A method for recovering valuable resources from underground brine

Abstract

A method for recovering valuable resources in underground brine, comprising the following steps: (1) pretreatment; (2) bromine recovery; (3) lithium recovery; (4) boron recovery; (5) potassium and sodium recovery.The valuable resources in underground brine are fully recovered and utilized; the valuable resources in underground brine are recovered and utilized, which provides strong support for widening the types and reserves of lithium, bromine, potassium and sodium mineral resources in China.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for recovering wastewater resources, in particular to a method for recovering valuable resources of underground brine. BACKGROUND

[0002] The common classification of brine is classified according to the burial conditions, which can be divided into two categories of surface salt lake brine and underground brine. The surface salt lake brine is distributed in some lakes in arid regions, for example, the water mineralization degree of Dabusun Lake in Qarhan Salt Lake in Qaidam Basin of China is more than 300g / L, and a large amount of salt lake brine is also distributed in Great Salt Lake in Utah, USA. The underground brine refers to the brine distributed in the brine storage layer in the deep part (usually hundreds to thousands of meters deep) of the sedimentary basin, for example, the deep underground brine in the middle of Sichuan Basin and the deep underground brine in Jiangling depression of Jianghan Basin.

[0003] At present, the salt lake brine resources have been large-scale exploited and used, such as Qarhan Salt Lake, and the exploitation and utilization degree of underground brine resources is still low. The underground brine mainly includes produced water of oil and gas fields and deep layer salt mining brine. The underground brine is rich in various useful components, such as bromine, sodium, iodine, boron, potassium, magnesium, lithium and other elements, and is a valuable resource. However, the utilization rate of underground brine resources is still low at present, which is mainly restricted by the complex composition of underground brine and the difficulty of utilization.

[0004] Therefore, it is beneficial to realize resource quantity implementation and sustainable development to develop a low-cost and green underground brine valuable resource recovery method. SUMMARY

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

[0006] The technical solution adopted by the present application to solve the technical problem is as follows:

[0007] A method for recovering valuable resources of underground brine, comprising the following steps:

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

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

[0010] (3) Lithium recovery (lithium extraction by adsorption): after the brine from which bromine is blown out in step (2) is adjusted to a certain pH value, an adsorbent is used for adsorption, and after adsorption, an adsorption tail liquid is obtained, and a lithium-rich qualified liquid is obtained by desorption of the adsorbent, and the lithium-rich qualified liquid is purified by removing impurities to obtain a lithium-rich mother liquor, which is concentrated to a lithium concentration of 20 g / L or more, and then lithium is precipitated to obtain lithium carbonate product;

[0011] (4) Boron recovery (boron resource recovery by membrane method + evaporation process): after the adsorption tail liquid obtained in step (3) is adjusted to a certain pH value, a nanofiltration membrane is used for separation to obtain fresh water and concentrated water, and borate is 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 from the boron recovery unit in step (4) is evaporated and concentrated, and sodium chloride is precipitated, and solid-liquid separation is performed to obtain sodium chloride precipitate and mother liquor 1, and 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 secondary lithium recovery step (6) can also be added: the mother liquor 2 obtained in step (5) is further concentrated to a lithium concentration of 20 g / L or more, and then lithium is precipitated to obtain lithium carbonate product. The method of lithium precipitation operation is the same as that in step (3).

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

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

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

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

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

[0019] Preferably, in step (2), the bromine solution after electro-oxidation is blown out, and air is used for blowing, with a gas-liquid ratio of 100-160 m 3 : 1 L. After blowing, the bromine gas is absorbed by liquid caustic soda (mass concentration of 10-32%), and urea is added, with a mass ratio of urea to sodium hydroxide of 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 for the bromine gas is reduced to 8, the bromine gas is stopped, and a saturated sodium bromide solution is obtained, which is then evaporated and crystallized to obtain a sodium bromide product.

