Method for recycling valuable resources of underground brine

Abstract

The invention discloses a method for recycling valuable resources of underground brine. The method comprises the following steps: (1) pretreatment; (2) bromine recovery; (3) recycling lithium; (4) recovering boron; and (5) recovering potassium and sodium. According to the invention, valuable resources in the underground brine are fully recycled; valuable resources in the underground brine are recycled, and powerful support is provided for widening the varieties and reserves of lithium, bromine, potassium and sodium ore resources in China.

Description

Technical Field

[0001] The present invention relates to a method for recycling wastewater resources, and in particular to a method for recycling valuable underground brine resources. Background Art

[0002] Brine is commonly classified according to its burial conditions and can be divided into two categories: surface salt lake brine and underground brine. Surface salt lake brine is found in lakes in arid regions. For example, the mineralization of the water in Dabson Lake in the Qarhan Salt Lake in the Qaidam Basin of my country is over 300g / L. A large amount of salt lake brine is also found in the Great Salt Lake in Utah, USA. Underground brine refers to brine that is distributed in brine reservoirs deep in sedimentary basins (usually hundreds to thousands of meters deep), such as the deep underground brine in the central Sichuan Basin and the deep underground brine in the Jiangling Depression of the Jianghan Basin.

[0003] Currently, salt lake brine resources, such as those in the Qarhan Salt Lake, are being exploited on a large scale, while underground brine resources remain largely unused. Underground brine primarily includes produced water from oil and gas fields and deep-seated salt brine. Rich in a variety of useful elements, such as bromine, sodium, iodine, boron, potassium, magnesium, and lithium, underground brine is a valuable resource. However, its utilization rate remains low, primarily due to its complex composition and the difficulty of its utilization.

[0004] Therefore, developing a low-cost, green and environmentally friendly method for recovering valuable underground brine resources is conducive to achieving resource utilization and sustainable development. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a method for recovering valuable resources in underground brine, which can effectively recover valuable resources in underground brine.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] A method for recovering valuable underground brine resources comprises the following steps:

[0008] (1) Pretreatment: A flocculation sedimentation process is used to reduce the suspended solids in the underground brine to below 20 mg / L; the calcium, magnesium, and barium plasma content is reduced to below 100 mg / L, and a step-by-step impurity removal process is used. The specific operation of the step-by-step impurity removal process is as follows: first, sulfate is added to react, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 1 and filtrate 1; filter residue 1 is a barium sulfate precipitate; alkali is added to filtrate 1 to a pH value of 11-12, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 2 and filtrate 2; filter residue 2 is a magnesium hydroxide precipitate; carbonate is added to filtrate 2, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 3 and filtrate 3, and filter residue 3 is a calcium carbonate precipitate;

[0009] (2) Bromine recovery: Bromine ions in the filtrate 3 are oxidized to bromine (bromine element) through an electro-oxidation bromine extraction process (mainly by controlling the electro-oxidation potential of electrode plates to oxidize bromide ions to bromine element), and the bromine is blown out to obtain bromine gas and brine from which the bromine is blown out; the bromine gas is then used to prepare sodium bromide product through processes such as absorption and evaporation concentration;

[0010] (3) lithium recovery (using adsorption method to extract lithium): after the brine from which bromine is blown out in step (2) is adjusted to a certain pH value, adsorption is performed using an adsorbent to obtain an adsorption tail liquid, the adsorbent is analyzed to obtain a lithium-rich qualified liquid, the lithium-rich qualified liquid is purified by impurity removal to obtain a lithium-rich mother liquor, which is concentrated to a lithium concentration of more than 20 g / L, and then lithium is precipitated to obtain a lithium carbonate product;

[0011] (4) Boron recovery (boron resource recovery by membrane method + evaporation process): the adsorption tail liquid obtained in step (3) is adjusted to a certain pH, and then separated by nanofiltration membrane to obtain fresh water and concentrated water. The borate ions are retained on the concentrated water side, and the concentrated water is further evaporated and crystallized to produce borax product;

[0012] (5) Potassium and sodium recovery: The fresh water obtained in the boron recovery unit of step (4) is evaporated and concentrated to precipitate sodium chloride, and solid-liquid separation is performed to obtain sodium chloride precipitate and mother liquor 1. The mother liquor 1 is cooled and crystallized, and solid-liquid separation is performed to obtain potassium chloride product and mother liquor 2.

[0013] A further step (6) for secondary lithium recovery can be added: the mother liquor 2 obtained in step (5) is further concentrated to a lithium content of more than 20 g / L, and then lithium is precipitated to obtain a lithium carbonate product. The lithium precipitation operation method is the same as that of step (3).

