Zinc Scrap

Zinc scrap is an interesting metal that has many different uses. Zinc Scrap comes in a variety of forms, including galvanized steel and sheet, alloying with copper for brass/bronze alloys (used in car parts) as well as zinc production from chemical plants. It also goes into the pharmaceutical industry where it’s used as a coating for pills. Zinc Scrap is a recycled product that can be obtained from various manufacturing industries such as the zinc processing industry, hot-dip galvanizing industry, and chemical producers.

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Zinc scrap is an interesting metal that has many different uses. Zinc Scrap comes in a variety of forms, including galvanized steel and sheet, alloying with copper for brass/bronze alloys (used in car parts) as well as zinc production from chemical plants. It also goes into the pharmaceutical industry where it's used as a coating for pills. Zinc Scrap is a recycled product that can be obtained from various manufacturing industries such as the zinc processing industry, hot-dip galvanizing industry, and chemical producers.

Zinc Scrap is a by-product obtained from zinc smelting. It comprises of metal objects that have been produced in chemical and metallurgical industry, which contain scrap mixed with other components such as slag or dross; this waste material contains valuable metals like zinc, iron, copper, etc. through recycling process these can be used for several applications such as alloying materials (in steel mills), fertilizers (zinc sulfate) and pigments(chrome oxide).

Zinc Processing Industry

The zinc processing industry is the complex of industrial processes used to refine zinc metal and other products. It involves smelting, converting, alloying, refining, or recycling material containing zinc compounds. The first step in the process is usually roasting which converts sulfide ore minerals into oxide concentrates that can be further refined through pyrometallurgy. Many modern applications of this process rely on reagents such as carbon monoxide (CO) introduced during hydrometallurgy to recover purer metallic forms after their initial separation from impurities. Pyrometallic recovered materials are often called "roasted" or "calcine".

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Different grades and varieties of zinc scrap is used for recycling purposes and to recover pure zinc from the scrap. Given in the table below are some of the important grades / types of zinc scrap used in recycling -

Type	Details
Old Mixed Zinc Scrap	It comprises of clean zinc solids including castings, sheet and clippings.
Old Zinc Die Cast Scarp	It consists of miscellaneous coated and uncoated zinc die castings.
New Zinc Die Cast Scrap	It comprises of new uncoated zinc die castings.
New Plated Zinc Die Cast Scrap	It include clean new coated (usually nickel plated) zinc die casting free of other metals, attachments, and foreign materials.
Zinc Borings or Turnings	Zinc Borings or Turnings contain zinc turnings, borings or grindings free of excessive oils.
Irony Zinc	This grade of zinc scrap consists of zinc solids contaminated with iron. Irony zinc shall contain a minimum 70% content of zinc with maximum 30% of total iron content. The scrap should be free of excessive oils, plastics or other sweat furnace prohibitive.
Remelt Die Cast	It consists of remelted zinc ingots or pigs from a sweat furnace operation and should be free of dross or slag materials. Ingots should be uniform in shape with a minimum of 25 lb, and a maximum of 75 lb in weight.
Remelt Die Cast Sows	Remelt Die Cast Sows contain remelted zinc slab or sow blocks from a sweat furnace operation. It should be free of dross or slag materials. Ingots should be of uniform size with a minimum weight of 500 lb and a maximum of 2,500 lb.
Galinizers Top Dross	Galinizers Top Dross include unsweated zinc skimmings from continuous galvanizing lines. It should contain a minimum content of 90 % zinc.
Galinizers Bottom Dross	It includes unsweated zinc dross removed from the bottom of a continuous line galvanizing bath. The grade should contain a minimum zinc content of 92%.
Zinc Dross	Zinc dross consists of slag, dross, skimmings or spillings from zinc die cast melting operations. It should contain a minimum zinc content of 85% and slabs chunks should not exceed 75 lb.
Zinc Oxide & ZnO Residues	Zinc Oxide & ZnO Residues are comprised of assorted zinc or zinc oxide powders, dusts or residues, free from aluminum or other metallic content. It may contain low grade or sweated zinc dross and may include pieces of metallic zinc.
Zinc Flue Dust	This grade contains assorted zinc or zinc oxide content materials including powders, dusts or residues, derived from bag houses or EAF dust collection systems. It may contain residues of iron, cadmium, lead, mercury provided that an analysis complete with pH specifications accompany the materials.
Other Zinc Scrap	It include any other zinc scrap materials, which are not included in the other listed grades.

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The secondary zinc industry processes metal scrap for the recovery of zinc in the form of zinc oxide, zinc slabs, or zinc dust. The process of zinc recovery involves three general operations, viz. -

Pretreatment
Melting
Refining

Secondary recovery starts with the separation of zinc-containing metals from other materials, typically by magnetics, sink-float, or hand sorting.

When non-ferrous metals have been mixed in shredder scrap, zinc metal can be separated from higher-melting metals, such as such copper and aluminum, through selective melting in a sweating furnace. A sweating furnace (rotary, reverberatory, or muffle furnace) slowly heats the scrap containing zinc and other metals to approximately 419.4°C; this temperature is adequate to melt zinc, however it is still below the melting point of the remaining metals.

In the case of zinc-galvanized steel, the zinc can be recovered largely in furnace dust after the scrap is charged into a steel making furnace and melted. Although it is expected that recycling will continue to be encouraged on the grounds of environmental sustainability. Almost all of the zinc in electric arc furnace dust is first retrieved in an upgraded, impure zinc oxide product, and is then shipped to primary pyro-metallurgical zinc smelter for refinement to metal.

According to International Zinc Association, there are 50 secondary zinc operators in the world with varying recycling processes. New scrap is usually just remelted. In the case of mixed non-ferrous shredded metal scrap, zinc is separated by hand or magnetically, before it is re-refined by retorting. An important source of secondary zinc is flue dust from secondary electric arc furnaces for production of iron, using galvanized iron scrap. 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.

The recycling picture for old scrap is quite confused. Based on the physical characteristics, most metallic zinc is theoretically recoverable, even after very long periods of use. According to International Lead and Zinc Study Group, the recovery efficiency for zinc, meaning the fraction of old scrap available for recycling, which is actually recycled, is 80 %; this is consistent with a very long lifetime of zinc products in use, as much as 100 years.

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.

In recent years, zinc has been recovered from flue dust, and advanced technology to de-zinc galvanized steel has been developed. This new de-zincing technique should increase the relatively low recycling rate of old zinc scrap, which enhances the sustainability of primary zinc production.