[0021] Preferably, in step (3), lithium is extracted using an adsorption process. The adsorbent for lithium extraction can be the product in CN111905700B, or other adsorbents for lithium extraction. The adsorption inflow is first adjusted to a pH of 5-7 (preferably pH=6). After adsorption, the lithium-rich qualified liquid is desorbed with pure water, and the conductivity of the pure water is required to be below 100 μS / cm (preferably below 50 μS / cm); the lithium-rich qualified liquid is treated by reverse osmosis + ion exchange resin to remove calcium, magnesium, barium and boron, and the concentration of calcium, magnesium, barium and boron is reduced to below 10 mg / L, and then evaporated and concentrated to a lithium ion concentration of above 20 g / L, and sodium carbonate solution is added for 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 purification is nanofiltration to remove calcium, magnesium and barium ions, then nanofiltration of fresh water is concentrated by reverse osmosis, and the concentrated water of reverse osmosis is subjected to ion exchange to remove calcium, magnesium, barium and boron, and the purified qualified liquid is concentrated to Li≥20 g / L by evaporation. The temperature of the lithium precipitation reaction is 80-90℃, and the reaction time is 0.5-2h; the mass concentration of the sodium carbonate solution is 15-25%.

[0023] Preferably, in step (3), the nanofiltration membrane, reverse osmosis membrane, ion exchange resin 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), the boron resource is recovered by membrane method + evaporation process, the pH of the adsorption tail liquid is adjusted to 9-11 (preferably pH=10), then the nanofiltration membrane is used to retain the borate in the adsorption tail liquid to the concentrated water end, and the concentrated water is subjected to evaporation crystallization to produce borax.

[0025] Preferably, in step (5), the method of high-temperature sodium precipitation and low-temperature potassium crystallization is used for potassium-sodium separation to obtain sodium chloride and potassium chloride products. When the fresh water is evaporated and concentrated to the potassium concentration in the mother liquor being 100-120 g / L, heating is stopped, filtration is performed, sodium chloride and mother liquor 1 are obtained, the mother liquor 1 is subjected to low-temperature potassium precipitation, the temperature is lowered to 5-40℃, potassium chloride is precipitated, filtration is performed, mother liquor 2 and potassium chloride products are obtained.

[0026] The present application first removes suspended solids and impurity ions such as calcium, magnesium and barium, which can effectively protect the electrode material of the electro-oxidation bromine extraction equipment, avoid electrode fouling, and is beneficial to prolonging the service life of the electrode; the bromine element extraction is mainly carried out by the electro-oxidation bromine extraction process, the pH of the water is adjusted to 2-4, then the pH is adjusted to 5-7 before the effluent is adsorbed, and the pH of the brine after electro-oxidation will rise to 3-4, so the bromine resource recovery can reduce the amount of alkali.

[0027] The present application can fully recover and utilize the valuable resources in underground brine, realize comprehensive utilization, step (1) of the present application removes suspended solids and divalent impurity ions in water to prepare for electro-oxidation bromine extraction; in step (2), the bromine element is extracted by the electro-oxidation bromine extraction process, and industrial sodium bromide products are prepared. In step (3), the lithium element is extracted by the adsorption lithium extraction process, and industrial-grade lithium carbonate products are prepared after impurity removal purification and concentration; in step (4), the boron element is separated and concentrated by the membrane process to prepare industrial borax products; in step (5), the obtained sodium chloride precipitate is dried to obtain first-grade industrial salt; the obtained potassium chloride precipitate is dried to obtain agricultural first-grade potassium chloride products. In step (6), the lithium concentration is increased after evaporation and concentration, the lithium resource is fully recovered and utilized by further evaporation and concentration to prepare industrial-grade lithium carbonate products.

[0028] The present application has the following beneficial effects:

[0029] 1. The valuable resources in underground brine are fully recycled and utilized;

[0030] 2. The recycling and utilization of valuable resources in underground brine provide strong support for expanding the types and reserves of lithium, bromine, potassium, and sodium mineral resources in China. DETAILED DESCRIPTION

[0031] The present application will be further described below in conjunction with specific embodiments.

[0032] The raw materials, products, and equipment used in the embodiments of the present application are obtained through conventional commercial channels unless otherwise specified.

[0033] In this specification, the percentage refers to the mass percentage unless otherwise specified.

