A gravimetric method for the determination of mixed oxides (niobium and tantalum pentoxides) in niobium-tantalum minerals

Abstract

A method is described in which the sample is dissolved by repeated evaporation with hydrofluoric acid, and the final solution then considerably diluted and filtered. The insoluble residue is reserved for determining tin, uranium and thorium, if required, and the filtrate made up to a fixed volume. A suitable aliquot is evaporated to fumes with sulphuric acid, diluted and the combined oxides precipitated with tannin. A second aliquot may be used, after evaporation to fumes with sulphuric acid, for determining niobium pentoxide by Pickup's method.