A method for producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer by producing bittern from seawater

Abstract

The present invention discloses a method for producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer by producing bittern from seawater. The present invention is directed to the bittern component of seawater and combines Na + , K + Mg 2+ 、Cl ‑ 、SO4 2‑ The invention realizes the comprehensive utilization of seawater salt brine and the simultaneous preparation of magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. In addition, K in seawater salt brine is used to produce magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. + Mg 2+ and SO4 2‑ The recovery rates were all above 80%.

Description

Technical Field

[0001] The invention relates to the technical field of seawater salt production, and in particular to a method for producing seawater salt brine and co-producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. Background Art

[0002] During the production of sea salt, about 1m3 of by-product is produced for every ton of raw salt produced. 3 Wastewater from salt production (commonly known as brine). Brine contains high concentrations of chloride ions, sulfate ions, potassium ions, magnesium ions, sodium ions and other ions, and is mostly used to produce industrial salt, magnesium chloride, potassium chloride and other products. The various chemical elements in brine are about 40 times more concentrated than those in seawater, making it an excellent raw material for extracting chemical elements from seawater. However, due to technological limitations, sea salt brine chemical companies are generally in a loss-making state. The comprehensive utilization of brine is an effective measure to solve the problem of insufficient land resources, a necessary guarantee for achieving energy conservation and emission reduction in sea salt production, and an urgent problem that needs to be solved in the sea salt brine chemical industry.

[0003] At present, the recovery and treatment of seawater salt brine usually involves evaporating the seawater salt brine and adding some old brine (concentrated brine) during the evaporation process. After the evaporation is completed, the temperature is lowered and the sedimentation is carried out under insulation. After the sedimentation solids are discharged, the temperature is further lowered to 35℃-50℃, and the re-crystallized solids are separated. The separated solid phase is carnallite, which mainly contains potassium chloride, magnesium chloride, and a small amount of sodium chloride; the liquid phase is old brine (also called concentrated brine), which mainly contains magnesium chloride and a small amount of potassium chloride, sodium chloride, and magnesium sulfate. The main products of this method are sodium chloride, magnesium sulfate, potassium chloride, and magnesium chloride. Due to the low market price of the products and high energy consumption, the salt chemical companies that process the salt brine are in a serious loss-making situation. How to reduce energy consumption and change the product structure is the key to turning losses into profits for sea salt brine chemical companies.

[0004] Magnesium sulfate, found in bittern, is the third largest marine resource and a naturally renewable resource. Industrial magnesium sulfate is generally a heptahydrate with the molecular formula MgSO4·7H2O. Agricultural magnesium sulfate is generally a monohydrate with the molecular formula MgSO4·H2O. Magnesium sulfate is an important inorganic chemical product, widely used in printing and dyeing, medicine, brewing, fermentation, pulp and paper, fireproofing, and other fields. In agriculture, magnesium sulfate monohydrate is an important dual-nutrient (sulfur and magnesium) chemical fertilizer. Furthermore, compared to traditional potassium sulfate products, potassium magnesium sulfate fertilizer contains more magnesium, which can promote chlorophyll formation, improve crop yield and quality, and extend the storage life of fruit. It is more suitable for cash crops such as vegetables, fruit trees, tobacco, tea, and flowers.

[0005] Currently, the main component of domestically produced potassium sulfate magnesium fertilizer is a series of dehydrated soft potassium magnesium vanadium products with the molecular formula K2Mg(SO4)2·nH2O (n=4-6), implemented according to GB / T20937-2007. The production method for potassium sulfate magnesium fertilizer in my country primarily utilizes a conversion-flotation-washing-drying process, whereby KCl and MgSO4·7H2O in the raw potassium mixed salt ore are converted into soft potassium magnesium vanadium by adding water. This is then enriched using flotation, and the concentrate is washed and dried to produce a qualified potassium sulfate magnesium fertilizer product. This existing process is widely used in salt lake potassium chloride production plants and features a simple process flow, low production costs, and high product quality. However, the potassium recovery rate in this existing process is generally around 65%, which is relatively low.

