A method and system for stepwise mineral separation using long distance transport of concentrated brine

Abstract

The application discloses a kind of long-distance conveying concentrated brine as raw material's cascade mineral separation method and system, belong to concentrated brine mineral extraction technical field.System includes membrane concentration device arranged in sequence, and bromine extraction unit, potassium extraction unit and magnesium extraction unit according to bromine→potassium→magnesium fixed order are connected in series in sequence.This application first utilizes membrane concentration device to concentrated brine that is conveyed through long-distance pipeline and is concentrated, obtains concentrated brine and fresh water;Subsequently, the residual heat accumulated in the long-distance conveying and membrane concentration process of concentrated brine is used, and the irreversible order of extracting bromine first, then extracting potassium, and finally extracting magnesium is used for cascade extraction, and any reversal or skipping of a certain stage cannot achieve the technical effect of the application.The final residual mother liquor is a high-purity sodium chloride solution, which is directly sent to a salt evaporation pond for crystallization, achieving full-component recovery and zero discharge of water, minerals and salts in concentrated brine.

Description

Technical Field

[0001] This invention belongs to the field of concentrated brine mineral extraction technology, specifically involving a method and system for using concentrated brine transported over long distances as raw material, first concentrating and recovering fresh water through membrane concentration, then extracting valuable minerals in an irreversible stepwise sequence of bromine → potassium → magnesium, and using the residual mother liquor for salt production. Background Technology

[0002] The concentrated brine produced by seawater desalination contains abundant valuable mineral elements, including bromine, potassium, and magnesium. However, existing technologies for extracting these minerals from concentrated brine face the following significant challenges: First, the extraction sequence lacks systematic optimization. Existing technologies often target the extraction of single elements independently, without considering the mutual influence between upstream and downstream elements in different processes. There is a naturally optimal extraction sequence for each element in concentrated brine, determined by its physicochemical properties: bromine is highly volatile and must be extracted first; potassium crystallizes preferentially over magnesium during cooling and should be extracted before magnesium; magnesium is best extracted last after bromine and potassium have been removed. Arbitrarily reversing or skipping any extraction stage will lead to a significant decrease in the recovery rate of downstream elements or substandard product purity. Secondly, there is a disconnect between membrane concentration for desalination and mineral extraction. Traditional solutions plan these two as separate projects, leading to energy waste and redundant investment. Third, energy utilization efficiency is low. During long-distance pipeline transportation and membrane concentration, the concentrated brine naturally heats up due to environmental heat absorption and pump friction heat, and this waste heat is wasted. However, the bromine extraction process requires a feed temperature of 25-30°C. Fourth, there is insufficient utilization of the residual mother liquor. After some minerals are extracted, the residual mother liquor still contains a large amount of sodium chloride and is often discharged as waste. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for cascade mineral separation using concentrated brine transported over long distances as raw material. Key Invention Point 1: Membrane Concentration and Freshwater Recovery as a Necessary Pre-process for Mineral Extraction This invention uses a membrane concentration device as the first stage of a mineral extraction system. "Membrane concentration device" includes, but is not limited to, any device that utilizes selectively permeable membranes to separate brine, such as reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), membrane distillation (MD), and electrodialysis (ED). Any concentration technology capable of concentrating brine salinity from 4%-7% to 15%-25%, regardless of whether membrane technology is used, as long as the resulting concentrated brine is subsequently extracted in a stepwise manner in the order of bromine → potassium → magnesium, utilizes the core concept of this invention and should fall within the scope of protection of this invention. 15%-25% is the optimal salinity range, but it is not a strict limitation on the protected range. As long as the salinity of the concentrated brine is significantly increased relative to the original concentrated brine (at least 8%), and the extraction is carried out in a stepwise manner in the order of bromine → potassium → magnesium, the core concept of this invention is still utilized. Core Invention Point Two: Irreversible Extraction Sequence of Bromine → Potassium → Magnesium The extraction sequence claimed in this invention is bromine → potassium → magnesium. This sequence is determined by the physicochemical properties of each element and is scientifically necessary and irreversible. Inserting extraction steps of other valuable minerals between bromine and potassium extraction, or between potassium and magnesium extraction, does not change the core extraction sequence of bromine → potassium → magnesium. Any stepwise extraction that substantially follows the sequence of first extracting bromine, then potassium, and finally magnesium, regardless of whether other steps are inserted in between, should fall within the scope of protection of this invention. Even if a different extraction sequence is used than that of this patent (such as magnesium first, then potassium, and finally bromine), as long as it essentially separates and recovers the three elements of bromine, potassium, and magnesium from the same batch of concentrated brine, and the final residual mother liquor is a high-purity sodium chloride solution used for salt drying, it still utilizes the core concept of this invention—the full-component cascade recovery—and should fall within the protection scope of this invention. Even if bromine, potassium salt, or magnesium product is extracted separately from concentrated brine, as long as the raw material comes from concentrated brine (salinity 15%-25%) after long-distance pipeline transportation and membrane concentration, and the extraction process utilizes the waste heat accumulated during long-distance transportation and membrane concentration, it still utilizes some of the core concepts of this invention and should fall within the protection scope of this invention. Even if potassium extraction is skipped and magnesium is extracted directly from the brine after bromine extraction (bromine → magnesium), as long as it utilizes the core sequential logic of this invention (bromine precedes magnesium) and the raw material comes from concentrated brine transported over long distances and concentrated by membrane, it should be considered an equivalent infringement. Air blowing is a preferred method for bromine extraction, but any method for separating bromine from concentrated brine (including but not limited to solvent extraction, ion exchange, adsorption, etc.) should fall within the scope of protection of this invention. Cold crystallization is a preferred method for potassium extraction, but any method for separating potassium salts from brine after bromine extraction (including but not limited to flotation, evaporation crystallization, solvent extraction, etc.) should fall within the scope of protection of this invention. Lime milk precipitation is a preferred method for magnesium extraction, but any method for separating magnesium products from residual mother liquor after potassium extraction (including but not limited to sodium hydroxide precipitation, ammonia precipitation, carbonate precipitation, etc.) should fall within the scope of protection of this invention. Key Invention Point 3: Targeted Utilization of Waste Heat in Bromine Extraction During the long-distance pipeline transportation and membrane concentration of concentrated brine (≥10km), the temperature typically rises by 5-8°C. This invention utilizes this waste heat in the bromine extraction unit. Even if the brine, after being heated during transportation, is intentionally cooled and then reheated, as long as the heat accumulated during the long-distance pipeline transportation and membrane concentration process is objectively utilized (i.e., the transportation and concentration process causes the brine temperature to be higher than the ambient temperature), the waste heat utilization concept of this invention is still applied and should fall within the scope of protection of this invention. Split Avoidance Statement Those skilled in the art should understand that separating the membrane concentration unit, bromine extraction unit, potassium extraction unit, and magnesium extraction unit into different legal entities or geographical regions does not change the fact that they operate as a complete system working in concert. Any attempt to separate pipeline transportation, mineral extraction, and salt pan production into different entities cannot circumvent infringement. Detailed Implementation

