Production of active zinc oxide

A Properties and uses Active zinc oxide is a white or yellowish spherical fine powder with a density of 5.47g/cm ³ and a melting point of 1800 °C.

, insoluble in water, soluble in acid, alkali, chlorinated and ammonia. It absorbs carbon dioxide from the air in humid air to form basic zinc carbonate.
According to the HG2572-94 standard of the Ministry of Chemical Industry, the ordinary zinc oxide has a particle size of 0.5 μm , a spherical shape, and a specific surface area of ​​35 to 45 m ² /g. The surface of the active zinc oxide can adsorb gas molecules to form a single molecule adsorption layer, from which the specific surface area can be calculated and the activity is judged.
Active zinc oxide and zinc oxide are chemically identical, and their differences are mainly manifested in physical properties, and thus their uses are also different. The purity of active zinc oxide is lower than that of zinc oxide produced by direct or indirect methods, but its unique physical and chemical properties can show its superiority. Zinc oxide is generally used in the rubber industry and is mainly used as an activator for natural rubber, synthetic rubber and latex. The active zinc oxide particles are fine and spherical, have a large surface area, have good dispersibility and good adsorption, and thus can promote the vulcanization, activation and anti-aging effects of the rubber, can strengthen the vulcanization process, and improve the tear resistance of the rubber product. Cracking, wear resistance.
Active zinc oxide is also used in white latex colorants and fillers, vulcanizing agents in chloroprene rubber, light stabilizers in the plastics industry, desulfurization catalysts in the synthetic ammonia industry, and in the chemical industries such as coatings, enamels, and pigments. The use of active zinc oxide in the rubber industry can reduce the amount of 1/3 to 1/4 compared to ordinary zinc oxide.
B Production process a Zinc salt soda ash method Sodium salt soda method, usually with 98% sulfuric acid and zinc-containing materials (mostly 90% of crude zinc oxide, requiring 0.2% of As; can also use zinc smelter in zinc smelter, Zinc waste liquid, low-grade zinc oxide, zinc-zinc ore with low zinc grade, etc.) are leached to obtain a zinc sulfate solution, and the iron , copper , tin and other impurities in the zinc sulfate solution are removed by KMn0 ₄ oxidation and zinc powder replacement, and purified. The zinc sulfate solution is neutralized by adding soda ash to obtain a basic zinc carbonate precipitate. The precipitate is calcined to obtain active zinc oxide. The production process of zinc oxide soda ash to produce active zinc oxide is shown in the figure below.

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b Ammonia complex method is a method of leaching crude zinc oxide or zinc soot, smithsonite and other materials with hydrogen carbonate and ammonia to dissolve zinc oxide to form zinc-ammonium complex, then purify the solution, and decompose the zinc-ammonium complex. That is, active zinc oxide is obtained. The ammonia leaching process is simple and low in cost, but the quality of the obtained active zinc oxide is somewhat worse than that of the zinc salt soda ash method. The production process of the ammonia complex method is shown in the figure below.

In the leaching tank, a solution of ammonium bicarbonate and ammonia water is added according to the ratio of the ingredients, and the crude zinc oxide is added under stirring, and heated to 40 ° C for about 2 hours. After the reaction is completed, the slurry is sent to a filter press for filtration, thereby obtaining a leachate and a filter residue. The main reaction formula is as follows:

Zn0+3NH ₃ ·H ₂ 0+NH ₄ HC0 ₃ ==== Zn(NH ₃ ) ₄ C0 ₃ +4H ₂ 0

Ammonia leaching can treat zinc-containing soot or sinter. China's major mines store a large amount of zinc oxide ore to be developed and utilized. The zinc in the oxidized ore is mainly in the form of smithsonite, and the zinc-containing grade is low, which is difficult to extract by conventional methods. The zinc oxide ore (river zinc ore) is leached with ammonia, and the ammonia complex method can obtain the active zinc oxide which meets the requirements. [next]
C Product Quality Standards The industrial activated zinc oxide (HG/T 2572-94) Ministry of Chemical Industry's Ministry of Standards is shown in the table below. This standard applies to industrially active zinc oxide prepared by the decomposition of zinc carbonate. It is mainly used as a reinforcing agent for rubber or cable, an active agent (natural rubber), a vulcanizing agent for natural rubber and chlorinated rubber.

Industrial activity ministerial standard zinc oxide (HG / T 2572 - 94)
project	index
	First grade	Qualified product
Zinc oxide ( ZnO ) content /%	9 5~98	95 to 98
Moisture content /%	≤0.7	≤0.7
Water soluble content /%	≤0.5	≤0.7
Loss of ignition /%	1 to 4	1 to 4
Hydrochloric acid insoluble content /%	≤0.02	≤0.05
Lead oxide (in terms of Pb ) content /%	≤0.01	≤0.05
Manganese oxide (in terms of Mn ) content /%	≤0.001	≤0.003
Copper oxide ( calculated as Cu ) content /%	≤0.001	≤0.003
Fineness (45 μ m sieve was the test sieve) /%	≤0.1	≤0.4
Specific surface area / ( m 2 · g -1 )	≥45	≥35
Bulk density / ( g · cm -3 )	≤0.35	≤0.40

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