[0006] Therefore, people hope to make full use of the ocean, a treasure trove of natural resources, realize high value-added utilization of bittern resources, change the existing bittern utilization product structure, improve the economic benefits of sea salt bittern chemical companies, and achieve high recovery rate and low cost preparation of magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer.

[0007] In order to solve the above problems, the present invention is proposed. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of the existing technology and proposes to use seawater brine to produce magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer, which not only realizes high value-added utilization of bittern resources, but also can achieve high recovery rate and low cost while preparing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer.

[0009] The present invention adopts the following technical solutions:

[0010] A first aspect of the present invention provides a method for producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer by producing bittern from seawater, which comprises the following steps:

[0011] (1) adding Na2SO4 and MgCl2 solids to seawater salt brine to mix and obtain a first mixed brine;

[0012] (2) adding the first mixed brine into a high-temperature evaporator for evaporation and salt precipitation; the evaporation temperature is 90° C.-130° C.;

[0013] (3) performing solid-liquid separation on the material discharged from the high-temperature evaporator to obtain a mixed salt containing magnesium sulfate monohydrate Kie and NaCl and a Kie extraction mother liquor;

[0014] (4) separating, washing and drying the mixed salt containing Kie and NaCl obtained by solid-liquid separation in step (3) to obtain a magnesium sulfate monohydrate MgSO4·H2O product;

[0015] (5) Cooling the mother liquor to a temperature of 60°C-85°C in a constant temperature crystallizer, while adding Na2SO4 and water for conversion;

[0016] (6) performing solid-liquid separation on the liquid discharged from the crystallizer to obtain a mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl and a Lan mother liquor;

[0017] (7) Mix the extracted mother liquor with KCl and Na2SO4 and add it into a low-temperature evaporator for evaporation and salt precipitation at an evaporation temperature of 60°C-85°C;

[0018] (8) performing solid-liquid separation on the material discharged from the low-temperature evaporator to obtain a mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl and a Lan circulating mother liquor;

[0019] (9) The recycled mother liquor is mixed with KCl and Na2SO4 and then circulated into the low-temperature evaporator;

[0020] (10) The mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl obtained by solid-liquid separation of the materials discharged from the constant temperature crystallizer and the low temperature evaporator is separated, washed and dried to obtain a potassium magnesium sulfate fertilizer product.

[0021] Preferably, in step (1), the seawater salt bittern used contains 50g / L-200g / L of NaCl, 100g / L-210g / L of MgCl2, 15g / L-45g / L of KCl and 40g / L-120g / L of MgSO4.

[0022] Preferably, in step (1), the mass of Na2SO4 added is 0%-15% of the mass of bittern, and the mass of MgCl2 added is 0%-15% of the mass of bittern. The mass of Na2SO4 and MgCl2 added needs to be determined according to the actual composition of bittern in the salt precipitation phase. Specifically, the mass of Na2SO4 and MgCl2 added needs to be determined according to the actual composition of bittern in the salt precipitation phase. + Mg 2+ 、Cl - 、SO4 2- The content can be selected by adding one or two of Na2SO4 and MgCl2. In most cases, one of Na2SO4 and MgCl2 is added.

[0023] Preferably, in step (2), the relative bittern steaming water loss rate is 45%-85%.

[0024] Preferably, in step (3), magnesium sulfate monohydrate Kie is MgSO4·H2O; in step (6), anhydrous potassium magnesium sulfate Lan is K2SO4·2MgSO4.

[0025] Preferably, in step (5), Na2SO4 and water are added to the Kie mother liquor after high-temperature evaporation and salt precipitation, ensuring that the Kie mother liquor after high-temperature evaporation and salt precipitation precipitates a mixed salt of solid phase Lan and NaCl at a low temperature of 60°C-85°C. The mass of Na2SO4 added is 0%-15% of the mass of the Kie mother liquor, and the mass of water added is 0%-10% of the mass of the Kie mother liquor. The mass of Na2SO4 added needs to be determined according to the actual composition of the Kie mother liquor.

