Pan amalgamation
Encyclopedia
The Pan amalgamation process is a method to extract silver
from ore, using mercury
. The process was widely used from 1609 through the 19th century; it is no longer used.
The patio process
had been used to extract silver
from ore since its invention in 1557. One drawback of the patio process was the long treatment time, usually weeks. Alvaro Alonso Barba
invented the faster pan process (in Spanish the cazo or fondo process) in 1609 in Potosí
, Bolivia
, in which ore was mixed with salt and mercury (and sometimes copper(II) sulfate) and heated in shallow copper
vessels. The treatment time was reduced to 10 to 20 hours. Whether patio or pan amalgamation was used at a particular location often depended on climate (warmer conditions speeded the patio process) and the availability and cost of fuel to heat the pans.
The amount of salt and copper(II) sulfate varied from one-quarter to ten pounds of one or the other, or both, per ton of ore treated. The loss of mercury in amalgamation processes was generally one to two times the weight of silver
recovered.
The Washoe process, a variation of pan amalgamation, was developed in the 1860s by Almarin Paul and others, to work the ore from the Comstock Lode
in Nevada
, United States (Washoe was an early name for the area; see Washoe Valley). In the Washoe process, the copper pans were replaced by iron tanks with mechanical agitators. Each tank ("pan") was circular, and commonly held 1,200 to 1,500 pounds of ore that had been crushed to sand size. Water was added to make a pulp, and 60 to 70 pounds of mercury, along with one-half to three pounds each of salt (sodium chloride
) and bluestone (copper(II) sulfate) were also added. A circular iron plate called a muller was mounted on a vertical shaft and lowered into the pan, and was rotated to provide both agitation and additional grinding. Heat was delivered to the pans by steam pipes. The iron filings worn from the muller and pan proved to be an essential ingredient in the process.
mining district around Austin, Nevada
. The Washoe process was found not to work well for ores with arsenic
or antimony
sulfides, or with galena
or sphalerite
. In 1869, Carl A. Stetefeldt of Reno
found that roasting the ore with salt converted the silver sulfides to silver chlorides, which could then be recovered in amalgamation pans. The process was introduced in the Reese River District in 1879, with great success.
Other silver-mining districts using the Reese River process included Georgetown, Colorado
, Caribou, Colorado
, and Silver Cliff, Colorado
.
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
from ore, using mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. The process was widely used from 1609 through the 19th century; it is no longer used.
The patio process
Patio process
The patio process was a process used to extract silver from ore. The process was invented by Bartolomé de Medina in Pachuca, New Spain , in 1554. The patio process was the first process to use mercury amalgamation to recover silver from ore. It replaced smelting as the primary method of extracting...
had been used to extract silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
from ore since its invention in 1557. One drawback of the patio process was the long treatment time, usually weeks. Alvaro Alonso Barba
Alvaro Alonso Barba
Alvaro Alonso Barba was a secular Catholic priest and metallurgist.Antonio says, "Baeticus ex oppido Lepe, apud Potosi"; hence Barba is assumed to be of Andalusian origin, from the ancient Roman province of Baetica...
invented the faster pan process (in Spanish the cazo or fondo process) in 1609 in Potosí
Potosí
Potosí is a city and the capital of the department of Potosí in Bolivia. It is one of the highest cities in the world by elevation at a nominal . and it was the location of the Spanish colonial mint, now the National Mint of Bolivia...
, Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
, in which ore was mixed with salt and mercury (and sometimes copper(II) sulfate) and heated in shallow copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
vessels. The treatment time was reduced to 10 to 20 hours. Whether patio or pan amalgamation was used at a particular location often depended on climate (warmer conditions speeded the patio process) and the availability and cost of fuel to heat the pans.
The amount of salt and copper(II) sulfate varied from one-quarter to ten pounds of one or the other, or both, per ton of ore treated. The loss of mercury in amalgamation processes was generally one to two times the weight of silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
recovered.
Washoe process
Comstock Lode
The Comstock Lode was the first major U.S. discovery of silver ore, located under what is now Virginia City, Nevada, on the eastern slope of Mount Davidson, a peak in the Virginia Range. After the discovery was made public in 1859, prospectors rushed to the area and scrambled to stake their claims...
in Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, United States (Washoe was an early name for the area; see Washoe Valley). In the Washoe process, the copper pans were replaced by iron tanks with mechanical agitators. Each tank ("pan") was circular, and commonly held 1,200 to 1,500 pounds of ore that had been crushed to sand size. Water was added to make a pulp, and 60 to 70 pounds of mercury, along with one-half to three pounds each of salt (sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
) and bluestone (copper(II) sulfate) were also added. A circular iron plate called a muller was mounted on a vertical shaft and lowered into the pan, and was rotated to provide both agitation and additional grinding. Heat was delivered to the pans by steam pipes. The iron filings worn from the muller and pan proved to be an essential ingredient in the process.
Reese River process
A variation of the Washoe process was developed in the Reese RiverReese River
The Reese River is a tributary of the Humboldt River, located in central Nevada in the western United States. It rises in the southern section of the Toiyabe Range, on the flanks of Arc Dome...
mining district around Austin, Nevada
Austin, Nevada
Austin is a small, unincorporated community located in Lander County, Nevada, in the United States. As of 2004, its population is approximately 340. It is located on the western slopes of the Toiyabe Range at an elevation of . U.S...
. The Washoe process was found not to work well for ores with arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
or antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
sulfides, or with galena
Galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
or sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
. In 1869, Carl A. Stetefeldt of Reno
Reno, Nevada
Reno is the county seat of Washoe County, Nevada, United States. The city has a population of about 220,500 and is the most populous Nevada city outside of the Las Vegas metropolitan area...
found that roasting the ore with salt converted the silver sulfides to silver chlorides, which could then be recovered in amalgamation pans. The process was introduced in the Reese River District in 1879, with great success.
Other silver-mining districts using the Reese River process included Georgetown, Colorado
Georgetown, Colorado
The historic town of Georgetown is a Territorial Charter Municipality that is the county seat of Clear Creek County, Colorado, United States. The former silver mining camp along Clear Creek in the Front Range of the Rocky Mountains was established in 1859 during the Pike's Peak Gold Rush...
, Caribou, Colorado
Caribou, Colorado
Caribou is a former silver-mining town, now a ghost town near Nederland in Boulder County, Colorado, United States. It was named after the Caribou silver mine nearby. The Caribou Ranch recording studio is several miles away, on the road from Nederland up to Caribou.-History:A prospector named...
, and Silver Cliff, Colorado
Silver Cliff, Colorado
Silver Cliff is a Statutory Town that is the most populous town in Custer County, Colorado, United States. The population was 512 at the 2000 census.-History:...
.