Effect of silicic acid and temperature on the formation of magnetite

Abstract

Banded iron formation (BIF) consists of alternation of iron oxide and silica layers. The major iron minerals included are hematite and magnetite. However, those iron oxides are not primary minerals but secondary minerals formed from amorphous hydrous iron oxide and/or siliceous ferric hydroxide due to diagenesis. In addition, the crystallization of iron oxide minerals is inhibited in the presence of silicic acid. In this study, assumed magnetite is principal iron oxide in BIF, the formation condition of magnetite and the effect of silicic acid and temperature on the formation of magnetite were experimentally examined. Ferrous bearing solution with a constant volume was prepared and pH of the solution was adjusted to 8. The suspension wasfiltered by 0.45µm membrane filter. The residue on the filter paper was analyzed by XRD and Fe, Si and REE in filtrate were determined by ICP-AES. As a result, we found the suitable concentration range of ferrous ion to form magnetite in a short reaction time. In the presence of silicic acid in the ferrous bearing solution, the formation of magnetite was retarded at room temperature but magnetite was formed at 60^。C.