The role of CaO in the extraction of Ni and Mo from carbonaceous shale by calcification roasting, sulphation roasting and water leaching

The role of CaO in the extraction of Ni and Mo from carbonaceous shale by calcification roasting, sulphation roasting and water leaching was studied. Experimental results showed that 97.23% Mo and 93.16% Ni were extracted from the Ni–Mo ore by mixing 100 g the raw Ni–Mo ore with 36 g CaO and grinding to less than 106 μm, then oxidation roasting at 700 °C for 2 h, sulphation roasting with 70 ml 98% sulphuric acid at 240 °C for 2 h and, water leaching at 98 °C for 2 h with a liquid/solid ratio of 2:1. But only 60.67% Ni was extracted for the oxidation roasting without adding CaO. The addition of CaO in the ore is both propitious to environment protection and nickel extraction. XRD analysis showed that the nickel in the calcification roasted ore was in the form of NiO, while the nickel in the oxidation roasted ore was in the form of NiFeO4. It was found that the NiFeO4 formed in the oxidation roasted Ni–Mo ore was included by chemically inert iron silicates, which results in the NiFeO4 irresolvable in sulphuric acid. Experiments confirmed that CaO can decompose not only the NiFe2O4 but also the iron silicates at the roasting temperature.

Research highlights
► The role of CaO in Extraction of Ni and Mo from carbonaceous shale by calcification roasting, sulphation roasting and water leaching was studied.
► 97.23% Mo and 93.16% Ni can be extracted from carbonaceous Ni–Mo ore by calcification roasting, sulphation roasting and water leaching.
► But only 60.67% Ni were extracted for the oxidation roasting without adding CaO.
► The NiFeO4 formed in the oxidation roasted ore is included by the chemically inert iron silicates and cannot be decomposed by sulphuric acid.
► CaO can not only avoid the formation of NiFe2O4 but also cause the decompositions of the NiFe2O4 and the iron silicates during the roasting.