Iron Nuggets & Taconite

Try "Direct Reduced Iron", published by ISS (Iron & Steel Society). It may now be available from the successor society, AIST (Association for Iron & Steel Technology). There direct reduction processes that incorporate either a gaseous reduction agent or a solid, carbon based reductant

Secondly, taconite is a magnetic iron ore. It is beneficiated by extremely fine grinding, magnetic separation, and in some instances, also, flotation, prior to pelletizing and subsequent induration. The end product is a hematite pellet.

The iron nuggets that you refer to I believe would be produced via a coal based reductant on a rotary hearth, or possibly a kiln.

Subsequent to my first post, I found out the Minnesota Iron Nuggets project was a cooperative venture with Kobe Steel of Japan. I googled Kobe and one of the hits had a fairly good descriptor of their Ttmk3 process. They claim a product similar to blast furnace pig iron from iron ore fines and pulverized coal smelted in a rotary hearth furnace. Kobe claims their Itmk3 process is superior to DRI. The US Dept of Energy counts as a positive the no need for coking of coal.

One thing that surprises me is the direct use of coal. It had always been my supposition that coking was done to drive off both sulfur and phosphorus (which are damned hard to remove in subsequent processes) and to get a desirable blast furnace form of carbon. Coal crushing and benefaction does extract tramp sulfur and phosphorus conpounds but does not remove the sulfur and phosphorus that is in intimate molecular association.

What is the initial mineralization of the taconite ores of northern Minnesota? The rich Minnesota hematites were exhausted by World War II. I would like to get my hands on some Gust Bitsianes research papers on the conversion of taconites to a magnetically separable material. I don't recall hearing that the separate was re-roasted back to a hematitic form. I never did get so far as learning how the process got rid of silica (which makes for a lousy slag compared to the limestone/dolomites).