阅读说明：本技术 高钠镁比工业废水净化除镁及制备氢氧化镁阻燃剂方法 (Method for purifying and removing magnesium from industrial wastewater with high sodium-magnesium ratio and preparing magnesium hydroxide fire retardant ) 是由 刘志启 闫东强 赵鹏程 周自圆 李娜 陈安琪 于 2021-09-29 设计创作，主要内容包括：本发明公开了一种高钠镁比工业废水净化除镁及制备氢氧化镁阻燃剂方法,属于氢氧化镁制备方法领域。该方法是利用高钠含量环境中低镁的工业废水与氢氧化钠溶液进行沉淀反应,待反应结束后沉降一定时间,将沉降后的上层清液进行抽滤,下层沉淀离心,滤液和离心液即为净化后的高纯硫酸钠溶液。离心后的沉淀加蒸馏水再浆后转入高压反应釜内进行水热反应,然后过滤洗涤再干燥后,得到形貌为六角片状的氢氧化镁阻燃剂。本发明解决了高钠镁比的工业废水的绿色资源化利用问题,具有工艺流程简单,生产成本低,无需任何添加剂,就可以制备纯度高的饱和硫酸钠溶液及形貌规整的纳米级氢氧化镁阻燃剂。(The invention discloses a method for purifying and removing magnesium from industrial wastewater with a high sodium-magnesium ratio and preparing a magnesium hydroxide flame retardant, belonging to the field of magnesium hydroxide preparation methods. The method comprises the steps of carrying out precipitation reaction on low-magnesium industrial wastewater in a high-sodium content environment and a sodium hydroxide solution, settling for a certain time after the reaction is finished, carrying out suction filtration on a supernatant after the settlement, centrifuging a lower-layer precipitate, and obtaining a filtrate and a centrifugate as a purified high-purity sodium sulfate solution. Adding distilled water into the centrifuged precipitate, repulping, transferring the precipitate into a high-pressure reaction kettle for hydrothermal reaction, filtering, washing and drying to obtain the magnesium hydroxide flame retardant with the hexagonal sheet shape. The method solves the problem of green resource utilization of industrial wastewater with high sodium-magnesium ratio, has simple process flow and low production cost, and can prepare high-purity saturated sodium sulfate solution and nano-scale magnesium hydroxide flame retardant with regular appearance without any additive.)

1. The method for purifying and removing magnesium from industrial wastewater with high sodium-magnesium ratio and preparing the magnesium hydroxide flame retardant is characterized by comprising the following steps of:

step 1, adding 0.5-2.5mol/L sodium hydroxide solution into industrial wastewater of sodium sulfate with high sodium-magnesium ratio at a constant reaction temperature of 25-100 ℃ and a certain stirring speed at a certain dropping speed for precipitation reaction for 30-60 min;

step 2, settling for 2-5 hours after the reaction in the step 1 is finished, carrying out suction filtration on the settled supernatant to leave a lower-layer precipitate, centrifuging the precipitate, adding water into the centrifuged precipitate, and then pulping;

step 3, placing the slurry repulped in the step 2 in a high-pressure reaction kettle for hydrothermal reaction at the temperature of 120 ℃ and 180 ℃ for 2-10 h;

and 4, after the reaction in the step 3 is finished, filtering and washing a product obtained in the high-pressure reaction kettle, and then drying the product at the temperature of 80-110 ℃ for 3-8h to obtain the hexagonal flaky nano-scale magnesium hydroxide flame retardant.

2. The preparation method of the nano magnesium hydroxide fire retardant according to claim 1, wherein in the step 1, the content of magnesium sulfate in the industrial wastewater with high sodium-magnesium ratio is 0.1-0.2mol/L, and the sodium-magnesium ratio is 20-40.

3. The method for purifying and removing magnesium and preparing magnesium hydroxide fire retardant for industrial wastewater with high sodium-magnesium ratio as claimed in claim 1, wherein in step 1, the ratio of the amount of the substance of sodium hydroxide to the amount of the substance of magnesium is n (Mg)²⁺)：n(OH^-) =1:1.2-1:2.4, and the pH range for complete precipitation is 10.5-12.5.