[0014] Preferably, in step (1), the mass content of each element in the raw underground brine is: lithium ion ≥0.004%; bromide ion ≥0.005%; sodium ion ≥1%; potassium ion ≥0.1%; boron content ≥0.01%; calcium ion ≤5%, barium ion ≤1%, and magnesium ion ≤1%.

[0015] Preferably, in step (1), the specific operation of the pretreatment is as follows: adding polyaluminum chloride (PAC) and polyacrylamide (PAM) to underground brine, filtering; adding sodium sulfate to the filtrate, stirring and reacting for more than 30 minutes, filtering to obtain barium sulfate precipitate and filtrate 1; adding sodium hydroxide to the filtrate 1 to adjust the pH to 11-12, stirring and reacting for more than 30 minutes, filtering to obtain magnesium hydroxide and filtrate 2; adding sodium carbonate to the filtrate 2, stirring and reacting for more than 30 minutes, filtering to obtain calcium carbonate and filtrate 3.

[0016] Preferably, in step (1), polyaluminium chloride (PAC) and polyacrylamide (PAM) are added in the form of a solution. The mass concentration of polyaluminium chloride is 5%-15% (preferably 10%), and the amount of solute added to the polyaluminium chloride solution is 0.1-1‰ (preferably 0.5‰) of the underground brine inflow. The mass concentration of polyacrylamide is 1-3‰ (preferably 2‰), and the amount of solute added to the polyacrylamide solution is 0.01-0.1‰ (preferably 0.05‰) of the underground brine inflow.

[0017] Preferably, in step (1), the amount of sulfate added is a molar ratio of sulfate to barium ion of 1-1.1:1 (preferably 1.15:1); the amount of carbonate added is a molar ratio of carbonate to calcium ion of 1.0-1.2:1.

[0018] Preferably, in step (2), the pH of the water inlet of the electro-oxidation bromine extraction process is adjusted to 2-4, preferably to 2. The electrode material anode of the electro-oxidation bromine extraction process is titanium ruthenium iridium, and the cathode is titanium; the constant voltage power supply is used, the oxidation voltage is 1-1.7V (preferably 1.5V), and the electro-oxidation time is 1.5-4h (preferably 3h).

[0019] Preferably, in step (2), the bromine solution after electrooxidation is blown out by air with a gas-liquid ratio of 100-160m 3 The bromine gas after blowing out is absorbed by liquid caustic soda (the mass concentration of liquid caustic soda is 10-32%), and urea is added at the same time. The mass ratio of urea to sodium hydroxide is 1:(4-6), preferably 1:5, to obtain a sodium bromide solution, which is then evaporated and crystallized to obtain a sodium bromide product.

[0020] Preferably, in step (2), when the pH of the absorption liquid to be absorbed bromine gas drops to 8, the introduction of bromine gas is stopped to obtain a saturated sodium bromide solution, which is then evaporated and crystallized to obtain a sodium bromide product.

[0021] Preferably, in step (3), an adsorption process is used to extract lithium. The adsorbent for adsorption and extraction of lithium can use the product in CN111905700B, or other adsorbents for adsorption and extraction of lithium. The pH of the adsorbed water is first adjusted to 5-7 (preferably pH=6). After adsorption, pure water is used for desorption to obtain a qualified lithium-rich liquid. The conductivity of the pure water is required to be below 100μS / cm (preferably below 50μS / cm); the qualified lithium-rich liquid is subjected to reverse osmosis + ion exchange resin to remove calcium, magnesium, barium and boron therein, and the concentration of calcium, magnesium, barium and boron is reduced to below 10mg / L, and then evaporated and concentrated to a lithium ion concentration of more than 20g / L, and sodium carbonate solution is added to carry out lithium precipitation reaction to obtain a lithium carbonate product.

[0022] Preferably, in step (3), the adsorption rate of the adsorbent is 3-8 BV / h; the desorption rate is 2-4 BV / h; the impurity removal and purification is to remove calcium, magnesium and barium ions by nanofiltration, then the nanofiltration fresh water is concentrated by reverse osmosis, and the reverse osmosis concentrated water is then subjected to ion exchange to remove calcium, magnesium, barium and boron, and the purified qualified liquid is then concentrated by evaporation to a Li ≥ 20 g / L. The temperature of the lithium precipitation reaction is 80-90°C, and the reaction time is 0.5-2 hours; the mass concentration of the sodium carbonate solution is 15-25%.

[0023] Preferably, in step (3), the nanofiltration membrane, reverse osmosis membrane, and ion exchange resin used for removing calcium, magnesium, barium, and boron can be purchased from the market. The above purification treatment is beneficial to the next step.

