Method for preparing magnesium sulfate in an environmentally friendly and efficient manner

Abstract

The present application belongs to the field of magnesium sulfate preparation, and relates to an environmentally-friendly and efficient method for preparing magnesium sulfate, comprising the following steps: (1) adding mother liquor and water into a reaction tank, and then adding light calcined powder and stirring uniformly; (2) slowly adding waste acid into the reaction tank, controlling the acid adding rate, and keeping the reaction for 30 minutes after reaching the standard; (3) adding a composite biological flocculant after the reaction is completed, stirring uniformly, and settling; (4) performing heat preservation treatment on supernatant, and performing solid-liquid separation on tank bottom slurry; (5) performing recrystallization on the supernatant, and performing water cleaning on the crystals; and (6) drying and screening the cleaned crystals, so that high-purity magnesium sulfate is obtained. The present application uses waste acid produced in the production of sulfamic acid as an acid source, replaces traditional sulfuric acid raw materials, realizes waste treatment with waste, combines filtrate and water washing liquid in the preparation process, reduces fresh water consumption and waste water discharge, uses the filter cake after slurry treatment as a cement building material raw material, and realizes high-value utilization of solid waste.

Description

Technical Field

[0001] This invention relates to an environmentally friendly and efficient method for preparing magnesium sulfate, belonging to the field of magnesium sulfate preparation. Background Technology

[0002] Magnesium sulfate is a colorless crystal or white powder, odorless, bitter, easily soluble in water and glycerol, and its aqueous solution is neutral. It dissolves in its own water of crystallization at 67.5℃ and is slightly soluble in ethanol. Magnesium sulfate is used directly as a wastewater treatment agent or as a raw material for wastewater treatment. It is used in industrial wastewater treatment to coagulate and settle wastewater, so that it meets the discharge standards. It is an important chemical raw material. In industrial production, high-purity magnesite is used as raw material. After low-temperature roasting, it forms light calcined powder, which is then produced by sulfuric acid leaching, soaking, and cooling crystallization in a crystallizer. This process is simple and is adopted by many production units. However, the following problems exist: (1) High-purity light calcined powder is used as raw material, which is costly. If low-purity light calcined powder is used to prepare magnesium sulfate, the product purity is not high; (2) High-concentration sulfuric acid is generally used, which is costly. Summary of the Invention

[0003] This invention provides an environmentally friendly and efficient method for preparing magnesium sulfate, which solves the problems of high cost and low purity caused by the use of lightly calcined powder and high-concentration sulfuric acid in the existing magnesium sulfate preparation process.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] An environmentally friendly and efficient method for preparing magnesium sulfate includes the following steps:

[0006] (1) Add mother liquor and water to the reaction tank, then add light calcined powder, and stir evenly at a speed of 200-400 r / min;

[0007] (2) Slowly add the waste acid generated during the production of aminosulfonic acid into the reaction tank, control the acid addition rate, control the pH value at the end of the reaction to be 6, and the Baume degree to reach 39-40°Bé. After reaching the standard, maintain the reaction for 30 minutes.

[0008] (3) After the reaction is complete, add the composite biological flocculant, stir evenly, and let the material in the reaction tank settle for 3-4 hours;

[0009] (4) The supernatant is transported to the buffer tank of the reaction tank for heat preservation treatment. Water is added to the bottom slurry to destroy its saturation. Then solid-liquid separation is carried out. The filter cake is washed with clean water. The filtrate and the washing liquid are combined as mother liquor and used to dissolve the light calcined powder in step (1). The washed filter cake is blown with air for 5-6 minutes and used as raw material for cement building materials.

[0010] (5) Recrystallize the supernatant, perform solid-liquid separation to obtain crystals, and wash the crystals with water. Combine the filtrate and washing water as mother liquor for dissolving the light calcined powder in step (1).

[0011] (6) Dry the cleaned crystals and sieve them to obtain high-purity magnesium sulfate;

[0012] (7) The waste gas generated during the drying and screening process is sprayed and washed, defoamed, and discharged. The washing liquid is used as water to dilute the bottom slurry.

