A method for extracting potassium magnesium sulfate fertilizer by evaporating and converting bittern from seawater for salt production

Abstract

The present invention discloses a method for extracting potassium sulfate and magnesium fertilizer by evaporating and converting bittern from seawater. The bittern from seawater is mixed with conversion mother liquor and then added into an evaporator for evaporation and salt precipitation. The material discharged from the evaporator is then subjected to solid-liquid separation to obtain mixed salt I and liquid phase old brine. The mixed salt I is separated to remove at least part of NaCl in the mixed salt I to obtain mixed salt II. Water is then added to the mixed salt II, and MgCl2 and / or MgSO4 and / or carnallite Car are added, and then mixed and converted. The converted liquid is subjected to solid-liquid separation to obtain a solid phase of crude potassium magnesium alum Leo, which is washed and dried to obtain a potassium sulfate and magnesium fertilizer product. The present invention targets the bittern components from seawater, obtains mixed salt by high-temperature evaporation, and converts the mixed salt into potassium sulfate and magnesium fertilizer at low temperature by adding water. The present invention realizes the comprehensive utilization of bittern from seawater, and the K in the bittern is used as the raw material. + 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 extracting potassium magnesium sulfate fertilizer by evaporating and converting bittern from seawater salt production. 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] Compared to traditional potassium sulfate products, potassium sulfate magnesium fertilizer contains an increased amount of magnesium, which promotes chlorophyll formation, improves crop yield and quality, and prolongs the shelf life of fruit. It is suitable for cash crops such as vegetables, fruit trees, tobacco, tea, and flowers. Currently, domestic potassium sulfate magnesium fertilizers primarily consist of a series of dehydrated soft potassium magnesium vanadium products with the molecular formula K2Mg(SO4)2·nH2O (n=4-6), complying with the GB / T20937-2007 standard. 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 by 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.

[0005] 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 potassium magnesium sulfate fertilizer.

[0006] In order to solve the above problems, the present invention is proposed. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the existing technology and proposes to use seawater brine to produce potassium magnesium sulfate fertilizer, which not only realizes high value-added utilization of brine resources, but also achieves high recovery rate and low cost in the preparation of potassium magnesium sulfate fertilizer.

[0008] The present invention adopts the following technical solutions:

[0009] A first aspect of the present invention provides a method for extracting potassium sulfate and magnesium fertilizer by evaporating and converting bittern from seawater for salt production, which comprises the following steps:

[0010] (1) mixing the seawater salt brine with the conversion mother liquor to obtain a first mixed brine;

[0011] (2) adding the first mixed brine into a high-temperature evaporator for evaporation and salt precipitation;

[0012] (3) subjecting the discharged material from the high-temperature evaporator to solid-liquid separation to obtain a mixed salt I containing magnesium sulfate monohydrate Kie, carnallite Car, bischofite MgCl2·6H2O and NaCl, as well as liquid phase old brine;

[0013] (4) separating the mixed salt I to remove at least part of the NaCl in the mixed salt I to obtain mixed salt II;

[0014] (5) adding water, MgCl2 and / or MgSO4 and / or carnallite Car to the mixed salt II, and then mixing and converting;

[0015] (6) performing solid-liquid separation on the converted feed liquid, whereby the obtained solid phase is crude potassium magnesium sulfate Leo, and the liquid phase is the conversion mother liquor;

[0016] (7) The conversion mother liquor is mixed with seawater salt bittern for recycling, and the crude potassium magnesium sulfate Leo is washed and dried to obtain a potassium magnesium sulfate fertilizer product.

[0017] The conversion mother liquor used in step (1) of the present invention comes from step (6). During the initial operation, since step (6) has not been reached, the conversion mother liquor is not added to step (1). After the first operation, the conversion mother liquor obtained in step (6) is returned to be added to the brine. What is described in the present invention is not the state of the initial operation, but the state of stable operation of the system after running for a period of time.

[0018] 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.

[0019] Preferably, in step (1), the mass ratio of the seawater salt-making bittern to the conversion mother liquor is 1.5:1-3.5:1.

