2 h 2 so 4 the sulfuric acid is regenerated and recycled to the leaching step. when galvanised feedstock is fed to an electric arc furnace, the zinc is recovered from the dust by a number of processes, predominantly the waelz process (90% as of 2014). environmental impact refinement of sulfidic zinc ores produces large volumes of sulfur dioxide and cadmium vapor. smelter slag and other residues contain significant quantities of metals. about 1.1 million tonnes of metallic zinc and 130 thousand tonnes of lead were mined and smelted in the belgian towns of la calamine and plombières between 1806 and 1882. the dumps of the past mining operations leach zinc and cadmium, and the sediments of the geul river contain non-trivial amounts of metals. about two thousand years ago, emissions of zinc from mining and smelting totaled 10 thousand tonnes a year. after increasing 10-fold from 1850, zinc emissions peaked at 3.4 million tonnes per year in the 1980s and declined to 2.7 million tonnes in the 1990s, although a 2005 study of the arctic troposphere found that the concentrations there did not reflect the decline. man-made and natural emissions occur at a ratio of 20 to 1. zinc in rivers flowing through industrial and mining areas can be as high as 20 ppm. effective sewage treatment greatly reduces this; treatment along the rhine, for example, has decreased zinc levels to 50 ppb. concentrations of zinc as low as 2 ppm adversely affects the amount of oxygen that fish can carry in their blood. historically responsible for high metal levels in the derwent river, the zinc works at lutana is the largest exporter in tasmania, generating 2.5% of the state's gdp, and producing more than 250,000 tonnes of zinc per year. soils contaminated with zinc from mining, refining, or fertilizing with zinc-bearing sludge can contain several grams of zinc per kilogram of dry soil. levels of zinc in excess of 500 ppm in soil interfere with the ability of plants to absorb other essential metals, such as iron and manganese. zinc levels of 2000 ppm to 180,000 ppm (18%) have been recorded in some soil samples. applications major applications of zinc include, with percentages given for the us galvanizing (55%) brass and bronze (16%) other alloys (21%) miscellaneous (8%) anti-corrosion and batteries hot-dip handrail galvanized crystalline surface zinc is most commonly used as an anti-corrosion agent, and galvanization (coating of iron or steel) is the most familiar form. in 2009 in the united states, 55% or 893,000 tons of the zinc metal was used for galvanization. zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away. a protective surface layer of oxide and carbonate (zn5(oh)6(co3)2) forms as the zinc corrodes. this protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away. the zinc is applied electrochemically or as molten zinc by hot-dip galvanizing or spraying. galvanization is used on chain-link fencing, guard rails, suspension bridges, lightposts, metal roofs, heat exchangers, and car bodies. the relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient sacrificial anode in cathodic protection (cp). for example, cathodic protection of a buried pipeline can be achieved by connecting anodes made from zinc to the pipe. zinc acts as the anode (negative terminus) by slowly corroding away as it passes electric current to the steel pipeline. zinc is also used to cathodically protect metals that are exposed to sea water. a zinc disc attached to a ship's iron rudder will slowly corrode while the rudder stays intact. similarly, a zinc plug attached to a propeller or the metal protective guard for the keel of the ship provides temporary protection. with a standard electrode potential (sep) of −0.76 volts, zinc is used as an anode material for batteries. (more reactive lithium (sep −3.04 v) is used for anodes in lithium batteries ). powdered zinc is used in this way in alkaline batteries and the case (which also serves as the anode) of zinc–carbon batteries is formed from sheet zinc. zinc is used as the anode or fuel of the zinc–air battery/fuel cell. the zinc-cerium redox flow battery also relies on a zinc-based negative half-cell. alloys a widely used zinc alloy is brass, in which copper is alloyed with anywhere from 3% to 45% zinc, depending upon the type of brass. brass is generally more ductile and stronger than copper, and has superior corrosion resistance. these properties make it useful in communication equipment, hardware, musical instruments, and water valves. cast brass microstructure at magnification 400x other widely used zinc alloys include nickel silver, typewriter metal, soft and aluminium solder, and commercial bronze. zinc is also used in contemporary pipe organs as a substitute for the traditional lead/tin alloy in pipes. alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. zinc has been the primary metal in american one cent coins (pennies) since 1982. the zinc core is coated with a thin layer of copper to give the appearance of a copper coin. in 1994, 33,200 tonnes (36,600 short tons) of zinc were used to produce 13.6 billion pennies in the united states. alloys of zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting, especially in the automotive, electrical, and hardware industries. these alloys are marketed under the name zamak. an example of this is zinc aluminium. the low melting point together with the low viscosity of the alloy makes possible the production of small and intricate shapes. the low working temperature leads to rapid cooling of