SILVER MINING
SILVER :
Silver a soft, white lustrous transition metal that possesses the highest electrical conductivity of any element, most silver is produced as a spin-off of copper, gold, lead, and zinc refining. The metal emerges naturally in its untainted, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. This long been valued metal is not only used as an accessory, industrially, they are used in electrical contacts and conductors, in specialized mirrors, window coatings and in catalysis of chemical reactions. The compounds of silver are also used in photographic film and X-rays.
In general, silver is extorted from ore by smelting or by means of modernized technique of chemical leaching. Europeans spotted a vast quantity of silver in the New World in the present Mexican State of Zacatecas (exposed in 1546) and Potosi (Bolivia, also discovered in 1546), which activated an period of price increases in Europe.
The conquistador Francisco Pizarro was told to have routed to having his horses shod with silver horseshoes owing to the metal's large quantity, in difference to the comparative need of iron in Peru. Silver, which was extremely valuable in China, became a worldwide article of trade, causative to the climb of the Spanish Empire. The ascension and descend of its worth exaggerated the world market.
MINING AND PROCESSING :
The Silver bearing ores are mined by either open-pit or underground mining methods after which they are crushed and ground. Despite of the existence of other technologies, this metal is mined through a process that uses gravity to break and extract its ores from large deposits. This extraction method of removing the ore varies depending on the physical characteristics of the rock which surrounds the metal and also the shape of the deposits in which the metal is contained. The deposits are often long and cylindrical and hence they are known as veins. The silver ores are strong and made of solid substances and can also be found in sand, gravel and other mineral deposits in the form of flakes.
Silver is often mined along with the metal gold, found together in the form of an alloy called electrum. It is also mined along with other elements on a regular basis which includes argentite, pyrargyrite and cerargyrite, forming the end product to be known as Horn Silver. Silver mostly occurs as a secondary element along with lead, copper and zinc ores, the reason because of which nearly 50 percent of the silver mined today is obtained when processing other kinds of ore. It is separated from other ores through the smelting process. When a new silver mine is worked on, a system of multi-layered crosscuts are made where each cut connects to a central shaft but is kept at a safe vertical distance to avoid collapses. Certain openings called raises are dug for the purpose of connecting each level. These raises divide the body of the ore into blocks. It is at this point, the silver mine is ready to begin extraction. Most often, the overhand stoping method is executed where the ore is removed starting at the bottom and working up one layer at a time. Generally mines include a network of tunnels and chambers designed to safely raise the pulverized ore up and out in mine cars. The oldest Silver mines still in operation are located in Peru and Norway.
SILVER ORES :
Even though certain silver bearing ores contain silver, none of them contain silver as their major constituent. A distinct ore might contain 0.085 percent silver, 0.5 percent lead, 0.5 percent copper, and 0.3 percent antimony and after flotation separation, the concentrate would contain 1.7 percent silver, 10 to 15 percent lead, 10 to 15 percent copper, and 6 percent antimony. It is known that accurately 25 percent of the silver produced comes from ores actually mined for their silver value whereas the other 75 percent comes from ores that have silver as their major metal value which can be either lead, copper, or zinc. All these mineral ores are generally sulfides where lead is present as galena (PbS), zinc as sphalerite (ZnS), and copper as chalcopyrite (CuFeS2). The mineralization of silver usually includes large amounts of pyrite (FeS2) and arsenopyrite (FeAsS). The major silver ores are considered to be argentite (Ag2S), proustite (Ag3AsS3), and polybasite [(Ag,Cu)16Sb2S11]. More than half of the world's reserve base of silver mineralization is held by the United States, Canada, Mexico, Peru, Kazakhstan and Russia.
EXTRACTING AND REFINING :
The metallurgy processes applied to a silver-bearing mineral concentrate depend on whether the major metal is copper, zinc, or lead. In most cases the ore is mined and then treated by either mechanical or gravitational means to concentrate the ore minerals and separate them from the mass of the non-ore material.
The chief ore of silver is argentite and silver is extracted from argentite by the hydrometallurgy process. Firstly, the silver ore is dissolved in cyanide solution to produce a soluble argento cyanide complex from which the metal can be obtained by the reduction method. The different steps involved in the extraction of silver are as follows:
a. Ore- Concentration :
The ore Argentite is a sulfide ore and is thus concentrated by the froth flotation process. After the ore is crushed and reduced to fine particles, it is kept in a large tank which contains water and pine oil as ingredients. This mixture is then interrupted by passing compressed air where the ore forms a froth with the pine oil and rises to the surface and the other impurities are remained in the water below.
b. Treatment with sodium cyanide :
The concentrated ore obtained from the above process is treated with 0.4% to 0.7% aqueous solution of sodium cyanide and a current of air is passed through it. As a result, the argentite ore gets dissolved in the sodium cyanide solution to form Sodium Argento Cyanide. The reaction is as follows:
Ag2S + 2NaCN ? 2Na [Ag(CN)2] + NO2S
The reaction is a reversible one and so, oxygen is passed to oxidize Na2S to Na2SO4 such that the equilibrium shifts towards the product.
