Study on Single and Cyclic Roasting of Vanadium Slag and Analysis of Thermodynamics and Kinetics

The factors respectively influencing the single and cyclic roasting of vanadium slag during the novel calcification process for vanadium extraction were studied,and the thermodynamics and kinetics were also analyzed.The results show that the morphology of clinker by single calcination with lump and sphere shape is different from that of the cyclic roasting slag having a loose structure.The conversion rate reaches above 90% at the cycle ratio of 0.50 for clinker cycle roasting,and it is 16.20 % for tailing cycle roasting.The conversion rate of single clinker roasting is 82.38 %,indicating that the single roasting is incomplete.The roasting of mixture for tailing and clinker could significantly increase the conversion rate,and the conversion rate is 89.55 % at R₂/R₁=0.67（tailing cycle ratio）.The CaO/V₂O₅ ratio for single roasting is 0.6～0.8,while the CaO/V₂O₅ for cyclic roasting is 0.40 and the residual calcium can be reused.The conversion rate of 4 h is about 85% for the single roasting and 88%～92% for the cyclic roasting.The cyclic roasting temperature is 30 ℃ lower than that of the single roasting,while the conversion rate for cyclic roasting is 5.54～7.18 percent points higher than that of single roasting.The equilibrium constant K at 870 ℃ is 35.17 and 132.44 for single and cycle roasting,respectively.ΔG for single and cycle roasting is respectively-33.84 kJ/mol and-46.48 kJ/mol.ΔS is-0.220 9 kJ/mol and-0.198 1 kJ/mol for single and cycle roasting,respectively.ΔH for single and cycle roasting is 216.88 kJ/mol and 183.92 kJ/mol,respectively.The single and cycle roasting of vanadium slag are both controlled by a zero-grade chemical reaction,with 37.36 kJ/mol and 30.65 kJ/mol of the activation energy E,and 7.32×10¹³ min^-1 and 3.11×10¹³ min^-1 of the pre-exponential factor A,respectively for the single and cycle roasting.