The Study On Crystallization Behavior Of Magnetite Phase From Modified Molten Nickel Slag

As an industrial waste slag,nickel slag produced in nickel smelting process contains many valuable metals,such as iron,nickel,cobalt and copper.Nickel slag,produced from nickel flash smelting with water quenching in Jinchuan Company,was used to recycle iron resources via a modified molten oxidation process,in which calcium oxide and air are used respectively as modifier and oxidant.The iron resource was obtained by the magnetic separation of the treated nickel slag due to the formation of magnetite phase.In this paper,the influence of the basicity,cooling rate,heating-up temperature,holding time on the performance of slag,the morphology of magnetite phase was investigated,and the precipitation and growth of magnetite phase in molten nickel slag was explored via building the kinetic model.The main contents and results show as follows:?1?The results show that Fe content in nickel slag is about 39.91% and with a small amount of Ni,Co,and Cu.The main phases are fayalite phase?Fe₂SiO₄?and the hortonolite phase [?Fe,Mg?SiO₄] with banded structure.The iron in the nickel slag can be enriched with magnetite phase during the molten modified oxidation process,and Ni,Co,Cu are simultaneously concentrated in magnetite phase.?2?The effects of the basicity on the precipitation and growth of magnetite in molten nickel slag show that the optimal basicity is about 0.6.In this condition,the phase in the slag is mainly magnetite phase,and its morphology exhibits irregularly granular shape with even distribution.The maximum amount of crystallization reaches 36.3%.?3?The effects of temperature control on the precipitation and growth of magnetite show that with the decrease of the cooling rate,the phase composition of the oxide slag changes little,while the grain size and the crystal quantity of the magnetite phase increase obviously with complete crystal shape and clear grain boundary.The optimal cooling rate is 3⁵?/min.Time for heat preservation affects significantly the precipitation and growth of magnetite.With the longer holding time,the bigger grains occur,and optimal time is 20 min for full precipitation of magnetite.With the decrease of the holding temperature,the crystallinity of the magnetite phase increases gradually,indicating that the appropriate super cooling degree favors the magnetite precipitation.The optimal holding temperature is 1350?.The isothermal crystallization kinetic process of magnetite can be described with the JMAK empirical equation,and the crystal growth index n is about 0.5 and the crystallization activation energy E is about-178.3kJ/mol accordingly.