[0024] Preferably, in step (4), boron resources are recovered by membrane method + evaporation process, by adjusting the pH of the adsorption tail liquid to 9-11 (preferably pH = 10), and then using a nanofiltration membrane to intercept the borate in the adsorption tail liquid to the concentrated water end, and the concentrated water is then evaporated and crystallized to produce borax.

[0025] Preferably, in step (5), potassium and sodium salt separation is performed by a method of high temperature sodium precipitation and cooling crystallization potassium precipitation to obtain sodium chloride and potassium chloride products. When the fresh water is evaporated and concentrated to a potassium concentration in the mother liquor of 100-120 g / L, heating is stopped and filtered to obtain sodium chloride and mother liquor 1. The mother liquor 1 is cooled to 5-40° C. to precipitate potassium chloride, and filtered to obtain mother liquor 2 and potassium chloride product.

[0026] The present invention first removes suspended matter and impurity ions such as calcium, magnesium and barium, which can effectively protect the electrode materials of the electro-oxidation bromine extraction equipment, avoid electrode scaling, and help extend the service life of the electrode; the bromine element is mainly extracted by adopting the electro-oxidation bromine extraction process, the pH of the inlet water is adjusted to 2-4, and then the pH is adjusted to 5-7 before the outlet water is adsorbed. After electro-oxidation, the pH of the brine will rise to 3-4, so recovering the bromine resource first can reduce the amount of alkali used.

[0027] The present invention can fully recycle and utilize valuable resources in underground brine to achieve comprehensive utilization. In step (1), the present invention pre-treats the water to remove suspended matter and divalent impurity ions, preparing for electro-oxidation bromine extraction. In step (2), bromine is extracted through an electro-oxidation bromine extraction process to produce an industrial sodium bromide product. In step (3), lithium is extracted through an adsorption lithium extraction process, and after impurity removal, purification, and concentration, an industrial-grade lithium carbonate product is produced. In step (4), boron is separated and concentrated using a membrane process to produce an industrial borax product. In step (5), the sodium chloride precipitate obtained is dried to produce a first-grade industrial salt. The potassium chloride precipitate is dried to produce an agricultural first-grade potassium chloride product. In step (6), the lithium concentration is increased after evaporation and concentration. Further evaporation and concentration are then performed to fully recycle the lithium resources and produce an industrial-grade lithium carbonate product.

[0028] Beneficial effects of the present invention:

[0029] 1. Fully recycle and utilize the valuable resources in underground brine;

[0030] 2. By recycling and utilizing valuable resources in underground brine, we can provide strong support for expanding the types and reserves of lithium, bromine, potassium and sodium mineral resources in my country. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Unless otherwise specified, the raw materials, products and equipment used in the embodiments of the present invention were obtained through conventional commercial channels.

[0033] In this specification, unless otherwise specified, the percentages are by mass.

[0034] Example 1

[0035] The main component data of the underground brine in this embodiment are shown in Table 1 below.

[0036] Table 1 Main components of underground brine

[0037] index <![CDATA[Li + ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Ba 2+ ]]> content(%) 0.0153 2.612 0.1945 0.1368 0.0469 0.1346 index B <![CDATA[Cl - ]]> <![CDATA[Br - ]]> SS content(%) 0.0365 4.6951 0.02843 122mg / L

[0038] The adsorbent used in this embodiment for lithium adsorption extraction is the product in CN111905700B.

[0039] The method for recovering valuable underground brine resources in this embodiment includes the following steps:

[0040] (1) Pretreatment: 15 kg of underground brine was taken, and 75 g of a 10% PAC solution and 250 g of a 0.3% PAM solution were added to the mixture using a flocculation sedimentation process. The mixture was stirred for 30 min and filtered. Then, 104 g of a 20% sodium sulfate solution was added to the filtrate. The mixture was stirred for 30 min and filtered to obtain a barium sulfate precipitate and a filtrate 1. Liquid alkali was added to the filtrate 1 to adjust the pH to 12. The mixture was stirred for 30 min and filtered to obtain a magnesium hydroxide precipitate and a filtrate 2. 300 g of a 20% sodium carbonate solution was further added to the filtrate 2. The mixture was stirred for 30 min and filtered to obtain calcium carbonate and a filtrate 3. The calcium ion concentration of the filtrate 3 was 82.3 mg / L, the magnesium ion concentration was 22.4 mg / L, the barium ion concentration was 5.6 mg / L, and the suspended matter was reduced to 12 mg / L.

