EP-4739629-A1 - METHOD AND SYSTEM FOR PROCESSING RAW SODIUM CHLORIDE BRINE

Abstract

The present invention relates to a method for processing raw sodium chloride brine, and to a system for carrying out said method. The method and the system can be used to obtain evaporated salt. In the method according to the invention, the raw sodium chloride brine is processed by precipitating magnesium hydroxide, calcium carbonate and a first portion of calcium sulphate by adding calcium oxide and/or calcium hydroxide in a first stage, and precipitating calcium carbonate by adding sodium carbonate and off-gas comprising carbon dioxide in a second stage. The method is characterised in that the precipitated calcium carbonate of the second stage is caused to react by adding hydrochloric acid in a secondary phase to form calcium chloride and carbon dioxide; in that the reacted calcium chloride is used to precipitate a second portion of calcium sulphate in the first stage; in that the reacted carbon dioxide is used to precipitate calcium carbonate in the second stage; and in that the supernatant from the second stage is obtained as processed pure sodium chloride brine.

Inventors

• LAUBER, MARTIN

Assignees

• Schweizer Salinen AG

Dates

Publication Date

20260513

Application Date

20240627

Claims (1)

1. PSALI001EP / June 25, 2024 1 Patent claims 1. Process for the treatment of sodium chloride crude 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), and 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); ^ that the converted calcium chloride is used to precipitate a second portion of calcium sulfate in the first stage (S1); ^ that the converted carbon dioxide is used to precipitate calcium carbonate in the second stage (S2); and ^ that the supernatant of the second stage (S2) is obtained as processed sodium chloride pure 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 /25.06.2024 2 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 substantially free of magnesium ions; b. 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 than PSALI001EP /25.06.2024 3 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 the mother liquor (ML) of the evaporative crystallization (VK) is added at least 80%, preferably at least 90%, even more preferably at least 95%, most preferably substantially completely in the first stage (S1) as mother liquor recycle (MLR). 7. Process according to one of the preceding claims, characterized in that per kilogram of hydrochloric acid added in the secondary stage (N) a maximum of 1.5 kg, preferably a maximum of 1.0 kg, most preferably a maximum of 0.5 kg of sodium carbonate is 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) a maximum of 1.0 kg, preferably a maximum of 0.5 kg, even more preferably a maximum of 0.2 kg, 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, wherein PSALI001EP /25.06.2024 4 ^ the precipitated calcium sulfate from the first stage (S1) is converted into calcium chloride and sulfuric acid in a second secondary stage by adding hydrochloric acid; ^ the converted calcium chloride and the converted sulfuric acid are used to precipitate calcium sulfate in the first stage (S1). 10. 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) to the first container (B); and ^ a second piping (VR) for transferring carbon dioxide from the third container (B) to 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 per hour through the first piping (VR). 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 kg can be transferred through the second piping (VR). PSALI001EP /25.06.2024 5 carbon dioxide per hour can be transferred. 13. Plant according to one of claims 10 to 12, wherein the plant has a control device which is 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 amounts 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).

Description

PSALI001EP /25.06.2024 1 Process and plant for the treatment of sodium chloride crude brine The present invention relates to a process for the treatment of sodium chloride crude brine and a plant for carrying out the process. The process and the plant can be used to extract 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 in order to extract the saturated sodium chloride crude brine. This process is called solution mining, salt leaching or brine extraction. Depending on the composition of the salt dome or salt deposit, a variety of chemical processing methods are necessary to remove undesirable secondary components such as sulfate, calcium and magnesium ions before the processed sodium chloride pure brine can be further processed in an evaporative crystallization to form solid evaporated salt. The lime soda process (also called the Schweizerhalle process) is a state-of-the-art process for processing sodium chloride raw brine (DE 140605 C, VON GLENCK KORNMANN & CIE FA, April 3, 1903). In the first stage, calcium hydroxide (also known as slaked lime) or calcium oxide (also known as quicklime) is added to the sodium chloride raw 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 content and the sulfate content of the solution. In addition, a further proportion of the calcium ions precipitates together with PSALI001EP /25.06.2024 2 hydrogen carbonate ions present in the brine precipitate 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 lime soda process, sodium carbonate (also known as soda) is used to almost completely precipitate the remaining calcium ions as calcium carbonate. In comparison to the classic lime soda process, in more recent processes, carbon dioxide is also used in the second stage in addition to sodium carbonate to precipitate calcium carbonate. The carbon dioxide is usually introduced into the reactor as flue gas. It is not possible to completely replace sodium carbonate with more economically advantageous flue gas, since the addition of carbon dioxide would cause the pH value of the brine to drop too much, with precipitated calcium carbonate being brought back into solution in the form of calcium hydrogen carbonate. For this reason, the basic sodium carbonate can only be partially dispensed with in the second stage. Evaporative crystallization can then be used to produce evaporated salt from the treated brine, leaving a mother liquor that is rich in dissolved sodium chloride. In order not to lose the sodium chloride in the mother liquor, it is advantageous if at least part 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 another advantage. A disadvantage of the processes mentioned is that the sulfate ions cannot be completely removed from the brine in the first stage with calcium oxide or calcium hydroxide due to the high PSALI001EP /25.06.2024 3 solubility product of calcium sulfate in the raw brine. If the entire mother liquor were to be returned to the first treatment stage again and again, sulfate ions would accumulate. In order to avoid the precipitation of sodium sulfate in the crystallizers, a portion of the mother liquor must be rejected each time. In practice, the mother liquor is usually rejected into flowing water, which leads to a significant increase in chloride ions and other undesirable substances. In addition to this ecological disadvantage, the rejection of mother liquor is also disadvantageous from an economic point of view, since sodium chloride is lost with each rejection. In the current state of the art, various processes are used in the processing of sodium chloride crude brine in order 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 processing brine, in which nanofiltration is carried out before evaporative crystallization in order to obtain a permeate with a low sulfate content. In addition to selectivity problems with these membranes, such processes require regular cleaning and maintenance work and the membranes must be replaced after a certain period