Fundamental Research On Smelting Reduction Of Modified Nickel Slag For Iron-Extraction

Nickel slag is an industrial waste generated in the pyrometallurgical process from nickel sulfide ore.Due to the valuable iron contents(generally reach up to 40%),nickel slag can be recycled as a potential secondary resource.Fayalite and hortonolite are the main phases in nickel slag,the dense structure and high stability of which cause a poor reducibility of iron.Therefore,modification is necessary to separate‘FeO' to facilitate the reduction and ironextraction processes.In this work,the quenched nickel slag from Jinchuan company was studied.In order to reduce the treatment cost and improve the comprehensive utilization of secondary sources,converter slag and aluminum dross were adopted as modifier and reducing agent,respectively.Theoretical calculation and high temperature experimental were carried out successively.The effects of modifier types,modified slag basicity and reduction temperature on the reduction behavior of iron oxides were investigated.The generation and growth characteristics of metal phase under different aluminum dross additions and reduction holding time were investigated.The main conclusions were given as follows:Either CaO or converter slag was the modifier,activity of‘FeO' obtained the maximum at basicity of 1.00,and the value was close to each other.However,the melting point of slag under the modification of converter slag was obviously lower than CaO modification,which provided a basis for converter slag acting as modifier.As the modified slag basicity increased from 0.75 to 1.50,the proportion of converter slag in raw material increased from 35.70%to 62.32%,while that of nickel slag decreased from 64.30%to 37.68%,resulting in the decreasing percentage of 'FeO' from 41.20%to 33.67%.Therefore,in order to ensure the iron grade in modified slag system,the proper modified basicity,the activity of 'FeO' and the melting point of slag should be taken into consideration.For the process of reduction and iron extraction from modified molten nickel slag by aluminum dross,considerable heat could be released upon the aluminothermic reduction.It required an external heat input in the early period of reduction process,however,a good kinetic condition could be guaranteed self-sustainingly in middle and late stages.The temperature variation in slag bath increased with the decreasing modified basicity,and after the reduction,slag temperature was 235.23?298.49 K higher than the initial one.Compared with the CaO,converter slag can also separate 'FeO' from the structure of fayalite,and the compositions of reduced metal phase were mainly Fe,Cu and P.After dephosphorization treatment,Fe-Cu alloy with higher value-added could be obtained.Therefore,converter slag as the modifier can not only recycle the iron resource in slag,but also achieve the purpose of "waste disposal by waste" and reduce the treatment cost.Under the modification of converter slag,the reduction degree of iron oxides and metallization rate of iron can both obtain the maximum values at basicity of 1.00.Increasing the reduction temperature could promote the reduction of iron oxides then achieve a better reduction indexes.Combining the heart balance calculation,the thermal-physical properties of slag system and the dependence of the reduction indexes of iron on reduction temperature,the modified slag basicity of 1.0 and the reduction temperature of 1773 K were suggested.Under the optimum conditions,the reduction degree of iron oxides reached up to 94.21%,the metallization rate of iron was 87.43%and the grade of iron in metal phase was 98.89%.The reduction holding time and the addition of aluminum dross both had a significant influence on the generation and growth of metal phase.The process of "iron-extraction from modified molten nickel slag by aluminum dross" could be divided into three stages:modification,melting reduction,and the coalescence and growth of metal phase.