4. The method for purifying and removing magnesium from industrial wastewater and preparing magnesium hydroxide fire retardant according to claim 1, wherein in step 1, the stirring speed is 200-600r/min, and the dropping speed of sodium hydroxide is 2.5-7.5 ml/min.

5. The method for purifying and removing magnesium from industrial wastewater and preparing magnesium hydroxide fire retardant according to claim 1, wherein in step 2, after the reaction is finished and settled, the supernatant is filtered, the lower layer is precipitated and centrifuged, the settling time is 2-5h, the centrifugation speed is 3000-4000r/min, and the centrifugation time is 3-8 min.

6. The method for purifying and removing magnesium and preparing the magnesium hydroxide fire retardant for the industrial wastewater with the high sodium-magnesium ratio as claimed in claim 1, wherein in the step 2, a solid-liquid separation method combining sedimentation, suction filtration and centrifugation is adopted after reaction precipitation, sedimentation and delamination.

7. The method for purifying and removing magnesium and preparing magnesium hydroxide fire retardant for industrial wastewater with high sodium-magnesium ratio as claimed in claim 1, wherein in step 2, the filtrate and the centrifugate are high-purity saturated sodium sulfate solution.

8. The method for purifying and removing magnesium and preparing magnesium hydroxide fire retardant for industrial wastewater with high sodium-magnesium ratio as claimed in claim 1, wherein the hydrothermal temperature is 120-180 ℃ and the hydrothermal time is 2-10 h.

9. The method for purifying and removing magnesium from industrial wastewater and preparing magnesium hydroxide fire retardant according to claim 1, wherein the magnesium hydroxide prepared in step 4 is hexagonal and flaky.

Technical Field

The invention relates to the field of magnesium hydroxide preparation methods, in particular to a preparation method of a nano magnesium hydroxide flame retardant.

Background

With the improvement of environmental protection standards in recent years in China, the green resource utilization of industrial waste liquid is greatly developed. At the present stage, the large-scale treatment of the high-salinity wastewater still has the characteristics of low treatment efficiency and high operation cost, and has a plurality of key technical problems which need to be broken through and solved. The industrial wastewater with high sodium-magnesium ratio is mainly derived from drainage generated in the production processes of enterprises such as printing and dyeing, refining, pharmacy, salt manufacturing and the like, and has the characteristics of high content of sodium sulfate and a small amount of magnesium sulfate. If the direct evaporation crystallization is not processed, the purity of the sodium sulfate is too low, and the magnesium resource cannot be comprehensively utilized, so that the resource is seriously wasted. If the waste water is directly discharged, the waste water can cause serious pollution to soil and water quality.

Magnesium hydroxide, as an inorganic material, has the characteristics of no toxicity, no odor, no corrosiveness, high decomposition temperature and the like, and has very important application in the fields of flame retardance, environmental protection, medical use, food, ceramics, cosmetics and the like. The advantages of magnesium hydroxide as an inorganic flame retardant are particularly prominent with the increasing demand for halogen-free flame retardants in recent years. The magnesium hydroxide flame retardant has a high decomposition temperature, generates water after decomposition, absorbs a large amount of heat to lower the surface temperature of a synthetic material filled therein in a flame, and has the effects of inhibiting the decomposition of a polymer and cooling the generated combustible gas, as with the aluminum hydroxide flame retardant. The magnesium oxide generated by decomposing the magnesium hydroxide is a good refractory material, can also help to improve the fire resistance of the synthetic material, and simultaneously, the water vapor emitted by the magnesium oxide can also be used as a smoke suppressant. Compared with similar inorganic flame retardants, the magnesium hydroxide has better smoke suppression effect, does not discharge harmful substances in the production, use and waste processes of the magnesium hydroxide, and can neutralize acidic and corrosive gases generated in the combustion process.

The main process for the preparation of magnesium hydroxide of the prior art is brine (MgCl)₂) And hydrated limeThe reaction is carried out to obtain; brine (MgCl)₂) Reacting with ammonia water to obtain the product; magnesite, hydrochloric acid and ammonia water. The process for purifying and removing magnesium from industrial wastewater containing magnesium and simultaneously producing the flame retardant magnesium hydroxide is not reported.

