Experimental Study On Removal Of Harmful Elements In Pre-reduction Sintering Process

The steel industry is a pillar industry in China.With the rapid development of the steel industry,steel production continues to increase.At the same time,a large amount of metallurgical dust is generated during the steel production process,with a total amount of approximately 10% of the steel production.In 2021,China’s crude steel production reached 1.033 billion tons,and metallurgical dust production also reached over 100 million tons.Blast furnace bag dust is a type of metallurgical dust that contains not only a large amount of Fe and C elements,but also harmful elements such as Zn,K,Na and other harmful elements.So far,the recycling rate of metallurgical dust in China is still relatively low,and most of it is still piled up or landfilled,which not only wastes limited resources,but also seriously damages the ecological environment.At present,domestic and foreign methods of comprehensive utilization of metallurgical dust mainly include recycling,pyrometallurgical process,hydrometallurgical process,etc.,but all of them have certain limitations.Therefore,it is necessary to find a method that can comprehensively utilize metallurgical dust while also removing harmful elements.Prereduction sintering is a production process in which the partial reduction of iron ore concentrate is completed during the sintering process,significantly reducing the reduction load and overall energy consumption of the blast furnace while removing most of the harmful elements.This study is based on the pre-reduction sintering theory.A simulated pre-reduction sintering experiment was first conducted using blast furnace bag dust ash and three kinds of iron ore concentrates as raw materials and graphite powder as reducing agent for mixing and briquetting,and roasted at a pre-reduction temperature of 1200°C and prereduction time of 20 min using a high temperature tube furnace.The effects of carbon content,alkalinity,and bag ash content on the Zn removal rate,metallization rate,and pre-reduction degree of pre-reduction sintered ore were studied.The phase changes of the product were observed by X-ray diffraction,and the microstructure and elemental distribution of the product were observed by scanning electron microscopy energy dispersion spectroscopy.The phase transition and distribution patterns of Fe and Zn during the pre-reduction process were analyzed.The results show that when the bag ash content is 10 wt%,the Zn removal rate,metallization rate,and pre reduction degree of pre-reduction sintered ore show a trend of first increasing and then decreasing with the increase of carbon content and alkalinity.After 20 minutes of reduction with a C/O molar ratio of 1.0 and alkalinity of 1.90,the Zn removal rate reached 90.40%,and the metallization rate and pre-reduction degree reached 81.69% and 87.74%,respectively.As the content of bag ash increases,the Zn removal rate and metallization rate gradually increase,reaching their maximum at bag ash content of 30 wt%,which is 97.57% and89.14%,respectively.Then sintering cup experiments were conducted to investigate the effect of different carbon allocation on the technical specifications of sintered ore under conventional and pre-reduction sintering conditions.The results show that the removal rates of Zn,K,and Na under pre-reduction sintering conditions are significantly improved compared to traditional sintering.It is sufficient to prove that the pre reduction sintering process is effective in removing harmful elements from bag ash.Based on the previous study,the effects of pre-reduction time and pre-reduction temperature on the Zn,K and Na removal rate,metallization rate and pre-reduction degree of pre-reduced sinter were investigated under laboratory conditions.With the extension of pre-reduction time and the increase of pre-reduction temperature,the removal rates of the three elements and metallization rate gradually increase.After reducing the briquettes with 20 wt% bag ash content at 1200°C for 20 min,the removal rates of Zn,K and Na reached 95.66%,79.97%,and 91.49%,respectively.The metallization rate and prereduction degree reached 84.77% and 89.56%,respectively.The results indicate that the pre-reduction sintering process can effectively achieve the removal of zinc,potassium,and sodium while meeting the requirements of subsequent blast furnace production.The research results can provide a certain theoretical basis for industrial production.