What is Zinc? – Its Compounds, Alloys, and Properties

What is Zinc?

With the atomic number 30 and the symbol Zn, zinc is a chemical element or silvery lustrous metal belonging to Group 12 or IIB. of the periodic chart. It’s used to make alloys, corrosion-resistant coatings, and dry cells, among other things. 

Only mercury creates a limited number of compounds in the +1-oxidation number or state among the periodic table’s group of 12 elements. In contrast, other elements like zinc and cadmium are from chemical compounds in the +2 state.

The d-electron gradually becomes a component of the inner core for the zinc atom as shielding electrons rise along the 3d-orbital. As a result, chemical bonding is limited to s-electrons.

Zinc is more plentiful in the earth’s crust than copper. The most common zinc ores are zinc blend (ZnS) and calamine (ZnCO₃).

Franklinite (ZnO, Fe₂O3) and willemite are two more minor significant ores (Z ₂SiO₄). It is primarily found in Canada, Russia, Australia, China, Peru, and the United States.

History of Zinc

Zinc metal manufacturing was quite popular in ancient India. Many mine sites in Rajasthan’s Zawarmala region were operating as early as 1300-1000 B.C.E.

In the 300 B.C.E. manuscript Charaka Samhita, there are references to zinc’s therapeutic benefits. The Rasa Ratna Samuccaya (800 C.E.) teaches that there are two types of metal ores for metal extraction and therapeutic uses.

For millennia, zinc alloys have been utilized. Brass (a copper-zinc alloy) items from 1000–1400 B.C.E. have been discovered in Israel, and zinc objects containing 87 percent zinc have been discovered in prehistoric Transylvania.

Isolated zinc tends to go up the chimney rather than be collected due to its low boiling point and intense chemical reactivity. As a result, the real nature of zinc in ancient times was unknown.

Brass was made by the Romans around 30 B.C.E. using a procedure that involved heating calamine (a zinc mineral) and copper together in a crucible.

Calamine’s zinc oxides were reduced, and the copper captured the free zinc metal, forming an alloy. The calamine brass that resulted was either cast or hammered into shape.

Smelting and extraction of impure forms of zinc were done in India and China as early as 1000 C.E. Impure zinc as a byproduct of melting ovens has been known in the West since antiquity. However, it was normally discarded as worthless.

The German Andreas Marggraf is credited with discovering pure metallic zinc around 1746, but the entire tale is disputed.

In 1597, Libavius, an English metallurgist, obtained a quantity of pure zinc metal, which had hitherto been unknown to the West.

After visiting the Zawar zinc mines in and near Zawarmala, Rajasthan, William Champion is credited with patenting in Great Britain a procedure to extract zinc from calamine in a smelter in 1738. The patent court rejected his initial invention because it plagiarized Indian technology.

Ores of Zinc

Zinc ores are found worldwide, although North America and Australia produce more than 40% of the total. Calamine ore and zinc blend are the two types of zinc ores.

Calamine is composed of zinc carbonate (carbonate ore), with the chemical formula ZnCO₃ZnCO₃. Zinc sulfide (sulfide ore) is the chemical compound found in the zinc blend, and its chemical formula is ZnS.

Manufacturing Process of Zinc

1. Mining

Eighty percent of zinc mines are underground, eight percent are open pits, and the rest are a combination of both. Underground mines offer up to 64 percent of total zinc output, combined underground/open pit mines provide 21%, and open-pit mines provide 15%.

When mined, the ore is rarely rich enough to be used directly by smelters; it must be concentrated. Zinc ores include between 5 and 15% zinc. It is crushed and ground to concentrate the ore to provide the best minerals separation.

A zinc concentrate typically includes around 55% zinc and some copper, lead, and iron. Zinc concentration is usually done at the mining site to keep transportation expenses to smelters to a minimum.

2. Roasting & Sintering

Zinc blend contributes to over 95% of global zinc production (ZnS). Apart from zinc, the concentrate also contains 25-30% sulfur and varying levels of iron, lead, silver, and other minerals.

Sulfur in the concentrate must be eliminated before hydrometallurgical or pyrometallurgical processes extract metallic zinc. 

It is done by roasting or sintering. The concentrate is heated to over 900°C when the zinc sulfide (ZnS) is converted to the more active zinc oxide (ZnO).

Simultaneously, sulfur combines with oxygen to produce sulfur dioxide, transformed into sulfuric acid, a valuable economic byproduct.

3. The Hydrometallurgical Process

The zinc oxide is isolated from the other calcines during the leaching stage. It is done with sulfuric acid. Zinc dissolves, whereas iron precipitates, leaving lead and silver undissolved.

However, the dissolved solution contains some impurities that must be removed before a high-purity zinc product can be obtained at the end of the manufacturing process. The solution is mostly purified by adding zinc dust.

Because all of the elements to be removed are below zinc in the electrochemical series, cementation can be used to precipitate them. The purified solution is electrolyzed between lead alloy anodes and aluminum cathodes in an electrolytic procedure.

An electrical current is routed through the electrolyte by supplying an electrical difference of 3.3-3.5 volts between the anode and cathode, causing the zinc to deposit high purity on the aluminum cathodes.

The zinc is taken from the deposit, dried, melted, and cast into ingots. High Grade 99.95 percent zinc ingots and Special High Grade 99.99 percent zinc ingots are available. Today, electrolytic plants produce over 90% of zinc produced hydrometallurgical.

4. The Pyrometallurgical Process

The Imperial Smelting process involves reducing zinc and lead to metal in a specially built Imperial Smelting furnace using carbon.