[0013] Furthermore, preferably, the lightly calcined powder contains, by weight percentage, MgO ≥ 85%, SiO2 ≤ 4%, CaO ≤ 4.0%, Fe2O3 ≤ 1.5%, and loss on ignition ≤ 10%.

[0014] Furthermore, preferably, the waste acid contains 55-60% sulfuric acid by weight.

[0015] Furthermore, preferably, the composite bio-flocculator comprises, by weight percentage, 35-40% γ-polyglutamic acid, 6-8% sodium citrate, 12-16% polyferric sulfate, 15-20% carboxymethyl chitosan, 10-15% polyaspartic acid, and 8-10% carboxymethyl cellulose.

[0016] Furthermore, preferably, the amount of the composite bioflocculant added is 80-100 ppm.

[0017] The beneficial effects of this invention are:

[0018] This invention uses waste acid from aminosulfonic acid production as the acid source to replace traditional sulfuric acid raw materials, achieving "waste treatment with waste". At the same time, the filtrate and washing liquid are combined and reused in the preparation process, reducing fresh water consumption and wastewater discharge. The filter cake after slurry treatment is used as a raw material for cement building materials, realizing high-value utilization of solid waste. It is a clean and environmentally friendly magnesium sulfate preparation process.

[0019] This invention employs a composite bio-flocculator, which, through optimization of its composition, enables precise flocculation and precipitation of impurities in low-purity light-burned powder, effectively improving the purity of magnesium sulfate, reducing impurity content, and increasing product value. At the same time, the use of the composite bio-flocculator to replace traditional chemical flocculants (PAC, PAM) can effectively reduce secondary pollution. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a process flow diagram for the production of magnesium sulfate according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are also described.

[0023] Raw materials used in this invention:

[0024] Lightly calcined powder: by weight percentage, MgO 86.5%, SiO2 2.8%, CaO 3.4%, Fe2O3 1.3%, loss on ignition 5.6%, other 0.4%.

[0025] The waste acid generated during the production of aminosulfonic acid contains 55.8% sulfuric acid by weight. The remaining raw materials are purchased from the market and have no special requirements, as long as they meet the relevant product standards.

[0026] Examples 1-5: Investigating the flocculation properties of raw materials for different composite bioflocculators

[0027] An environmentally friendly and efficient method for preparing magnesium sulfate includes the following steps:

[0028] (1) Add a certain amount of water to the beaker, then add the light calcined powder and stir well;

[0029] (2) Slowly add the waste acid generated during the production of aminosulfonic acid into the beaker, control the acid addition rate, control the pH value of the reaction endpoint to 6, and the Baume degree to reach 40°Bé. After reaching the standard, maintain the reaction for 30 minutes.

[0030] (3) After the reaction is completed, add 100 ppm of disposable composite biological flocculant, stir evenly, let the material settle for 4 hours, and then measure the content of magnesium ions, calcium ions and iron ions in the supernatant. Calculate the removal rate of magnesium ions, calcium ions and iron ions. See Table 1 for the specific results.

[0031] Table 1. Results of flocculation tests on composite bio-flocculators using different raw materials.

[0032]

[0033] As shown in Table 1, the composite bio-flocculator of the present invention can effectively improve the removal rate of calcium sulfate and ferric sulfate, reduce the removal rate of magnesium sulfate, and thus effectively improve the product yield and purity.

[0034] In the composite bioflocculant of this invention, the carboxyl group of γ-polyglutamic acid forms a strong chelate with calcium ions, promoting calcium sulfate precipitation and maintaining high selectivity. Sodium citrate, as an auxiliary chelating agent, preferentially binds with calcium ions to form a stable complex, accelerating precipitation and reducing magnesium ion interference. Polyferric sulfate hydrolyzes under acidic conditions to generate ferric hydroxide precipitate, efficiently removing iron ions. Carboxymethyl chitosan coordinates with iron ions through its carboxyl group, synergistically forming precipitate with polyferric sulfate. Polyaspartic acid selectively adsorbs calcium / iron ions using its carboxyl structure. Carboxymethyl cellulose enhances the floc bridging ability, promotes particle aggregation, and its carboxyl group can assist in calcium ion adsorption.