[0041] (2) Bromine recovery: the pH of the filtrate 3 was adjusted to 2, the voltage of the electrooxidizer power supply was adjusted to 1.5 V for electrooxidation, and the oxidation time was 3 h. After electrooxidation, the brine was blown out with air at a gas-liquid ratio of 120:1 (L / L). The bromine after blowing out was absorbed by 11 g of a 20% sodium hydroxide solution by mass, and 1.3 g of a 40% urea solution by mass was added. When the pH of the absorption liquid for absorbing bromine gas dropped to 8, the introduction of bromine gas was stopped to obtain a saturated sodium bromide solution, which was evaporated to obtain a sodium bromide product. After drying, 4.1 g of sodium bromide was obtained with a product purity of 98.73%;

[0042] (3) Lithium recovery: The brine after blowing out in step (2) was adjusted to pH 6 with sodium hydroxide solution, and then selective adsorption of lithium was performed using a continuous ion exchange device. The remaining solution was the lithium adsorption tail liquid; the adsorbent loading amount was 3825 mL, the adsorption rate was 5 BV / h, and pure water was used for desorption at a desorption rate of 3 BV / h. 4.856 kg of selectively adsorbed lithium-rich desorption liquid was obtained. The components of the lithium-rich desorption liquid are shown in the following table;

[0043] Table 2 Main components of lithium-rich desorption solution

[0044] Element <![CDATA[Ca 2+ ]]> <![CDATA[K + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Ba 2+ ]]> <![CDATA[Li + ]]> B content(%) 0.0023 0.0154 0.0008 0.1451 0.0026 0.0425 0.0027

[0045] The lithium-rich qualified solution was subjected to reverse osmosis concentration, resulting in 1.350 kg of reverse osmosis concentrated water with a lithium ion concentration of 1.266 g / L; the reverse osmosis concentrated solution was passed through ion exchange resins to remove calcium, magnesium, barium and boron from the solution, respectively. The feed rate of the resin column for removing calcium, magnesium and barium was 2 BV / h, and the calcium ion concentration in the effluent was 5.36 mg / L, the magnesium ion concentration was 2.57 mg / L, and the barium ion concentration was 4.54 mg / L. The feed rate of the boron removal resin was 1.5 BV / h, and the boron concentration in the boron removal effluent was 8.58 mg / L; after boron removal, the solution was evaporated and concentrated to obtain 0.091 kg of concentrated solution with a lithium ion concentration of 20.62 g / L, to which 60.3 g of 20% sodium carbonate solution was added for lithium precipitation reaction at a reaction temperature of 90° C. and a reaction time of 1 hour to obtain 8.36 g of lithium carbonate with a purity of 99.21%;

[0046] (4) Boron recovery: 15 kg of lithium adsorption tail liquid was taken, and the main component data are shown in Table 3 below;

[0047] Table 3 Main components of underground brine lithium extraction tailings

[0048] Element <![CDATA[K + ]]> <![CDATA[Na + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Li + ]]> <![CDATA[Ba 2+ ]]> B content(%) 0.2134 2.2650 0.0053 0.0007 0.0032 0.0006 0.0315

[0049] The adsorption tail liquid was adjusted to pH 9.5, and then subjected to primary nanofiltration to obtain 4.653 kg of nanofiltration concentrated water with a boron concentration of 0.89 g / L. The obtained primary nanofiltration concentrated water was further subjected to secondary nanofiltration to obtain 2.069 kg of secondary nanofiltration concentrated water with a boron concentration of 1.98 g / L. Then, 14.53 g of borax product was obtained by evaporation and crystallization with a purity of 96.32%;

[0050] (5) Potassium and sodium recovery: 12.42 kg of the nanofiltered fresh water from step (4) was evaporated. After evaporating 12.13 kg of water, the mixture was filtered to obtain 0.25 kg of mother liquor 1 and 0.78 kg of wet sodium chloride. The wet sodium chloride was dried to obtain 0.65 kg of industrial salt. The mother liquor 1 was then cooled and crystallized. The crystallization was stopped when the mother liquor temperature dropped to 20° C. and filtered to obtain 13.3 g of wet potassium chloride. The wet potassium chloride was dried to obtain 10.2 g of agricultural first-grade potassium chloride.

[0051] Example 2

[0052] The main component data of the underground brine in this embodiment are shown in the following table.

[0053] Table 4 Main components of underground brine lithium extraction tailings

[0054]

[0055] The adsorbent used in this embodiment for lithium adsorption extraction is the product in CN111905700B.