Because the Imperial Smelting process is energy-intensive, it has become prohibitively expensive as energy prices have raised. Only China, India, Japan, and Poland have Imperial Smelting furnaces today.

Compounds of Zinc

1. Zinc Oxide

Zinc oxide has the molecular formula ZnO and is the most common zinc oxide. Heating ZnS in the air or thermal decomposition of zinc carbonate produce ZnO. At room temperature, it is white.

The loss of oxygen from the ZnO lattice causes ZnO to turn yellow, resulting in non-stoichiometric compositions like Zn1+xO.

The empty lattice points could trap electrons excited by visible electromagnetic radiation, resulting in yellow color. It is amphoteric, forming Zn+2 ions when dissolved in acids.

2. Zinc Sulfide

We are all too familiar with zinc sulfide (chemical formula ZnS) in ordinary group analysis. The direct reaction of aqueous Zn (II) with hydrogen sulfide produces ZnS.

Zinc blend and wurtzite are two solid crystalline forms of ZnS. At 1020 °C, they transform each other. It dissolves easily in dilute acids.

3. Zinc Sulfate

The zinc sulfide (chemical formula ZnS) is well-known in regular group analysis. Aqueous Zn (II) reacts directly with hydrogen sulfide to form ZnS. Wurtzite and zinc blend is two solid crystalline forms of ZnS. They change at 1020 °C. It dissolves readily in dilute acids.

4. Zinc Halide

ZnF₂, ZnCl₂, ZnBr₂, and ZnI₂ are the four metal halides of zinc that are known. Zinc chloride, bromide, and iodide are ionic compounds with significant electric polarization. Layer lattice crystallizes from them. Ionic fluoride, such as ZnF₂, is very soluble in water.

Alloys of Zinc

Some common alloys of zinc are as follows:

1. Brass

Brass is a zinc alloy that contains anywhere from 3% to 45 percent zinc, depending on the type of brass. Brass is more malleable, stronger, and corrosion-resistant than copper.

It is helpful in communication equipment, hardware, musical instruments, and water valves because of these qualities.

2. Nickel Silver

Nickel silver is a group of copper, nickel, and zinc alloys with a silvery appearance but no silver content. Its nickel content ranges from 7 to 30%, with 18% nickel silver being the most popular alloy (18 percent nickel, 62 percent copper, 20 percent zinc).

It’s utilized in jewelry, silverware, model railway lines, and musical instruments because of its gleaming silver appearance.

3. Zinc Die Casting Alloys

It contains 78% zinc by weight. It typically contains minor amounts (less than a few percentage points) of Pb, Sn, Cu, Al, and Mg to casting qualities and mechanical properties.

It’s utilized to create complicated little shapes and is appropriate for moving machine parts. Pot metal is the cheapest of these alloys, and it’s used as a steel substitute.

 Properties of Zinc

• In most commercial grades, zinc is a bluish-white, glossy, diamagnetic metal with a dull sheen.
• It is somewhat less dense than iron and has a hexagonal crystal structure with a distorted type of tight hexagonal packing.
• The metal is hard and brittle at most temperatures, but between 100 and 150 °C, it becomes malleable.
• The metal becomes brittle at temperatures exceeding 210°C and can be crushed by beating.
• Zinc is a good conductor of electricity.
• Zinc is present in several alloys, including brass. Zinc binary alloys have long been known to contain antimony, bismuth, gold, iron, lead, mercury, silver, tin, magnesium, cobalt, nickel, tellurium, and sodium.
• Zinc is a metal with low melting and boiling temperatures. All d-block metals except mercury and cadmium have the lowest melting points; as a result, zinc, cadmium, and mercury are generally not considered transition metals like the rest of the d-block metals.

Uses of Zinc

• Zinc is commonly utilized in iron to give a corrosion-resistant coating. Electrolysis or dipping in molten zinc can be used to deposit a small coating of metal on the Fe electrode (cathode). The metal coating can also be applied to other metals by sparingly applying zinc or heating with Zn-powdered.
• The second major application of zinc in producing various alloys, such as brass. Tumbling, valves, cartridge cases, and die-casting are examples of machine parts that utilize such alloys.
• Zinc is also used to make dry cells or batteries for flashlights, transistors, automobiles, electrical equipment, and hardware.
• Paints, rubber, cosmetics, medicines, plastics, inks, soaps, and batteries contain zinc oxide as the main constituent. Zinc oxide is also widely used in the textile and pharmaceutical industries.

Effect of Zinc on Health

Zinc is a micronutrient required by plants, people, and animals. Zinc deficiency has a minor impact on a plant’s health, interfering with reproduction. Zinc is used to make D.N.A. molecules. D.N.A. is a molecule in our bodies instructing cells on which chemicals to produce. 

Human reproduction is also controlled by it. Zinc deficiency in fetuses can lead to mental and physical issues later in life.

Hair loss and skin lesions can occur in young children who do not obtain enough zinc in their diet. They may also develop dwarfism, which is a type of growth retardation. 

Zinc is a micronutrient that humans require. However, too much or too little might be harmful to one’s health.

On the other side, too much zinc might harm your health. Zinc dust inhalation can induce throat irritation, coughing, weakness and ache, chills, fever, nausea, and vomiting.

A sweet feeling in the tongue that is not connected with consuming sweet foods is one indicator of zinc poisoning. Zinc compounds can also be hazardous to your health. For example, zinc chloride (ZnCl₂) can produce skin rashes and a sore throat.

FAQs

References:

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