Bog iron
Bog iron is a form of impure iron deposit that develops in bogs or swamps by the chemical or biochemical oxidation of iron carried in solution. In general, bog ores consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)).
Iron-bearing groundwater typically emerges as a spring and the iron in it forms ferric hydroxide upon encountering the oxidizing environment of the surface. Bog ore often combines goethite and magnetite, and may include vugs and stained quartz. Oxidation may occur through enzyme catalysis by iron bacteria. It is not clear whether the magnetite precipitates upon the first contact with oxygen, then oxidizes to ferric compounds, or whether the ferric compounds are reduced when exposed to anoxic conditions upon burial beneath the sediment surface and reoxidized upon exhumation at the surface.Template:Citation needed
Bog iron, like other hydrous iron oxides, has a specific affinity for heavy metals.<ref>Template:Cite journal</ref> This affinity combined with the porous structure and high specific surface area of bog iron make it a good natural sorbent.<ref name=":0">Template:Cite journal</ref> These properties combined with the fact that bog iron is cheap to obtain are incentives for its utilization in environmental protection technologies.<ref name=":0" />
Iron made from bog ore will often contain residual silicates, which can form a glassy coating that imparts some resistance to rusting.
FormationEdit
Iron is carried to bogs in low-pH, low-dissolved oxygen iron-bearing groundwater that reaches the surface through springs, along with structures of fractures, or where groundwater intersects surface flows.<ref name=":3">Template:Cite journal</ref> The iron in the water is then oxidized by dissolved oxygen or, through enzyme catalysis by iron bacteria (e.g., Thiobacillus ferrooxidans and Thiobacillus thiooxidans) that concentrate the iron as part of their life processes.<ref name=":4">Template:Cite journal</ref> Presence of these bacteria can be detected by the oily film they leave on the surface of the water.<ref name=":3" /> This change of oxidation state causes the precipitation of fine-grained iron solids near the point of groundwater discharge.<ref name=":3" /> A variety of iron minerals, such as goethite, magnetite, hematite, schwertmannite, and amorphous iron-aluminum-sulfate-rich solids, can be formed via oxidation of ferrous iron under the acidic conditions present.<ref name=":4" /> All photosynthesizers play dual roles as oxygen producers, and thus passive iron oxidizers, and as surfaces to which the iron can sorb or bind.<ref name=":4" /> This causes aquatic plants to become heavily encrusted with a light-orange floc of iron oxyhydroxide near the point of oxygen gas released from the plants.<ref name=":4" /> Factors such as local geology, parent rock mineralogy, ground-water composition, and geochemically active microbes and plants influence the formation, growth, and persistence of iron bogs.<ref name=":4" /> Bog iron is a renewable resource; the same bog can be harvested about once each generation.<ref name=":3" />
Iron extractionEdit
Europeans developed iron smelting from bog iron during the Pre-Roman Iron Age of the 5th/4th–1st centuries BCE, and most iron of the Viking Age (late first millennium CE) was smelted from bog iron.<ref name=":3" /> Humans can process bog iron with limited technology, since it does not have to be molten to remove many impurities.<ref name=":2">Template:Cite journal</ref> Due to its easy accessibility and reducibility, bog iron was commonly used for early iron production.<ref>Template:Cite journal</ref> Early metallurgists identified bog-iron deposits by indicators such as withered grass, a wet environment, hygrophilous grass-dominated vegetation, and reddish-brown solutions or depositions in nearby waters.<ref name=":1" /> They stabbed wooden or metal sticks into the ground to detect larger ore-deposits,<ref name=":1" /> and cut and pulled back layers of peat in the bog using turf knives to extract smaller, pea-sized nodules of bog iron.<ref name=":3" /> Early iron-production from bog ore mostly occurred in bloomery furnaces.<ref name=":1" /> The resources necessary for production were wood for charcoal, clay for the construction of bloomery furnaces, and water for processing.<ref name=":1" /> Iron in the ore is reduced to a spongy iron bloom that stays in the upper part of the furnace while the undesirable elements stream downwards as slag.<ref>Template:Cite journal</ref> Smelting with a bloomery furnace often results in between 10 and 20 mass percent Fe being reduced to iron bloom, while the rest is transferred into the slag.<ref>Template:Cite book </ref> The bloom must then be consolidated with a hammer to make usable wrought iron. There is some archaeological evidence that lime was added to furnaces to treat silica-rich ores that were difficult to smelt by the bloomery process.<ref name=":3" />
EuropeEdit