Disclosure of Invention

The invention aims to provide a preparation method of a nano magnesium hydroxide flame retardant, which aims to solve the problem of preparing flame-retardant magnesium hydroxide from magnesium-containing industrial wastewater in the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the method for purifying and removing magnesium from industrial wastewater with high sodium-magnesium ratio and preparing the magnesium hydroxide flame retardant comprises the following steps:

step 1, adding 0.5-2.5mol/L sodium hydroxide solution into industrial wastewater of sodium sulfate with high sodium-magnesium ratio at a constant reaction temperature of 25-100 ℃ and a certain stirring speed at a certain dropping speed for precipitation reaction for 30-60 min;

step 2, settling for 2-5 hours after the reaction in the step 1 is finished, carrying out suction filtration on the settled supernatant to leave a lower-layer precipitate, centrifuging the precipitate, adding water into the centrifuged precipitate, and then pulping;

step 3, placing the slurry repulped in the step 2 in a high-pressure reaction kettle for hydrothermal reaction at the temperature of 120 ℃ and 180 ℃ for 2-10 h;

and 4, after the reaction in the step 3 is finished, filtering and washing a product obtained in the high-pressure reaction kettle, and then drying the product at the temperature of 80-110 ℃ for 3-8h to obtain the hexagonal flaky nano-scale magnesium hydroxide flame retardant.

Further, in the step 1, the content of magnesium sulfate in the industrial wastewater with high sodium magnesium ratio is 0.1-0.2mol/L, and the sodium magnesium ratio is 20-40.

Further, in step 1, the ratio of the amount of the substance of sodium hydroxide to the amount of the substance of magnesium added is n (Mg)²⁺)：n(OH^-) =1:1.2-1:2.4, and the pH range for complete precipitation is 10.5-12.5.

Further, in the step 1, the stirring speed is 200-600r/min, and the dropping speed of the sodium hydroxide is 2.5-7.5 ml/min.

Further, in step 2, after the reaction is finished and the sedimentation is finished, the supernatant is filtered, the lower layer is precipitated and centrifuged, the sedimentation time is 60-300min, the centrifugation speed is 3000-4000r/min, and the centrifugation time is 3-8 min.

Further, in the step 2, a solid-liquid separation method combining sedimentation, suction filtration and centrifugation is adopted after reaction precipitation, sedimentation and delamination.

Further, in the step 2, the filtrate and the centrifugate are high-purity saturated sodium sulfate solution.

Further, in the step 3, the hydrothermal temperature is 120-180 ℃, and the hydrothermal time is 2-10 h.

Further, in the step 4, the prepared magnesium hydroxide flame retardant is hexagonal sheet-shaped.

The preparation method of the nano-scale magnesium hydroxide flame retardant comprises the following steps of (1) carrying out precipitation reaction between industrial wastewater containing sodium sulfate with a high sodium-magnesium ratio and strong base (sodium hydroxide), and reacting magnesium ions and hydroxide ions to generate magnesium hydroxide precipitate: the reaction equation is as follows:

MgSO₄+2NaOH=Na₂SO₄+Mg(OH)₂↓

compared with the prior art, the invention has the advantages that: the method solves the problem of green resource utilization of the industrial wastewater with high sodium-magnesium ratio, and converts magnesium into the magnesium hydroxide flame retardant with use value while purifying and removing magnesium to obtain high-purity sodium sulfate; compared with the prior art, the raw materials are easy to obtain, the process flow for preparing the magnesium hydroxide flame retardant by purifying and removing magnesium is simple, the production cost is low, and the problem of slow filtration in the strong alkali method for producing the magnesium hydroxide is solved by a solid-liquid separation mode of sedimentation, filtration and centrifugation.

Drawings

FIG. 1 shows the ratio of the amount of sodium hydroxide material to the amount of magnesium material added in the present invention is n (Mg)²⁺)：n(OH^-) Graph of magnesium content in filtrate at 1:1.2-1: 2.4.

FIG. 2 is an X-ray diffraction pattern of the product of example 1 of the present invention.

FIG. 3 is a scanning electron micrograph of a product according to example 1 of the present invention.

