Method for preparing gypsum through underground regulation and control of salt-alkali combined cycle

Abstract

The invention belongs to the technical field of mining, salt manufacturing and alkali manufacturing industries, and particularly discloses a method for preparing gypsum through underground regulation and control of salt and alkali combined circulation. Calcium chloride in alkali manufacturing waste liquid and mirabilite resources in nitrate type salt mine are subjected to denitration treatment on the ground, so that the calcium chloride resources in alkali manufacturing calcium liquid are converted into calcium sulfate products, and the calcium sulfate products are recycled. The method not only can fully recover the mirabilite resource in the normally mined or abandoned mirabilite type salt mine resource and improve the utilization rate of the rock salt resource, but also solves the problem that the salt-alkali-calcium combined cycle production process is difficult to exert large-scale economic benefits due to the market capacity of calcium chloride products, is a supplement and improvement on the existing salt-alkali-calcium combined cycle process, and has a wide application prospect. Meanwhile, based on establishment of an injection well model, a quick calculation formula for regulating and controlling brine mining is provided, and the participation reaction amount of alkali-making calcium liquid, salt-making mother liquid and nitrate type ore brine for brine mining can be conveniently, quickly and accurately controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of mining, salt making and alkali making industries, and relates to a method for preparing gypsum by regulating and controlling salt-alkali combined circulation underground. Background Art

[0002] In order to extend the salt chemical industry chain, Jiangsu Suyan Jingshen Co., Ltd. and Jiangsu Salt Industry Research Institute Co., Ltd. conducted in-depth research on the ammonia-soda alkali production process and the well salt production process, and proposed the "Salt, alkali and calcium combined circulation process using well salt" (patent number: ZL201110006672.X). This process is based on well salt mining, with the ammonia-soda alkali production process as the main body, and auxiliary salt production (including brine refining) and calcium production processes. It organically combines the ammonia-soda alkali production process and well salt production, and solves the major technical problems of the treatment of waste liquid and waste residue of the ammonia-soda process, which not only saves energy and reduces production costs, but also reduces waste emissions, maximizes the comprehensive utilization rate of mineral salt resources, and achieves the purpose of circular economy and clean production.

[0003] However, this process requires a large amount of calcium chloride as a byproduct, and the market capacity of calcium chloride is limited, which restricts the scale of consumption of alkali calcium liquid, and then restricts the scale of alkali production, making it difficult to give full play to the scale economy benefits of the saline-alkali calcium circulation process. Therefore, based on the saline-alkali calcium circulation process, it is urgent to explore a process method with mature and reliable technology and good economic benefits to consume alkali calcium liquid, while not affecting the saline-alkali calcium circulation process, so as to maximize the comprehensive utilization of alkali calcium liquid and rock salt resources and realize circular economy and clean production. Summary of the invention

[0004] In order to solve the problems existing in the prior art and meet the needs of developing salt chemical industry and extending the industrial chain, the present invention proposes a method for preparing gypsum by underground regulation of salt-alkali combined circulation based on the research of nitrate salt mine resource mining method and salt-alkali calcium combined circulation process. The present invention utilizes the characteristics that alkali calcium liquid contains a large amount of calcium chloride and nitrate rock salt contains a certain amount of sodium sulfate, takes nitrate salt mine as a regulation reactor, couples ground denitrification, purification and decalcification technologies, and uses reasonable process routes and process parameters to convert calcium chloride in alkali calcium liquid and sodium sulfate in nitrate salt mine into gypsum and low-nitrate ore brine respectively, basically realizing 100% recycling of sodium sulfate and sodium chloride resources, and at the same time, low-nitrate brine is used as raw material for salt and alkali production, realizing salt, alkali, gypsum combined circulation and clean production, and promoting sustainable development of production.

[0005] The present invention is achieved through the following technical solutions:

[0006] The invention controls a reasonable reaction blending ratio to fully mix the alkali-making calcium liquid with the nitrate-type brine mined from the water-mined nitrate-type salt mine and the salt-making mother liquor on the ground for reaction; the generated dihydrate gypsum is filtered through sedimentation, washed and dried to form a gypsum product; the generated unsaturated brine is injected into the nitrate-type mine group; the nitrate-type mine dissolution cavity is used as a control reaction device for adjusting the brine saturation and sulfate content; the sodium chloride and sodium sulfate in the nitrate-type salt mine group are dissolved; a small amount of calcium chloride in the unsaturated brine reacts chemically with the dissolved sodium sulfate in the salt mine; low-nitrate saturated brine (sulfate content is about 0-15 g / L) is mined; the brine is purified and decalcified to form refined low-nitrate saturated brine; according to the different matching degrees of salt making and alkali making, there are two process routes: one is that the salt making and alkali making are completely matched, and the low-nitrate brine is all used for salt making and alkali making. A part of the refined low-nitrate saturated brine enters the salt-making device for evaporation and crystallization to produce refined salt and salt-making mother liquor. The salt-making mother liquor is returned to participate in the denitration reaction together with the nitrate-type brine of the alkali-making calcium liquid. Another part of the refined low-nitrate saturated brine is used as the raw material for alkali-making to produce soda ash; Second, there is a mismatch between salt-making and alkali-making, and part of the refined low-nitrate saturated brine is sold externally. A part of the refined low-nitrate saturated brine is evaporated and crystallized in the salt-making device to produce refined salt and salt-making mother liquor. The salt-making mother liquor is returned to participate in the denitration reaction together with the nitrate-type brine of the alkali-making calcium liquid. Another part of the refined low-nitrate saturated brine is used as the raw material for alkali-making to produce soda ash, and the remaining refined low-nitrate saturated brine is sold externally for use by downstream chemical customers.