Na2S + O2 ? Na2SO4
The entire solution is filtered and the filtrate containing Sodium Argento Cyanide undergoes precipitation to recover the silver metal.
c. Precipitation of Silver :
The filtered solution of Sodium Argento Cyanide obtained is treated with zinc scrap where zinc displaces silver from its complex. Thus, Sodium Zinc Cyanide is produced and silver gets precipitated.
Zn + 2Na [Ag (CN)2] ? NO2[Zn (CN)4] + 2Ag
This silver precipitate is then collected, washed and fused to get a compact mass of silver.
d. Refining :
The ore containing silver needs to be refined to obtain pure silver as an end product. The silver precipitate obtained previously may contain some impurities and so the impure silver is purified by the electrolytic method. The process requires a block of impure metal to be the anode while a thin strip of pure silver is fetched as cathode. A mixture of silver nitrate solution is taken as the electrolyte. On passing current through the electrolytic tank, the impure silver gets dissolved and an equivalent amount of pure silver is deposited at the cathode.
AgNO3(aq) ? Ag+ + NO3
At cathode: Ag+ + e ? Ag
At anode: Ag ? Ag+ +e
TOP SILVER PRODUCING COUNTRIES :
1. China: China is currently the world's number one silver producer, producing 4,300 metric tons in 2019. The nation has long been a major player in the silver market, and its production has increased steadily in recent years. China's top silver producing provinces include Shandong, Inner Mongolia, and Henan.
2. Mexico: Mexico is the second-largest silver producer in the world, producing 3,700 metric tons in 2019. The country has a long history of silver mining, and its production has been steadily increasing since 2015. The Mexican states of Zacatecas, Chihuahua, and Durango are the top silver producing states in the country.
3. Peru: Peru is the third-largest silver producer in the world, producing 2,900 metric tons in 2019. The country has a long history of silver mining, and its production has been steadily increasing since 2014. The Peruvian provinces of Arequipa, Puno, and Cajamarca are the top silver producing states in the country.
4. Russia: Russia is the fourth-largest silver producer in the world, producing 1,800 metric tons in 2019. The country has a long history of silver mining, and its production has been steadily increasing since 2011. The Russian regions of Sverdlovsk and Orenburg are the top silver producing regions in the country.
5. Australia: Australia is the fifth-largest silver producer in the world, producing 1,700 metric tons in 2019. The country has a long history of silver mining, and its production has been steadily increasing since 2012. The Australian states of New South Wales and Western Australia are the top silver producing states in the country.
USES OF SILVER :
It is used in making ornaments, coins, decorative articles etc.
It is used in electroplating of silver, making silver mirror etc.
Silver halides are used in conventional x-ray film as an image receptor.
Silver sulfadiazine is used as a topical cream to treat burns, which is an anti-infective medicine.
Silver is used in bandages and dressings to prevent the spread of infections, as well as in gels and ointments for minor scrapes and cuts.
Silver nitrate is used from a long time as drops for newborn babies to prevent pink eye.
Colloidal silver is used to treat ceramic water filters to aid in killing bacteria and pathogens and also to help bring clean water to developing nations.
Silver Coat technology is used in Foley catheters in urology to prevent urinary tract infections from catheter use.
ANNUAL SILVER USAGE :
The annual silver usage rate can vary significantly depending on the type of silver being used and the purpose for which it is being used. Silver is used for a variety of industrial, medical, and decorative purposes.
Industrial: Silver is commonly used as a catalyst in industrial processes, such as the production of chemicals, pharmaceuticals, and electronics. It can also be used in plating, soldering, and electrical equipment. According to the International Silver Trade Association, the annual silver usage rate in industry was around 1,500 tons in 2017.
Medical: Silver is used in medical applications such as medical implants and wound dressings due to its antimicrobial properties. According to the World Silver Survey, the annual silver usage rate for medical applications was around 350 tons in 2017.
Decorative: Silver is also used in decorative applications, such as jewelry and tableware. According to the World Silver Survey, the annual silver usage rate for decorative applications was around 1,000 tons in 2017.
SILVER PRODUCTION IN THE WORLD :
Countries like Peru, Poland, Norway, Canada and the U.S. are world leaders in Silver mining, with Mexico serving as the country with the largest annual silver production. Silver is also mined in Bolivia. In Europe, all the silver mined is known to be extracted in the form of lead sulfide ore, also known as Galena. In Australia, the Cannington mine is one of the world's largest mines in terms of silver reserves. A very few mines in North America extract Silver alone while the U.S. mines primarily dig for zinc, lead and copper. The United States that lead in Silver mining are Arizona, Montana, Nevada and Idaho. The topmost five countries are as follows:
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