Occurrence forms evolution and leaching kinetics of vanadium and nickel in the petroleum coke gasification slags

Petroleum coke gasification slags(POX slags) are byproducts of petroleum coke gasification process which are recognized as hazardous solid wastes. However, these wastes are also secondary resources for production of Ni and V products, but relevant research is still rare. Herein, the effect of decarburization by calcination before extraction of metals on distribution and occurrence forms of V and Ni is studied and the leaching kinetics is also investigated. The POX ash generated by calcination of the POX slags show core-shell structure within which the core enriches with Silicon (Si) and Aluminum (Al) while the shell enriches with Sulfur (S) and Calcium (Ca). The V and Ni species are aggregated in the POX ash with smaller particle size obtained at lower calcination temperature. The higher calcination temperature converts the V and Ni into more stable residual form while has no significant effect on their spatial distribution. The kinetic studies show that the leaching of V and Ni follows the Avrami model and is controlled by surface chemical reactions and internal diffusion. The activation energy for acid leaching of V and Ni is respectively 28.85 kJ/mol and 40.35 kJ/mol, which indicates the faster leaching speed of V than Ni in the POX ash. All the results support establishment of method and technology for recovery of Ni and V from the POX slags wastes.