[0020] Preferably, in step (2), the evaporation temperature is 90°C-130°C, and the water loss rate relative to the feed brine is 55%-90%. The solid phase separated after evaporation is ensured to be a mixed salt composed of two or more of MgSO4·H2O (Kie), carnallite KCl·MgCl2·6H2O (Car), bischofite MgCl2·6H2O, and NaCl. The water loss rate here refers to the ratio of the mass of water lost by evaporation to the mass of water in the feed solution.

[0021] Preferably, in step (3), Kie is MgSO4·H2O, and carnallite Car is KCl·MgCl2·6H2O.

[0022] Preferably, in step (4), the mass of the removed portion of NaCl accounts for 70%-100% of the total mass of NaCl.

[0023] Preferably, in step (5), water, MgCl2, MgSO4 and Car are added to the mixed salt after removing NaCl and mixed to ensure that the conversion is carried out at a temperature of 15°C-60°C to obtain a solid containing potassium magnesium sulfate K2SO4·MgSO4·4H2O (Leo); the conversion temperature is 15°C-60°C; the amount of water added is 80%-150% of the mass of mixed salt II, the amount of MgCl2 added is 0%-20% of the mass of mixed salt II; the amount of MgSO4 added is 0%-20% of the mass of mixed salt II; the amount of Car added is 0%-20% of the mass of mixed salt II. The mass of MgCl2, MgSO4 and carnallite Car added needs to be determined according to the actual bittern composition of the salt precipitation phase area. Specifically, according to the K content in the bittern of the salt precipitation phase area, + Mg 2+ 、Cl - 、SO4 2- The content of MgCl2, MgSO4, and carnallite Car can be optionally added. In most cases, one or two of MgCl2, MgSO4, and carnallite Car are added.

[0024] Preferably, in step (6), the potassium magnesium sulfate Leo is K2SO4·MgSO4·4H2O.

[0025] 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.

[0026] The MgCl2, MgSO4 and Car described in the present invention are not limited to industrial MgCl2, MgSO4 and Car products, and can be complex salts and solutions containing corresponding substances.

[0027] In the present invention, Kie is MgSO4·H2O, Car is KCl·MgCl2·6H2O, and Leo is K2SO4·MgSO4·4H2O.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention is aimed at the bittern component of seawater salt production, and combines Na + , K + Mg 2+ 、Cl - 、SO4 2- The five-element interactive system with H2O is used to obtain mixed salt by high-temperature evaporation, and the mixed salt is converted into potassium magnesium sulfate fertilizer by adding water at low temperature to realize the extraction of potassium magnesium sulfate fertilizer products from seawater salt bittern. The present invention realizes the comprehensive utilization of seawater salt bittern. K in bittern is used to produce potassium magnesium sulfate fertilizer. + and SO4 2- The recovery rates were all above 80%.

[0030] 2. The mass fractions of K2O, Mg, S, Cl and Na in the potassium magnesium sulfate fertilizer product prepared by the present invention all meet the standard requirements of GB / T20937-2007 potassium magnesium sulfate fertilizer.

[0031] 3. The present invention realizes the extraction of potassium sulfate and magnesium fertilizer from seawater salt brine, and completes the high added value utilization of seawater salt brine. The method of the present invention can obtain about 0.05 tons of potassium sulfate and magnesium fertilizer products for each ton of bittern. The current market price of potassium sulfate and magnesium fertilizer is about 2,100 yuan / ton, so the income from processing each ton of bittern is about 105 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the method for extracting potassium sulfate and magnesium fertilizer by evaporating and converting bittern from seawater to make salt. DETAILED DESCRIPTION

[0033] 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.

[0034] The specific steps of the method of the present invention are as follows:

[0035] Example 1

[0036] One ton of seawater salt brine is mixed with 525 kg of low-temperature conversion mother liquor to form a brine; wherein, the seawater salt 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 ratio of the brine to the low-temperature conversion mother liquor is 1.9:1. The mixed brine is pumped into a single-effect evaporator for negative pressure evaporation, and the evaporation temperature is controlled at 100 ° C. The water loss rate relative to the feed brine is 69.5%; the mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt and old brine containing MgSO4·H2O (Kie), carnallite KCl·MgCl2·6H2O (Car) and NaCl; after removing 82% of the NaCl in the mixed salt by screening, 90% of the mass of the converted mixed salt is added with water, and 2.23% of the mass of the converted mixed salt is added with MgS O4·7H2O; after conversion at 25°C, solid-liquid separation is carried out to obtain the solid phase of crude potassium magnesium sulfate K2SO4·MgSO4·4H2O (Leo), and the liquid phase is the conversion mother liquor; the crude potassium magnesium sulfate Leo is washed and dried to obtain potassium magnesium sulfate fertilizer product, in which the mass fraction of K2O is 25.31%, the mass fraction of Mg is 6.82%, the mass fraction of S is 18.32%, the mass fraction of Cl is 2.1%, and the mass fraction of Na is 0.91%, meeting the first-class requirements of GB / T 20937-2007 potassium magnesium sulfate fertilizer standard. The recovery rate of K in bittern during the whole process is 90%, SO4 2- The recovery rate was 94%, which was higher than 80%.

