Experimental Research On Direct Reduction Of Carbon-bearing Pellets Within Copper Slag

China owns world's largest copper production and consumption;its copper production reached 7 million tons in 2013.In the process of pyrotechnics,every ton of refined copper will produce 2.2?3 tons of copper slag accompany.The temperature of smelting copper slag could reach 1300? which involves high heat quality,but it is not well-used by the existing water quenching method.At the same time,it's also rich in valuable metals in copper slag resources.Among the existing metal secondary recycling method for copper slag,the direct reduction method can be finished at a lower temperature and its production direct reduction iron(DRI)has excellent performance,which has a broad development prospect.Coal is the most common solid based reducing agent,but in order to response to the world's call on energy conservation and emission reduction,the use of biomass as reductant can effectively reduce the cost and reduce carbon emission.Therefore,based on the recovery of both the waste heat and recycling valuable metals in copper slag,this paper proposed a centrifugal granulating-direct reduction system to deal with the smelting copper slag.Above all,this paper chooses coal and biomass respectively,as reductants and makes deep researches of the direct reduction of carbon-bearing pellets.(1)The results of biomass thermogravimetric characteristics analysis indicate that the pyrolysis of biomass finished at about 650?,so the main component which participates in the reduction of copper slag is fixed carbon.When the temperature reaches 700?,reactions between carbon and iron oxide in copper slag began,CO generated through the reactions will also participate in the reduction process.When the temperature is above 700?,the carbon gasification reaction will occur.The addition of CaO increases the Gibbs free energy variations of the reduction of fayalite.(2)The energy consumption calculation of the proposed system is put forward.The energy consumptions are 6.53kgce/tFe and 2.35kgce/tFe when using biomass and coal as reductant respectively.When it is faced at the cold granulated copper slag,the consumptions are 6.61kgce/tFe and 2.42kgce/tFe.Comparing with that of blast furnace which using coal as raw material,the energy consumption reduced by 74.5%.(3)This paper uses biomass and coal as reductant,combining with copper slag powder and granulated copper slag to make carbon-bearing pellets by cold-bonded method without any binder inside.The compressive strengths of the pellets are also tested.The effects of the type of reducing agent,the particle size of copper slag,the mass of pellets,the pressure compressed on the ball and the addition ratio of CaO were discussed.It is found that reductants have important influence on the quality of cold-bonded carbon-bearing pellets,adding biomass can improve the compressive strengths of the pellets.Under the condition that the mass of the pellets was 7g,the pressure was 50 MPa and the CaO ratio was 0.3,the compressive strength of the coal pellet was only 58 N,while the compressive strength of the biomass pellet was 2870 N.Under the experimental conditions,the compressive strength of pellets increased with the increase of the mass,the increase of the pressure and the decrease of the diameter of the copper slag.The addition of CaO has a weakening effect on the compressive strength of the pellets,but not the impact on the pulverized coal pellets.(4)Under N2 atmosphere,the prepared carbon-bearing pellets are calcined.The influences of the variety of reducing agent,reaction temperature,constant temperature time,particle size of copper slag and CaO added ratio on the reduction weight loss fraction are discovered.The study found that the reduction mass loss fractions of biomass pellets are significantly higher than that of coal pellets.The reduction mass loss fraction increases with the reduction temperature and reaction time,and decreases with the increase of the diameter of copper slag.The addition of CaO is beneficial to the reaction,but it can still lower the reaction fraction when it is overdosed.The optimal CaO ratio is 1:0.3.When the temperature was 1150?,the constant temperature time is 1.5h,the CaO ratio is 0.3,composite pellets containing both pulverized coal and biomass are prepared and calcined and the reduction mass loss fraction increased with the increasing biomass ratio.