[0035] γ-Polyglutamic acid and polyferric sulfate work synergistically to form a stable complex by doubly chelating calcium ions with their carboxyl groups, thus avoiding competition for magnesium ions. Sodium citrate preferentially complexes calcium ions, further reducing calcium activity and accelerating precipitation. The carboxyl groups of polyferric sulfate and carboxymethyl cellulose have low affinity for magnesium, preventing non-specific adsorption.

[0036] The composite bio-flocculator of the present invention achieves highly efficient and selective precipitation of calcium and iron ions during the preparation of magnesium sulfate from lightly calcined powder through the synergistic effect of γ-PGA, polyferric sulfate, carboxymethyl chitosan, polyaspartic acid, carboxymethyl cellulose and sodium citrate, while ensuring a very low adsorption rate of magnesium ions.

[0037] Examples 6-9

[0038] It is basically the same as Example 5, except that the raw material ratio in the composite bio-flocculator formulation is different, as shown in Table 2.

[0039] Table 2. Flocculation test results of different embodiments

[0040]

[0041] As shown in Table 2, the composite bio-flocculator of the present invention has good flocculation selectivity, good flocculation effect on calcium sulfate and magnesium sulfate, removal rate of calcium sulfate is over 86%, removal rate of ferric sulfate is over 85%, and removal rate of magnesium sulfate is low, below 5%.

[0042] Example 10

[0043] like Figure 1As shown, an environmentally friendly and efficient method for preparing magnesium sulfate includes the following steps:

[0044] (1) Light calcined powder ton bags are transported to the powder silo by unpacking machine and tubular chain conveyor; mother liquor and water are injected into the reaction tank, and the double-shaft spiral conveyor at the bottom of the powder silo is turned on to add the powder evenly and continuously into the reaction tank at 400r / min. Under the stirring action, it is fully mixed with mother liquor and water.

[0045] (2) Open the dilute acid valve and slowly add the waste acid generated during the aminosulfonic acid production process into the reaction tank. Control the acid addition rate, observe the changes in liquid level and temperature in the reaction tank, and observe the data displayed on the pH meter while adding acid. Control the pH value at the end of the reaction to be 6, and test the Baume degree to reach 39-40°Bé. After reaching the standard, maintain the reaction for 30 minutes;

[0046] (3) After the reaction is complete, add 80 ppm of composite biological flocculant, continue stirring for 2 minutes and then stop stirring. Let the material in the reaction tank settle for 3 hours.

[0047] (4) The supernatant is transported to the buffer tank of the reaction tank by a pneumatic diaphragm pump and kept at 80°C. The bottom slurry is added with the washing water of the drying tail gas to break its saturation. The stirring is turned on at 400r / min and pumped to the middle tank of the bottom slurry. Then it is pumped into the filter press for solid-liquid separation. The filter cake is washed with clean water. The filtrate and the washing liquid flow into the mother liquor tank as mother liquor for dissolving the light calcined powder in step (1). The washed filter cake is blown with instrument air for 5-6 minutes and unloaded as raw material for cement building materials.

[0048] (5) The main equipment for the crystallization separation process is the OSLO type continuous crystallizer and the screw discharge filter centrifuge. The OSLO type continuous crystallizer device consists of a high-flow axial flow circulation pump, a heat exchanger, and the OSLO type crystallizer. A submersible pump is installed on the reaction liquid buffer tank to quantitatively and continuously transport the filtrate into the upper circulation outlet pipe of the OSLO type crystallizer and enter the material circulation process of the OSLO type crystallizer. When the material circulates to the external tube heat exchanger, it exchanges heat with the cooling water, which increases the supersaturation of the circulating liquid, precipitates crystal nuclei and grows continuously, and finally falls into the bottom of the crystallizer from the central guide tube of the OSLO type crystallizer. It flows into the screw discharge filter centrifuge quantitatively and continuously with the mother liquor through the valve control from the bottom side of the OSLO type crystallizer, realizing solid-liquid separation and water washing of free acid radical ions on the surface of the crystals. The crystals continuously fall into the drying silo, and the filtrate and washing water enter the mother liquor tank for dissolving the light calcined powder in step (1).