[0026] Preferably, in step (7), KCl and Na2SO4 are added to the Lan extract mother liquor after low-temperature crystallization and salt precipitation, so as to ensure that the Lan extract mother liquor after low-temperature crystallization and salt precipitation can be further evaporated at a low temperature of 60°C-85°C to precipitate a mixed salt of solid phase Lan and NaCl. The added KCl is 0%-10% of the mass of the Lan extract mother liquor, and the added Na2SO4 is 0%-15% of the mass of the Lan extract mother liquor. The relative mother liquor evaporation water loss rate is 2.5%-15%. The mass of Na2SO4 and KCl added needs to be determined according to the actual composition of the Lan extract mother liquor. The evaporation water loss rate of the present invention refers to the mass of the evaporation water loss divided by the mass of the water in the feed liquid.

[0027] Preferably, in step (9), the Lanzhou circulating mother liquor after low-temperature evaporation and salt precipitation can be ensured to be circulated back into the low-temperature evaporator by adding KCl and Na2SO4 to ensure that the Lanzhou circulating mother liquor can continue to evaporate and precipitate the mixed salt of solid phase Lan and NaCl. The amount of KCl added is 0%-10% of the mass of the Lanzhou circulating mother liquor, and the amount of Na2SO4 added is 0%-15% of the mass of the Lanzhou circulating mother liquor. The mass of Na2SO4 and KCl added needs to be determined according to the actual composition of the Lanzhou circulating mother liquor.

[0028] Preferably, in step (10), the mixed salt containing anhydrous langbeinite Lan and NaCl is subjected to reverse flotation, washed with water, and dried to obtain a potassium magnesium sulfate fertilizer product. In addition, any separation method in the prior art can be used as long as it can achieve the separation of anhydrous langbeinite Lan and NaCl, and is not limited to the above-mentioned reverse flotation.

[0029] The potassium magnesium sulfate fertilizer product prepared by the invention is suitable for application to economic crops such as vegetables, fruit trees, tobacco, tea and flowers, and the prepared magnesium sulfate monohydrate can be used in industry.

[0030] The Na2SO4, MgCl2 and KCl described in the present invention are not limited to industrial Na2SO4, MgCl2 and KCl products, and can be complex salts and solutions containing corresponding substances.

[0031] In the present invention, Kie is MgSO4·H2O, and Lan is K2SO4·2MgSO4.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention is aimed at the bittern component of seawater salt production, and combines Na + , K + Mg 2+ 、Cl - 、SO4 2- The invention realizes the comprehensive utilization of seawater salt brine and the simultaneous preparation of magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. In addition, K in seawater salt brine is used to produce magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. + Mg 2+ and SO4 2- The recovery rates were all above 80%.

[0034] 2. The mass fractions of Mg and Cl in the magnesium sulfate monohydrate product prepared by the present invention meet the requirements of HGT 2680-2017 industrial magnesium sulfate standard, and the mass fractions of K2O, Mg, S, Cl, and Na in the prepared potassium magnesium sulfate fertilizer product meet the requirements of GB / T20937-2007 potassium magnesium sulfate fertilizer standard.

[0035] 3. The present invention realizes the co-production of magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer from seawater salt brine, completing the high added value utilization of seawater salt brine. 0.015 tons to 0.065 tons of magnesium sulfate monohydrate and 0.1 tons to 0.3 tons of potassium magnesium sulfate fertilizer can be obtained for each ton of brine processed. The current market price of magnesium sulfate monohydrate is about 1,800 yuan / ton, and the price of potassium magnesium sulfate fertilizer is about 2,100 yuan / ton. Therefore, the total income from processing each ton of brine is 237 yuan to 747 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of the method for producing seawater brine and co-producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer. DETAILED DESCRIPTION

[0037] The present invention is further illustrated below by way of examples, which are not intended to be limiting. Experimental procedures not specifically specified in the examples generally followed conventional conditions, those described in the manual, or those recommended by the manufacturer. The general equipment, materials, and reagents used were all commercially available unless otherwise specified.

