A method for preparing potassium magnesium sulfate fertilizer by evaporating bittern from seawater salt production

Abstract

The present invention discloses a method for preparing potassium-magnesium sulfate fertilizer by evaporating brine obtained from seawater salt production, comprising the following steps: (1) adding solid Na2SO4 and / or KCl to the seawater salt production brine for mixing and brine adjustment to obtain a first mixed brine; (2) adding the first mixed brine to an evaporator for evaporation and salt precipitation; (3) subjecting the material discharged from the evaporator to solid-liquid separation to obtain a mixed salt containing anhydrous kaolinite Lan and NaCl and a Lan extraction mother liquor; and (4) separating, washing, and drying the mixed salt containing anhydrous kaolinite Lan and NaCl obtained from the solid-liquid separation in step (3) to obtain a potassium-magnesium sulfate fertilizer product. The present invention not only realizes high-value-added utilization of bittern resources, but also realizes high recovery rate and low-cost preparation of potassium-magnesium sulfate fertilizer.

Description

Technical Field

[0001] The invention relates to the technical field of seawater salt production, and in particular to a method for preparing potassium magnesium sulfate fertilizer by evaporating 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 preparing potassium magnesium sulfate fertilizer by evaporating bittern from seawater salt production, which comprises the following steps:

[0010] (1) adding Na2SO4 and / or KCl solid to seawater salt brine to mix and obtain a first mixed brine;

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

[0012] (3) performing solid-liquid separation on the material discharged from the high-temperature evaporator to obtain a mixed salt containing anhydrous potassium magnesium sulfate Lan (K2SO4·2MgSO4) and NaCl and a Lan extraction mother liquor;

[0013] (4) The mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl obtained by solid-liquid separation in step (3) is separated, washed and dried to obtain a potassium magnesium sulfate fertilizer product.

[0014] 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.

[0015] Preferably, in step (1), the mass of Na2SO4 added is 0%-20% of the mass of bittern; the mass of KCl added is 0%-15% of the mass of bittern. Here, the specific mass of Na2SO4 added and the mass of KCl added need to be determined according to the actual composition of bittern in the salt precipitation phase. + , K + 、Cl - 、SO4 2-The content can be selected by adding one or two of Na2SO4 and KCl. In most cases, one of Na2SO4 and KCl is added.

[0016] Preferably, in step (2), the evaporation temperature is 90°C-130°C, and the relative bittern water loss rate is 40%-80%. The water loss rate of the present invention refers to the ratio of the mass of water lost by evaporation to the mass of water in the feed liquid.

[0017] Preferably, in step (3), the anhydrous potassium magnesium sulfate Lan is K2SO4·2MgSO4.

[0018] Preferably, in step (4), the mixed salt of anhydrous langbeinite Lan and NaCl is subjected to reverse flotation, washed with fresh 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.

[0019] Preferably, the following steps are further included between step (3) and step (4):

[0020] (A) adding Na2SO4 and / or KCl solid to the brine mother liquor obtained by solid-liquid separation in step (3) to mix and add brine to obtain a second mixed brine;

[0021] (B) The second mixed brine is used as a circulating mother liquid and circulated to an evaporator to continue evaporating and precipitating salt.

[0022] Preferably, in step (A), the mass of Na2SO4 added is 5%-25% of the mass of the extracted mother liquor, and the mass of KCl added is 0%-10% of the mass of the extracted mother liquor. The mass of KCl added here is also determined according to the bittern composition in actual conditions.

[0023] 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.

[0024] The Na2SO4 and KCl described in the present invention are not limited to industrial Na2SO4 and KCl products, and can be complex salts and solutions containing corresponding substances.

[0025] In the present invention, Lan is K2SO4·2MgSO4.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 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 realized by adding Na2SO4 and / or KCl to the bittern of seawater salt production to ensure that the bittern of seawater salt production evaporates at a high temperature of 90℃-130℃ to precipitate a solid phase of mixed salt containing Lan and NaCl, which is then separated, washed and dried to obtain potassium magnesium sulfate fertilizer products. The present invention realizes the comprehensive utilization of bittern of seawater salt production, and the K in bittern is + Mg 2+ and SO4 2- The recovery rates were all above 80%.

[0028] 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.

[0029] 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 0.2 tons to 0.4 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 per ton, and the income from processing each ton of bittern is 420 yuan to 840 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of a method for preparing potassium magnesium sulfate fertilizer by evaporating bittern from seawater. DETAILED DESCRIPTION

[0031] 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.