[0049] (6) The free water content of magnesium sulfate crystals in the silo before drying is generally around 5%. It is quantitatively and evenly added into the drum dryer by a screw conveyor. As the material is lifted by the lifting plate, multiple material curtains are formed in the drum. Hot air is sent in from the feed section of the drum dryer to remove the moisture on the surface of the crystals. The dried crystals enter the drum screen and are screened to separate two different particle sizes, coarse and fine. The products are then transported to the finished product warehouse, metered, packaged, and stored.

[0050] (7) During the drying and screening process, fine powdery crystals will float out with the blower and generate waste gas. The waste gas is then sprayed and washed by the Venturi tube bidirectional vortex nozzle, defoamed in the empty tower, and discharged through the chimney. The washing liquid is used as water to dilute and replenish the bottom slurry of the synthesis reaction tank or as mother liquor.

[0051] The above process was used to scale up production on the production line, producing 10 batches. The product data obtained is shown in Table 3.

[0052] Table 3 Quality inspection data of magnesium sulfate products

[0053]

[0054] As shown in Table 3, the magnesium sulfate product produced by the process of this invention has high purity and high yield, and does not generate large-scale waste, making it green and environmentally friendly.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An environmentally friendly and efficient method for preparing magnesium sulfate, characterized in that, Includes the following steps: (1) Add mother liquor and water to the reaction tank, then add light calcined powder, and stir evenly at a speed of 200-400 r / min; (2) Slowly add the waste acid generated during the production of aminosulfonic acid into the reaction tank, control the acid addition rate, control the pH value at the end of the reaction to be 6, and the Baume degree to reach 39-40°Bé. After reaching the standard, maintain the reaction for 30 minutes. (3) After the reaction is complete, add the composite biological flocculant, stir evenly, and let the material in the reaction tank settle for 3-4 hours; (4) Heat preservation treatment of supernatant, water is added to the slurry at the bottom of the pool to destroy its saturation, and then solid-liquid separation is carried out. The filter cake is washed with clean water, and the filtrate and washing liquid are combined as mother liquor, which is used to dissolve the light calcined powder in step (1). The filter cake after washing is blown with air for 5-6 minutes and used as raw material for cement building materials. (5) Recrystallize the supernatant, perform solid-liquid separation to obtain crystals, wash the crystals with water, combine the filtrate and washing water as mother liquor, and then use it to dissolve the light calcined powder in step (1); (6) Dry the cleaned crystals and sieve them to obtain high-purity magnesium sulfate; (7) The waste gas generated during the drying and screening process is sprayed and washed, defoamed, and discharged. The washing liquid is used as water to dilute and replenish the sludge at the bottom of the pool. In the lightly calcined powder, by weight percentage, MgO ≥ 85%, SiO2 ≤ 4%, CaO ≤ 4.0%, Fe2O3 ≤ 1.5%, and loss on ignition ≤ 10%; The composite bio-flocculator, by weight percentage, comprises 35-40% γ-polyglutamic acid, 6-8% sodium citrate, 12-16% polyferric sulfate, 15-20% carboxymethyl chitosan, 10-15% polyaspartic acid, and 8-10% carboxymethyl cellulose; the addition amount of the composite bio-flocculator is 80-100 ppm.

2. The method for preparing magnesium sulfate in an environmentally friendly and efficient manner according to claim 1, characterized in that: The waste acid contains 55-60% sulfuric acid by weight.

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