[0034] Example 1

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

[0036] Table 1 Main components of underground brine

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

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

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

[0040] (1) Pretreatment: Take 15 kg of underground brine, use flocculation and sedimentation process, add 75 g of PAC solution with a mass concentration of 10%, 250 g of PAM solution with a mass concentration of 0.3%, stir for 30 min, then filter, then add 104 g of sodium sulfate solution with a mass concentration of 20% to the filtrate, stir and react for 30 min, then filter to obtain barium sulfate precipitate and filtrate 1, add liquid caustic to the filtrate 1 to adjust the pH to 12, stir and react for 30 min, then filter to obtain magnesium hydroxide precipitate and filtrate 2, continue to add 300 g of sodium carbonate solution with a mass concentration of 20% to the filtrate 2, stir and react for 30 min, then filter to obtain calcium carbonate and filtrate 3, the calcium ion concentration in the filtrate 3 is 82.3 mg / L, the magnesium ion concentration is 22.4 mg / L, the barium ion concentration is 5.6 mg / L, and the suspended solids are reduced to 12 mg / L;

[0041] (2) Bromine recovery: adjust the pH of filtrate 3 to 2, adjust the voltage of the steady voltage power supply of the electro-oxidizer to 1.5V to perform electro-oxidation, and oxidize for 3h. After electro-oxidation, air is blown into the brine according to a gas-liquid ratio of 120:1 (L / L). The bromine gas after blowing is absorbed by 11g of a 20% sodium hydroxide solution, and 1.3g of a 40% urea solution is added at the same time. When the pH of the absorption liquid of the absorbed bromine gas is reduced to 8, the bromine gas is stopped, and a saturated sodium bromide solution is obtained. Evaporation obtains sodium bromide product, which is dried to obtain 4.1g of sodium bromide with a purity of 98.73%;

[0042] (3) Lithium recovery: adjust the pH of the brine after blowing in step (2) to 6 with a sodium hydroxide solution, and then use a continuous ion exchange device to selectively adsorb and extract lithium. The remaining solution is the lithium extraction adsorption tail liquid. The adsorbent loading capacity is 3825mL, the adsorption rate is 5BV / h, the desorption uses pure water, and the desorption rate is 3BV / h. A lithium-rich desorption liquid obtained by selective adsorption is 4.856kg, and the composition of the lithium-rich desorption liquid is shown in the following table;

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

[0044] Ingredient Ca 2+ ]]> K + ]]> Mg 2+ ]]> Na + ]]> Ba 2+ ]]> Li + ]]> B Content (%) 0.0023 0.0154 0.0008 0.1451 0.0026 0.0425 0.0027

[0045] The lithium-rich qualified liquid is concentrated by reverse osmosis. The reverse osmosis concentrated water is 1.350kg, and the lithium ion concentration is 1.266g / L. The reverse osmosis concentrated liquid is passed through ion exchange resin to remove calcium, magnesium, barium and boron in the solution. The feed rate of the calcium, magnesium and barium removal resin column is 2BV / h, the calcium ion concentration in the effluent is 5.36mg / L, the magnesium ion concentration is 2.57mg / L, and the barium ion concentration is 4.54mg / L. The feed rate of the boron removal resin is 1.5BV / h, and the boron concentration in the effluent after boron removal is 8.58mg / L. After boron removal, evaporation concentration is performed to obtain a concentrated liquid of 0.091kg, a lithium ion concentration of 20.62g / L, and 60.3g of a 20% sodium carbonate solution is added to perform lithium precipitation reaction. The reaction temperature is 90℃, and the reaction time is 1h. 8.36g of lithium carbonate with a purity of 99.21% is obtained;

[0046] (4) Boron recovery: take 15kg of lithium extraction adsorption tail liquid, and the main component data is shown in the following table 3;

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

[0048] Ingredient K + ]]> Na + ]] Ca 2+ ]] Mg 2+ ]]> Li + ]] Ba 2+ ]] B Content (%) 0.2134 2.2650 0.0053 0.0007 0.0032 0.0006 0.0315

[0049] The adsorption tail liquid is 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 is subjected to secondary nanofiltration to obtain 2.069 kg of secondary nanofiltration concentrated water with a boron concentration of 1.98 g / L. Then, through evaporation crystallization, 14.53 g of borax product with a purity of 96.32% is obtained.