[0007] Specifically, a method for preparing gypsum by regulating salt-alkali combined circulation underground comprises the following steps:

[0008] S1: The alkali-making calcium solution, the salt-making mother solution and the nitrate-type brine from water-soluble mining are subjected to two-stage coarse filtration and one-stage fine filtration to remove particulate insoluble impurities, and then the alkali-making calcium solution, the salt-making mother solution and the nitrate-type brine are filtered through an inorganic ceramic membrane filter to obtain refined alkali-making calcium solution, refined salt-making mother solution and refined nitrate-type brine;

[0009] S2: Detect the content of calcium chloride and sodium chloride in refined alkali calcium solution, sodium chloride and sodium sulfate in refined salt mother liquor, sodium chloride and sodium sulfate in refined nitrate-type brine, and the average content ratio of sodium sulfate to sodium chloride in the nitrate-type salt mine as a control reactor;

[0010] S3: Determine the content of sodium chloride and sulfate in the refined low-nitrate saturated brine to be produced, substitute the results of S2 detection into the precise control model of injection well brine production, and calculate the matching amount of refined alkali calcium solution, refined salt mother liquor, and refined nitrate-type brine participating in the denitrification reaction;

[0011] S4: According to the result calculated in S3, the refined nitrate-type brine, the refined salt-making mother liquor and the refined alkali-making calcium liquor are continuously and evenly mixed with the circulating liquid under the action of external circulation lifting in accordance with the calculated matching ratio (the amount of circulating liquid is determined by 3 to 10 times the flow rate of the refined nitrate-type brine). The calcium chloride in the refined alkali-making calcium liquor reacts with the nitrate-type brine and the sodium sulfate in the salt-making mother liquor to generate unsaturated brine and fine calcium sulfate dihydrate. The newly generated fine calcium sulfate dihydrate grows on the calcium sulfate dihydrate seeds carried in the circulating liquid to form larger calcium sulfate dihydrate crystals that settle to the bottom of the denitrification reaction barrel. Some small particles of calcium sulfate dihydrate are removed along with the circulating liquid under the action of external circulation lifting. The calcium sulfate dihydrate slurry is lifted to the top of the denitration reaction barrel as a seed for calcium sulfate crystallization. The upper clear liquid overflows to the sedimentation barrel and is stored in the clear liquid brine pool after sedimentation. The fine calcium sulfate dihydrate at the bottom of the sedimentation barrel can be pumped to the denitration reaction barrel as a calcium sulfate seed. When the solid-liquid ratio of the calcium sulfate dihydrate slurry that descends to the bottom of the denitration reaction barrel reaches an appropriate concentration (the solid-liquid ratio reaches 30-40%), the calcium sulfate dihydrate slurry is discharged from the bottom discharge port and sent to a centrifuge to remove the entrained mother liquor to obtain large-particle calcium sulfate dihydrate, which is then washed with steam condensate from a salt-making device. The washed wet material is sent to a fluidized bed for dehydration and drying (drying temperature 100-150°C) to prepare a dihydrate gypsum product.

[0012] S5: The unsaturated brine obtained from the S4 clear brine pool is injected into the nitrate salt mine group. On the one hand, it dissolves the sodium chloride and sodium sulfate in the nitrate salt mine group. On the other hand, a small amount of calcium chloride in the unsaturated brine reacts with the dissolved sodium sulfate, and a small amount of calcium sulfate generated naturally settles to the bottom of the nitrate salt mine group cavity, and finally a nearly saturated brine with low nitrate and low calcium is mined;

[0013] S6: sodium carbonate is added to the nearly saturated brine with low nitrate and low calcium obtained in S5 for purification and decalcification to prepare a refined low nitrate saturated brine, and calcium carbonate precipitate is purified and decalcified to be washed with steam condensate from a salt making device. The washed wet material is respectively sent to a centrifuge and a fluidized bed for dehydration and drying to prepare a calcium carbonate product;

[0014] S7: Part of the refined low-nitrate saturated brine obtained in the S6 process enters the salt-making device to produce refined salt, and part enters the alkali-making device to produce soda ash. If there is any surplus, it can also be sold as a product for use in the downstream chemical industry. The steam condensate produced by the salt-making device is used to wash the dihydrate gypsum and calcium carbonate, and then injected into the nitrate salt mine group to mine the nitrate brine.