FIG. 4 is an X-ray diffraction pattern of the product of example 2 of the present invention.

FIG. 5 is a scanning electron micrograph of a product of example 2 of the present invention.

FIG. 6 is an X-ray diffraction pattern of the product of example 3 of the present invention.

FIG. 7 is a scanning electron micrograph of a product according to example 3 of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Example 1

Preparation of the nano magnesium hydroxide flame retardant: measuring 300ml of industrial waste liquid with magnesium ion concentration of 0.1mol/L and sodium ion concentration of 3mol/L, heating to 60 ℃, measuring 120ml of 0.5mol/L sodium hydroxide solution, adding the solution into the high-sodium magnesium-containing solution, stirring for reaction for 1h, settling for 2h after the reaction is finished, carrying out suction filtration on the settled supernatant, measuring the magnesium content of the filtrate, carrying out lower-layer precipitation centrifugation, and adding distilled water into the centrifuged precipitate for repulping. And transferring the slurry into a high-pressure reaction kettle to react for 6 hours at 140 ℃, and filtering and washing after the reaction kettle is naturally cooled. Drying the washed product at 95 ℃ for 4h to obtain Mg (OH)₂And (3) a flame retardant.

Example 2

Preparation of the nano magnesium hydroxide flame retardant: measuring 300ml of industrial waste liquid with magnesium ion concentration of 0.1mol/L and sodium ion concentration of 3mol/L, heating to 60 ℃, measuring 120ml of 0.5mol/L sodium hydroxide solution, adding the solution into the high-sodium magnesium-containing solution, stirring for reaction for 1h, settling for 2h after the reaction is finished, carrying out suction filtration on the settled supernatant, measuring the magnesium content of the filtrate, carrying out lower-layer precipitation centrifugation, and adding distilled water into the centrifuged precipitate for repulping. And transferring the slurry into a high-pressure reaction kettle to react for 8 hours at the temperature of 140 ℃, and performing suction filtration and washing after the reaction kettle is naturally cooled. The washed product is placed at the temperature of 95 ℃ for 4 hours to obtain Mg (OH)₂And (3) a flame retardant.

Example 3

Preparation of the nano magnesium hydroxide flame retardant: measuring 300ml of industrial waste liquid with magnesium ion concentration of 0.1mol/L and sodium ion concentration of 3mol/L, heating to 60 ℃, measuring 120ml of 0.5mol/L sodium hydroxide solution, and adding into high-sodium magnesium-containing solutionStirring the solution for reaction for 1h, settling for 2h after the reaction is finished, carrying out suction filtration on the settled supernatant, measuring the magnesium content of the filtrate, centrifuging the lower-layer precipitate, adding distilled water into the centrifuged precipitate, and repulping. And transferring the slurry into a high-pressure reaction kettle to react for 6 hours at 180 ℃, and performing suction filtration and washing after the reaction kettle is naturally cooled. The washed product is placed at the temperature of 95 ℃ for 4 hours to obtain Mg (OH)₂And (3) a flame retardant.

As shown in FIG. 1, the analysis of FIG. 1 by inductively coupled plasma spectrometer can show that the magnesium content in the original solution is gradually reduced when the added precipitant is gradually increased, and when n (Mg)²⁺)：n(OH^-) And when the ratio is 1:1.4-1:2.4, the magnesium content in the solution is 5-10 ppm. This shows that the process can remove the magnesium in the industrial waste liquid with high sodium-magnesium ratio.

The X-ray diffraction pattern analysis in fig. 2, 4 and 6 shows that the prepared sample is consistent with the standard card of magnesium hydroxide, which indicates that the product obtained by the above method is consistent with the product of the present invention.

As can be seen from the scanning electron micrographs at 8 ten thousand times magnification in fig. 3, 5 and 7, the morphology of the product is a regular hexagonal sheet shape and the size is in the nanometer level, which indicates that the product obtained by the above method is consistent with the product of the present invention.

The embodiments of the present invention are described only for the preferred embodiments of the present invention, and not for the limitation of the concept and scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall into the protection scope of the present invention, and the technical content of the present invention which is claimed is fully set forth in the claims.