Process for recovering high purity tungsten compositions from wolframite ores

Claim 1

In a process for the recovery of tungsten values, in the form of ammonium paratungstate, from wolframite-bearing concentrates, wherein the concentrate has been ground, to approximately 100 mesh size or less caustic leached to form a tungstate solution, the tungstate solution chemically treated with an inorganic metal salt to precipitate silica, the resultant tungstate solution solvent extracted utilizing amine and organic solvent mixtures, and the solvent solution treated with ammoniated water to strip ammonium paratungstate from the solvent solution, the improvement which comprises: (a) accomplishing said caustic leaching at pressures of from about 35 to about 355 psig and temperatures of from about 135° to about 255° C to produce a slurry; thereafter (b) filtering said slurry to obtain a filtered tungstate solution; (c) in said chemical treatment, the steps of adding acid to the tungstate solution to reduce the pH to about 8 to 11, adding said inorganic metal salt to precipitate silica, and recovering a tungstate solution substantially free of silica; (d) acidifying to reduce the pH of the resultant tungstate solution prior to solvent extraction to a range from about 1 to 1.8 and maintaining the pH in this range during solvent extraction, whereby, upon solvent extraction, loading in the solvent phase in excess of about 100 grams per liter of tungstic oxide is achieved; (e) accomplishing said stripping while maintaining the aqueous phase at a pH of about 7.5 to 8.5 and allowing sufficient retention time, accompanied by agitation, such that solids of ammonium paratungstate formed redissolve; and (f) recovering ammonium paratungstate from the resulting solution.