[0056] The method for recovering valuable underground brine resources in this embodiment includes the following steps:

[0057] (1) Pretreatment: 18 kg of underground brine was taken, and 90 g of a 10% PAC solution and 300 g of a 0.3% PAM solution were added by flocculation and sedimentation process, stirred for 30 min, and filtered. Then, 125 g of a 20% sodium sulfate solution was added to the filtrate, stirred for 30 min, and filtered to obtain a barium sulfate precipitate and filtrate 1. Liquid caustic soda was added to the filtrate 1 to adjust the pH to 12, stirred for 30 min, and filtered to obtain a magnesium hydroxide precipitate and filtrate 2. 358 g of a 20% sodium carbonate solution was further added to the filtrate 2, stirred for 30 min, and filtered to obtain calcium carbonate and filtrate 3. The calcium ion concentration of filtrate 3 was 75.6 mg / L, the magnesium ion concentration was 26.8 mg / L, and the barium ion concentration was 6.3 mg / L. The suspended matter was reduced to 19 mg / L.

[0058] (2) Bromine recovery: the pH of the filtrate 3 was adjusted to 2, the voltage of the electrooxidizer power supply was adjusted to 1.5 V for electrooxidation, and the oxidation time was 3 h. After electrooxidation, the brine was blown out with air at a gas-liquid ratio of 120:1 (L / L). The bromine after blowing out was absorbed by 11 g of a sodium hydroxide solution with a mass concentration of 20%, and 1.1 g of a urea solution with a mass concentration of 40% was added at the same time. When the pH of the absorption liquid for absorbing bromine gas dropped to 8, the introduction of bromine gas was stopped to obtain a saturated sodium bromide solution, which was evaporated to obtain a sodium bromide product. After drying, 5.3 g of sodium bromide was obtained with a product purity of 98.16%;

[0059] (3) Lithium recovery: The brine after being blown out in step (2) was adjusted to pH=6 with sodium hydroxide solution, and then selective adsorption of lithium was performed using a continuous ion exchange device. The remaining solution was the lithium adsorption tail liquid; the adsorbent loading amount was 3825 mL, the adsorption rate was 6 BV / h, and pure water was used for desorption at a desorption rate of 3 BV / h to obtain 5.58 kg of selectively adsorbed lithium-rich desorption liquid. The components of the lithium-rich desorption liquid are shown in the following table;

[0060] Table 5 Main components of lithium-rich desorption solution

[0061] Element <![CDATA[Ca 2+ ]]> <![CDATA[K + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Ba 2+ ]]> <![CDATA[Li + ]]> B content(%) 0.0028 0.0168 0.0011 0.1323 0.0023 0.0398 0.0031

[0062] The lithium-rich qualified solution was subjected to reverse osmosis concentration, resulting in 1.5 kg of reverse osmosis concentrated water with a lithium ion concentration of 1.315 g / L; the reverse osmosis concentrated solution was passed through ion exchange resins to remove calcium, magnesium, barium and boron from the solution, respectively. The feed rate of the resin column for removing calcium, magnesium and barium was 3 BV / h, and the calcium ion concentration in the effluent was 6.32 mg / L, the magnesium ion concentration was 2.77 mg / L, and the barium ion concentration was 5.31 mg / L. The feed rate of the boron removal resin was 1.5 BV / h, and the boron concentration in the boron removal effluent was 8.58 mg / L; after boron removal, the solution was evaporated and concentrated to obtain 0.094 kg of concentrated solution with a lithium ion concentration of 20.86 g / L, to which 64.6 g of 20% sodium carbonate solution was added for lithium precipitation reaction at a reaction temperature of 90° C. for a reaction time of 1 hour, to obtain 8.82 g of lithium carbonate with a purity of 99.14%;

[0063] (4) Boron recovery: 18 kg of lithium adsorption tail liquid was taken, and the main component data are shown in the following table;

[0064] Table 6 Main components of underground brine lithium extraction tailings

[0065] Element <![CDATA[K + ]]> <![CDATA[Na + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Li + ]]> <![CDATA[Ba 2+ ]]> B content(%) 0.2027 2.2232 0.0061 0.0008 0.0036 0.0008 0.0368

[0066] The adsorption tail liquid was adjusted to pH 10, and then subjected to primary nanofiltration to obtain 5.625 kg of nanofiltration concentrated water with a boron concentration of 0.96 g / L. The obtained primary nanofiltration concentrated water was further subjected to secondary nanofiltration to obtain 2.531 kg of secondary nanofiltration concentrated water with a boron concentration of 2.26 g / L. Then, 20.26 g of borax product was obtained by evaporation and crystallization with a purity of 95.37%;

[0067] (5) Potassium and sodium recovery: 15.36 kg of the nanofiltered fresh water from step (4) was evaporated. After evaporating 14.15 kg of water, the mixture was filtered to obtain 0.31 kg of mother liquor 1 and 0.87 kg of wet sodium chloride. The wet sodium chloride was dried to obtain 0.73 kg of industrial salt. The mother liquor 1 was then cooled and crystallized. The crystallization was stopped when the mother liquor temperature dropped to 15° C. and filtered to obtain 14.85 g of wet potassium chloride. The wet potassium chloride was dried to obtain 11.64 g of agricultural first-grade potassium chloride.

