DIRECT REDUCTION CARBURIZATION OF SCHEELITE WITH CARBON

Thermogravimetry, XRD and SEM have been used to study the direct reduc tion-carburisation of CaWO4 with C at 1500K. CaO, W, WC are the produc ts of the process. The reduction process was studied with solid carbon under an argon atmosphere and under vacuum. Reduction under an atmosp here of CO was then studied and it was found that, compared to argon a nd vacuum, reduction under CO was very slow and the products were not fully carburised. This led to the conclusion that the first step in th e reduction process is a solid-solid reduction reaction with carbon pr oducing tricalcium tungstate (Ca3WO6) as an intermediate product. This tricalcium tungstate is then further reduced to W before carburisatio n to WC. The overall rate of the process was found to be controlled by the W-WC stage. Copyright (C) 1996 Elsevier Science Ltd