1. Identify Core Applications (The Most Important Prerequisite)
The purpose for which you purchase magnesium hydroxide directly determines the key indicators you should consider. First, clearly define your application:
Flame retardant (most common application): Magnesium hydroxide Used in polymer materials such as plastics, rubber, cables, and coatings.
Environmentally friendly neutralizer: Magnesium hydroxide Used in industrial wastewater treatment, flue gas desulfurization, and acidic soil improvement.
Pharmaceutical raw material: Magnesium hydroxide Used in the preparation of antacids (such as "milk of magnesia") and laxatives.
Food additive: Magnesium hydroxide Used as an alkaline agent, desiccant, etc.
Chemical raw material: Magnesium hydroxide Used in the preparation of other magnesium salts (such as magnesium oxide and magnesium sulfate).
Different application areas have different priorities:
Flame retardant applications: The most critical considerations are purity, particle size and distribution, and surface activation.
Environmentally friendly neutralization applications: The most critical considerations are purity, reactivity (neutralization speed), and price.
Pharmaceutical/food applications: The most critical considerations are purity, the content of harmful impurities such as heavy metals, and microbiological indicators. Must comply with pharmacopoeias (e.g., CP, USP) or food-grade standards (e.g., FCC, GB).
2. Focus on Key Technical Specifications
After determining your application, request a Certificate of Analysis (COA) from the supplier and focus on the following specifications:
a. Purity (magnesium hydroxide content)
Importance: High purity means fewer impurities and more stable performance. For flame retardant applications, high purity ensures higher flame retardant efficiency.
Common Grades: Industrial-grade purity is typically ≥90%-95%; high-purity grades can reach ≥98% or even ≥99%.
Recommendation: Choose based on application requirements. Don't blindly pursue the highest purity, but ensure that impurities do not affect the performance of your final product.
b. Particle Size and Specific Surface Area
Importance: This is a key factor affecting product performance.
Flame retardant applications: Ultrafine particle size (e.g., D50 below 1-3 microns) and large surface area enable more uniform dispersion in polymer materials, forming a denser barrier carbon layer and significantly improving flame retardancy. Furthermore, fine particles have less negative impact on the material's mechanical properties.
Environmentally neutralizing applications: Particle size requirements are relatively relaxed, but finer particles generally exhibit higher reactivity and faster reaction speeds.
How to determine: Suppliers are required to provide particle size distribution (D10, D50, D90) and surface area (BET method) data.
c. Impurity Content
Heavy metals (such as lead, arsenic, cadmium, and mercury): Pharmaceutical and food-grade products must be tested, and their content must strictly comply with relevant standards. Industrial-grade products also require attention, especially when used in contact products.
Chloride (Cl-): Excessive levels may cause corrosion to processing equipment.
Iron (Fe), calcium (Ca), etc.: These impurities can affect the whiteness of the product and are particularly important for flame retardants used in light-colored or white products.