Backyard bog iron deposit

Discussion in 'General foundry chat' started by Mark's castings, Jan 13, 2020.

  1. After watching a few videos about the precise conditions for bacterial bog iron to form deposits:
    • Swamp area with spring water.
    • Acid soil.
    • Plenty of aquatic plant life to supply oxygen.
    • Characteristic bacterial slicks on the water that look a bit like oil rainbows on water.
    I realized the low depression of land in the bushland 100 metres behind my house met all the criteria. The area is 12" underwater with rain run off for four+ months of the year when reeds grow abundantly and they even give off small streams of oxygen in the water like a fine stream of champagne bubbles. The dried clay mud like deposit is a tan orange when all other soil in the area is black acidic sandy soil.

    So today I took a plastic pail and grabbed a few clay soil samples four inches below and 12 inches below the surface. It varies from very dark brown on the surface, to grey with orange chunks. I put some wet grey clay sample in a glass jar and mixed it thoroughly with water and put a neodymium magnet on the side of the jar: no attraction whatsoever. After a similar sample was calcined in a small firebrick furnace with my blowtorch for heat, I noticed the hot clay was partially melted and bits could be pressed together in the flames and stick to each other. After cooling, the hottest part was black and the rear area away from the flame was brown, it was solid lump that took a bit of effort to break up and crush to powder. At this point the calcined mud had about 20% of the total become magnetic and be able to separated from the rest: Success!!.

    At this point , I'll try and reduce a calcined sample with powdered coke, and later down the track I can induce a brain snap with certain forum members by actually doing some "smelting" of iron ore :D. I wonder what the market is for authentic ingots of "Bog Iron" amongst the blacksmith crowd?.
  2. Peedee

    Peedee Silver

    I don't think pig iron has much value in itself, wrought iron on the other hand...... That said I'm sure someone would see value in the novelty.
  3. Isn't wrought iron made by hammering or rolling pig iron into strips or sheet?. It might only have value from the downright tedious process of making a bloomery and hammering a useful chunk of iron from that. Having an ingot that has to be wrought may not be as good... you'd have to have slag inclusions to get the "grain" happening.
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    joe yard likes this.
  5. Yeah, nah, I don't think I want to commit to the point of having a puddling furnace in the backyard :D.... come to think of it can you imagine the complaints if you had a small steel Bessemer converter in the backyard with it's white hot volcano of sparks as the silicon burns out. Also makes me wonder what the carbon content of iron bloom the bog iron guys are actually making. The Japanese Tamahagane guys were making forged steel blades with 0.7% carbon with a similar furnace, and that would be after a lot of carbon burns out during the forging of the blade.
    I think the wrought iron made from bloom iron has a higher carbon content than wrought iron from a puddling furnace.
    Last edited: Jan 13, 2020
  6. Tobho Mott

    Tobho Mott Silver Banner Member

    FWIW, I know a blacksmith who's actually told me before that he does want a puddling furnace in his backyard...

    Mark's castings likes this.
  7. That's probably the only way to get decent amounts of wrought iron for smithing. 1018 mild steel would come close but have no perceptible grain from the slag layers in the iron.

    It's interesting to see that a bloomery feeds CO, carbon monoxide into the furnace by burning rich and takes an atom of carbon away from the iron to form CO2. To gas case harden steel, you pack the steel to be hardened in carbon powder in a box and then heat it all up and flow CO2 into the box where it forms CO with the carbon powder which can then transfer carbon into the steel surface to a decent depth through diffusion: one process is the reverse of the other.
  8. Rotarysmp

    Rotarysmp Copper

    Hmmm, you need to reread that thought. CO + C does not equal CO2.

    From the Wiki for bloomery:
    Inside the furnace, carbon monoxide from the incomplete combustion of the charcoal reduces the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily forgeable, it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable.

    The bloomery does not remove carbon from the iron, it operates below the iron melting temp to prevent the iron from absorbing excessive carbon in the first place. The liquid phase of iron has much greater solubility of carbon. So if you heat the iron above the upper boundary line of the phase diagram, in a carbon rich environment, it can and will dissolve carbon well above the limits for steels. = pig iron.

    Modern steel making just accepts this, using a blast furnace to make pig iron, and removes the excessive carbon with a further step. The Linz-Donawitz process is most common.

    Where the puddling furnace oxidised the carbon out by blowing air across the melt and stirring it, the LD convertor blows high pressure jets of oxygen into the melt.
    Last edited: Jan 14, 2020
    Pete K likes this.