[0004] Example 1: Mineral Extraction System with an Annual Production Capacity of One Million Tons This embodiment receives concentrated brine from a coastal desalination plant, transported via a pipeline approximately 40 kilometers long. The brine has a salinity of about 5.8%, a temperature of about 28°C, and a processing capacity of about 30,000 m³ / day. Membrane concentration and freshwater recovery: High-pressure reverse osmosis membrane concentration unit, operating pressure 6.5MPa, increases salinity from 5.8% to approximately 20%, with a freshwater recovery rate of approximately 45%. It produces approximately 13,500 m³ of high-quality freshwater per day. Bromine extraction (first stage): The concentrated brine is heated to 28°C, and the pH is adjusted to 2.5 with dilute sulfuric acid. Chlorine gas is then passed through for oxidation. Air is blown out in a counter-current flow from the blow-out tower to release free bromine. This bromine is absorbed by the sulfur dioxide aqueous solution in the absorption tower to generate hydrogen bromide solution. Secondary oxidation, separation, and condensation yield the bromine product. The annual processing capacity is 10.95 million tons of concentrated brine, with a bromine recovery rate of approximately 85% and an annual bromine production of approximately 13,000 tons. Potassium Extraction (Second Stage): After bromine extraction, the brine is cooled to 15°C. Potassium salts, due to a significant decrease in solubility, preferentially crystallize out, while magnesium ions remain completely dissolved. Centrifugation yields the potassium salt product. Potassium recovery rate is approximately 80%, with an annual production of approximately 157,000 tons of potassium salt. Magnesium Extraction (Third Stage): After potassium extraction, lime slurry is added to the residual mother liquor, causing magnesium ions to precipitate as magnesium hydroxide. The precipitate is then separated by plate and frame filtration, washed, and dried. The magnesium recovery rate is approximately 90%, with an annual production of approximately 407,000 tons of magnesium hydroxide. The residual mother liquor, with a sodium chloride purity ≥95%, is sent to a salt pan. Salt production: The residual mother liquor from magnesium extraction is naturally evaporated and crystallized in a fully seepage-proof salt production pond, producing approximately 19.5 million tons of high-quality industrial salt with a purity of ≥99.5% annually. Material balance throughout the entire process: Approximately 200 million tons / year of freshwater + 13,000 tons / year of bromine + 157,000 tons / year of potash + 407,000 tons / year of magnesium hydroxide + 19.5 million tons / year of industrial salt. Zero waste discharge. Comparative Example 1: Magnesium was extracted first, then potassium, and finally bromine. The bromine recovery rate plummeted from 85% to less than 20%. Comparative Example 2: Potassium was extracted first, then bromine, and finally magnesium was extracted. The bromine recovery rate decreased by about 15-20%. Comparative Example 3: Skipping bromine extraction and directly extracting potassium and magnesium results in a bromine recovery rate close to zero, leading to annual losses of hundreds of millions of dollars. Example 2: Bromine extraction by solvent extraction The bromine extraction unit uses solvent extraction, with the extractant being a kerosene solution of tributyl phosphate (TBP), which is an equivalent of the present invention. Example 3: Potassium Extraction by Flotation The potassium extraction unit uses flotation and octadecylamine as the collector, which is an equivalent of the present invention. Example 4: Magnesium extraction by sodium hydroxide precipitation method The magnesium extraction unit uses sodium hydroxide instead of lime milk as a precipitant, which is an equivalent solution of the present invention. Example 5: Thermal concentration as an alternative to membrane concentration The concentration device uses multi-effect evaporation (MED) instead of high-pressure reverse osmosis membrane to concentrate the salinity of brine from 5.8% to 20%, which is an equivalent solution of the present invention. Example 6: Direct extraction of bromine to magnesium (skipping potassium) After bromine extraction, the brine is directly fed into the magnesium extraction unit with lime milk for precipitation without potassium extraction. Although the potassium is not recovered, resulting in a decrease in economic benefits, it utilizes the core sequential logic of this invention (bromine precedes magnesium) and is an equivalent solution of this invention. The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stepwise mineral separation method using concentrated brine transported over long distances as raw material, characterized in that, Includes the following steps: S1: Obtain concentrated brine transported over a long distance through a pipeline, with a salinity of not less than 4%, and concentrate the concentrated brine using at least one stage of membrane concentration device to obtain concentrated brine and fresh water. The concentrated brine has a salinity of 15%-25%, and the fresh water is recycled. S2: The concentrated brine is subjected to a stepwise extraction of valuable minerals, the stepwise extraction including: preferentially extracting bromine to obtain bromine-extracting brine; extracting potassium salts after bromine extraction to obtain potassium-extracting residual mother liquor; and extracting magnesium products after potassium extraction to obtain magnesium-extracting residual mother liquor. S3: The residual mother liquor from magnesium extraction is sent to a salt-evaporating pool for natural evaporation and crystallization to obtain sodium chloride.

