Recovery of Tungsten in the Process of Preparation of Calcium Sulfate Whiskers from Scheelite Decomposed Residue

When treating complex co–associated low–grade scheelite with sulfur and phosphorus mixed acid co–decomposition techniques, the deterioration in tungsten resource endowment can result in significantly lower decomposition rates, with tungsten content in the decomposition residue (gypsum residue) as high as 2%. In this paper, it is envisaged that by dissolving the gypsum residue in hydrochloric acid to separate it from insoluble tungsten and then regulating the supersaturation of calcium sulfate in the hydrochloric acid solution to prepare calcium sulfate whiskers, not only can the tungsten in the decomposition residue be recovered but also the resource utilization of gypsum can be realized. The effect of Fe3+, Na+, and NH4+ on the crystallization process and morphology of calcium sulfate whiskers was investigated using atmospheric pressure acidification. When the addition amount of gypsum residue was 5.75 g/100 mL, the concentration of hydrochloric acid was 100 g/L, the stirring rate was 100 rpm, the addition amount of NaCl was 30 g/L, the temperature was reduced from 80 to 50 °C, and the L/D ratio of calcium sulfate whiskers could reach 48. The effect of mother liquor circulation on the morphology of calcium sulfate whiskers was also investigated, and the morphology of calcium sulfate whiskers was still good after 10 cycles. During the cycling process, tungsten could be enriched in the residue, and the residue tungsten content could be increased from 3 to 14%.