[0015] Nitrate salt mines refer to mineral deposits containing sodium chloride and sodium sulfate, including nitrate salt mines suitable for salt-nitrate co-production and nitrate-salt co-production and abandoned nitrate salt mines that do not meet the requirements of salt-nitrate co-production and nitrate-salt co-production. The brine mined by injecting fresh water into this type of mine is nitrate brine, usually with the composition of Na2SO4: 10-260g / L, NaCl: 60-310g / L. The alkali calcium solution contains CaCl2: 95-115g / L, NaCl: 50-55g / L. The mother liquor for salt production contains Na2SO4: 50-70g / L, NaCl: 250-270g / L.

[0016] A further improvement of the present invention is:

[0017] The primary coarse filter screen described in step S1 is 1mm-3mm, the secondary coarse filter screen is 0.1mm-0.2mm, the fine filter screen is <0.1mm, and the pore size of the inorganic ceramic membrane is 30-100nm.

[0018] Furthermore, the amount of circulating liquid in step S4 is determined according to 3 to 10 times the amount of refined nitrate-type brine; when the solid-liquid ratio of the calcium sulfate dihydrate slurry at the bottom of the denitration reaction barrel reaches 30 to 40%, the calcium sulfate dihydrate slurry is discharged from the bottom.

[0019] Furthermore, the nitrate salt mine group described in step S5 refers to a mirabilite-type rock salt mine or an abandoned rock salt mine with a high mirabilite content.

[0020] Furthermore, the matching amount between the materials in the process of accurately controlling the brine extraction and preparing gypsum in the present invention can be calculated by establishing a mathematical model based on the content of the low-nitrate saturated brine component to be refined, the content of the components in the alkali calcium solution and the nitrate brine and the salt mother liquor, and the average content ratio of sodium sulfate and sodium chloride in the nitrate salt mine to be injected, and the calculation method is as follows:

[0021] Assume that the volume of the alkali-making calcium solution involved in the reaction is V1 (10,000 m 3 ), the sodium chloride content is x1 g / L (value 45-55 g / L), the calcium chloride content is y2 g / L (value 95-115); the volume of nitrate-type brine involved in the reaction is V2 (10,000 m 3 ), the sodium chloride content is x2g / L (value ranges from 60 to 310), the sodium sulfate content is y2g / L (value ranges from 10 to 260); the volume of the mother liquor involved in the reaction is V3 (10,000 m 3 ), the content of sodium chloride is x3 g / L (value ranges from 250 to 270 g / L), the content of sodium sulfate is y3 g / L (value ranges from 50 to 70 g / L); the volume of unsaturated brine generated by ground denitrification reaction is V4 (10,000 m 3), the content of sodium chloride is n (g / L), the content of calcium chloride is m (g / L); the mass ratio of sodium sulfate to sodium chloride in the nitrate-type salt mine is f (value 0-1); the production-injection ratio is η (value 0.85-0.98); the volume of unpurified saturated brine mined from the unsaturated brine injection well is V5 (10,000 m 3 ), whose components are sodium chloride δg / L (value 305-320), sodium sulfate content x (g / L), calcium sulfate content y (g / L); the volume of refined low-nitrate saturated brine is V6 (10,000 m 3 ), the content of sodium chloride is δg / L (value 305-320), the content of sodium sulfate is ag / L (value 0-15), and the volume of refined low-nitrate saturated brine used for alkali production is V7 (10,000 m 3 ), the volume of refined low-nitrate saturated brine used for salt production is V8 (10,000 m 3 ), the volume of refined low-nitrate saturated brine for sale is V9 (10,000 m 3 ); the solubility product of calcium sulfate is Ksp (mol / L) 2 ; The salt production is B million tons / year, the alkali production is A million tons / year, and the amount of alkali calcium liquid produced per ton of alkali is λm 3 / ton (value ranges from 8 to 10).

[0022] The solubility product of calcium sulfate in nearly saturated bittern is almost linearly related to the sodium chloride content. When the NaCl content is 300 g / L, Ksp is about 1.8×10 -3 (mol / L) 2 ; When the NaCl content is 240g / L, Ksp is 2.2×10 -3 (mol / L) 2 . Using the interpolation method, we can deduce:

[0023]

[0024] Since the properties of sodium sulfate in the mineral brine remain unchanged after injection well mining, a mathematical model is established based on the total amount of sodium sulfate in the material before and after the mining reaction, that is: the amount of Na2SO4 in the mineral brine mined out + the amount of Na2SO4 reacted with CaCl2 in the mixed brine of the injection well = the total amount of Na2SO4 brought out when mining rock salt. After deduction, the injection well model formula is:

[0025] V1·(δ·fx-x1·f-1.05·y1·f-1.28·y1)+V2·(δ·fx-x2·f+y2)+V3·(δ·fx-x3·f+y3)=0 Formula (1-2)

[0026] According to the process route of refining low-nitrate saturated brine, combined with the well injection model, the composition and matching amount of nitrate brine, salt making mother liquor, and refined low-nitrate brine for salt making are calculated as follows:

[0027] In the low-nitrate, low-calcium saturated brine mined from injection wells:

[0028] Na2SO4 content (g / L):

[0029] CaSO4 content (g / L):