[0032] The specific steps of the method of the present invention are as follows:

[0033] Example 1

[0034] One ton of seawater brine is mixed with 43.78 kg of Na2SO4 and 48.44 kg of KCl. The brine contains 70 g / L of NaCl, 192 g / L of MgCl2, 38 g / L of KCl, and 54 g / L of MgSO4, with the added Na2SO4 accounting for 4.4% of the brine's mass and the added KCl accounting for 4.8% of the brine's mass. The mixed brine is pumped into a single-effect evaporator for negative pressure evaporation at a controlled evaporation temperature of 100°C, with a relative brine water loss rate of 51.5%. The mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt of Lan and NaCl containing 52.3% Kie by mass and a Lan mother liquor. KCl and Na2SO4 are added to the Lan mother liquor at a mass fraction of 2.40% and 11.57% of the Lan mother liquor's mass, respectively, to serve as a circulating mother liquor and return it to the evaporator for further evaporation and salt precipitation. The mixed salt of Lan and NaCl obtained from solid-liquid separation is subjected to reverse flotation, fresh water washing and drying to obtain a potassium magnesium sulfate fertilizer product. The mass fraction of K2O in the product is 21.8%, the mass fraction of Mg is 11.4%, the mass fraction of S is 23.4%, the mass fraction of Cl is 2.2%, and the mass fraction of Na is 1.3%, meeting the qualified product requirements of the GB / T 20937-2007 potassium magnesium sulfate fertilizer standard. The recovery rate of K in the bittern during the entire process is 86%, the recovery rate of Mg is 87%, and the recovery rate of SO4 is 1.3%. 2- The recovery rate was 92%, which was higher than 80%.

[0035] Example 2

[0036] One ton of seawater brine is mixed with 16.06 kg of Na₂SO₄ and 35.15 kg of KCl. The brine contains 144 g / L of NaCl, 117 g / L of MgCl₂, 23 g / L of KCl, and 51 g / L of MgSO₄, with the added Na₂SO₄ accounting for 1.6% of the brine's mass and the added KCl accounting for 3.5% of the brine's mass. The mixed brine is pumped into an MVR evaporator for vacuum evaporation at a controlled evaporation temperature of 100°C, achieving a relative brine water loss rate of 67.0%. The mother liquor discharged from the evaporator is subjected to solid-liquid separation to obtain a mixed salt of Lan and NaCl containing 42.5% K₂O₄ and a Lan extract mother liquor. KCl and Na₂SO₄, each accounting for 2.60% and 12.17% of the Lan extract mother liquor's mass, are added to the Lan extract mother liquor as a circulating mother liquor, which is returned to the evaporator for further evaporation and salt precipitation. The mixed salt of Lan and NaCl obtained from solid-liquid separation is subjected to reverse flotation, fresh water washing and drying to obtain a potassium magnesium sulfate fertilizer product. The mass fraction of K2O in the product is 21.4%, the mass fraction of Mg is 11.9%, the mass fraction of S is 22.7%, the mass fraction of Cl is 2.6%, and the mass fraction of Na is 1.1%, meeting the qualified product requirements of the GB / T 20937-2007 potassium magnesium sulfate fertilizer standard. The recovery rate of K in the bittern during the entire process is 83%, the recovery rate of Mg is 82%, and the recovery rate of SO4 is 1.1%. 2- The recovery rate was 89%, all higher than 80%.

[0037] 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 preparing potassium magnesium sulfate fertilizer by evaporating bittern from seawater salt production, characterized in that: It includes the following steps: (1) adding Na2SO4 and / or KCl solid to seawater brine to mix and 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 containing anhydrous potassium magnesium sulfate Lan and NaCl and Lan extraction mother liquor; (4) The mixed salt containing anhydrous potassium magnesium sulfate Lan and NaCl obtained by solid-liquid separation in step (3) 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%-20% of the mass of the bittern; the mass of KCl added is 0%-15% of the mass of the bittern; In step (2), the evaporation temperature is 90°C-130°C, and the relative bittern water loss rate is 40%-80%.

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

3. The method according to claim 1, characterized in that In step (4), the mixed salt of anhydrous potassium magnesium sulfate Lan and NaCl is subjected to reverse flotation, water washing and drying to obtain potassium magnesium sulfate fertilizer product.

4. The method according to claim 1, wherein There are the following steps between step (3) and step (4): (A) adding Na2SO4 and / or KCl solid to the brine mother liquor obtained by solid-liquid separation in step (3) to mix and add brine to obtain a second mixed brine; (B) The second mixed brine is used as a circulating mother liquid and circulated to the evaporator to continue evaporating and precipitating salt.

5. The method according to claim 4, characterized in that In step (A), the mass of Na2SO4 added is 5%-25% of the mass of the blue mother liquor, and the mass of KCl added is 0%-10% of the mass of the blue mother liquor.

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