[0050] (5) Potassium and sodium recovery: The nanofiltration dilute water 12.42 kg of step (4) is evaporated. After 12.13 kg of water is evaporated, filtration is performed to obtain 0.25 kg of mother liquor 1 and 0.78 kg of wet sodium chloride. The wet sodium chloride is dried to obtain 0.65 kg of industrial salt. The mother liquor 1 is subjected to cooling crystallization. The temperature of the mother liquor is lowered to 20°C and stopped. Filtration is performed to obtain 13.3 g of wet potassium chloride. The wet potassium chloride is dried to obtain 10.2 g of agricultural primary potassium chloride.

[0051] Example 2

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

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

[0054]

[0055] The adsorbent used in the lithium extraction of this example is the product in CN111905700B.

[0056] The method for recovering valuable resources from the underground brine of this example includes the following steps:

[0057] (1) Pretreatment: Take 18 kg of underground brine, use flocculation and sedimentation process, add 90 g of PAC solution with a mass concentration of 10%, 300 g of PAM solution with a mass concentration of 0.3%, stir for 30 min, then filter, then add 125 g of sodium sulfate solution with a mass concentration of 20% to the filtrate, stir and react for 30 min, then filter to obtain barium sulfate precipitate and filtrate 1, add liquid caustic to the filtrate 1 to adjust the pH to 12, stir and react for 30 min, then filter to obtain magnesium hydroxide precipitate and filtrate 2, continue to add 358 g of 20% sodium carbonate solution to the filtrate 2, stir and react for 30 min, then filter to obtain calcium carbonate and filtrate 3, the calcium ion concentration in the filtrate 3 is 75.6 mg / L, the magnesium ion concentration is 26.8 mg / L, the barium ion concentration is 6.3 mg / L, and the suspended solids are reduced to 19 mg / L;

[0058] (2) Bromine recovery: adjust the pH of filtrate 3 to 2, adjust the voltage of the steady voltage power supply of the electro-oxidizer to 1.5V to perform electro-oxidation, and oxidize for 3h. After electro-oxidation, air is blown into the brine according to a gas-liquid ratio of 120:1 (L / L). The bromine gas after blowing is absorbed by 11g of a 20% sodium hydroxide solution, and 1.1g of a 40% urea solution is added at the same time. When the pH of the absorption liquid of the absorbed bromine gas is reduced to 8, the bromine gas is stopped, a saturated sodium bromide solution is obtained, and sodium bromide is obtained by evaporation. After drying, 5.3g of sodium bromide is obtained, and the purity of the product is 98.16%;

[0059] (3) Lithium recovery: adjust the pH of the brine after blowing in step (2) to about 6 by using a sodium hydroxide solution, and then use a continuous ion exchange device to selectively adsorb and extract lithium. The remaining solution is the lithium extraction adsorption tail liquid. The loading capacity of the adsorbent is 3825mL, the adsorption rate is 6BV / h, the desorption is performed by using pure water, and the desorption rate is 3BV / h. A lithium-rich desorption liquid obtained by selective adsorption is 5.58kg, and the components of the lithium-rich desorption liquid are shown in the following table;

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

[0061] Ingredient Ca 2+ ]] K + ]]> Mg 2+ ]]> Na + ]]> Ba 2+ ]]> Li + ]]> B Content (%) 0.0028 0.0168 0.0011 0.1323 0.0023 0.0398 0.0031

[0062] The lithium-rich qualified liquid is concentrated by reverse osmosis. The reverse osmosis concentrated water is 1.5kg, and the lithium ion concentration is 1.315g / L. The reverse osmosis concentrated liquid is removed from the solution by ion exchange resin to remove calcium, magnesium, barium and boron. The feed rate of the calcium, magnesium and barium removal resin column is 3BV / h, the calcium ion concentration in the effluent is 6.32mg / L, the magnesium ion concentration is 2.77mg / L, and the barium ion concentration is 5.31mg / L. The feed rate of the boron removal resin is 1.5BV / h, and the boron concentration in the effluent after boron removal is 8.58mg / L. After boron removal, evaporation concentration is performed to obtain a concentrated liquid of 0.094kg, and the lithium ion concentration is 20.86g / L. Then, 64.6g of 20% sodium carbonate solution is added to perform lithium precipitation reaction, the reaction temperature is 90℃, and the reaction time is 1h. Lithium carbonate 8.82g is obtained, and the purity is 99.14%;

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

[0064] Table 6 Main components of the lithium extraction tail liquid of the underground brine

[0065] Ingredient K + ]]> Na + ]] Ca 2+ ]] Mg 2+ ]] Li + ]] Ba 2+ ]] B Content (%) 0.2027 2.2232 0.0061 0.0008 0.0036 0.0008 0.0368

[0066] The adsorption tail liquid is 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 is subjected to secondary nanofiltration to obtain 2.531 kg of secondary nanofiltration concentrated water with a boron concentration of 2.26 g / L. Then, through evaporation crystallization, 20.26 g of borax product with a purity of 95.37% is obtained.