  9. Yes you're right, I stand corrected. Ironically I'm wearing a T shirt that reads: "I'm not arguing, I'm just explaining why I'm correct". So in short, hot iron oxide will give up oxygen in the presence of CO and form iron and CO2, while hot metallic iron will soak up a carbon from two CO molecules to form iron carbide and CO2
    Last edited: Jan 14, 2020
  10. Rotarysmp

    Rotarysmp Copper

    Nice shirt :)

    I wonder how they managed to control the Bloomery to not overheat and melt the iron. If I was doing it, I'd be blowing is as much air as possible to get it over with :)

    I guess the generations of knowledge/experience in an iron making village led to Furnace size and shape, charging rate, blower technology etc, that produced reproducable blooms.

    Although those bellows look like really hard work.
  11. So much like hard work that they abandoned the process of smelting iron as soon as other sources of iron and steel came along, according to the video. The bog iron'll have to wait until I'm in a post apocalyptic scenario for it to be worth exploiting, though it's really cool to recognize such a deposit. I could use my old experimental furnace to calcine the ore to convert it to magnetite, crush it and magnetically concentrate it before smelting it, or just stick to brake rotors.:rolleyes:
  12. Rotarysmp

    Rotarysmp Copper

    Sounds like the 21st century plan!
  13. Zapins

    Zapins Silver

    I always find myself wondering why primitive iron making people use bellows or leather bags to pump air in rather than making something like a radial blower or fan. Seems like it would be easier to operate a blower using a belt driven pedal or potters wheel type setup than pumping bags for hours...? Did it just never occur to them or are blowers difficult to make work correctly?
  14. I think it would be quite a mental leap to the concept of rotary propellors or centrifugal impellors compared to a bladder of some kind and a flap valve. A centrifugal blower needs a person to realize air has mass that allows it to be flung which may be too subtle a concept versus squeezing a bladder. The Youtuber "Primitive Technology" made a crude clay blower with a stick for the shaft so it is do-able.
  15. Petee716

    Petee716 Silver Banner Member

    Many of us have seen this guy
    He has the distinct advantage of this blower technology already existing. Kudos to him for how he applied it, but it's kind of a "Connecticut Yankee in King Arthur's Court" thing.
    It's interesting to note that blower technology seems to have progressed from wind to bags to bellows and back to something reminiscent of bags - blowing tubs or cylinders. And then finally the modern blower. Note the late date that the modern blower was invented.
    Here's a very interesting read.

  16. rocco

    rocco Silver

    Hey Pete, that second link isn't working for me, I just get "Server Not Found"
  17. Petee716

    Petee716 Silver Banner Member

  18. rocco

    rocco Silver

    It seems that site doesn't like Canada, I have to use a U.S. based proxy to view it.
    Any other non-U.S. forum members having problems with this site too?
    Last edited: Feb 9, 2020
  19. Petee716

    Petee716 Silver Banner Member

    The first image you see on their homepage is an angry looking soldier so there's bound to be someone they don't like. Don't they know how damned nice Canadians are? Lol.
  20. Jason

    Jason Gold Banner Member

    Evolution of Blast Furnace Iron Making

    The origin of the first smelting of iron is concealed in the unrecorded history of human civilization. The first evidence of iron implements being used in ancient times actually comes from Egypt where an iron tool was found in a joint between two stones in a pyramid. The origin of many prehistoric iron implements was probably meteoric iron. Meteoric iron contains 5 % to 26 % nickel (Ni) while smelted iron contains only traces of Ni and hence iron artifacts made from meteors can be differentiated from objects of smelted iron.

    More than 4,000 years ago, people discovered meteoric iron. But it was another 2,000 years before the production of iron from mined iron ore began. The earliest finds of smelted iron in India date back to 1800 BCE (Before Common Era). The smelting of iron is said to have taken place among the Calybes of Armenia, subjects of the Hittite Empire, at about 1500 BCE. When their empire collapsed around 1200 BCE, the various tribes took the knowledge of iron making with them, spreading it across Europe and Asia. The knowledge of ironworking in all of Europe and Western Asia is ultimately traced to this source. The Iron Age began with the discovery of smelting of iron.

    Beginning of iron smelting

    As with the reduction of copper sulfide ores, the first reduction of iron oxide was probably accidental. It was the powers of observation that led these ancient metallurgists (who were the miners, chemists, and technologists of their day) to realize that iron could be produced in simple furnaces by direct carbon (C) reduction of the oxide ore. The first recorded depiction of a smelting process was found on the wall of an Egyptian tomb dating to about 1500 BCE. (Fig. 1) This process was a simple pit with ore and unknown fuel that had the fire intensified through the use of foot-operated bellows. For the next 3000 years, techniques for the production of iron did not significantly change with iron sponge produced by C reduction of the oxides and iron products made by pounding the sponge.


