Patent ID: 8034319

Claim:
A process for preparing a water-soluble complex oxide, the process comprising: reacting an oxide of at least one metal selected from the group consisting of cobalt, nickel, and elements of Periodic Table groups 13, 4, 5, 6 and 7 and/or a precursor of the metal oxide, or a substance containing the metal oxide and/or precursor thereof, with an alkali metal salt and/or alkaline earth metal salt, the step of reacting further comprises: co-milling a mixture of the metal oxide and/or a precursor thereof, or a mixture of a substance containing the metal oxide and/or a precursor thereof, with an alkali metal salt and/or alkaline earth metal salt to a median particle size for the metal oxide and/or precursor thereof, or for the metal oxide and/or precursor-containing substance, of 10 μm or less, analyzing the co-milled product by a Differential Thermal Analysis (DTA) and a Thermo Gravimetry (TG), determining a temperature to conduct a solid-phase reaction of the co-milled product, wherein the temperature is determined from a data obtained by the DTA and TG analysis of the co-milled product, heating the co-milled product to the determined temperature to conduct a solid-phase reaction, and extracting the water-soluble complex oxide from the reaction product by using an aqueous solvent, thereby recovering the water-soluble complex oxide in the aqueous solvent.