2. The method according to claim 1, characterized in that, The extraction sequence of the step-by-step extraction is bromine → potassium → magnesium, and this sequence cannot be reversed, nor is it allowed to skip any stage. Inserting extraction steps of other valuable minerals between bromine extraction and potassium extraction, or between potassium extraction and magnesium extraction, does not change the core extraction sequence and should still fall within the protection scope of this claim. Even if other extraction sequences are used, as long as they essentially separate and recover the three elements of bromine, potassium, and magnesium from the same batch of concentrated brine, and the final residual mother liquor is a high-purity sodium chloride solution used for salt production, it should still fall within the protection scope of this claim.

3. A cascade mineral separation system using long-distance transport of concentrated brine as raw material, characterized in that, include: A concentrated brine inlet is provided for receiving concentrated brine transported over long distances through pipelines, with a salinity of not less than 4%. At least one membrane concentration unit, whose inlet is connected to the concentrated brine inlet, is used to concentrate the concentrated brine and separate fresh water and concentrated brine, wherein the concentrated brine has a salinity of 15%-25% and the fresh water is recycled; a bromine extraction unit, whose inlet is connected to the concentrated brine outlet of the membrane concentration unit, is used to extract bromine from the concentrated brine. A potassium extraction unit, whose inlet is connected to the outlet of the bromine extraction unit, is used to extract potassium salt from the brine after bromine extraction; a magnesium extraction unit, whose inlet is connected to the outlet of the potassium extraction unit, is used to extract magnesium product from the residual mother liquor after potassium extraction; the outlet of the residual mother liquor of the magnesium extraction unit is connected to the downstream salt drying pond.

