THE EFFECT OF SULFUR ON TUNGSTEN RECOVERY FROM SCHEELITE CONCENTRATESBY ALKALI FUSION

A low-grade scheelite concentrate, obtained from Uludag Tungsten Plant (Bursa, Turkey), was used in this study. It contained approximately 3 5% WO3, 5.2% S and 27% Fe. The optimum conditions of alkali fusion wer e: a temperature of 900-degrees-C, twice the stoichiometrically requir ed Na2CO3, and 1 h treatment time. Tungsten was dissolved with a maxim um efficiency at the end of 1 of leaching with water at a solid/liquid weight ratio of 1/5 at 80-degrees-C under continuous stirring. A diss olution efficiency of 97% was obtained when the sulphur content of sch eelite concentrate was decreased to 0.7% by roasting in a rotary furna ce operating at 750-degrees-C and with 100% excess amount of air, whil e only 78% of tungsten dissolution efficiency could be reached when th e original scheelite concentrate was not roasted prior to the alkali f usion. Phase analyses showed that the sulphur in concentrate has forme d a matte phase as Na3FeS3 and confined some part of the tungsten as C aWO4, during the alkali fusion, and decreased its dissolution efficien cy.