Siliceous iron ore

Tiemann (T8) studied the dissolution of silica from a siliceous iron ore by sintering the ore with sodium carbonate followed by leaching the sodium silicate with water. The reaction rates were found to be low after sintering for 4 hr at 1450°F. The residual concentrate was analyzed to be 56% iron, corresponding to 88% dissolution of the silica. Partial to complete fusion resulted when the temperature was increased. 

The removal of silica from a siliceous iron ore, such as the taconites found in Minnesota and Wisconsin, has been studied by Tiemann (T7, T9). Caustic concentrations from 25-500 gm/liter were used to digest the ore in a bomb at temperatures from 312 to 408°F. The leaching pressures in the bomb correspond closely to the equilibrium vapor pressures of the sodium hydroxide solutions used. A residual concentrate containing around 65% iron was obtained with —200 mesh material in 60 min of contact time. The high rate of dissolution of the silica was attributed to its occurrence in the form of microcrystalline (chalcedonic) varieties with high specific surface. The dissolution rate of pure quartz is directly proportional to the surface area and an average rate of 17 X 10 gm moles/cm sec was obtained for a 100 gm/liter NaOH solution at 312°F for the —400 mesh fraction. 

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