Studies on solid state reactions in a NiOMgOSiO2 system

Abstract The solid-solid reactions among MgO, NiO and SiO 2 have been studied by differential thermal analysis with the aid of X-ray diffraction analysis and infrared absorption spectra as a basic research for the treatment of laterite or garnierite. The main reactions involved in this system are as follows: 1. (1) MgO+SiO 2 →Mg 2 SiO 4 (olivine) and MgSiO 3 (pyroxene) 2. (2) MgO+MgSiO 3 →Mg 2 SiO 4 3. (3) Mg 2 SiO 4 +SiO 2 →MgSiO 3 4. (4) Mg 2 SiO 4 +NiO→(Mg,Ni) 2 SiO 4 (Mg,Ni-olivine) 5. (5) MgSiO 3 +NiO→(Mg,Ni) 2 SiO 4 It was found that the Mg 2 SiO 4 appeared at the beginning of the reaction, followed by the formation of (Mg 1− x Ni x ) 2 SiO 4 through the replacement of MgO with NiO. It may be considered that MgO behaves like a catalyst in the solid phase reactions in the MgO-NiO-SiO 2 system. The activation energy required for diffusion of MgO and NiO in the silicate (Mg,Ni) 2 SiO 4 was determined to be about 42 and 56 kcal./mol, respectively.