[0068] Example 3

[0069] The main component data of the underground brine in this embodiment are shown in the following table.

[0070] Table 7 Main components of underground brine lithium extraction tailings

[0071] index <![CDATA[Li + ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Ba 2+ ]]> content(%) 0.0165 2.782 0.2673 0.1568 0.0462 0.1891 index B <![CDATA[Cl - ]]> <![CDATA[Br - ]]> SS content(%) 0.0412 4.968 0.0287 139mg / L

[0072] The adsorbent used in this embodiment for lithium adsorption extraction is the product in CN111905700B.

[0073] The method for recovering valuable underground brine resources in this embodiment includes the following steps:

[0074] (1) Pretreatment: 16 kg of underground brine was taken, and 80 g of 10% PAC solution and 266.7 g of 0.3% PAM solution were added by flocculation sedimentation process, stirred for 30 min and filtered, and then 156 g of 20% sodium sulfate solution was added to the filtrate, stirred and reacted for 30 min, and filtered to obtain barium sulfate precipitate and filtrate 1. Liquid alkali was added to filtrate 1 to adjust the pH to 12, stirred and reacted for 30 min, and filtered to obtain magnesium hydroxide precipitate and filtrate 2. 365 g of 20% sodium carbonate solution was further added to filtrate 2, stirred and reacted for 30 min, and filtered to obtain calcium carbonate and filtrate 3. The calcium ion concentration of filtrate 3 was 67.2 mg / L, the magnesium ion concentration was 23.4 mg / L, and the barium ion concentration was 5.6 mg / L. The suspended matter was removed to 14 mg / L.

[0075] (2) Bromine recovery: the pH of the filtrate 3 was adjusted to 2, the voltage of the electrooxidizer power supply was adjusted to 1.5 V for electrooxidation, and the oxidation time was 3 h. After electrooxidation, the brine was blown out with air at a gas-liquid ratio of 120:1 (L / L). The bromine after blowing out was absorbed by 12 g of a 20% sodium hydroxide solution with a mass concentration of 1.3 g of a 40% urea solution. When the pH of the absorption liquid for absorbing bromine gas dropped to 8, the introduction of bromine gas was stopped to obtain a saturated sodium bromide solution, which was evaporated to obtain a sodium bromide product. After drying, 4.7 g of sodium bromide was obtained with a product purity of 98.24%;

[0076] (3) Lithium recovery: The brine after being blown out in step (2) was adjusted to pH=6 with sodium hydroxide solution, and then selective adsorption and lithium extraction were carried out using a continuous ion exchange device. The remaining solution was the lithium extraction adsorption tail liquid; the adsorbent loading amount was 3825 mL, the adsorption rate was 6 BV / h, and pure water was used for desorption at a desorption rate of 3 BV / h. 4.88 kg of selectively adsorbed lithium-rich desorption liquid was obtained. The components of the lithium-rich desorption liquid are shown in the following table;

[0077] Table 8 Main components of lithium-rich desorption solution

[0078] Element <![CDATA[Ca 2+ ]]> <![CDATA[K + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[Ba 2+ ]]> <![CDATA[Li + ]]> B content(%) 0.0039 0.0236 0.0013 0.213 0.0032 0.0428 0.0042

[0079] The lithium-rich qualified solution was subjected to reverse osmosis concentration, resulting in 1.3 kg of reverse osmosis concentrated water with a lithium ion concentration of 1.63 g / L; the reverse osmosis concentrated solution was passed through ion exchange resins to remove calcium, magnesium, barium and boron from the solution, respectively. The feed rate of the resin column for removing calcium, magnesium and barium was 3 BV / h, and the calcium ion concentration in the effluent was 4.52 mg / L, the magnesium ion concentration was 3.68 mg / L, and the barium ion concentration was 6.24 mg / L. The feed rate of the boron removal resin was 1.5 BV / h, and the boron concentration in the boron removal effluent was 8.58 mg / L; after boron removal, the solution was evaporated and concentrated to obtain 0.106 kg of concentrated solution with a lithium ion concentration of 20.25 g / L, to which 69.2 g of 20% sodium carbonate solution was added for lithium precipitation reaction at a reaction temperature of 90° C. and a reaction time of 1 hour to obtain 9.5 g of lithium carbonate with a purity of 99.18%;