4. The system according to claim 3, characterized in that, The bromine extraction unit, potassium extraction unit, and magnesium extraction unit are connected in series in the order of bromine → potassium → magnesium, and this order cannot be reversed; the outlet of the bromine extraction unit is connected only to the inlet of the potassium extraction unit, and the outlet of the potassium extraction unit is connected only to the inlet of the magnesium extraction unit.

5. The system according to claim 3, characterized in that, The membrane concentration device uses a high-pressure reverse osmosis membrane module to concentrate the salinity of the brine from 4%-7% to 15%-25%, and the freshwater recovery rate of the membrane concentration device is between 30%-60%.

6. The system according to claim 3, characterized in that, After being transported over long distances through pipelines and concentrated via membrane, the temperature of the concentrated brine is 5-8°C higher than that of the original seawater. This temperature increase is due to the environmental heat absorbed by the concentrated brine during long-distance transport and the frictional heat from pumping. The bromine extraction unit utilizes the residual heat provided by this temperature increase to maintain the temperature of the feed brine at 25-30°C to meet the temperature requirements of the bromine extraction process, eliminating the need for additional heating devices.

7. The system according to claim 3 or 6, characterized in that, When the bromine extraction unit uses the air blowing method, it sequentially includes, along the process flow direction: an acidification device for adding sulfuric acid or hydrochloric acid to the concentrated brine to adjust the pH of the brine to 2-3; an oxidation device connected to the acidification device for introducing chlorine gas or sodium hypochlorite into the acidified brine to oxidize bromide ions into free bromine; a blowing tower connected to the oxidation device for introducing air to blow free bromine from the brine into the gas phase; an absorption tower connected to the gas phase outlet of the blowing tower for absorbing the bromine in the blown gas with a sulfur dioxide aqueous solution or alkaline solution to generate a hydrogen bromide solution or a sodium bromide solution; and a secondary oxidation separation device connected to the absorption tower for introducing chlorine gas again into the hydrogen bromide solution or sodium bromide solution to oxidize bromide ions into free bromine again, and obtaining the bromine product after separation and condensation.

8. The system according to claim 3, characterized in that, When the potassium extraction unit adopts the cold crystallization method, it includes, in sequence along the process flow direction: a cooling device, used to reduce the temperature of the brine after bromine extraction to 10-20°C, so that the potassium salt will crystallize out preferentially due to the significant decrease in solubility as the temperature decreases, while magnesium ions are still completely dissolved in the brine in this temperature range and do not co-crystallize with the potassium salt; and a crystallization separation device, connected to the cooling device, used to separate the precipitated potassium salt crystals from the residual mother liquor.

9. The system according to claim 3, characterized in that, When the magnesium extraction unit uses the lime slurry precipitation method, it sequentially includes, along the process flow direction: a lime slurry preparation device for mixing and digesting lime with water to prepare lime slurry; a precipitation reactor, the inlet of which is connected to the outlet of the lime slurry preparation device and the outlet of the residual mother liquor of the potassium extraction unit, for adding lime slurry to the residual mother liquor after potassium extraction, so that magnesium ions react with calcium hydroxide to form magnesium hydroxide precipitate; and a solid-liquid separation device connected to the precipitation reactor for separating magnesium hydroxide precipitate from the residual mother liquor, wherein the separated residual mother liquor is mainly a high-purity sodium chloride solution with a sodium chloride purity ≥95%.

10. The system according to claim 3, characterized in that, The concentrated brine inlet is directly or indirectly connected to the outlet of a long-distance transmission pipeline system, the long-distance transmission pipeline system having a laying length of ≥10km, and its inlet being connected to the concentrated brine output interface of the coastal seawater desalination plant.

11. The system according to claim 3, characterized in that, The residual mother liquor outlet of the magnesium extraction unit is connected to the inlet of a fully seepage-proof salt-drying pond located in an inland desert area. The residual mother liquor from magnesium extraction is naturally evaporated and crystallized in the salt-drying pond to obtain sodium chloride salt with a purity of ≥99.5%.

12. The system according to claim 3, characterized in that, Any combination of any two adjacent units among the bromine extraction unit, potassium extraction unit, and magnesium extraction unit, i.e., the combination of the bromine extraction unit and the potassium extraction unit, or the combination of the potassium extraction unit and the magnesium extraction unit, constitutes an operable subsystem of the cascade mineral separation system; the operable subsystem also falls within the protection scope of this claim.