Mg(OH)2 is not just a flame retardant
Magnesium hydroxide, chemical formula Mg(OH)2, formula quantity 58.32.White amorphous powder.The suspension of Magnesium hydroxide in water is called Magnesium hydroxide emulsion (Magnesium hydroxide for short), and its English name is Magnesium hydroxide.Magnesium hydroxide is a colorless hexagonal crystal or white powder, insoluble in water and alcohol, soluble in dilute acid and ammonium salt solutions, aqueous solutions are slightly alkaline.The solubility in water is very small, but the part dissolved in water completely disassociates.The concentration of saturated aqueous solution was 1.9 mg/l (18 ° C).Heating to 350 ° C loses water to form magnesium oxide.Brucite, a natural mineral of magnesium hydroxide.Can be used for sugar and magnesium oxide.Because magnesium hydroxide is abundant in nature and is chemically similar to aluminum, users began to use it in deodorants instead of aluminum chloride.Used as an analytical reagent, also used in the pharmaceutical industry.
When a certain amount of flame retardant is added into the material, the flame retardant performance of the material will be improved correspondingly, but it will often affect the mechanical properties or other properties of the material, and sometimes bring inconvenience to the processing.Therefore, in order to maintain the comprehensive properties of flame retardant composites, the comprehensive properties of flame retardant should be considered.
As a flame retardant material, magnesium hydroxide has many advantages:
(1) The decomposition temperature of magnesium hydroxide is high, and the ignition point is higher than that of aluminum hydroxide, which improves the heating temperature of polymer materials;
(2) MgO generated after combustion and dehydration is a refractory material, and is an alkaline oxide, can absorb acid gas;
(3) Strong heat absorption ability, high flame retardant efficiency;
(4) low cost, easy to process in different polymer materials.
In recent years, magnesium hydroxide, as a green flame retardant, has been widely used.
Two aspects of preparation of magnesium hydroxide need to be controlled most:
(1) Filtration performance, if the precipitation performance of magnesium hydroxide slurry is poor, it will affect the washing and separation operation process, lead to the prolonged synthesis cycle of magnesium hydroxide, and will affect the production of magnesium hydroxide;
(2) Morphography control. Because magnesium hydroxide with regular morphology has better flame retardant effect, appropriate production methods and technological conditions are needed to meet the requirements.
The main production process of magnesium hydroxide includes direct precipitation method, magnesium-bearing ore grinding method, magnesium oxide hydration method and so on.
Use of magnesium hydroxide
Magnesium hydroxide is widely used, flame retardant and environmental protection are the main application fields of magnesium hydroxide.In addition, due to the high activity of magnesium hydroxide slurry, good adsorption performance, easy adjustment can be controlled, magnesium hydroxide can also be used as a neutralizer for acidic waste liquid and sulfur-rich oxide treatment, heavy metal removal, improve the acidity of the soil, but also as an antacid used in pharmacy, fertilizer additives.
Flame retardant applications
Magnesium hydroxide is an important halogen-free, environment-friendly and green flame retardant. The flame retardant mechanism is to generate stable coating layer of magnesium oxide and water vapor, and the flame retardant efficiency is low. In order to achieve good flame retardant effect, the addition amount of magnesium hydroxide should be up to 50%~60%.The usual method is surface modification of magnesium hydroxide and synergistic effect of magnesium hydroxide on flame retardant.
Magnesium hydroxide flame retardants can be used 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 can not only obtain better flame retardant effect, but also reduce the amount of flame retardant, thus reducing the cost.
Environmental applications
(1) Acid wastewater treatment
The neutralization reaction speed of magnesium hydroxide is slow, and the particle size produced after the neutralization reaction is larger and quickly sedimentation.In the treatment of acid containing wastewater, magnesium hydroxide can simplify the operation procedure, reduce the operation time, have good controllability and reduce the treatment cost.
(2) Removal of heavy metals
Due to the large specific surface area of magnesium hydroxide particles, has a strong adsorption capacity, can be removed from the industrial wastewater waste liquid harmful to the environment of Ni2+, Cd2+, Mn2+ and other heavy metal ions, other heavy metal elements such as Mo, Co, Fe, W and V can also be used to remove magnesium hydroxide, light burning 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 main advantages of magnesium hydroxide desulfurization process are high desulfurization efficiency, less investment cost, low operating cost, high comprehensive benefits, reliable operation and no secondary pollution.
