Study On The Process Optimization And Mechanism Of Recovery Iron From Nickel Slag By Deep Reduction Method

Nickel slag is a high iron-bearing by-product from the nickel smelter, but it is difficult to recovery iron from nickel slag by conventional mineral process because iron is mainly distributed in fayalite phase. In recent years, the study of iron-bearing material deep reduction and separation method was very active, and its objects involved from complex refractiory iron ores extend to iron-bearing smelting slag such as nickel slag. Nickel slag is synthetic and different from the natural ore, however there are less relative research on it. So it is necessary to investigate the nickel slag deep reduction process to provide theoretical basis for recovery iron from nickel slag.As research object in this study, the nickel slag contains 39.46%iron and its main iron-bearing phase is fayalite. The single factors influence study of nickel slag deep reduction and iron separation process was carried on firstly for preliminary optimaization. The effect of factors such as raw material particle size, additive CaO and reductive coke dosage, temperature, time on the deep reduction iron indexes was investigated successively.Consider to reduce the raw material costs and improve resources comprehensive utilization, the industrial solid waste carbide slag and coal slurry were used to replace partially or completely CaO and coke as additive and reductive respectively. The influence study of ingredient replacement were conducted and the results showed that cabide slag have less effect on the microscopic apperance and recovery indexes, but coal slurry have significant poorer effect with iron indexes decline and sulphur content rise obviously.To solve the limitation of present deep reduction process factor optimization study, the subsequent optimization was further studied. The key influence factors were sifted out by Plackett-Burman Design method. The results showed that reduction temperature and time were both critical to iron indexes and CaO dosage was critical to sulphur indexes. Response surface optimization study of three factors mentioned above by Certral Composite Design method and specific study of sulphur were followed. The final optimization process conditions were the mass ratio of nickel slag:CaO:coke= 100:38.37:19.50, reduction temperature of 1287 ℃, reduction time of 2.8 h, two stages of grinding and low intensity magnetic separation at 159.11 kA/m, grinding fitness of-0.074 mm 90% at first stage, grinding fitness of-0.048 mm 72.28% at second stage. The iron metallization ratio of reduction product was achieved 95.28%, and the final iron concentrate powders were obtained with iron grade of 92.22%, iron recovery of 92.13%, sulphur content of 0.05%, nickel grade of 0.24%, nickel recovery of 47.45%, copper grade of 0.24%, copper recovery of 52.72%.Conjoint with the thermodynamics and dynamics analysis, Thermodynamic Software FactSage, X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) were adopted to explore the reaction process and mircoscopic change mechanism of nickel slag deep reduction. The results showed that FeO release process from fayalite and reduction process have multiple pathway, in addition to the known Fe2SiOâ†'FeOâ†'Fe, which also include Fe2SiO4â†'Fe2-xCaxSiO4â†'FeOâ†'Fe and Fe2SiO4â†'FeSiO3â†'Fe1-xCaxSiO3â†'FeO-Fe.