A fundamental study on the molybdenum recovery from the copper smelting slag by slow cooling

Copper smelting slag has been produced in large quantities every year all over the world. The slag contains various value metals, such as molybdenum, iron, copper, and zinc. However, it is difficult to economically recover these metals from the slag since it is rapidly cooled into an amorphous structure in granulation water. On the other hand, a lot of minerals in slags can be crystalized by slow cooling. Then, molybdenum recovery from copper smelting slags was investigated using crystallization by slow cooling under rate controlling and solid/solid separation in this study. A water cooled slag of 0.2 wt% Mo was used as sample. Mo concentration in slag was controlled from 0.2 to 4 wt% by adding MoO3 reagent, heated at 1300 °C for 1 hour in Ar atmosphere by super kanthal furnace, cooled and ground under 125 μm. Pyrite (FeS ₂) was added to this slag to achieve reduction atmosphere and sulfurize molybdenum as molybdenum sulfide (MoS₂) to achieve 2 or 5 of S/Mo molar ratio. This sample was heated at 1300 °C for 1 hour in Ar atmosphere and slowly cooled at up to 18 °C/min. The slow cooling slag was analysed by XRF, XRD, SEM-EDS, XAFS (XANES) to know selective molybdenum sulfurization and crystallization of minerals including molybdenum sulfide. MoS₂ crystal was identified in Mo 2 wt-% slag (S/Mo =5) and 4 wt-% slag (S/Mo = 2, 5) and maximum particle diameter was 150 μm. The ratio of MoS₂ to all Mo in slag was determined by XANES analysis, resulted in 95.83 % of MoS₂ in Mo 4 wt-% slag (S/Mo = 5). 16.7 wt% Mo concentrate was obtained by flotation after grinding under 125 μm and using PAX and MIBC at pH 6.6.