[0038] The specific steps of the method of the present invention are as follows:

[0039] Example 1

[0040] One ton of seawater brine is mixed with 24.22 kg of Na2SO4 to prepare the brine; the seawater brine used contains 70 g / L of NaCl, 192 g / L of MgCl2, 38 g / L of KCl and 54 g / L of MgSO4, and the mass of the added Na2SO4 is 2.4% of the mass of the brine. The bittern after adding Na2SO4 is pumped into a single-effect evaporator for negative pressure evaporation, the evaporation temperature is controlled at 100°C, and the relative bittern water loss rate is 59.4%; the mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt of Kie and NaCl containing a Kie mass fraction of 50.3% and a Kie-extracted mother liquor; the mixed salt of Kie and NaCl containing a Kie mass fraction of 50.3% is subjected to sedimentation centrifugation, fresh water washing and drying to obtain a monohydrate magnesium sulfate product. The magnesium sulfate monohydrate product has a Mg mass fraction of 16.2% and a Cl mass fraction of 1.0%, meeting the first-class product requirements in the HGT 2680-2017 industrial magnesium sulfate standard.

[0041] The high-temperature Kie mother liquor was cooled to 75°C and Na2SO4 was added with a mass of 7.6% of the Kie mother liquor for crystallization, and further solid-liquid separation was performed to obtain a mixed salt of Lan and NaCl with a Lan mass fraction of 45.8% and a Kie mother liquor; KCl and Na2SO4 with a mass of 1.55% and 5.22% of the Lan mother liquor were added to the Lan mother liquor, respectively, and the mixture was pumped into a single-effect evaporator for negative pressure evaporation, the evaporation temperature was controlled at 75°C, and the relative mother liquor evaporation water loss rate was 8.65%; the mother liquor discharged from the evaporator was subjected to solid-liquid separation to obtain a mixed salt of Lan and NaCl with a Lan mass fraction of 54.7% and a Kie mother liquor. n circulating mother liquor; add KCl and Na2SO4 with the mass of 1.55% and 5.22% of the mass of the Lan circulating mother liquor respectively to the Lan circulating mother liquor, mix them evenly and return them to the single-effect evaporator with an evaporation temperature of 75℃ to continue evaporating Lan; the Lan and NaCl mixed salts obtained by cooling, crystallizing and evaporation are subjected to reverse flotation, fresh water washing and drying to obtain potassium magnesium sulfate fertilizer products. The mass fraction of K2O in the product is 21.7%, the mass fraction of Mg is 11.2%, the mass fraction of S is 22.1%, the mass fraction of Cl is 2.6%, and the mass fraction of Na is 1.3%, meeting the qualified product requirements of the GB / T20937-2007 potassium magnesium sulfate fertilizer standard. During the whole process, the recovery rate of K in bittern is 86%, the recovery rate of Mg is 88%, and the recovery rate of SO4 is 1.3%. 2- The recovery rate was 92%, which was higher than 80%.

[0042] Example 2

[0043] One ton of seawater brine is directly pumped into an MVR evaporator for negative pressure evaporation. The seawater brine contains 144 g / L NaCl, 117 g / L MgCl2, 23 g / L KCl, and 51 g / L MgSO4. The evaporation temperature is controlled at 100°C, and the relative brine water loss rate is 73.3%. The mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt of Kie and NaCl with a Kie mass fraction of 28.5% and a Kie-extracted mother liquor. The mixed salt of Kie and NaCl with a Kie mass fraction of 28.5% is subjected to sedimentation centrifugation, fresh water washing, and drying to obtain a monohydrate magnesium sulfate product. The magnesium sulfate monohydrate product has a Mg mass fraction of 15.9% and a Cl mass fraction of 1.3%, meeting the first-class product requirements of the HGT 2680-2017 industrial magnesium sulfate standard.