[0067] (5) Potassium and sodium recovery: The nanofiltration dilute water 15.36 kg of step (4) is subjected to evaporation. After 14.15 kg of water is evaporated, filtration is performed to obtain 0.31 kg of mother liquor 1 and 0.87 kg of wet sodium chloride. The wet sodium chloride is dried to obtain 0.73 kg of industrial salt. The mother liquor 1 is subjected to cooling crystallization. The temperature of the mother liquor is stopped at 15℃. Filtration is performed to obtain 14.85 g of wet potassium chloride. The wet potassium chloride is dried to obtain 11.64 g of agricultural primary potassium chloride.

[0068] Example 3

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

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

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

[0072] The adsorbent used in the lithium extraction of this example is the product in CN111905700B.

[0073] The method for recovering valuable resources from the underground brine of this example includes the following steps:

[0074] (1) Pretreatment: Take 16 kg of underground brine, use flocculation and sedimentation process, add 80 g of 10% PAC solution and 266.7 g of 0.3% PAM solution, stir for 30 min, then filter, then add 156 g of 20% sodium sulfate solution to the filtrate, stir for 30 min, then filter to obtain barium sulfate precipitate and filtrate 1, add liquid caustic to the filtrate 1 to adjust the pH to 12, stir for 30 min, then filter to obtain magnesium hydroxide precipitate and filtrate 2, continue to add 365 g of 20% sodium carbonate solution to the filtrate 2, stir for 30 min, then filter to obtain calcium carbonate and filtrate 3, the calcium ion concentration in the filtrate 3 is 67.2 mg / L, the magnesium ion concentration is 23.4 mg / L, and the barium ion concentration is 5.6 mg / L, and the suspended solids are reduced to 14 mg / L;

[0075] (2) Bromine recovery: adjust the pH of filtrate 3 to 2, adjust the voltage of the steady voltage power supply of the electro-oxidizer to 1.5 V to perform electro-oxidation, and oxidize for 3 h. After electro-oxidation, air is blown into the brine according to a gas-liquid ratio of 120:1 (L / L). The bromine gas after blowing is absorbed by 12 g of a 20% sodium hydroxide solution with a mass concentration of 20%, and 1.3 g of a urea solution with a mass concentration of 40% is added at the same time. When the pH of the absorption liquid of the absorbed bromine gas is reduced to 8, the bromine gas is stopped from being introduced. A saturated sodium bromide solution is obtained, and sodium bromide is obtained by evaporation. After drying, 4.7 g of sodium bromide is obtained, and the purity of the product is 98.24%;

[0076] (3) Lithium recovery: the brine after blowing in step (2) is adjusted to pH = 6 by a sodium hydroxide solution, and then selective adsorption is performed by using a continuous ion exchange device to extract lithium. The remaining solution is the lithium extraction adsorption tail liquid. The loading amount of the adsorbent is 3825 mL, the adsorption rate is 6 BV / h, the elution is performed by using pure water, and the elution rate is 3 BV / h. A lithium-rich desorption liquid obtained by selective adsorption is 4.88 kg, and the components of the lithium-rich desorption liquid are shown in the following table.

