. A portion of the mother liquor (ML) is reused in a mother liquor recycle (MLR) in the first stage (S1), and the remainder is disposed of as mother liquor reject (MLA). Comparison process 2 (Comparison 2) differs from Comparison 1 in that the mother liquor recycle (MLR) is higher and the mother liquor reject (MLA) is lower.A higher mother liquor recirculation (MLR) than in Comparison 2 would lead to excessive sulfate enrichment in the mother liquor, and there would be a risk that sodium sulfate could precipitate together with the desired sodium chloride during evaporative crystallization. Table 2: Volume flow rates (Q) and mass flow rates (q) of the individual species in the treatment process of sodium chloride crude brine (RoS) in the process according to the invention, as well as in three comparison processes. Species Invention Comparison Comparison Comparison Q: m. 3 / h; q: dung 1 2 3 kg / h Q(RoS) 105.4 116.7 107.8 165.0 q(CaO) 189.5 189.5 189.5 210.0 Q(F) 9.6 9.6 9.6 0.0 q(Na2CO3) 90.0 179.0 105.0 383.0 q(CO2, RG) 0.0 86.0 90.0 82.0 q(HCl) 150.9 0.0 0.0 0.0 q(CaCl2) 229.7 0.0 0.0 0.0 q(CO2, N) 92.0 0.0 0.0 0.0 Q(ReS) 165.0 165.0 165.0 165.0 Q(ML) 50.0 50.0 50.0 50.0 Q(MLR) 50.0 38.7 47.5 0.0 Q(MLA) 0.0 11.3 2.5 50.0 q(NaCl) 35'342 35'100 35'100 35'100 q(Mg(OH)2) 6.8 7.5 6.9 10.6PSALI001EP / 25.06.202425 Species Invent Comparison Comparison Comparison Q: m 3 / h; q: dung 1 2 3 kg / hq(CaSO4·2 H2O) 786.5 379.1 436.2 318.0 q(CaCO3) 363.1 400.5 370.5 540.6 The comparison processes 1 and 2 have a significantly higher demand for sodium carbonate and flue gas (RG) than the process according to the invention. In addition, a significant proportion of the mother liquor (ML) is discharged into flowing water. The use of hydrochloric acid required by the process according to the invention is more than offset by these resource savings and the lower environmental impact. Although the process according to the invention produces more calcium sulfate dihydrate, this can be used, for example, in the gypsum industry. Comparative Process 3 (Comparative 3) in Table 2 differs from the inventive process and Comparative Processes 1 and 2 in that an excess of calcium oxide is used. Here, too, more sodium carbonate and flue gas (RG) are required than in the inventive process.In addition, the entire mother liquor (ML) is rejected and cannot be recycled (Table 2). Comparing the costs incurred for the chemical additives for the treatment of the crude sodium chloride brine (RoS) for the individual processes, it becomes clear that the process according to the invention is significantly more cost-effective (Table 3). PSALI001EP / 25.06.202426 Table 3: Relative costs of the specified chemicals based on comparison process 3 (100%). The costs for the CO relate to the heating oil (extra light) used to produce flue gas (RG). Excipient Invention Comparison 1 Comparison 2 Comparison 3 Cost % Cost % Cost % Cost % CaO 85 % 15.0 15.1 15.1 16.7 CO2 0.0 18.8 19.2 17.5 Na2CO3 15.3 30.7 18.0 65.8 HCl 31 % 17.5 0.0 0.0 0.0 Total 47.9 64.6 52.3 100.0.
Claims
PSALI001EP / 25.06.20241 Patentansprüche 1.A process for the treatment of crude sodium chloride brine (RoS), in particular for the production of evaporated salt, by precipitation of magnesium hydroxide, calcium carbonate, and a first portion of calcium sulfate by adding calcium oxide and / or calcium hydroxide in a first stage (S1), as well as precipitation of calcium carbonate by adding sodium carbonate and flue gas (RG) comprising carbon dioxide in a second stage (S2), characterized in that ^ the precipitated calcium carbonate of the second stage (S2) is converted into calcium chloride and carbon dioxide by adding hydrochloric acid in a secondary stage (N); ^ the converted calcium chloride is used to precipitate a second portion of calcium sulfate in the first stage (S1); ^ the converted carbon dioxide is used to precipitate calcium carbonate in the second stage (S2); and ^ the supernatant of the second stage (S2) is obtained as processed pure sodium chloride brine (ReS). 2.Process according to claim 1, characterized in that the supernatant of the first stage (S1) ^ has a hydroxide concentration of at least 20 mmol / l, preferably at least 25 mmol / l, more preferably at least 30 mmol / l, most preferably at least 34 mmol / l; and / or ^ is used essentially completely in the second stage (S2).PSALI001EP / 25.06.20242 3. Process according to one of the preceding claims, characterized in that a. the content of magnesium ions in the pure sodium chloride brine (ReS) is less than 0.10 mg / kg, preferably less than 0.05 mg / kg, most preferably that the pure sodium chloride brine (ReS) is essentially free of magnesium ions; b. that the content of calcium ions in the pure sodium chloride brine (ReS) is less than 15.0 mg / kg, preferably less than 5.0 mg / kg, most preferably that the pure sodium chloride brine (ReS) is substantially free of calcium ions; c.that the content of sulfate ions in the pure sodium chloride brine (ReS) is less than 10.5 g / kg, preferably less than 8.5 g / kg, most preferably that the pure sodium chloride brine (ReS) is substantially free of sulfate ions; or d. that several of the conditions a. to c. are met.