[0037] Example 2

[0038] One ton of seawater salt brine is mixed with 477kg of low-temperature conversion mother liquor to form a brine; wherein, the seawater salt brine used contains 144g / L of NaCl, 117g / L of MgCl2, 23g / L of KCl and 51g / L of MgSO4, and the mass ratio of the brine to the low-temperature conversion mother liquor is 2.1:1. The mixed brine is pumped into a single-effect evaporator for negative pressure evaporation, and the evaporation temperature is controlled at 100°C. The water loss rate relative to the feed brine is 77.1%; the mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt and old brine containing MgSO4·H2O (Kie), carnallite KCl·MgCl2·6H2O (Car) and NaCl; after removing 90% of the NaCl in the mixed salt by screening, 101% of the mass of the converted mixed salt is added, and 11.6% of the mass of the converted mixed salt is added. Car; after conversion at 25°C, solid-liquid separation is performed to obtain a solid phase of crude potassium magnesium sulfate K2SO4·MgSO4·4H2O (Leo), and a liquid phase of conversion mother liquor; the crude potassium magnesium sulfate Leo is washed and dried to obtain a potassium magnesium sulfate fertilizer product, in which the mass fraction of K2O is 24.31%, the mass fraction of Mg is 6.92%, the mass fraction of S is 18.94%, the mass fraction of Cl is 2.4%, and the mass fraction of Na is 0.96%, meeting the first-class requirements of the GB / T 20937-2007 potassium magnesium sulfate fertilizer standard. The recovery rate of K in bittern during the entire process is 86%, SO4 2- The recovery rate was 93%, all higher than 80%.

[0039] 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 extracting potassium sulfate and magnesium fertilizer by evaporating and converting bittern from seawater, characterized in that: It includes the following steps: (1) mixing the seawater salt brine with the conversion mother liquor to obtain a first mixed brine; (2) adding the first mixed brine into an evaporator for evaporation and salt precipitation; (3) The material discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt I containing magnesium sulfate monohydrate Kie, carnallite Car, bischofite MgCl2·6H2O and NaCl and liquid phase old brine; (4) separating the mixed salt I and removing at least part of the NaCl in the mixed salt I to obtain mixed salt II; (5) adding water, MgCl2 and / or MgSO4 and / or carnallite Car to the mixed salt II, and then mixing and converting; (6) The converted liquid is subjected to solid-liquid separation, and the obtained solid phase is crude potassium magnesium sulfate Leo, and the liquid phase is the conversion mother liquor; (7) The conversion mother liquor is mixed with seawater salt brine for recycling, and the crude potassium magnesium sulfate Leo is 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 ratio of the seawater salt-making bittern to the conversion mother liquor is 1.5:1-3.5:1; In step (2), the evaporation temperature is 90°C-130°C, and the water loss rate relative to the feed brine is 55%-90%; In step (4), the mass of the removed NaCl accounts for 70%-100% of the total mass of NaCl; In step (5), the conversion temperature is 15°C-60°C; the amount of water added is 80%-150% of the mass of mixed salt II, the amount of MgCl2 added is 0%-20% of the mass of mixed salt II; the amount of MgSO4 added is 0%-20% of the mass of mixed salt II; and the amount of Car added is 0%-20% of the mass of mixed salt II.

2. The method according to claim 1, characterized in that In step (3), Kie is MgSO4·H2O, and carnallite Car is KCl·MgCl2·6H2O.

3. The method according to claim 1, characterized in that In step (6), potassium magnesium sulfate Leo is K2SO4·MgSO4·4H2O.

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