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

[0078] Ingredient Ca 2+ ]]> K + ]]> Mg 2+ ]]> Na + ]]> Ba 2+ ]] Li + ]]> B Content (%) 0.0039 0.0236 0.0013 0.213 0.0032 0.0428 0.0042

[0079] The lithium-rich qualified liquid is concentrated by reverse osmosis. The reverse osmosis concentrated water is 1.3 kg, and the lithium ion concentration is 1.63 g / L. The reverse osmosis concentrated liquid is removed from the solution by ion exchange resin to remove calcium, magnesium, barium and boron. The feed rate of the calcium, magnesium and barium removal resin column is 3 BV / h, the calcium ion concentration in the effluent is 4.52 mg / L, the magnesium ion concentration is 3.68 mg / L, and the barium ion concentration is 6.24 mg / L. The feed rate of the boron removal resin is 1.5 BV / h, and the boron concentration in the effluent after boron removal is 8.58 mg / L. After boron removal, evaporation concentration is performed to obtain a concentrated liquid of 0.106 kg, and the lithium ion concentration is 20.25 g / L. Then, 69.2 g of a 20% sodium carbonate solution is added to perform lithium precipitation reaction. The reaction temperature is 90°C, and the reaction time is 1 h. Lithium carbonate 9.5 g is obtained, and the purity is 99.18%;

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

[0081] Table 9 Main components of the lithium extraction tail liquid of the underground brine

[0082] Ingredient K + ]]> Na + ]] Ca 2+ ]]> Mg 2+ ]] Li + ]]> Ba 2+ ]] B Content (%) 0.237 2.3267 0.0056 0.0007 0.0038 0.0011 0.0379

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

[0084] (5) Potassium and sodium recovery: the nanofiltration dilute water 13.85 kg of step (4) is evaporated, after 13.75 kg of water is evaporated, filtration is carried out to obtain 0.32 kg of mother liquor 1 and 0.85 kg of wet sodium chloride, the wet sodium chloride is dried to obtain 0.71 kg of industrial salt; the mother liquor 1 is subjected to cooling crystallization, the temperature of the mother liquor is stopped at 40℃, filtration is carried out to obtain 15.26 g of wet potassium chloride and mother liquor 2, the wet potassium chloride is dried to obtain 12.72 g of agricultural primary potassium chloride.

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

Claims

1. A method for recovering valuable resources from a subsurface brine, characterized in that, Comprising the following steps: (1) Pretreatment: adopt flocculation sedimentation process to reduce the suspended solids in the underground brine to below 20 mg / L; reduce the content of calcium, magnesium and barium ions to below 100 mg / L, adopt step-by-step impurity removal process, the specific operation of the step-by-step impurity removal process is as follows: first add sulfate reaction, after the reaction is completed, solid-liquid separation is performed to obtain filter residue 1 and filtrate 1; the filter residue 1 is barium sulfate precipitate; add alkali to the filtrate 1 until the pH value is 11-12, after the reaction is completed, solid-liquid separation is performed to obtain filter residue 2 and filtrate 2; the filter residue 2 is magnesium hydroxide precipitate; add carbonate to the filtrate 2, after the reaction is completed, solid-liquid separation is performed to obtain filter residue 3 and filtrate 3, the filter residue 3 is calcium carbonate precipitate; In step (1), the mass content of each element in the raw material underground brine is: lithium ion ≥0.004%; bromine ion ≥0.005%; sodium ion ≥1%; potassium ion ≥0.1%; boron content ≥0.01%; calcium ion ≤5%, barium ion ≤1%, magnesium ion ≤1%; (2) Bromine recovery: through the electric oxidation bromine extraction process, the bromine ion in the filtrate 3 is oxidized into bromine, the bromine is blown out to obtain bromine gas and brine in which the bromine is blown out; the bromine gas is prepared into sodium bromide product through absorption and evaporation concentration process; In step (2), the water pH of the electric oxidation device of the electric oxidation bromine extraction process is adjusted to 2-4; the electrode material of the electric oxidation device of the electric oxidation bromine extraction process is titanium ruthenium iridium for the anode and titanium for the cathode; the constant voltage power supply is powered, the oxidation voltage is 1-1.7 V, and the electric oxidation time is 1.5-4 h; In step (2), the bromine solution after electro-oxidation is blown out, air is used for blowing, the gas-liquid ratio is 100-160 m 3 :1L; the bromine gas after blowing is absorbed by liquid alkali, urea is added, the mass ratio of urea to sodium hydroxide is 1:(4-6), a sodium bromide solution is obtained, and the sodium bromide product is obtained by evaporation crystallization. In step (2), when the pH of the absorption liquid for absorbing the bromine gas is reduced to 8, the bromine gas is stopped from being introduced, a saturated sodium bromide solution is obtained, and the saturated sodium bromide solution is subjected to evaporation crystallization to obtain sodium bromide product; (3) Lithium recovery: after the brine in which the bromine is blown out in step (2) is adjusted to a certain pH value, an adsorbent is used for adsorption, an adsorption tail liquid is obtained after adsorption, a lithium-rich qualified liquid is obtained by desorption of the adsorbent, the lithium-rich qualified liquid is purified by removing impurities to obtain lithium-rich mother liquor, the lithium-rich mother liquor is concentrated to a lithium concentration of 20 g / L or more, and then lithium is precipitated to obtain lithium carbonate product; (4) Boron recovery: after the adsorption tail liquid obtained in step (3) is adjusted to a certain pH, the adsorption tail liquid is separated by using a nanofiltration membrane to obtain fresh water and concentrated water, and the borate is retained on the concentrated water side, the concentrated water is further evaporated and crystallized to produce borax product; (5) Potassium and sodium recovery: the fresh water obtained from the boron recovery unit in step (4) is evaporated and concentrated, sodium chloride is precipitated, solid-liquid separation is performed to obtain sodium chloride precipitate and mother liquor 1, the mother liquor 1 is cooled and crystallized, solid-liquid separation is performed to obtain potassium chloride product and mother liquor 2.