    Fig 1 Iron smelting process depicted in Egyptian tomb

    Iron oxide ores are present in many areas of the planet earth. Thus, roughly at the same time when reduction of iron ores was taking place in Egypt, it also was being done in other areas. India, China, Africa, and Malaya served as sites for this initial development of iron making practices. It is perhaps significant that the furnaces developed in these countries were all quite similar. There were differences in shape and size, but the furnaces were functionally identical. The chemical reduction to iron occurred without melting, and the resulting metal was relatively pure and soft and was termed wrought iron. It could be hammered into useful shapes. Spears, arrow tips, daggers, and other tools and weapons could be fabricated from this wrought iron.

    For about 2000 years, until about the end of the first millennium CE (Common Era), the iron was produced in small local hearths by the ‘bloomery’ process. The size of these structures is not available in the archaeological investigations but a modern reconstruction of a bloomery furnace had internal dimensions of 300 mm dia. x 1000 mm high. In the bloomery process a hearth was constructed and in it was placed multiple layers of charcoal and iron ore until a mound was produced. Around this mound was built a casing of clay and brick leaving a hole at the top for the exhaust gasses and a hole at the bottom for a blast of air produced by operating bellows. The charcoal was then lit and the bellows operated until the charcoal was exhausted. The casing was then broken open, and if the process had proceeded well then there was a pile of spongy iron and a puddle of slag. The hot spongy iron was beaten by hammer to produce an iron billet or iron products. The reactions taking place during the smelting in the bloomery process are described here. The charcoal fire produced carbon monoxide (CO) and the heat drove off water from the bog ore to produce hematite. The CO reduced the hematite to ferrous oxide, wüstite. The CO then reduces the wüstite to elemental iron. The reaction did not go all the way; it proceeded to an equilibrium position and so the resulting gas was a mixture of CO and carbon dioxide (CO2). However, wüstite could also react with any sand to produce iron olivine, (fayalite), which is the major component of the slag produced. This fayalite was a dead end as far as the smelting process was concerned because it could not be reduced to elemental iron under the furnace conditions. The iron produced had a melting point of approx. 1,540 deg C, whereas the slag melting point was at around 1,100 deg C. The temperatures reached were high enough to melt the slag, but not high enough to melt the iron. The process worked well enough, although the remaining slag still contained much iron, often up to and over 60 % FeO (ferrous oxide). The slag was of two varieties, being partly of the open porous nature of bog-ore dross, and partly compact, hard, and very infusible, as obtained from red iron ore.

    Developments in iron making process

    Improvements in this first iron making process were made by lining the smelting hole with stones as well as mud and using bellows made of wood and leather (Fig 2). In China, the use of iron appeared about 600 BCE, spreading widely during the period 403BCE to 222 BCE. The Chinese developed superior iron making technology and liquid iron was produced as early as 200 BCE based upon the discovery of cast iron utensils. Ancient writings in both China and India refer to iron smelting. Other artifacts include swords, axes, sickles and hoes. By CE 310 a sufficient quantity of iron could be produced to allow the erection of the famous iron pillars of Delhi and Dhar in India. The wrought iron pillar in Delhi is 18 m tall, 410 mm in diameter and weighs 17 tons. In Japan, the traditional iron and steelmaking process known as ‘Tatara’ was not fully developed until the 17th century CE. In North America, South America and Australia, iron smelting was not known to the ancient inhabitants. Iron making technology was brought to these countries by the Europeans.

    The iron making process developed around the Mediterranean Sea had spread northward through Europe. The Phoenicians, Celts and Romans helped in spreading iron making technology. One of the iron making techniques spread by the Romans as far north as Great Britain was the early bowl or shaft furnace. This furnace consisted of a bowl-shaped vessel or a cylindrical shaft 2 m high being built into the side of a hill. The air used to fan the fire inside the furnace was provided by an opening built near the bottom of the bowl which faced into the prevailing wind. The furnace was filled through the top opening with layers of charcoal and iron ore that were ignited through the lower opening.

    There are two theories on how the iron smelting was driven, one that the wind blasted in through the bottom opening providing air which heated the process and the other that the wind blew over the open top, creating a low pressure area along the inside front wall which sucked air in through the lower opening (Fig 2). In both the cases, the process was dependent on wind and was not reliable throughout the year. The product was once again a mass of sponge iron, which was removed through the lower opening and then hammered into its final form.

    Another type of early iron smelter was the beehive furnace (Fig 2). This furnace was constructed on flat ground by piling alternate layers of charcoal and iron ore. The mound was covered with a thick layer of clay and blowpipes connected to bellows were inserted through the lower side walls. The bottom layer of charcoal was ignited and pressurized air was provided by the bellows. At the end of this batch type smelt, the clay dome collapsed. The sponge iron produced was dug out of the demolished beehive furnace for hammering. The production in these furnaces was small lumps of iron and the smelting furnace had to be demolished and rebuilt after each production run.

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