The Research On Decarburization Of Copper-Containing Hot Metal Smelted By CO₂ Injection

With the development of economic,the global consumption of refined copper increases gradually,and a large number of copper slag is accumulated.The copper slag contains a large number of harmful elements,which can cause irreversible damage to land if not treated in time.w[Fe]in oxygen-rich copper slag is usually above 40%and w[Cu]is above 0.5%,higher than the iron ore mining grade,20%.Copper slag used reasonablely is significant.At present,the main utilization of copper slag is getting iron or copper from the slag only and the methods are mainly beneficiation and pyrometallurgy depletion.Our group proposes a new technology that smelting copper containing antibacterial stainless steel with hot iron abtained from copper slag.That is,after morderately dilution of copper slag,matte with copper and precious metals is recovered by separation.Then the slag was deeply reduced by carbon and copper-rion was got.Finally,the copper-containing antibacterial stainless steel after decarburization and alloying was abtained.Decarburization is one of the most important steps in this process.In this paper,the thermodynamics and kinetics of decarbarization by CO2 injection were analyzed.The effects of reaction temperature,gas flow,reaction time,Ar partial pressure and O2 partial pressure on the decarburization process were investigated.The chemical analysis,XRD,SEM,ICP,carbon sulfur analyzer and other means were used to analyse the iron after decarburization.The conclusions are as follows.(1)When the reaction temperature is 1623K,1723K,1823K and 1923K,and the utilization rate is 80%,the system shows endothermic.The syetem can satisfy self-heating when the molar ratio of CO2 to O2 is 5.4.(2)The fomulation(?)is got relying on themedynamic calculations.The pCO decreases with the decrease of carbon content in molten iron when temperature and ?[Cr]are constant.When the carbon content is 0.35%,selective oxidation temperature of C and Cr is 1876.23K.When the carbon content is low,such as 0.05%,the temperature should be higher than 2173K,which is difficult to meet in industry and can be achieved by making pCO decreasing.The selective oxidation temperature of C-Cr can be reduced to 1923K when the partial pressure is decreased to 17.78%.(3)The optimum conditions abtained from single-facter experiments for the decarburization of copper-iron are reaction temperature 1923K,reaction time 60 min,total gas flow(CO2-Ar)670ml/min,and the Ar partial pressure 30%.On this conditions,w[C]decreases to 0.066%,?[Cr]is 11.70%and w[Cu]is 3.09%.The result is the same to the composition of steel 30Cr13Cu3.(4)The decarburization reaction is controlled by gas mass transfer because of Rln(?[C]/m[C]0)>R?[C]0-?[C].The reaction of CO2 and[C]in molten iron is an apparent zero-order reaction because Ea is 30.85kJ/mol,less than 150kJ/mol,and the value of pre-factor A is 0.00461.It was found that the limiting part of the decarburization reaction in high-carbon hot metal(w[C]>0.5%)was controlled by gas-phase mass transfer.The decarburization rate of high carbon hot metal(w[C]>0.5%)is 0.0404%/min at 1923K.The rate of decarburization is related to the content of carbon in molten iron,which is basically divided by the carbon content 0.5%.When the carbon content is higher than this value,the rate of decarburization is basically the same,0.0404%/min.The rate of decarburization decreases after the carbon content less than 0.5%,and the difficulty of decarburization increases.(5)High temperature is not conducive to the oxidation of chromium and large gas flow will increases the loss of chromium.For CO2-Ar system,increasing the partial pressure of Ar will help decreasing the burning of Cr.For CO2-O2 system,decreasing the partial pressure of O2 helps to decreasing the burning of Cr,but it will increase the heat consumption.Copper in hot metal will not be oxidized.(6)According to the thermodynamic software Factsage,the most favorable conditions for dephosphorization are obtained.The slagging amount is 10%of the mass of molten iron,w(Fe2O3)=30%,w(CaO)=52.5%,w(SiO2)=17.5%,w(CaF2)=10%·w(CaO),and the reaction temperature is 1673K.