The brief introduction of metal zinc

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Zinc is a kind of grey metal of which the density is 7.14, the melting point is 419.5 degrees celsius and the boiling point is 911 degrees celsius. It is rather crisp in room temperature, but it is getting soft in 100-150 degrees celsius and returning to crisp again when the temperature is more than 200 degrees celsius. Zinc has a very active chemical property. The surface of zinc will generate a layer of thin and compact of alkaline zinc carbonate membrane which will prevent it from further oxidation. When the temperature reaches 225 degrees celsius, the oxidization of zinc is fierce. When it is burned, it emits blue-green flame. Zinc is easily soluble in acid and also can easily displace such as gold, silver and copper from the solution.

The symbiosis of lead and zinc is very close in nature, especially in the primary deposite. They share common ore-forming material sources and very similar geochemistry behavior. They have similar outer electronic structure and both have a strong pro-sulfur property. They form the same soluble complex. They both have a very close condition of adsorption by iron-manganese qualitative, clay and organic matter. The average concentration of lead in the earth’s crust is approximately 15×10-6 and the average concentration of zinc in the earth’s crust is approximately 80×10-6.

At present, there are more than 250 species of lead-zinc mineral found in the earth’s crust. Of which 1/3 are the kinds of sulfides and sulfates, and only 17 species are available for industrial use. Among them, the lead industrial minerals are galena, boulangerite, jamesonite, bournonite, cerusite, anglesite, crocoite, pyromorphite, minetisite, vanadinite and wulfenite; the zinc industrial minerals are blende, wurtzite, smithsonite, calamine, willemite and hydrozincite. The ordinary content of zinc concentrate ore which is produced by the flotation of sulphur lead zinc mine is: zinc in around 50 percents, sulphur in around 30 percents and iron 5-14 percents; it also contains small amounts of lead, cadmium, copper, and precious metals as well as trace amounts of germanium, gallium, indium, thallium and other rare metals.

Pyrometallugy and hydrometallurgy are the two methods of zinc smelting by using zinc sulphide concentrate ore in china. Zinc pyrometallugy is to transform the zinc sulphide into zinc oxide by   roasting the zinc sulphide concentrate ore before using the carbonaceous reducing agent to restore and generate the zinc vapor in the high temperature and strong reducing atmosphere. After the condensation of zinc vapor, the metal zinc is obtained. Currently, the main methods of zinc pyrometallugy are vertical retort process and blast furnace process. Due to the increasingly stringent environmental protection requirements, higher energy prices and other reasons, the horizontal retort process has been nearly eliminated and the zinc amount produced by vertical retort process is declined gradually. Since the 70’s, using blast furnace process to produce zinc is in dead state, some even have been shut down or switch over to lead smelting. However, hydrometallurgy of zinc has been developed constantly and the new zinc smelting plant are all adopting this method in the last ten years.

Hydrometallurgy of zinc mainly includes the processes of roasting, leaching, purification of leaching liquor, electrowinning and so on. After the zinc concentrate ore is roasted, using spent electrolyte for neutral leaching and dissolve most of the zinc oxide in which the obtained pulp is isolated into supernatant and the underflow pulp. After the supernatant is purified, the metal zinc is produced by electrowinning before casting it into ingots. The underflow pulp is in acidic leaching in order to dissolve the remanent zinc oxide and the acid leaching liquid returns to the neutral leaching; the acid leaching residue containing about 20 percents of zinc need to be further disposed and the traditional method is using rotary kiln volatilization which recycles its zinc, lead and parted rare metals.

As the zinc surface will form a protective film at room temperature, the largest use of zinc is used in the galvanizing industry. Zinc can form alloys with many non-ferrous metals. Among them, the alloys composed by zinc together with aluminum and copper are widely used in the die casting. The brass composed by zinc together with copper, tin and lead is used in machinery manufacturing. The zinc plate containing few elements such as lead and cadmium can be made into zinc-manganese dry battery cathode and zinc printing plates. Zinc powder, lithopone and zinc chrome can be used as pigment. Zinc oxide can also be used in the industries of pharmaceutical, rubber, paint and so on.