Thermal Upgrading Effect: Saprolite versus Limonite

The mineralogical properties of saprolite and limonite from Indonesia were investigated by X-ray diffraction, X-ray fluorescence, atomic absorption spectro-photometer, field-emission scanning electron microscopy, and differential thermal analysis. The percentages of Ni, Fe, Mg, Al, and Si in saprolite are given in 1.82, 30.47, 10–20, 4.86, and 8.1 wt%, and in limonite are 1.4, 50.5, 1.81, 4.86, and 16.5 wt%. Saprolite has 53.1% goethite, 38.3 % lizardite, 8.7 % silicate, and limonite has 94.4 % goethite and 5.6 % silicate. According to DTA, saprolite and limonite have the same phase transition from goethite to hematite at low temperatures (250 °C); at 900 °C the magnesioferrite crystallization for limonite and the crystallization of forsterite for saprolite, and the growth of ferronickel in 1150 °C; however, transformation of lizardite at 600–700 °C for saprolite is observed. It is a suitable phase to optimize nickel diffusion in iron. Furthermore, the thermal upgrading approach was utilized for limonite and saprolite at low temperatures.