The first iron smelting attempts date to the 2nd millennium BCE in the Near East.<ref name=":1">Template:Cite journal</ref> The technology then spread throughout Europe in the following two millennia, reaching Poland in the 2nd century BCE.<ref name=":1" /> Iron production reached Scandinavia around 800–500 BCE. Iron production sites in central Sweden are dated to the late Bronze Age and the innovation might have been transmitted from both the south and the east. The ore used was limonite in the form of red soil and bog ore. From 200 CE ore from limonite-deposits in lakes was used. The ore was reduced in bloomeries. There is evidence of a direct relationship between Viking settlements in northern Europe and North America and bog iron deposits.<ref name=":2" /> Bog iron dominated the iron production of Norse populated areas, including Scandinavia and Finland, from 500 to 1300 CE.<ref name=":2" /> Large scale production of bog iron was also established in Iceland at sites known as "iron farms".<ref name=":2" /> Smaller scale production sites in Iceland consisted of large farmsteads and some original Icelandic settlements, but these seemed to only produce enough iron to be self-sufficient.<ref name=":2" /> Even after improved smelting technology made mined ores viable during the Middle Ages, bog ore remained important into modern times, particularly in peasant iron production.<ref>Maria Sjöberg and Anton Tomilov, "Iron-Making in Peasant Communities," in Iron-making Societies: Early Industrial Development in Sweden and Russia, 1600–1900, ed. Maria Ågren, 33–60 (New York: Berghahn, 1998), 33–36, 59–60; Anders Florén, Göran Rydén, Ludmila Dashkevich, D. V. Gavrilov and Sergei Ustiantsev, "'The Social Organisation of Work at Mines, Furnaces, and Forges," in Iron-making Societies: Early Industrial Development in Sweden and Russia, 1600–1900, ed. Maria Ågren, 61–138 (New York: Berghahn, 1998), 62–65.</ref> In Russia, bog ore was the principal source of iron until the 16th century, when the superior ores of the Ural Mountains became available.Template:Citation needed
North AmericaEdit
Pre-ColumbianEdit
Iron was produced by the Vikings on Newfoundland around 1021 CE.<ref name="KuitemsEtAl">Template:Cite journal</ref> Excavations at L'Anse aux Meadows have found considerable evidence for the processing of bog iron and the production of iron ore.<ref name=":2" /> The settlement at L'Anse aux Meadows was situated immediately east of a sedge peat bog and 15 kg of slag was found at the site, which would have produced around 3 kg of usable iron.<ref name=":2" /> Analysis of the slag showed that considerably more iron could have been smelted out of the ore, indicating that the workers processing the ore had not been skilled.<ref name=":2" /> This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.<ref name=":2" /> Ninety-eight nail fragments were also found at the site as well as considerable evidence for woodworking which points to the iron produced at the site possibly being used only for ship repair and not tool making.<ref name=":2" /><ref>Template:Cite book</ref>
Colonial North AmericaEdit
Bog iron was widely sought in colonial North America. The earliest known iron mines in North America are the mines from St. John's, Newfoundland, reportedly in operation by Anthony Parkhurst in 1578.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The first mining efforts in Virginia occurred as early as 1608. In 1619 Falling Creek Ironworks was established in Chesterfield County, Virginia. It was the location of the first blast furnace facility in North America.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Lake Massapoag in Massachusetts was drawn down by deepening the outlet channel in a search for bog iron.<ref>Diana Muir, Reflections in Bullough's Pond, University Press of New England, 2000.</ref> The Saugus Iron Works National Historic Site, on the Saugus River in Saugus, Massachusetts, operated between 1646 and 1668. The site contains a museum and several reconstructed buildings.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The success of the Saugus Iron Works, and the rapid depletion of the region's natural bog iron, led the owners to send prospectors into the surrounding countryside. In 1658 the company bought Template:Convert of land which covered areas that are now Concord, Acton, and Sudbury. They set up a large production facility in Concord, Massachusetts, along the Assabet River with dams, ponds, watercourses, and hearths, but by 1694 the natural bog iron there had also been exhausted, and the land was sold for farming.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} The Concord Iron Works</ref>
In Central and Southern New Jersey, bog ore was mined and refined for the production of naturally rust-resistant tools and wrought iron rails, many of which still grace staircases in Trenton and Camden.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> During the American Revolution, bog iron cannonballs were cast for the colonial forces.
19th century United StatesEdit
Bog iron was also found on the Eastern Shore of Maryland. The remains of a commercial smelting operation near Snow Hill, Maryland, are now a state and national historic site. Known as Furnace Town, it was called the Nassawango Iron Furnace after the nearby creek. The commercial furnace ran from about 1825 to 1850.
The Shapleigh Iron Company constructed a smelter at North Shapleigh, Maine, in 1836 to exploit a small bog iron deposit in Little Ossipee Pond. The plant commenced operation in 1837, but according to an 1854 history of Shapleigh "the business [proved] unprofitable, therefore after a few years it was abandoned."<ref>Loring, Rev. Amasa. A History of Shapleigh, Portland, ME: Brown and Thurston, 1854. p. 39.</ref><ref>Leonard, Edward H. A monthly field trip of the Maine Mineralogical and Geological Society. Rocks and Minerals 5(2):49 (June 1930).</ref><ref>Weddle, Thomas K. The Iron Age of Maine, Part II: The Shapleigh Iron Company: A Foray into Industrial (geo)Archaeology in Maine Geologic Facts and Localities. Augusta, Maine: Maine Geological Survey, November 2003. https://digitalmaine.com/mgs_publications/370/ accessed 6/9/2019.</ref>
See alsoEdit
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- Template:Annotated link (iron-oxidizing bacteria)
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ReferencesEdit
External linksEdit
- ASME PDF file with detailed reconstruction drawings of the furnace and surroundings.
- Template:MHT url at the Maryland Historic Trust.
- Template:Cite AmCyc