[0030] Volume of alkali-making calcium solution (10,000 m 3 ): V1 = λ·A; Formula (1-5)

[0031] Nitrate type brine volume (10,000 m 3 ):

[0032]

[0033] Salt production mother liquor volume (10,000 m 3 ):

[0034] Unsaturated brine volume (10,000 m 3 ): V4 = V1 + V2 + V3 formula (1-8.1)

[0035] NaCl content (g / L):

[0036] Na2SO4 content (g / L):

[0037] The volume of low-nitrate and low-calcium saturated brine produced by injection wells (10,000 m 3 ): V5 = η·V4 Formula (1-9)

[0038] Refined low-nitrate saturated brine volume (10,000 m 3 ): V6 = V5 Formula (1-10)

[0039] in:

[0040] Volume of low nitrate brine for alkali production (10,000 m 3 ):

[0041] Volume of low-nitrate brine for salt production (10,000 m 3 ): V8=(x3·V3+B·1000) / δ Formula (1-12a)

[0042] Volume of refined low-nitrate saturated brine for sale (10,000 m 3 ):V9=V6-V7-V8 Formula (1-13)

[0043] When the annual output of alkali production (A), annual output of salt production (B), components of alkali-making calcium liquid, nitrate brine and salt-making mother liquor (x1, y1; x2, y2; x3, y3), the amount of alkali-making calcium liquid produced per ton of alkali (λ), the resource composition of the injection well (f) and the production-injection ratio η are known, and the requirements for the sodium chloride content (δ) and sulfate content (a) in the refined low-nitrate saturated brine are clear, the above formula can be used to quickly calculate the matching amounts of alkali-making calcium liquid, salt-making mother liquor and nitrate-type brine participating in the reaction, and the output of refined low-nitrate saturated brine can be estimated.

[0044] Furthermore, the sodium chloride content x1 of the alkali-making calcium liquid is 50-55g / L, and the calcium chloride content y2 is 95-115g / L; the sodium chloride content x2 of the nitrate-type brine is 60-310g / L, and the sodium sulfate content y2 is 10-260g / L; the sodium chloride content x3 of the salt-making mother liquor is 250-270g / , and the sodium sulfate content y3 is 50-70g / L; the mass ratio f of sodium sulfate to sodium chloride in the nitrate-type salt mine group is 0-1; the production-injection ratio η is 0.85-0.98; the sodium chloride content δ of the refined low-nitrate saturated brine is 305-320g / L, and the sodium sulfate content a is 0-15g / L; the amount of alkali-making calcium liquid λ produced per ton of alkali is 8-10m 3 / ton.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention converts calcium chloride and sodium chloride in the alkali calcium liquid into gypsum products and refined low-nitrate brine respectively by coupling ground denitrification and injection well saturation control without changing the main process of the saline-alkali calcium circulation. This solves the problem of limited consumption of the alkali calcium liquid due to the limited market capacity of calcium chloride. The process route is reasonable, the process control is simple, the material flows are interconnected and recycled, which makes up for the defects of the saline-alkali calcium circulation process and improves the toughness of the saline-alkali calcium circulation process.

[0047] 2. The present invention establishes a calculation formula for precise control of injection well brine extraction by establishing a well injection model, which can quickly and conveniently calculate the matching amount between various materials involved in the preparation of gypsum based on the salt-alkali-calcium circulation production system, thereby facilitating precise control of various materials.

[0048] 3. The present invention can recycle sodium sulfate resources in normally mined nitrate salt mines, and can also recycle sodium sulfate resources in abandoned nitrate salt mines, thereby realizing the comprehensive utilization of rock salt resources and improving the resource utilization rate of rock salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the salt-alkali-calcium combined cycle process;

[0050] Figure 2This is a schematic diagram of the process flow of denitrification and gypsum production;

[0051] Figure 3 This is a schematic diagram of the process flow for preparing gypsum by precisely controlling brine extraction based on the salt-alkali-calcium combined process. DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with specific embodiments.

[0053] Example 1

[0054] Under the scale of 1.8 million tons of salt and 600,000 tons of alkali per year, the process of preparing gypsum by accurately controlling the brine extraction based on the co-production of salt, alkali and calcium includes the following steps:

[0055] S1: The alkali calcium liquid produced by the 600,000 tons / year alkali production unit, the salt mother liquor produced by the 1.8 million tons / year salt production unit, and the nitrate-type brine produced by water-soluble mining are respectively filtered through a 1mm primary coarse filter and a 0.05mm secondary coarse filter box to remove granular insoluble impurities, and then settled in a settler. The upper clear liquid is filtered through an inorganic ceramic membrane with a membrane pore size of 60nm to obtain refined alkali calcium liquid, refined salt mother liquor, and refined nitrate-type brine.