4. Process according to one of the preceding claims, characterized in that in a third stage, sodium chloride as a solid and a mother liquor (ML) are produced from the pure sodium chloride brine (ReS) in an evaporation crystallization (VK).
5. Process according to claim 4, characterized in that i. that the content of magnesium ions in the mother liquor (ML) is less than 0.10 mg / kg, preferably less than 0.05 mg / kg, most preferably that the mother liquor (ML) is substantially free of magnesium ions; ii. that the content of calcium ions in the mother liquor (ML) is less than 15 mg / kg, preferably less thanPSALI001EP / 25.06.20243 5 mg / kg, most preferably that the mother liquor (ML) is substantially free of calcium ions; iii. that the content of sulfate ions in the mother liquor (ML) is less than 35.0 g / kg, preferably less than 24.0 g / kg, most preferably that the mother liquor (ML) is substantially free of sulfate ions; or iv. that several of the conditions i. to iii. are met.
6. Process according to one of claims 4 to 5, characterized in that at least 80%, preferably at least 90%, even more preferably at least 95%, of the mother liquor (ML) is added to the evaporation crystallization (VK) as mother liquor recycle (MLR) in the first stage (S1).
7. Process according to one of the preceding claims, characterized in that per kilogram of hydrochloric acid added in the secondary stage (N) at most 1.5 kg, preferably at most 1.0 kg, most preferably at most 0.5 kg of sodium carbonate are added in the second stage (S2).
8. Process according to one of the preceding claims, characterized in that per kilogram of hydrochloric acid added in the secondary stage (N), at most 1.0 kg, preferably at most 0.5 kg, even more preferably at most 0.2 kg, and most preferably no carbon dioxide at all is added as a component of flue gas in the second stage (S2).
9. Process according to one of the preceding claims, whereinPSALI001EP / 25.06.20244 ^ the precipitated calcium sulfate from the first stage (S1) is converted into calcium chloride and sulfuric acid by adding hydrochloric acid in a second secondary stage; ^ the converted calcium chloride and the converted sulfuric acid are used to precipitate calcium sulfate in the first stage (S1).Plant for carrying out the process according to one of claims 1 to 9, the plant comprising ^ a first container (B) for carrying out the first stage (S1) of the process; ^ a second container (B) for carrying out the second stage (S2) of the process; ^ a third container (B) for carrying out the secondary stage (N) of the process; ^ a first piping (VR) for transferring calcium chloride from the third container (B) into the first container (B); and ^ a second piping (VR) for transferring carbon dioxide from the third container (B) into the second container (B).
11. Plant according to claim 10, characterized in that at least 18 kg, preferably at least 90 kg, even more preferably at least 180 kg, most preferably at least 230 kg of calcium chloride can be transferred through the first piping (VR) per hour. 12.Plant according to one of claims 10 to 11, characterized in that at least 7 kg, preferably at least 35 kg, even more preferably at least 70 kg, most preferably at least 90 kgPSALI001EP / 25.06.20245 of carbon dioxide can be transferred through the second piping (VR) per hour.
13. Plant according to one of claims 10 to 12, wherein the plant has a control device configured such that in the second stage (S2), when used as intended, only so much flue gas (RG) is added that the sum of the added quantities of carbon dioxide from the secondary stage (N) and carbon dioxide of the flue gas (RG) corresponds to the carbon dioxide requirement of the second stage (S2).
14. Plant according to one of claims 10 to 13, wherein the first container (B), the second container (B), the third container (B), or a combination of containers (B) is equipped with a stirring device (R). 15.System according to one of claims 10 to 14, wherein the first piping (VR) and / or the second piping (VR) is / are equipped with a valve (V) for regulating the mass flow (q) and / or volume flow (Q).
16. System according to one of claims 10 to 15, wherein the first piping (VR) and / or the second piping (VR) is / are equipped with a pump (P) for regulating the mass flow (q) and / or volume flow (Q).