[0044] The high-temperature Kelvin extraction mother liquor was cooled to 75°C and crystallized by adding Na2SO4 and water at 6.0% and 4.9% by mass of the Kelvin extraction mother liquor, respectively. Further solid-liquid separation was performed to obtain a mixed salt of Lan and NaCl with a Lan content of 41.7% by mass. KCl and Na2SO4 were added to the Lan mother liquor at 0.93% and 3.29% by mass of the Lan mother liquor, respectively. After uniform mixing, the mixture was pumped into a single-effect evaporator for negative pressure evaporation. The evaporation temperature was controlled at 75°C, and the relative water loss rate of the mother liquor was 5.42%. The mother liquor discharged from the evaporator was subjected to solid-liquid separation to obtain a Lan mother liquor with a Lan content of 54. 7% Lan and NaCl mixed salt and Lan extraction circulating mother liquor; add KCl and Na2SO4 with the mass of 0.93% and 3.29% of the mass of Lan extraction circulating mother liquor respectively to the Lan extraction circulating mother liquor, mix them evenly and return them to the single-effect evaporator with an evaporation temperature of 75℃ to continue evaporating Lan; the Lan and NaCl mixed salt obtained by cooling, crystallization and evaporation is subjected to reverse flotation, fresh water washing and drying to obtain potassium magnesium sulfate fertilizer product, the mass fraction of K2O in the product is 21.9%, the mass fraction of Mg is 11.8%, the mass fraction of S is 22.4%, the mass fraction of Cl is 2.3%, and the mass fraction of Na is 1.1%, meeting the qualified product requirements of GB / T 20937-2007 potassium magnesium sulfate fertilizer standard. During the whole process, the recovery rate of K in bittern is 82%, the recovery rate of Mg is 84%, and the recovery rate of SO4 is 1.1%. 2- The recovery rate was 91%, and both were higher than 80%.

[0045] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for producing magnesium sulfate monohydrate and potassium magnesium sulfate fertilizer by using seawater brine, characterized in that: It includes the following steps: (1) adding Na2SO4 and MgCl2 solids to seawater salt brine to mix and obtain a first mixed brine; (2) adding the first mixed brine into a high-temperature evaporator for evaporation and salt precipitation; the evaporation temperature is 90°C-130°C; (3) The material discharged from the high-temperature evaporator is subjected to solid-liquid separation to obtain a mixed salt containing magnesium sulfate monohydrate Kie and NaCl and a Kie extraction mother liquor; (4) separating, washing and drying the mixed salt containing Kie and NaCl obtained by solid-liquid separation in step (3) to obtain magnesium sulfate monohydrate MgSO4·H2O product; (5) Cooling the mother liquor to a temperature of 60°C-85°C in a constant temperature crystallizer, while adding Na2SO4 and water for conversion; (6) The liquid discharged from the crystallizer is subjected to solid-liquid separation to obtain a mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl and a Lan extraction mother liquor; (7) Mix the extracted mother liquor with KCl and Na2SO4 and add it into a low-temperature evaporator for evaporation and salt precipitation at an evaporation temperature of 60°C-85°C; (8) The material discharged from the low-temperature evaporator is subjected to solid-liquid separation to obtain a mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl and a Lan circulating mother liquor; (9) The circulating mother liquor from the extraction process is mixed with KCl and Na2SO4 and then circulated into the low-temperature evaporator; (10) The mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl obtained by solid-liquid separation of the materials discharged from the constant temperature crystallizer and the low temperature evaporator is separated, washed and dried to obtain a potassium magnesium sulfate fertilizer product; In step (1), the seawater bittern used contains 50g / L-200g / L of NaCl, 100g / L-210g / L of MgCl2, 15g / L-45g / L of KCl and 40g / L-120g / L of MgSO4; In step (1), the mass of Na2SO4 added is 0%-15% of the mass of the bittern, and the mass of MgCl2 added is 0%-15% of the mass of the bittern; In step (2), the relative bittern steaming water loss rate is 45%-85%; In step (5), the mass of Na2SO4 added is 0%-15% of the mass of the Kie mother liquor, and the mass of water added is 0%-10% of the mass of the Kie mother liquor; In step (7), the amount of KCl added is 0%-10% of the mass of the extracted mother liquor, the amount of Na2SO4 added is 0%-15% of the mass of the extracted mother liquor, and the relative water loss rate of the mother liquor is 2.5%-15%; In step (9), the amount of KCl added is 0%-10% of the mass of the circulating mother liquor of the extraction process, and the amount of Na2SO4 added is 0%-15% of the mass of the circulating mother liquor of the extraction process.

2. The method according to claim 1, characterized in that In step (3), magnesium sulfate monohydrate Kie is MgSO4·H2O; in step (6), anhydrous potassium magnesium sulfate Lan is K2SO4·2MgSO4.

3. The method according to claim 1, characterized in that In step (10), the mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl is subjected to reverse flotation, water washing and drying to obtain potassium magnesium sulfate fertilizer product.

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