Process for producing high purity tantalum oxide

A process for producing optical grade tantalum oxide from an impure tantalum oxide, said process comprising:

• (a) contacting said impure tantalum oxide with an aqueous solution of hydrofluoric acid of sufficient strength to solubilize said impure tantalum oxide,
• (b) separating said aqueous solution of hydrofluoric acid containing the tantalum values from any insolubles,
• (c) adjusting the pH of said aqueous solution of hydrofluoric acid containing said tantalum values to from about 6.0 to about 8.0 with a base to precipitate the tantalum values,
• (d) separating the precipitate of tantalum values from the pH adjusted aqueous hydrofluoric acid mother liquor,
• (e) contacting said precipitate of tantalum with an oxalic acid solution of sufficient strength to dissolve said precipitate of tantalum,
• (f) adjusting the pH of the oxalic acid solution containing the tantalum values to from about 5.1 to about 5.5,
• (g) digesting the resulting oxalate solution containing the tantalum values at above about 80.degree. C. for a sufficient time to produce a high purity compound of tantalum,
• (h) separating said high purity compound of tantalum from the oxalate solution mother liquor and,
• (i) digesting said high purity compound of tantalum in an aqueous solution of hydrochloric acid having a strength of from about 1N to about 10N, at a sufficient temperature and for a sufficient time to dissolve said high purity compound of tantalum in said aqueous solution of hydrochloric acid and continuing digesting for a sufficient time to subsequently precipitate pure optical grade tantalum oxide and,
• (j) separating said precipitate from the hydrochloric acid mother liquor.