Production Method of Aluminum Hydroxide Flame Retardant

Aluminum hydroxide flame retardant is currently the most widely used and extensively applied inorganic flame retardant additive.

Aluminum hydroxide flame retardant is currently the most widely used and extensively applied inorganic flame retardant additive. As a flame retardant, it not only inhibits combustion but also suppresses smoke generation without producing dripping or toxic gases, making it highly versatile. Let's explore its industrial production methods together:

1. Alumina in bauxite ore is dissolved by heating with sodium hydroxide solution to produce sodium aluminate solution. After separating the solution from the residue (red mud), the mixture is cooled. Aluminum hydroxide is added as a seed crystal, and after prolonged stirring, the sodium aluminate decomposes, precipitating aluminum hydroxide flame retardant.

2. Alkali-lime sintering method. Suitable for processing high-silica bauxite. Bauxite, sodium carbonate, and lime are mixed in specific proportions and sintered in a rotary kiln to form a clinker composed of sodium aluminate, sodium ferrate, calcium silicate, and sodium titanate. Sodium aluminate is then leached from the clinker using a dilute alkali solution. At this stage, NaOH hydrolyzed from ferrite sodium also enters the solution. Under properly controlled dissolution conditions, calcium orthosilicate does not react significantly with the sodium aluminate solution but is discharged as red mud composed of calcium titanate. The sodium aluminate solution obtained from leaching the clinker undergoes a specialized desilification process to form hydrated sodium aluminosilicate (known as sodium silicate slag) or hydrated garnet, thereby purifying the solution. CO₂ gas is passed into the refined sodium aluminate solution, followed by the addition of seed crystals and stirring to produce aluminum hydroxide flame retardant.

Applications of Aluminum Hydroxide Flame Retardant: ATH serves diverse purposes beyond flame retardancy, including smoke suppression and reduction of corrosive gas generation in materials. It functions effectively both as a standalone agent and in combination with other flame retardants. For polymers processed below ATH's decomposition temperature (190–230°C), ATH proves an excellent flame retardant for elastomers, thermosetting resins, thermoplastics, and similar materials. It is also extensively used in producing styrene-butadiene latex for flame-retardant carpets, as well as in manufacturing flame-retardant insulated rubber cables, thermal insulation foams, conveyor belts, roofing ceilings, and hoses. Applications include bathroom appliances, decorative walls, various covers, automotive protective shields, seats, truck components, and electronic components—including insulators, circuit boards, and construction equipment. Nano-aluminum hydroxide can also be used in engineering plastics (aerospace materials, military vessels, etc.).

When added at 40%, ATH significantly lowers the thermal decomposition temperature of polyethylene, polypropylene, polyvinyl chloride, and butadiene/styrene copolymers, delivering excellent flame retardancy and smoke suppression. Polyolefins containing 50% aluminum hydroxide are primarily used in Japan for food packaging materials. Flame-retardant polyolefins with 60% aluminum hydroxide content can serve as construction materials and interior components for automobiles and ships.