Preparation Of Aluminium Hydroxide Flame Retard Ant From Industrial Residues Of Aluminum Alloy Surface Treatment Peocess

Large amount of industrial residue was produced by aluminum alloy surface treatment process with 2-7% of aluminum substrate dissolved. Landfill is usual method to dispose the industrial residue, which not only brought seriously pollution, but also caused the loss of aluminum resources and the waste of land resources. Aluminium hydroxide is becoming one of the largest production of flame retardants for its non-toxic, non-halogen and environment friendly features. Bauxite is the main raw material to preparing aluminum hydroxide in China, but facing the present situation of shortage of bauxite resources, lower grades, and high energy consumption of the production. In this thesis, the preparation of aluminum hydroxide from industrial residues of aluminum alloy surface treatment process was investigated. The aluminum hydroxide particles as different size were gained by sulfuric acid precipitation method and high gravity technology, which used as flame retardant for polypropylene materials, to achieved the high value utilization of industrial residue.In this paper, X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), Thermo gravimetric comprehensive thermal analyzer-differential thermal analysis (TG-DTA) were used to analysis the chemical composition, structure and thermo-gravimetric behavior of the industrial residue. The results showed that the moisture content of industrial waste residue was 40.4%, and the Al element was 28.7% in the dry residues, which existed as the form of A1(OH)3 crystal. The mass loss of industrial residues was 33.4% in the range of room temperature to 800℃.The preparation of aluminum hydroxide from industrial residues of aluminum alloy surface treatment process was investigated. This paper studied the majorization process of leaching Al element from the industrial residues by NaOH solution. The effects of preparation parameters, such as the concentration and dosage of alkali or acid, reaction temperature and time were emphatically discussed. Process optimization was obtained by orthogonal test. The optimum leaching process were molar ratio of NaOH added to Al(OH)3 in the industrial residues 2.88:1, reaction temperature 75℃, reaction time 55 min. At these conditions, the maximum yield of aluminum element in leaching process reached up to 97.5%. At the optimal conditions of precipitation process of Al(OH)3, such as molar ratio of H2SO4 added to AlO2-in leaching solution (0.95-1.10):1 and pH value 5.5, the precipitation yield of Al(OH)3 reached up to 89.2%, and the total recovery rate of aluminum element was obtained by 87.1%. The morphology of A1(OH)3 product was amorphous and the diameter of particles was about 17μm. The purity of Al(OH)3 in the product was up to 95.5%.For the preparation of aluminum hydroxide product with small particle size, The process of reactive carbonation in rotating packed bed was explored, the factors affecting the particle size of ATH, such as the concentration of NaA102 in leaching solution, G/L ratio and reaction temperature were analyzed. The optimum preparation conditions were concentration of NaA102 in leaching solution 2.0 mol·L-1, G/L ratio 1.0, reaction temperature below 30℃. At these conditions, ATH particle size was less than 0.9μm in reaction liquid, and 4 μm after drying. Al2O3 content in ATH products was 69.9%, exceeded the national standard (GB/T 4294-2010), and other indicators approached the national standard. The Al element existed as the form of Al(OH)3 crystal in the products.Examined the flame retardant properties of aluminum hydroxide product with different sizes in polypropylene substrate. The properties of polypropylene-aluminium hydroxide (PP-ATH) composite materials, i.e. oxygen index, smoke density, cone calorimetry, thermal stability and tensile properties were measured. The results showed that the flame retardant performance was significantly improved when ATH was added to PP materials, while the tensile strength was reduced. However, the smaller particle size of ATH product was helpful to increasing flame resistance and maintaining the tensile strength of the composite materials.