Study On Physical Property Transformation Of Roasted Copper Slag And Magnetic Separation And Enrichment Of Iron

At present,the annual output of copper slag in China has exceeded 15 million tons,most of which have been abandoned after simple flotation.On one hand,a large amount of copper slag not only occupies land,but also causes serious environmental pollution.On the other hand,about 40%of Fe in copper slag can't be properly recycled,resulting in a great waste of resources.Referring to the current research status of iron recovery from copper slag at home and abroad,this study carried out an experimental study on the formation and enrichment of magnetite after roasting copper slag in CO₂-CO atmosphere.By means of XRD,SEM,EDS and element content analysis,the effects of copper slag roasting in CO₂-CO atmosphere on the phase,microstructure,grade and recovery of magnetite from magnetic separation were studied.The XRD phase composition of copper slag prepared from roasting at medium and low temperatures shows that fayalite in copper slag gradually transforms into magnetite and CaSiO₃,accompanied by a small amount of kirschsteinite.Fayalite in copper slag is gradually decomposed and transformed to magnetite,which migrate and accumulate continuously to larger magnetite grains and eventually adhere to the surface of pyroxene.However,excessive roasting temperature CO₂ inlet velocity or overly long roasting time is not conducive to the nucleation and aggregation growth of magnetite particles.The iron grade of magnetite concentrate is 54.79%and the iron recovery rate is 80.14%after calcining copper slag with 25%CaO,1050?,190 mL·min^-1 of CO₂ and 10 mL·min^-1 of CO respectively,holding time of 2h,separation particle size of 74-25?m,magnetic field intensity of 170 mT.The recovery of iron from copper slag has been basically realized.Fe₂SiO₄ in copper slag has been transformed into Fe₃O₄ crystals by isothermal roasting at1300?with 25%CaO and copper slag,and flake Fe₃O₄ particles with particle size ranging from 30 to 100?m have been formed by continuous growth and migration.Excessive temperature will accelerate the formation of kirschsteinite with free Ca₂SiO₄,hinder the migration and accumulation of Fe₃O₄,resulting in the reduction of iron concentrate grade and iron recovery.Melting roasting of copper slag with CO₂ and CO inlet flow rates of 190 mL·min^-1 and 10 mL·min^-1 respectively,the size of produced Fe₃O₄ crystal particles is 30-80?m,some of them reach 100?m,and almost no impurities.Extending the roasting time in the early stage of the reaction is beneficial to the separation of Fe₂SiO₄ and the formation of Fe₃O₄.However,after a period of time,more and more Fe₃O₄ crystals were formed in copper slag and precipitated,which led to the increase of slag viscosity and inhibited the migration and aggregation of Fe₃O₄.Ca₂SiO₄ would combine with free FeO to form kirschsteinite,which would aggravate the loss of Fe.The optimum holding time is 2 hours.