[0056] S2: It was detected that the refined alkali calcium solution contained CaCl250g / L and NaCl100g / L, the refined salt mother liquor contained NaCl260g / L and Na2SO460g / L, the refined nitrate-type brine contained NaCl240g / L and Na2SO480g / L, and the average content ratio of sodium sulfate to sodium chloride in the nitrate-type salt mine group to be injected was 22 / 298;

[0057] S3: Salt and alkali production requires that the sulfate in the refined low-nitrate saturated brine is less than 5g / L. In this embodiment, the refined low-nitrate brine used for salt and alkali production is 310g / L NaCl and 7g / L Na2SO4. The detection result of S2 is substituted into the injection well brine refining control formula to calculate the components and matching amounts of the refined alkali calcium liquid, refined salt mother liquor, refined nitrate brine and other materials. The specific results are detailed in Example 2;

[0058] S4: According to the matching ratio of refined alkali calcium solution, refined salt mother liquor and refined nitrate brine, 2232m3 / h nitrate brine (NaCl: 240g / L, Na2SO4: 80g / L), 234.65m 3 / h of salt production mother liquor and 1687.5m 3 / h of refined alkali calcium solution is added to the denitration reaction barrel with an external circulation lifting device at the same time, and the denitration reaction barrel is turned on for mixed denitration. After the reaction for 1 hour, the external circulation lifting device is turned on and the circulation liquid lifting flow rate is set to 4000m 3 / h; then adjust the flow of refined alkali calcium solution, refined salt mother liquor, and refined nitrate-type brine according to the proportion between the three. 3 / h of nitrate-type brine (NaCl: 240g / L, Na2SO4: 80g / L), 93.86m 3 / h of salt production mother liquor and 675m 3 / h of refined alkali-making calcium liquid and circulating liquid jointly react with denitrification, and the generated calcium sulfate dihydrate grows on the calcium sulfate dihydrate crystals carried by the circulating liquid. The formed calcium sulfate dihydrate with larger particle size settles to the bottom of the denitrification reaction barrel, and some fine calcium sulfate dihydrate is lifted to the top of the denitrification reaction barrel with the circulating liquid under the lifting effect of the external circulation as the seed of calcium sulfate crystallization; with the continuous addition of refined alkali-making calcium liquid, refined salt-making mother liquor, and refined nitrate-type brine, part of the overflow liquid containing fine calcium sulfate dihydrate overflows to the sedimentation tank. The sedimentation is carried out in a sedimentation vessel, and the upper clear liquid after sedimentation flows into the clear liquid brine pool. The mud discharged from the bottom of the sedimentation vessel can be pumped to the denitration reaction barrel as a calcium sulfate seed. When the solid-liquid ratio of the calcium sulfate dihydrate slurry that descends to the bottom of the denitration reaction barrel reaches 30%, the calcium sulfate dihydrate slurry is discharged from the bottom discharge port and sent to a centrifuge to remove the entrained mother liquor to obtain large-particle calcium sulfate dihydrate, which is then washed with steam condensate from a salt making device. The washed wet material is sent to a fluidized bed at 100°C for dehydration and drying to prepare a dihydrate gypsum product.

[0059] S5: The unsaturated brine (NaCl: 202.16g / L, CaCl2: 4.37g / L) obtained from the S4 clear brine pool is injected into the nitrate salt mine group. On the one hand, it dissolves the sodium chloride and sodium sulfate in the nitrate salt mine group. On the other hand, a small amount of calcium chloride in the unsaturated brine reacts with the dissolved sodium sulfate, and the small amount of calcium sulfate generated naturally settles to the bottom of the nitrate salt mine group cavity, and finally low-nitrate and low-calcium nearly saturated brine (NaCl: 310g / L, Na2SO4: 2.01g / L, CaSO4: 4.37g / L) is mined.

[0060] S6: Sodium carbonate is added to the nearly saturated brine with low nitrate and low calcium obtained in S5 for purification and decalcification to prepare refined low nitrate saturated brine. At the same time, the calcium carbonate precipitate is purified and decalcified to be washed with steam condensate from a salt making device. The washed wet material is sent to a fluidized bed for dehydration and drying at 100°C to prepare a calcium carbonate product.

[0061] Example 2

[0062] With an annual production scale of 1.8 million tons of salt and 600,000 tons of alkali, the material components and matching quantities in the process of brine extraction and gypsum preparation are precisely controlled based on the co-production of salt, alkali and calcium.

[0063] It is known that the annual output of alkali production is 600,000 tons and the annual output of salt production is 1.8 million tons. After testing, the composition of nitrate-type brine is NaCl240g / L, Na2SO480g / L, the composition of salt production mother liquor is NaCl 260g / L, Na2SO460g / L, and the amount of alkali production calcium liquid produced by one ton of alkali is 9m 3 The composition of the alkali calcium solution is CaCl2: 100g / L, NaCl 50g / L, the average content ratio of sodium sulfate to sodium chloride in the low-nitrate salt mine to be injected is 22 / 298, and the injection-production ratio η is about 0.95.

[0064] The production of salt and alkali requires the refined low-nitrate saturated brine to be NaCl 310g / L and Na2SO4 7g / L. That is: A=60, B=180, λ=9, f=22 / 298, x1=50g / L, y1=100g / L, x2=240g / L, y2=80g / L, x3=260g / L, y3=60g / L, δ=310g / L, a=7g / L. η=0.95.

