Sodium hydroxide tests were performed to test the digestibility of the completely oxidized ferrotungsten material. Two digestion procedures were used, "low NaOH" and "high NaOH." The "low NaOH" tests were performed by adding the desired amount of NaOH to 0.2 1 of deionized (DI) water. The molar ratio of NaOH/W for each test is given in Table 1. Each "low NaOH" test was roughly sized for approximately 150 ml of 25% (8 to 9N) NaOH per 60 g of WO3. The caustic solution was cooled to between 10° C. to 15° C. and the completely oxidized ferrotungsten material was added. After slurrying for 1 hour, the slurried material was added to a stainless steel reactor and digested at 120° C. for 4 hours. The slurry was diluted with 0.2 to 0.3 1 of DI water and filtered. The solids were slurried with about 0.3 1 of hot DI water for 1 hour and filtered. Both filtrates were combined and analyzed for tungsten by atomic absorbance (AA). The solids were analyzed by x-ray fluorescence (XRF). The "high NaOH" digestions were performed by adding the desired amount of NaOH to a stainless steel reactor and heating to 120° C. These tests were roughly sized for approximately 150 ml of 50% (.about.19N) NaOH per 60 g of contained WO3. The completely oxidized ferrotungsten was slowly added to the reactor and digested for 3 hours. The slurry was diluted with 0.5 1 of DI water and filtered. The solids were twice slurried with 0.5 1 of DI water and filtered. A final wash was performed in the filter with 0.3 l of DI water. The filtrates were combined and analyzed by AA. Solids were analyzed by XRF. The results of the digestion tests are given in Table 1. The tungsten recovery efficiency is defined as the total tungsten recovered in solution divided by the sum of the tungsten recovered in solution and the tungsten remaining in the solids.
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