Thermodynamic Study On Enrichment Iron Resources Form Nickel Slag Via Molten Oxidation Process

A large amount of nickel slags are accumulated in the nickel metallurgical enterprises every year in China,and only in Jinchuan Group of Gansu Province the accumulative amount of nickel slags is up to 40 million tons.The total iron content in the nickel slag is about 40 wt%and existing as fayalite phase,and it is difficult to recovery and reuse by traditional reduction technology.In this project,Jinchuan's flash furnace water quenched nickel slag was employed to study and its iron component could be transformed from the fayalite phase into the magnetite phase by means of molten modification and oxidation magnetization.Then the recovery of iron resources in nickel slag was achieved via magnetic separation process.In this paper,the Ca O-Fe O-Mg O-SiO₂ quaternary slag system is systematically studied.The thermodynamic analysis and calculation of the enrichment of iron components during the process of molten modification and oxidation and melting are carried out and verified by the experiments.This will provide a theoretical foundation for the recovery of iron from nickel slag.The main contents and conclusions are given as follows:?1?Using the ion-molecule coexistence theory,we established a model for calculating the activity of Ca O-Fe O-Mg O-Si O₂ quaternary slag system,and analyzed the influence of the binary alkalinity,the mass fraction of Fe O and the mass fraction of Mg O on the activity of Fe O in nickel slag.The results show that:with the increasing of the alkalinity of the system,the activity of Fe O increases first and then decreases and reach maximum value at the alkalinity of 1.1 at 1500?;the activity of Fe O increases linearly with the increase of mass fraction of Fe O;the critical value of activity of Fe O for magnetite precipitation is about 0.06,which is much smaller than the activity of Fe O calculated by the model,implying the magnetite phase can be precipitated from the slag.?2?The thermodynamic analysis of the molten modification and oxidation process of nickel slag was carried out by using of Fact Sage thermodynamic software.The results show that the addition of the modifier Ca O is favorable for the decomposition of the fayalite phase and the produce of free Fe O.The magnetite phase thus is precipitated by the air or oxygen oxidatio,resulting in the iron enrichment phase changes from fayalite phase into magnetite phase.?3?The phase diagrams of Ca O-SiO₂-Fe O-Mg O quaternary slag system and its subsystem were analyzed by Fact Sage thermodynamics software.The results show that:the temperature has a significant effect on the liquid phase line position and phase equilibrium of the quaternion phase diagram.The liquid phase region expands and the primary crystal region decreases with the increase of temperature.The alkalinity also has a significant inflence on the phase equilibrium of the quaternary slag system.When the basicity increases from 0.38 to 1.2,the primary crystal region of the spinel increases first and then decreases.The spinel solid solution is preferred to precipitate in the slag,and the precipitation amount reaches maximum value when the basicity is0.6.?4?The accuracy of thermodynamic simulation is verified by experimental research.It can be observed that the iron components in nickel slag are transformed into magnetite phase by means of molten modification and oxidation,and the crystallization amount of magnetite phase is up to the largest when basicity is 0.6.