[0065] Substituting δ = 310 g / L and a = 7 g / L into equations (1-1), (1-3) and (1-4), we get Ksp = 1.73 × 10 -3 (mol / L) 2 , x = 2.01 g / L, y = 4.78 g / L; then A = 600,000 tons / year, B = 1.8 million tons / year are inserted into formulas (1-5), (1-6) and (1-7), and V1 = 540 (10,000 m 3 ), V2=714.24(10,000m 3 ), V3=75.09(10,000 m 3 ); then substitute the obtained data into equations (1-8.1) to (1-8.3), (1-9) to (1-10), (1-11), (1-12) and (1-13) in turn, and obtain V4 = 1329.33 (10,000 m 3 ), n=202.16g / L, m=4.37g / L, V5=V 6＝ 1262.86 (10,000 m 3 ), V7 = 300.73 (10,000 m 3 ), V8 = 643.62 (10,000 m 3 ), V9 = 318.51 (10,000 m 3 ).Right now:

[0066] 540m3 of 600,000 tons / year of soda ash discharge 3 Calcium solution for alkali production (CaCl2: 100g / L, NaCl: 50g / L) and 7.1424 million m 3 / year of nitrate-type brine (NaCl: 240g / L, Na2SO4: 80g / L) and 750,900m3 The mother liquor of salt production (NaCl: 260g / L, Na2SO4: 60g / L) is mixed and denitrated, and the generated calcium sulfate dihydrate is precipitated, separated, washed, dehydrated and dried to produce gypsum products. The generated unsaturated brine (NaCl: 202.16g / L, CaCl2: 4.37g / L) is injected into the low-nitrate mine group. The mined saturated brine is purified and decalcified, and can produce 12.6286 million m 3 / year refined low-nitrate saturated brine (NaCl: 310g / L, Na2SO4: 7g / L), including: 3.0073 million m 3 / year refined low-nitrate saturated brine is used as raw material to produce 600,000 tons / year of soda ash, 6.4362 million m 3 / year refined low-nitrate saturated brine is used to produce 1.8 million tons / year of refined salt, and the remaining 3.1851 million m 3 / year refines low-nitrate saturated brine and sells it to downstream chemical companies.

[0067] Example 3

[0068] With an annual production scale of 800,000 tons of soda ash and 2.4 million tons of salt, the material components and matching quantities in the process of brine extraction and gypsum preparation are precisely controlled based on the co-production of salt, alkali and calcium.

[0069] It is known that the annual output of alkali production is 800,000 tons and the annual output of salt production is 2.4 million tons. After testing, the composition of nitrate-type brine is NaCl256g / L, Na2SO464g / L, the composition of salt production mother liquor is NaCl 270g / L, Na2SO450g / L, and the amount of alkali production calcium liquid produced by one ton of alkali is 8m 3 , the composition of alkali calcium solution is CaCl2: 110g / L, NaCl 45g / L, the average content ratio of sodium sulfate to sodium chloride in the low-nitrate salt mine to be injected is 1 / 7, and the injection-production ratio η is about 0.9. Salt and alkali production requires the refined low-nitrate saturated brine composition to be NaCl 305g / L and Na2SO410g / L. That is: A=80, λ=8, f=1 / 7, x1=50g / L, y1=105g / L, x2=256g / L, y2=64g / L, x3=270g / L, y3=50g / L, δ=305g / L, a=10g / L, η=0.96.

[0070] Substituting δ = 305 g / L and a = 10 g / L into equations (1-1), (1-3) and (1-4), we get Ksp = 1.77 × 10 -3 (mol / L) 2 , x = 6.43 g / L, y = 3.42 g / L; then A = 800,000 tons / year, B = 2.4 million tons / year are inserted into formulas (1-5), (1-6) and (1-7), and V1 = 6.40 (10,000 m 3), V2=1047.05(10,000 m 3 ), V3 = 1,912,400 m 3 ); then substitute the obtained data into equations (1-8.1) to (1-8.3), (1-9) to (1-10), (1-11), (1-12) and (1-13) in turn, and obtain V4 = 1878.29 (10,000 m 3 ), n = 220.82 g / L, m = 3.91 g / L, V5 = V6 = 1803.16 (10,000 m 3 ), V7 = 306.73 (10,000 m 3 ), V8 = 956.18 (10,000 m 3 ), V9 = 540.25 (10,000 m 3 ).Right now:

[0071] 800,000 tons / year of soda ash discharged from 640m 3 Calcium solution for alkali production (CaCl2: 105g / L, NaCl: 50g / L) and 10.4705 million m 3 / year of nitrate-type brine (NaCl: 256g / L, Na2SO4: 64g / L) and 1.9124 million m 3 The mother liquor of salt production (NaCl: 270g / L, Na2SO4: 50g / L) is mixed and denitrated, and the generated calcium sulfate dihydrate is precipitated, separated, washed, dehydrated and dried to produce gypsum products. The generated unsaturated brine (NaCl: 220.82g / L, CaCl2: 3.91g / L) is injected into the nitrate mine group. The mined saturated brine is purified and decalcified, and can produce 18.7829 million m 3 / year refined low-nitrate saturated brine (NaCl: 305g / L, Na2SO4: 10g / L), including: 3.0673 million m 3 / year refined low-nitrate saturated brine is used as raw material to produce 800,000 tons / year of soda ash, 9.5618 million m 3 / year refined low-nitrate saturated brine is used to produce 2.4 million tons / year of refined salt, and the remaining 5.4025 million m 3 / year refines low-nitrate saturated brine and sells it to downstream chemical companies.