2. The method of recovery of valuable resources from underground brines 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 concentration of 20 g / L or more, and then lithium is precipitated to obtain lithium carbonate product.

3. The method for recovery of valuable resources from underground brines according to claim 1 or 2, characterized in that, In step (1), the specific operation of the pretreatment is as follows: after polyaluminum chloride and polyacrylamide are added to the underground brine, filtration is performed; sodium sulfate is added to the filtrate, stirred for more than 30 min, filtered to obtain barium sulfate precipitate and filtrate 1; sodium hydroxide is added to the filtrate 1 to adjust the pH to 11-12, stirred for more than 30 min, filtered to obtain magnesium hydroxide and filtrate 2; sodium carbonate is added to the filtrate 2, stirred for more than 30 min, filtered to obtain calcium carbonate and filtrate 3.

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

1.

5. The method for recovery of valuable resources from underground brines according to claim 1 or 2, characterized in that, In step (3), the adsorption inflow is first adjusted to pH 5-7; after adsorption, the lithium-rich qualified liquid is desorbed by using pure water, and the conductivity of the pure water is required to be below 100 μS / cm; the lithium-rich qualified liquid is treated by reverse osmosis + ion exchange resin to remove calcium, magnesium, barium and boron therein, the concentration of calcium, magnesium, barium and boron is reduced to below 10 mg / L, and then evaporation concentration is carried out to a lithium ion concentration of above 20 g / L, sodium carbonate solution is added to carry out lithium precipitation reaction, and lithium carbonate product is obtained.

6. The method for recovery of valuable resources from underground brines 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 are nanofiltration to remove calcium, magnesium and barium ions, then nanofiltration fresh water is concentrated by reverse osmosis, the reverse osmosis concentrated water is subjected to ion exchange to remove calcium, magnesium, barium and boron, and the purified qualified liquid is concentrated by evaporation to Li≥20 g / L; the temperature of the lithium precipitation reaction is 80-90℃, the reaction time is 0.5-2 h; the mass concentration of the sodium carbonate solution is 15-25%.

7. The method for recovery of valuable resources from underground brines according to claim 1 or 2, characterized in that, In step (4), the boron resource is recovered by the membrane method + evaporation process, the pH of the adsorption tail liquid is adjusted to 9-11, then the nanofiltration membrane is used to retain the borate in the adsorption tail liquid to the concentrated water end, and the concentrated water is subjected to evaporation crystallization to produce borax.

8. The method for recovery of valuable resources from underground brines according to claim 1 or 2, characterized in that, In step (5), the method of high-temperature sodium precipitation and cooling crystallization potassium is used to carry out potassium-sodium separation, and sodium chloride and potassium chloride products are obtained; when the fresh water is evaporated and concentrated to a potassium concentration of 100-120 g / L in the mother liquor, heating is stopped, filtration is carried out, sodium chloride and mother liquor 1 are obtained, and the mother liquor 1 is cooled to 5-40℃ to precipitate potassium chloride, filtration is carried out, mother liquor 2 and potassium chloride product are obtained.

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