[0080] (4) Boron recovery: 16 kg of lithium adsorption tail liquid was taken, and the main component data are shown in the following table;

[0081] Table 9 Main components of underground brine lithium extraction tailings

[0082] Element <![CDATA[K + ]]> <![CDATA[Na + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Li + ]]> <![CDATA[Ba 2+ ]]> B content(%) 0.237 2.3267 0.0056 0.0007 0.0038 0.0011 0.0379

[0083] The adsorption tail liquid was adjusted to a pH of about 10, and then subjected to primary nanofiltration to obtain 4.85 kg of nanofiltration concentrated water with a boron concentration of 1.03 g / L. The obtained primary nanofiltration concentrated water was further subjected to secondary nanofiltration to obtain 2.19 kg of secondary nanofiltration concentrated water with a boron concentration of 2.35 g / L. Then, 17.43 g of borax product was obtained by evaporation and crystallization with a purity of 96.53%;

[0084] (5) Potassium and sodium recovery: 13.85 kg of the nanofiltered fresh water from step (4) was evaporated. After evaporating 13.75 kg of water, the mixture was filtered to obtain 0.32 kg of mother liquor 1 and 0.85 kg of wet sodium chloride. The wet sodium chloride was dried to obtain 0.71 kg of industrial salt. The mother liquor 1 was then cooled and crystallized. The crystallization was stopped when the mother liquor temperature dropped to 40° C. and filtered to obtain 15.26 g of wet potassium chloride and mother liquor 2. The wet potassium chloride was dried to obtain 12.72 g of agricultural first-grade potassium chloride.

[0085] (6) Secondary lithium recovery: The mother liquor 2 obtained in step (5) was further concentrated to a lithium content of more than 20 g / L, and then lithium precipitation was performed to obtain 156.3 g of lithium carbonate product with a purity of 99.12%. The lithium precipitation operation method was the same as that in step (3).

Claims

1. A method for recovering valuable underground brine resources, characterized in that: The following steps are involved: (1) Pretreatment: A flocculation sedimentation process is used to reduce the suspended solids in the underground brine to below 20 mg / L; the calcium, magnesium, and barium plasma content is reduced to below 100 mg / L, and a step-by-step impurity removal process is used. The specific operation of the step-by-step impurity removal process is as follows: first, sulfate is added to react, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 1 and filtrate 1; filter residue 1 is a barium sulfate precipitate; alkali is added to filtrate 1 to a pH value of 11-12, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 2 and filtrate 2; filter residue 2 is a magnesium hydroxide precipitate; carbonate is added to filtrate 2, and after the reaction is completed, solid-liquid separation is performed to obtain filter residue 3 and filtrate 3, and filter residue 3 is a calcium carbonate precipitate; (2) Bromine recovery: The bromide ions in the filtrate 3 are oxidized to bromine by an electro-oxidation bromine extraction process, and the bromine is blown out to obtain bromine gas and brine from which the bromine is blown out; the bromine gas is then absorbed and concentrated by evaporation to produce sodium bromide product; (3) lithium recovery: the brine from which bromine is blown out in step (2) is adjusted to a certain pH value, and then adsorbed with an adsorbent to obtain an adsorption tail liquid, which is then analyzed by the adsorbent to obtain a lithium-rich qualified liquid, which is then purified by impurity removal to obtain a lithium-rich mother liquor, which is then concentrated to a lithium concentration of more than 20 g / L, and then lithium is precipitated to obtain a lithium carbonate product; (4) Boron recovery: The adsorption tail liquid obtained in step (3) is adjusted to a certain pH, and then separated by nanofiltration membrane to obtain fresh water and concentrated water. The borate ions are retained in the concentrated water side, and the concentrated water is further evaporated and crystallized to produce borax product; (5) Potassium and sodium recovery: The fresh water obtained in the boron recovery unit of step (4) is evaporated and concentrated to precipitate sodium chloride, and solid-liquid separation is performed to obtain sodium chloride precipitate and mother liquor 1. The mother liquor 1 is cooled and crystallized, and solid-liquid separation is performed to obtain potassium chloride product and mother liquor 2.

2. The method for recovering valuable underground brine resources according to claim 1, characterized in that: Step (6) secondary lithium recovery: the mother liquor 2 obtained in step (5) is further concentrated to a lithium content of more than 20 g / L, and then lithium is precipitated to obtain a lithium carbonate product.

3. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (1), the mass content of each element in the raw underground brine is: lithium ion ≥0.004%; bromide ion ≥0.005%; sodium ion ≥1%; potassium ion ≥0.1%; boron content ≥0.01%; calcium ion ≤5%, barium ion ≤1%, and magnesium ion ≤1%.

4. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (1), the specific operation of the pretreatment is as follows: adding polyaluminum chloride and polyacrylamide to underground brine, filtering; adding sodium sulfate to the filtrate, stirring and reacting for more than 30 minutes, filtering to obtain barium sulfate precipitate and filtrate 1; adding sodium hydroxide to the filtrate 1 to adjust the pH to 11-12, stirring and reacting for more than 30 minutes, filtering to obtain magnesium hydroxide and filtrate 2; adding sodium carbonate to the filtrate 2, stirring and reacting for more than 30 minutes, filtering to obtain calcium carbonate and filtrate 3.

5. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (1), polyaluminum chloride and polyacrylamide are added in the form of a solution; the mass concentration of polyaluminum chloride is 5%-15%, and the amount of solute added to the polyaluminum chloride solution is 0.1-1‰ of the underground brine inflow; the mass concentration of polyacrylamide is 1-3‰, and the amount of solute added to the polyacrylamide solution is 0.01-0.1‰ of the underground brine inflow; and / or, in step (1), the amount of sulfate added is a molar ratio of sulfate to barium ion of 1-1.1:1; the amount of carbonate added is a molar ratio of carbonate to calcium ion of 1.0-1.2:

1.

6. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (2), the pH of the water inlet of the electro-oxidizer of the electro-oxidation bromine extraction process is adjusted to 2-4; the electrode material of the electro-oxidizer of the electro-oxidation bromine extraction process is titanium ruthenium iridium anode, and titanium cathode; a constant voltage power supply is used, the oxidation voltage is 1-1.7V, and the electro-oxidation time is 1.5-4h; And / or, in step (2), the bromine solution after electrooxidation is blown out by air with a gas-liquid ratio of 100-160m 3 ∶1L; and / or, the bromine gas after blowing out is absorbed by liquid alkali, and urea is added at a mass ratio of urea added to sodium hydroxide of 1: (4-6) to obtain a sodium bromide solution, which is evaporated and crystallized to obtain a sodium bromide product; And / or, in step (2), when the pH of the absorption liquid to be absorbed bromine gas drops to 8, the introduction of bromine gas is stopped to obtain a saturated sodium bromide solution, which is then evaporated and crystallized to obtain a sodium bromide product.

7. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (3), the pH of the adsorbed water is first adjusted to 5-7; after adsorption, pure water is used for desorption to obtain a qualified lithium-rich solution, and the conductivity of the pure water is required to be below 100 μS / cm; the qualified lithium-rich solution is subjected to reverse osmosis + ion exchange resin to remove calcium, magnesium, barium and boron therein, and the concentration of calcium, magnesium, barium and boron is removed to below 10 mg / L, and then evaporated and concentrated to a lithium ion concentration of more than 20 g / L, and sodium carbonate solution is added to carry out lithium precipitation reaction to obtain a lithium carbonate product.

8. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (3), the adsorption rate of the adsorbent is 3-8 BV / h; the desorption rate is 2-4 BV / h; the impurity removal and purification is nanofiltration to remove calcium, magnesium and barium ions, and then the nanofiltration fresh water is concentrated by reverse osmosis, and the reverse osmosis concentrated water is then subjected to ion exchange to remove calcium, magnesium, barium and boron, and the purified qualified liquid is then concentrated by evaporation to Li ≥ 20 g / L; the temperature of the lithium precipitation reaction is 80-90 ° C, and the reaction time is 0.5-2h; the mass concentration of the sodium carbonate solution is 15-25%.

9. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (4), boron resources are recovered by membrane method + evaporation process. The pH of the adsorption tail liquid is adjusted to 9-11, and then the borate in the adsorption tail liquid is intercepted to the concentrated water end by nanofiltration membrane. The concentrated water is then evaporated and crystallized to produce borax.

10. The method for recovering valuable underground brine resources according to claim 1 or 2, characterized in that: In step (5), potassium and sodium salts are separated by high-temperature sodium precipitation and cooling crystallization to obtain sodium chloride and potassium chloride products; when the fresh water is evaporated and concentrated to a potassium concentration in the mother liquor of 100-120 g / L, heating is stopped, and the mother liquor 1 is filtered to obtain sodium chloride and mother liquor 1, and the mother liquor 1 is cooled to 5-40° C. to precipitate potassium chloride, and filtered to obtain mother liquor 2 and potassium chloride products.

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