[0072] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing gypsum by regulating salt-alkali combined circulation underground, characterized in that: The following steps are involved: S1: The alkali-making calcium solution, the salt-making mother solution and the nitrate-type brine from water-soluble mining are subjected to two-stage coarse filtration and one-stage fine filtration to remove particulate insoluble impurities, and then the alkali-making calcium solution, the salt-making mother solution and the nitrate-type brine are filtered through an inorganic ceramic membrane filter to obtain refined alkali-making calcium solution, refined salt-making mother solution and refined nitrate-type brine; S2: Detect the content of calcium chloride and sodium chloride in refined alkali calcium solution, sodium chloride and sodium sulfate in refined salt mother liquor, sodium chloride and sodium sulfate in refined nitrate-type brine, and the average content ratio of sodium sulfate to sodium chloride in the nitrate-type salt mine as a control reactor; S3: Determine the content of sodium chloride and sulfate in the refined low-nitrate saturated brine to be produced, substitute the results of S2 detection into the precise control model of injection well brine production, and calculate the matching amount of refined alkali calcium solution, refined salt mother liquor, and refined nitrate-type brine participating in the denitrification reaction; S4: According to the result calculated in S3, the refined nitrate-type brine, the refined salt-making mother liquor and the refined alkali-making calcium liquor are continuously and evenly mixed with the circulating liquid under the action of external circulation lifting in accordance with the calculated matching ratio. The calcium chloride in the refined alkali-making calcium liquor reacts with the nitrate-type brine and the sodium sulfate in the salt-making mother liquor to generate unsaturated brine and fine calcium sulfate dihydrate. The newly generated fine calcium sulfate dihydrate grows on the calcium sulfate dihydrate crystal seeds carried in the circulating liquid to form larger-sized calcium sulfate dihydrate crystals that settle to the bottom of the denitrification reaction barrel. Some small particles of calcium sulfate dihydrate are carried along the circulating liquid under the action of external circulation lifting. The liquid is lifted to the top of the denitration reaction barrel as a seed for calcium sulfate crystallization, the upper clear liquid overflows to the sedimentation barrel and is stored in the clear liquid brine pool after sedimentation, and the fine calcium sulfate dihydrate at the bottom of the sedimentation barrel can be pumped to the denitration reaction barrel as a calcium sulfate seed; when the solid-liquid ratio of the calcium sulfate dihydrate slurry that descends to the bottom of the denitration reaction barrel reaches an appropriate concentration, the calcium sulfate dihydrate slurry is discharged from the bottom discharge port and sent to a centrifuge to remove the entrained mother liquor to obtain large particles of calcium sulfate dihydrate, which are then washed with steam condensate from a salt making device, and the washed wet material is sent to a fluidized bed for dehydration and drying to prepare a dihydrate gypsum product; S5: The unsaturated brine obtained from the S4 clear brine pool is injected into the nitrate salt mine group. On the one hand, it dissolves the sodium chloride and sodium sulfate in the nitrate salt mine group. On the other hand, a small amount of calcium chloride in the unsaturated brine reacts with the dissolved sodium sulfate, and a small amount of calcium sulfate generated naturally settles to the bottom of the nitrate salt mine group cavity, and finally a nearly saturated brine with low nitrate and low calcium is mined; S6: sodium carbonate is added to the nearly saturated brine with low nitrate and low calcium obtained in S5 for purification and decalcification to prepare a refined low nitrate saturated brine, and calcium carbonate precipitate is purified and decalcified to be washed with steam condensate from a salt making device. The washed wet material is respectively sent to a centrifuge and a fluidized bed for dehydration and drying to prepare a calcium carbonate product; S7: Part of the refined low-nitrate saturated brine obtained in the S6 process enters the salt-making device to produce refined salt, and part enters the alkali-making device to produce soda ash. If there is any surplus, it can also be sold as a product for use in the downstream chemical industry. The steam condensate produced by the salt-making device is used to wash the dihydrate gypsum and calcium carbonate, and then injected into the nitrate salt mine group to mine the nitrate brine.

2. The method for preparing gypsum by regulating salt-alkali combined circulation in underground wells according to claim 1, characterized in that: The primary coarse filtration screen described in step S1 is 1mm~3mm, the secondary coarse filtration screen is 0.1mm~0.2mm, the fine filtration screen is <0.1mm, and the pore size of the inorganic ceramic membrane is 30~100nm; the alkali-making calcium solution in step S1 contains CaCl2: 95~115g / L, NaCl: 50~55g / L, the salt-making mother liquor contains Na2SO4: 50~70g / L, NaCl: 250~270g / L, and the nitrate-type brine contains Na2SO4: 10~260g / L, NaCl: 60~310g / L.

