Editing Iron ore (section)

== Extraction ==
{{See also|Mineral processing|Environmental impact of iron ore mining}}
{{Unreferenced section|date=October 2012}}
Lower-grade sources of iron ore generally require [[beneficiation]], using techniques like crushing, [[Mill (grinding)|milling]], [[Gravity separation|gravity or heavy media separation]], screening, and silica [[froth flotation]] to improve the concentration of the ore and remove impurities. The results, high-quality fine ore powders, are known as fines.

=== Magnetite ===
[[Magnetite]] is [[magnetic]], and hence easily separated from the [[gangue]] minerals and capable of producing a high-grade concentrate with very low levels of impurities.

The grain size of the magnetite and its degree of commingling with the silica [[Matrix (geology)|groundmass]] determine the grind size to which the rock must be comminuted to enable efficient magnetic separation to provide a high-purity magnetite concentrate. This determines the energy inputs required to run a milling operation.

Mining of banded iron formations involves coarse crushing and screening, followed by rough crushing and fine grinding to [[Comminution|comminute]] the ore to the point where the crystallized magnetite and quartz are fine enough that the quartz is left behind when the resultant powder is passed under a magnetic separator.

Generally, most magnetite banded iron formation deposits must be ground to between {{convert|32|and|45|µm|abbr=on}} in order to produce a low-silica magnetite concentrate. Magnetite concentrate grades are generally in excess of 70% iron by weight and usually are low in phosphorus, aluminium, titanium, and silica and demand a premium price.

===Hematite===
Due to the high [[density]] of [[hematite]] relative to associated [[silicate]] gangue, hematite beneficiation usually involves a combination of beneficiation techniques.  One method relies on passing the finely-crushed [[ore]] over a slurry containing [[magnetite]] or other agent such as [[ferrosilicon]] which increases its density. When the density of the slurry is properly calibrated, the hematite will sink and the [[silicate mineral]] fragments will float and can be removed.<ref>Gaudin, A.M, Principles of Mineral Dressing, 1937</ref>