Magnesium hydroxide is not just a flame retardant

As a flame retardant material, magnesium hydroxide has many advantages:


(1) Magnesium hydroxide has higher decomposition temperature and higher ignition point than aluminum hydroxide, which increases the heating temperature of polymer materials;


(2) MgO generated after combustion dehydration is a refractory and an alkaline oxide, which can absorb acid gas;


(3) Strong heat absorption capacity and high flame retardant efficiency;


(4) Low cost and easy to process in different polymer materials.


In recent years, magnesium hydroxide has been widely used as a green flame retardant.


Preparation of magnesium hydroxide


There are two aspects that need to be controlled most in the preparation of magnesium hydroxide: (1) filtration performance. If the sedimentation performance of magnesium hydroxide slurry is poor, it will affect the washing and separation operation process, prolong the synthesis cycle of magnesium hydroxide, and affect the output of magnesium hydroxide; (2) Control the morphology, because the flame retardant effect of magnesium hydroxide with regular morphology is good, it needs to adopt appropriate production methods and process conditions to meet the requirements.


The main production processes of magnesium hydroxide include direct precipitation method, grinding method of magnesium containing ore, magnesium oxide hydration method, etc.


Direct precipitation method


At present, there are many methods to synthesize magnesium hydroxide, among which the most used method is precipitation method. Because of its low price, simple and easy operation, it is easy to control the crystal morphology. In the precipitation method, salt solution precipitation is mainly used, and strong bases such as ammonia or sodium hydroxide are usually used. Magnesium chloride, magnesium sulfate and magnesium nitrate are most widely used in magnesium salts, and organic magnesium salt magnesium acetate is also occasionally used.


The preparation of magnesium hydroxide by ammonia method in the direct precipitation method is divided into one-step method and continuous precipitation method. The continuous precipitation method realizes the recycling of resources, reduces the production cost and ensures the quality of products.


Hydrothermal method


Hydrothermal reaction can effectively control the morphology and size of magnesium hydroxide. The properties of the product mainly depend on the type of precursor magnesium salt, the control of solvent and reaction temperature; The morphology of the product mainly depends on the pH of the solution and the reaction temperature. By adjusting the pH, the morphology of magnesium hydroxide is nano flower, needle, flake and spherical.


The advantage of hydrothermal synthesis is that magnesium hydroxide with specific surface area greater than 100m2 / G can be obtained. The disadvantage is that high temperature and high pressure are used in industry, and the cost is high.


Sonochemical synthesis


Sonochemical method is to use ultrasound in the frequency range of 20khz-10mhz to trigger the formation and collapse of micro cells, and produce active sites at high temperature and high pressure. Compared with the traditional method, this method occurs under extreme conditions, which can greatly increase the reaction rate and produce small crystals with more uniform morphology. The characteristic of sonochemical synthesis is that different structural types of materials can be produced by changing the reaction medium.


Sol-gel method


Sol-gel method is to use highly active metal compounds as precursors, to mix in liquid phase, to hydrolyze, to form condensation, and to form metal hydroxides. A stable transparent sol is formed, which is slowly polymerized by aging, forming a network structure and losing the solvent in the reaction process to form a gel. The nanomaterials were prepared by subsequent drying and sintering.


The reaction process of this method is that the precursor is dispersed and dissolved, hydrolyzed to form monomer, polymerized to form sol, and nano magnesium hydroxide is prepared through drying and heat treatment.


Application of magnesium hydroxide


Magnesium hydroxide is widely used. Flame retardant and environmental protection are the main application fields of magnesium hydroxide. In addition, magnesium hydroxide slurry has high activity, good adsorption performance, convenient adjustment and control. Magnesium hydroxide can also be used as a neutralizer for the treatment of acidic waste liquid and sulfur rich oxides, the removal of heavy metals and the improvement of soil acidity. It can also be used as an antacid for pharmacy, fertilizer additives, etc.


Application of flame retardant


Magnesium hydroxide is an important halogen-free environmental friendly green flame retardant. The flame retardant mechanism is to generate stable coating magnesium oxide and water vapor. The flame retardant efficiency is low. In order to achieve good flame retardant effect, the addition amount is generally as high as 50% ~ 60%. At this time, the mechanical properties and processing properties of flame retardant composites are seriously reduced, The usual method is to modify the surface of magnesium hydroxide and synergistic flame retardant of magnesium hydroxide.


Magnesium hydroxide flame retardant can be used not only alone, but also in combination with other synergistic agents, such as magnesium hydroxide / red phosphorus, magnesium hydroxide / zinc borate, magnesium hydroxide / carbon nanotubes and magnesium hydroxide / carbon black. The synergistic flame retardant of magnesium hydroxide will not only obtain better flame retardant effect, but also reduce the amount of flame retardant and reduce the cost.


Application in the field of environmental protection


(1) Acid containing wastewater treatment


The neutralization reaction of magnesium hydroxide is slow, and the particle size produced after the neutralization reaction is large and settles quickly. In the treatment of acid containing wastewater, magnesium hydroxide can simplify the operation process, reduce the operation time, have good controllability and reduce the treatment cost.


(2) Heavy metal removal


Due to its large specific surface area and strong adsorption capacity, magnesium hydroxide particles can remove Ni2 +, Cd2 +, Mn2 + and other heavy metal ions harmful to the environment from industrial wastewater. Other heavy metal elements such as Mo, Co, Fe, W and V can also be removed with magnesium hydroxide, light burned magnesium oxide or aluminum magnesium carbonate.


(3) Flue gas desulfurization


At present, there are nearly 20 kinds of mature desulfurization technologies, among which magnesium hydroxide desulfurization technology is economical and practical, and has a good development prospect in the future. The advantages of magnesium hydroxide desulfurization process mainly include high desulfurization efficiency, low investment cost, low operation cost, high comprehensive benefit, reliable operation and no secondary pollution.


As a flame retardant, magnesium hydroxide has excellent properties in all aspects, and its application range will be more and more extensive. And magnesium hydroxide has the advantage of low price, which saves the cost for factory production. The preparation of magnesium hydroxide by light burning magnesium powder improves the added value of products, realizes the effective utilization of resources, and can effectively enhance the competitiveness of enterprises in the market economy.