the cast products and fast production for assembly. another alloy, marketed under the brand name prestal, contains 78% zinc and 22% aluminium, and is reported to be nearly as strong as steel but as malleable as plastic. this superplasticity of the alloy allows it to be molded using die casts made of ceramics and cement. similar alloys with the addition of a small amount of lead can be cold-rolled into sheets. an alloy of 96% zinc and 4% aluminium is used to make stamping dies for low production run applications for which ferrous metal dies would be too expensive. for building facades, roofing, and other applications for sheet metal formed by deep drawing, roll forming, or bending, zinc alloys with titanium and copper are used. unalloyed zinc is too brittle for these manufacturing processes. as a dense, inexpensive, easily worked material, zinc is used as a lead replacement. in the wake of lead concerns, zinc appears in weights for various applications ranging from fishing to tire balances and flywheels. cadmium zinc telluride (czt) is a semiconductive alloy that can be divided into an array of small sensing devices. these devices are similar to an integrated circuit and can detect the energy of incoming gamma ray photons. when behind an absorbing mask, the czt sensor array can determine the direction of the rays. other industrial uses zinc oxide is used as a white pigment in paints. roughly one quarter of all zinc output in the united states in 2009 was consumed in zinc compounds; a variety of which are used industrially. zinc oxide is widely used as a white pigment in paints and as a catalyst in the manufacture of rubber to disperse heat. zinc oxide is used to protect rubber polymers and plastics from ultraviolet radiation (uv). the semiconductor properties of zinc oxide make it useful in varistors and photocopying products. the zinc zinc-oxide cycle is a two step thermochemical process based on zinc and zinc oxide for hydrogen production. zinc chloride is often added to lumber as a fire retardant and sometimes as a wood preservative. it is used in the manufacture of other chemicals. zinc methyl (zn(ch3)2) is used in a number of organic syntheses. zinc sulfide (zns) is used in luminescent pigments such as on the hands of clocks, x-ray and television screens, and luminous paints. crystals of zns are used in lasers that operate in the mid-infrared part of the spectrum. zinc sulfate is a chemical in dyes and pigments. zinc pyrithione is used in antifouling paints. zinc powder is sometimes used as a propellant in model rockets. when a compressed mixture of 70% zinc and 30% sulfur powder is ignited there is a violent chemical reaction. this produces zinc sulfide, together with large amounts of hot gas, heat, and light. zinc sheet metal is used as a durable covering for roofs, walls, and countertops, the last often seen in bistros and oyster bars, and is known for the rustic look imparted by its surface oxidation in use to a blue-gray patina and susceptibility to scratching. 64zn, the most abundant isotope of zinc, is very susceptible to neutron activation, being transmuted into the highly radioactive 65zn, which has a half-life of 244 days and produces intense gamma radiation. because of this, zinc oxide used in nuclear reactors as an anti-corrosion agent is depleted of 64zn before use, this is called depleted zinc oxide. for the same reason, zinc has been proposed as a salting material for nuclear weapons (cobalt is another, better-known salting material). a jacket of isotopically enriched 64zn would be irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, forming a large amount of 65zn significantly increasing the radioactivity of the weapon's fallout. such a weapon is not known to have ever been built, tested, or used. 65zn is used as a tracer to study how alloys that contain zinc wear out, or the path and the role of zinc in organisms. zinc dithiocarbamate complexes are used as agricultural fungicides; these include zineb, metiram, propineb and ziram. zinc naphthenate is used as wood preservative. zinc in the form of zddp, is used as an anti-wear additive for metal parts in engine oil. organic chemistry addition of diphenylzinc to an aldehyde organozinc chemistry is the science of compounds that contain carbon-zinc bonds, describing the physical properties, synthesis, and chemical reactions. many organozinc compounds are important. among important applications are the frankland-duppa reaction in which an oxalate ester (rococoor) reacts with an alkyl halide r'x, zinc and hydrochloric acid to form the α-hydroxycarboxylic esters rr'cohcoor on the downside, organozincs are much less nucleophilic than grignards, and they are expensive and difficult to handle. commercially available diorganozinc compounds are dimethylzinc, diethylzinc and diphenylzinc. in one study, the active organozinc compound is obtained from much cheaper organobromine precursors. zinc has found many uses as a catalyst in organic synthesis including asymmetric synthesis, being cheap and easily available alternative to precious metal complexes. the results (yield and enantiomeric excess) obtained with chiral zinc catalysts are comparable to those achieved with palladium, ruthenium, iridium and others, and zinc becomes a metal catalyst of choice. dietary supplement gnc zinc 50 mg tablets. the amount exceeds what is deemed the safe upper limit in the united states (40 mg) and european union (25 mg) zinc gluconate is one compound used for the delivery of zinc as a dietary supplement.