3. The method for preparing gypsum by regulating salt-alkali combined circulation in underground wells according to claim 1, characterized in that: The amount of circulating liquid in step S4 is determined according to 3 to 10 times the amount of refined nitrate-type brine; when the solid-liquid ratio of the calcium sulfate dihydrate slurry at the bottom of the denitration reaction barrel reaches 30 to 40%, the calcium sulfate dihydrate slurry is discharged from the bottom.

4. The method for preparing gypsum by regulating salt-alkali combined circulation in underground mines according to claim 1, characterized in that: The nitrate salt mine group described in step S5 refers to a mirabilite-type rock salt mine or an abandoned rock salt mine with a high mirabilite content.

5. The method for preparing gypsum by regulating salt-alkali combined circulation underground according to claim 1, characterized in that: The calculation process of the injection well model is: Assume that the volume of the alkali-making calcium solution involved in the reaction is V1 (10,000 m 3 ), the content of sodium chloride is x1 (g / L), the content of calcium chloride is y2 (g / L); the volume of nitrate-type brine involved in the reaction is V2 (10,000 m 3 ), the content of sodium chloride is x2g / L, the content of sodium sulfate is y2(g / L); the volume of the mother liquor involved in the reaction is V3(10,000 m 3 ), the content of sodium chloride is x3 (g / L), the content of sodium sulfate is y3 (g / L); the volume of unsaturated brine generated by ground denitrification reaction is V4 (10,000 m 3 ), the content of sodium chloride is n (g / L), the content of calcium chloride is m (g / L); the mass ratio of sodium sulfate to sodium chloride in the nitrate-type salt mine is f; the production-injection ratio is η; the volume of unpurified saturated brine mined from the unsaturated brine injection well is V5 (10,000 m 3 ), whose components are sodium chloride δ (g / L), sodium sulfate content x (g / L), and calcium sulfate content y (g / L); the volume of refined low-nitrate saturated brine is V6 (10,000 m 3 ), the content of sodium chloride is δ (g / L), the content of sodium sulfate is a (g / L), and the volume of refined low-nitrate saturated brine used for alkali production is V7 (10,000 m 3 ), the volume of refined low-nitrate saturated brine used for salt production is V8 (10,000 m 3 ), the volume of refined low-nitrate saturated brine for sale is V9 (10,000 m 3 ); the solubility product of calcium sulfate is Ksp (mol / L) 2 ; The output of salt production is B (10,000 tons), the output of alkali production is (A 10,000 tons), and the amount of alkali-making calcium liquid produced per ton of alkali is λ (m 3 / ton); the above parameters satisfy the following relationship: V1·(δ·fx-x1·f-1.05·y1·f-1.28·y1)+V2·(δ·fx-x2·f+y2)+V3·(δ·fx-x3·f+y3)=0.

6. The method for preparing gypsum by regulating salt-alkali combined circulation underground according to claim 5, characterized in that: The calculation method for the composition and matching amount of nitrate-type brine, salt-making mother liquor, and refined low-nitrate brine for salt making is as follows: Solubility product of calcium sulfate in nearly saturated brine (mol / L) 2 ): Volume of alkali-making calcium solution (10,000 m 3 ): V1 = λ·A; Nitrate type brine volume (10,000 m 3 ): Salt production mother liquor volume (10,000 m 3 ): The volume of unsaturated brine generated by denitrification reaction (10,000 m 3 ): V4 = V1 + V2 + V3; Its composition: NaCl content (g / L): Na2SO4 content (g / L): The volume of low-nitrate and low-calcium saturated brine produced by injection well mining (10,000 m 3 ): V5 = η·V4; Its composition: Na2SO4 content (g / L): CaSO4 content (g / L): Refined low-nitrate saturated brine volume (10,000 m 3 ): V6 = V5; in: Volume of low nitrate brine for alkali production (10,000 m 3 ): Volume of low-nitrate brine for salt production (10,000 m 3 ): V8=(x3·V3+B·1000) / δ; Volume of refined low-nitrate saturated brine for sale (10,000 m 3 ):V9=V6-V7-V8.

7. The method for preparing gypsum by regulating salt-alkali combined circulation underground according to claim 5, characterized in that: The sodium chloride content x1 of the alkali-making calcium liquid is 50-55g / L, and the calcium chloride content y2 is 95-115g / L; the sodium chloride content x2 of the nitrate-type brine is 60-310g / L, and the sodium sulfate content y2 is 10-260g / L; the sodium chloride content x3 of the salt-making mother liquor is 250-270g / , and the sodium sulfate content y3 is 50-70g / L; the mass ratio f of sodium sulfate to sodium chloride in the nitrate-type salt mine group is 0-1; the production-injection ratio η is 0.85-0.98; the sodium chloride content δ of the refined low-nitrate saturated brine is 305-320g / L, and the sodium sulfate content a is 0-15g / L; the amount of alkali-making calcium liquid λ produced per ton of alkali is 8-10m 3 / ton.

Images