Zinc brings a multitude of social and economic benefits to society. Man has discovered a wide range of uses for this versatile natural element with valuable characteristics and properties for various industrial applications.
The most important use of zinc is in protecting steel from corrosion using hot-dip galvanizing technique. The metal is used to prolong the durability of steel, which is one of the most used materials on the planet. Both zinc and steel are 100% recyclable. The zinc-steel combination has considerable economic benefits in terms of life-cycle costs. Improved air quality in several industrialized countries, with diminishing levels of sulfur dioxide (SO2), means that today zinc coatings facilitate even longer protection for steel.
Increased attention to life-cycle costing is prompting the designers, specifiers and investors to prefer zinc-coated steel in many traditional and new applications, from electricity distribution poles to safety barriers, from construction to automobiles and from farm gates to ski-lifts.
Approximately 60% of the zinc consumed worldwide originates from mined ores and the remaining 40% from recycled or secondary zinc. The level of recycling increases each year, in step with progress in zinc production and recycling technology.
For the zinc and steel industries, recycling of zinc-coated steel provides an important new source of raw material. Historically, the generation of zinc-rich dusts from steel recycling was a source of loss from the life-cycle (landfill); however, today technologies exist which provide incentive for steel recyclers to minimize waste. Thus, the recycling loop is endless – both zinc and steel can be recycled again and again without any loss of their physical or chemical properties.
Zinc is recycled at all stages of production and use, including waste that arises during the production of galvanized steel sheet, scrap generated during manufacturing and installation processes and from end-of-life products. The presence of zinc coating on steel does not affect steel’s recyclability, and all types of zinc-coated products are recyclable. Similarly, the presence of zinc in alloys does not affect its recyclability; the alloys are remelted and used to manufacture new products of the same alloy.
Consumption of refined zinc metal in recent years has been slightly more than total metal production, perhaps due to the considerable amount of refined zinc includes zinc used directly in alloys irrespective of source material, whether concentrates, slags, residues or scrap.
Zinc recovery from recycled galvanized iron and steel is becoming more and more important, but is still small; the remainder was primarily from brass products, flue dust, old die casting and old rolled zinc products.
A major problem for recyclers is that secondary zinc is almost invariably associated with other metals, including lead, copper, cadmium, arsenic and chromium.
Depending on the type of steel and the galvanizing process, between 10 % and 40 % of the total consumed zinc ends up in residues. Zinc that is metallurgically combined with steel during galvanizing process, cannot be easily separated from galvanized steel scrap. It is generally recovered from flue dust generated during the reprocessing of steel scrap.
Zinc containing materials are highly variable and include automobile scrap, brass scrap, flux skimming dross from the wet galvanizing process, zinc ash from the dry process, arc furnace dust, and so on. Composition may vary widely, and the recovery processes would have to be equally variable.
Scrap produced only at the end of the useful life of the product into which it is incorporated is more difficult to recover; and hence, only a small portion is recycled. Until 1993, about, all zinc used in galvanized steel products was lost either in landfills or in slag at steel scrap processing plants.