Zinc refining
Encyclopedia
Zinc refining is the process of purifying zinc
to super high grade (SHG) zinc, which is at least 99.995% pure. This process isn't usually required when smelting zinc through electrolysis
processes, but is needed when zinc is produced by pyrometallurgical processes, because it is only 98.5% pure.
There are various refining methods, but the refluxing process is the most commonly used.
High purity zinc is required industrially to avoid zinc pest
, a slow distortion and cracking of zinc die castings caused by impurities precipitating out.
invented this process in 1930.
The process take advantage of the relatively low boiling point of zinc (907 °C (1,664.6 °F)) as compared to the impurities being removed in the first "column": iron
and aluminium
. Therefore, in the first column the zinc is heated above its boiling point and allowed to rise to a condenser. The other impurities sink to the bottom in the form of a solid or liquid. There is still lead
and cadmium
, in the form of vapor, impurities. In order to remove the lead 2-3% of the vapor is condensed, which draws the majority of the lead out of the vapor; down to the point where it is only 0.003% of the total contents. Finally the vapor is pumped into the cadmium column where it is cooled to an intermediate temperature below the boiling point zinc, but still above the boiling point of cadmium (767 °C (1,412.6 °F)). The zinc leaves out the bottom as a refined liquid, while the cadmium leaves out the top as vapor.
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
to super high grade (SHG) zinc, which is at least 99.995% pure. This process isn't usually required when smelting zinc through electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
processes, but is needed when zinc is produced by pyrometallurgical processes, because it is only 98.5% pure.
There are various refining methods, but the refluxing process is the most commonly used.
High purity zinc is required industrially to avoid zinc pest
Zinc pest
Zinc pest, , is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities. It was first discovered to be a problem in 1923....
, a slow distortion and cracking of zinc die castings caused by impurities precipitating out.
Refluxing process
The New Jersey Zinc CompanyNew Jersey Zinc Company
The Horsehead Corporation , formerly the New Jersey Zinc Company, is an American producer of zinc and related materials.The New Jersey Zinc Company was for many years the largest producer of zinc and zinc products in the United States. The company thrived in the period from 1897 to 1966, at which...
invented this process in 1930.
The process take advantage of the relatively low boiling point of zinc (907 °C (1,664.6 °F)) as compared to the impurities being removed in the first "column": iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
. Therefore, in the first column the zinc is heated above its boiling point and allowed to rise to a condenser. The other impurities sink to the bottom in the form of a solid or liquid. There is still lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
, in the form of vapor, impurities. In order to remove the lead 2-3% of the vapor is condensed, which draws the majority of the lead out of the vapor; down to the point where it is only 0.003% of the total contents. Finally the vapor is pumped into the cadmium column where it is cooled to an intermediate temperature below the boiling point zinc, but still above the boiling point of cadmium (767 °C (1,412.6 °F)). The zinc leaves out the bottom as a refined liquid, while the cadmium leaves out the top as vapor.