Seawater desalination brine full resource utilization process

Abstract

This invention provides a fully resource-efficient process for desalination brine. The process utilizes pretreatment with sodium carbonate to regulate pH, effectively separating calcium and magnesium ions and converting them into solid carbonate byproducts. Subsequently, ultra-high pressure reverse osmosis (HPRO) technology is employed to achieve a high freshwater recovery rate. For the remaining high-concentration brine, sulfuric acid is introduced for replacement, converting sodium chloride into hydrochloric acid and sodium sulfate. The hydrochloric acid, combined with quicklime, is evaporated and crystallized to produce calcium chloride hexahydrate. Further processes, including air-blowing brine extraction, nanofiltration (NF) membrane, evaporation crystallization, and electrolysis, produce a diverse range of products including bromine, freshwater, sodium sulfate, liquid potassium fertilizer, finished salt, hydrogen, hydrochloric acid, and sodium hydroxide. Finally, sodium hydroxide is added to carbon sequestration to produce sodium carbonate, which can be recycled throughout the process. This process not only achieves internal recycling of industrial reagents but also completely eliminates the damage to the marine ecosystem caused by brine discharge from desalination plants, achieving both economic and environmental goals.

Claims

1. A process for the complete resource utilization of seawater desalination brine, comprising the following steps: (a) providing pretreated seawater; (b) the pretreated seawater entering a seawater desalination reverse osmosis treatment to produce freshwater and brine; (c) the brine entering a decalcification precipitation tank, wherein sodium carbonate is added to the decalcification precipitation tank to adjust the pH value to ≤9.5 to facilitate decalcification, so that calcium combines with carbonate ions to precipitate calcium carbonate, thus completing the decalcification of brine; (d) the decalcified brine entering a demagnesification precipitation tank, wherein sodium carbonate is added to the demagnesification precipitation tank to adjust the pH value to ≤10.5 to facilitate demagnesification, so that magnesium combines with carbonate ions to precipitate magnesium carbonate, thus completing the demagnesification of brine; (e) the decalcified and demagnesified brine entering an ultra-high pressure reverse osmosis treatment to produce freshwater and concentrated brine; (f) the concentrated brine entering a sulfate reaction tank, wherein insufficient sulfuric acid is slowly added to the sulfate reaction tank to produce sodium sulfate and hydrochloric acid, wherein sodium and chlorine are not completely reacted and remain partially. (g) In step (f), the hydrochloric acid enters an acid-base neutralization reaction tank, where quicklime is added to produce water-soluble calcium chloride. The water-soluble calcium chloride enters an evaporation crystallization tank to evaporate the water and then condense the fresh water, producing fresh water and calcium chloride hexahydrate; (h) In step (f), the brine containing sodium sulfate enters a gas-lifting tank, where chlorine gas is blown into the brine containing sodium sulfate to separate and extract bromine, producing bromine gas; (i) The brine after bromine extraction enters a nanofiltration membrane for treatment. The nanofiltration membrane with a pore size of 1 to 10 nanometers can effectively retain the sodium sulfate produced in step (f), while chlorine, sodium, and potassium pass through the nanofiltration membrane; (j) In step (i), the sodium sulfate enters an evaporation crystallization tank to evaporate the water and then condense the fresh water, producing fresh water and sodium sulfate decahydrate; (k) In step (i), the brine containing chlorine, sodium, and potassium is treated by the nanofiltration membrane and then enters an evaporation crystallization tank to evaporate the water and then condense it into fresh water, producing fresh water, liquid potassium fertilizer, and sodium chloride; (l) In step (k), a portion of the sodium chloride is used to produce finished salt; (m) In step (k), a portion of the sodium chloride enters an electrolytic cell, which produces hydrogen, chlorine, and liquid sodium hydroxide; (n) In step (m), a portion of the liquid sodium hydroxide is used to produce sodium carbonate by adding carbon fixation, which is used to adjust the pH value in steps (c) and (d).

2. The seawater desalination brine full resource utilization process as described in claim 1, wherein, (a) The pretreatment of seawater in step (a) removes impurities such as silt, organic matter, microorganisms, algae and various suspended particles mixed in the original seawater.

3. The seawater desalination brine full resource utilization process as described in claim 1, wherein, (b) In this step, the seawater desalination reverse osmosis process produces 45% freshwater and 55% brine.

4. The seawater desalination brine full resource utilization process as described in claim 3, wherein, (e) In step (e), the ultra-high pressure reverse osmosis treatment produces 80% fresh water and 20% concentrated brine from the decalcified and demagnesified brine. The amount of fresh water is 80%, which is 41.6% of the fresh water from the pretreated seawater in step (a).

5. The seawater desalination brine full resource utilization process as described in claim 1, wherein, (f) The amount of sulfuric acid added in step (f) is controlled to be 50% of the sodium and chlorine used in the reaction.

6. The seawater desalination brine full resource utilization process as described in claim 1, wherein, (i) In step (i), the nanofiltration process can be repeated to obtain more sodium sulfate and more concentrated brine containing chlorine, sodium and potassium.

7. The seawater desalination brine full resource utilization process as described in claim 1, wherein, In step (m), the liquid sodium hydroxide can provide the product of solid sodium hydroxide.

8. The seawater desalination brine full resource utilization process as described in claim 1, wherein, In step (m), the chlorine gas can be used to extract bromine in step (h).

9. The seawater desalination brine full resource utilization process as described in claim 1, wherein, In step (m), the chlorine gas can be used to produce hydrochloric acid.

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