Zinc dust, pyrophoric

The processing of bauxite aluminium ore (hydrated alumina oxides) exemplifies these processes. In the Bayer process hot concentrated sodium hydroxide dissolves alumina which is subsequently separated and crystallized as aluminium hydroxide (hydrometallurgy). This is calcined to anhydrous alumina (pyrometallurgy) before being reduced in the Hall process (electrometallurgy) wherein alumina serves as the electrode from which elemental aluminium is deposited on the cathode. 

Metal scrap also includes enormous quantities of post-use items such as industrial machinery, vehicles, metal furniture, washing machines, and other consumer equipment, as well as metal residues from electroplating baths, wastewater treatment sludges, and the like. 

Magnesium alloys, see Metals, Alloys, p.l51 Metal, see Terminology, Metals, p.242 

Powder, see Terminology, Powder, p.246 and Metals, Elemental Products, p. 153 Self-heating, see Spontaneously Combustible Materials and Division 4.2, p.226 

Aluminium Processing By-Products. The material, consisting of skimmings of virgin aluminium, rising to the surface of impure molten aluminium metal. ICAO A2 

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Reductions with zinc are usually performed in hot or refluxing solvents, and some take many hours to complete. After the reaction is over the residual zinc, if any, is filtered off, and the products are isolated in ways depending on their chemical nature. If zinc dust has been used care must be taken in disposing of it since it may be pyrophoric in the dry state. 

Cleaning Up Spread the zinc out on a watch glass for about 20 min before wetting it and placing it in the nonhazardous solid waste container. Sometimes zinc dust from a reaction like this is pyrophoric (spontaneously flammable in air) because it is so finely divided and has such a large, clean surface area able to react with air. The aqueous filtrate should be neutralized with sodium carbonate, zinc salts removed by vacuum filtration, and the filtrate diluted with water and flushed down the drain. The zinc salts are placed in the nonhazardous solid waste container. The filtrate from the fractional crystallization should all be placed in the organic solvents container. Allow the solvent to evaporate from the sodium sulfate in the hood and then place it in the nonhazardous solid waste container. 

ZINC ZINC DUST or ZINC POWDER or ZINC, PYROPHORIC... 

Metals — Several metals react with water and air with the extent of reactivity being dependent upon the physical state of the metal. The highly reactive metals such as lithium, sodium, and potassium are pyrophoric (i.e., they ignite spontaneously in air without an ignition source). In contrast, the less reactive metals such as magnesium, zirconium, titanium, aluminum, and zinc are highly pyrophoric only as dusts. 

EARTHS. A strong reducing agent. Moderate fire hazard ignites spontaneously in air at 150-180°. Moderate explosion hazard in the form of dust when exposed to flame. The metal or its alloys spark with friction. Many alloys are pyrophoric in air. See also IRON DUST. Explosive reaction with zinc. Very exothermic reaction with antimony or bismuth. Ignites when heated in atmospheres of CO2 + N2, CI2, or Br2. Violent reaction when heated with phosphoms (400°Q, silicon (1400°C). 

CI3OP Noncombustible liquid. Fumes in moist air. Contact with water, steam, or alcohols produces hydrochloric acid, phosphoric acid, and phosphine gas, which is pyrophoric, with possible ignition or explosion (may be a delayed reaction). Contact with air produces corrosive fumes. Violent reaction with acetone and possibly other ketones carbon disulfide, 2,6-dimethylpyridine-A-oxide, dimethyl sulfoxide, ethers (especially when metal salts are present) ferrocene-l,l -dicarboxylie acid, pyridine, zinc powder or dust. Reacts, possibly violently, with acids, bases, amines, amides, inorganic hydroxides alkali metals, alkalis, combustible materials, dimethyl... 

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