The Research On Microwave Carbothermal Reduction Of Copper Slag

With the development of copper smelting technology in China,the output of copper is increasing,and the discharge of copper slag is increasing year by year.Because copper slag contains a large amount of iron and considerable copper resources,it can be considered as a high quality secondary resource,but a large amount of copper slag is still stored as solid waste.In order to realize the high efficiency and low energy consumption extraction of copper and iron in copper slag and the comprehensive utilization of copper slag without slag,the research group came up with a new idea" Copper slag microwave solid-phase reduction with melting(or mineral processing)to obtain copper-containing iron,and then prepare copper-containing wear-resistant cast iron." This paper mainly studies the process of microwave solid phase reduction of copper slag.In this thesis,the thermodynamic analysis of microwave carbon-thermal solid-phase reduction of copper slag is performed.The microwave absorption characteristics of copper slag,coke and other materials in the microwave field are measured,and the heating rate is studied;the effects of reaction temperature,reaction time,alkalinity,carbon content,and particle size of copper slag on microwave carbothermal reduction were studied using single-factor experiments;chemical analysis,XRD,SEM and other methods were used to analyze the composition of the material after reduction,the composition and phase of the copper-containing molten iron and final slag obtained after melting.The reaction mechanism was studied by analyzing the micromorphology of the product after microwave reduction.The main conclusions were as follows:(1)At room temperature to 800?,the dielectric constant of coke is between 10.01 and 11.72,and the dielectric loss factor is between 0.1 and 1.2,which increases with temperature;the dielectric constant of copper slag powder is between 7.1?8,and the dielectric loss factor is between 0.04 and 0.18,which increases with increasing temperature;The dielectric constant of calcium oxide is between 13.5?16.9,and the dielectric loss factor is between 2×10-4 to 2× 10-4;The change of the loss tangent of the three substances is consistent with the change trend of the dielectric loss factor.(2)The study of the heating rate of materials in the microwave field shows that:Heating in a microwave field with a power of 2 kW and a frequency of 2.45 GHz,The average heating rate of 50 g coke is 57?/min,the average heating rate of copper slag of the same quality is 40?/min,and the average heating rate of calcium oxide of the same quality is 20?/min;The heating performance of copper slag and coke is good,and the heating performance of calcium oxide is poor.The heating rate and microwave power of copper slag mixture are closely related to the quality of the material;when the quality is constant,the heating rate increases with the power of the microwave;when the power is constant,the heating rate of the copper slag decreases as the mass increases.(3)Thermodynamic calculations show:The reaction starting temperature of iron olivine and carbon in copper slag is 1080 K;after adding calcium oxide,the initial reaction temperature drops greatly;the reduction reaction between iron olivine and CO occurs between 900 K and 1600 K after adding CaO The internal standard Gibbs free energy all becomes negative,so indirect reduction reactions can occur.(4)The single factor experimental research on the microwave carbothermal reduction process of copper slag shows that the suitable reaction time is 60 min,the reduction temperature is 1100?,the carbon ratio is 1.6,the basicity is 1.2,and the copper slag particle size is 0.104?0.089 mm Over time,the reduction rate of iron in copper slag was the highest,at which time the reduction rate was 91.93%.(5)Perform melting experiment on the reduced product,and keep it at 1400? for 60 min:After smelting,the iron content in the metal is 94.15%,the copper content is 1.30%,and the S content is 2.06%.After calculation,the iron yield is 92.75%and the metal copper yield is 95.54%;the copper content in the slag 0.023%,iron content 2.90%,metallic iron content 0.44%;the main phase in the slag is the calcium silicate phase,and the olivine phase disappears;the yield of copper is lower,which may be due to the shorter holding time and the incomplete settlement of copper.The magnetic separation was used to separate the reduction products,and recovery rate of the iron and copper after magnetic separation were 85.72%and 40.9%,respectively.(6)When the copper slag was conventionally heated to 900? and 1000? and the reaction time was 60 minutes,no obvious reaction phenomenon was observed.When conventionally heated to 1100? and holding time for 20 min,the copper slag powder turned into a black porous solid with a metal phase;when heated in a microwave field at 900? for 20 minutes,the metal phase began to appear.During the microwave thermal slag carbothermal reduction process,the copper slag phase is broken.This phenomenon does not exist during conventional heating;the occurrence of the break phenomenon increases the contact area between the copper slag and the reducing agent,improves external diffusion conditions,and provides good kinetic conditions to the indirect reduction;with the appearance of a large number of gaps,the metal phase is enriched near the gaps.(7)Based on the study of microstructure in copper slag after carbothermal reduction in a microwave field,the reaction mechanism is speculated as follows:When the copper slag mixture is heated by microwave,the direct reduction reaction of copper slag and coke occurs first,and the metal phase produced is mainly distributed around the oxides in the copper slag;The CO produced by the direct reduction passes freely through the gap generated by microwave heating,and continues to undergo indirect reduction reactions with the oxides and calcium oxide in the copper slag to form metals and CO2.CO2 reacts with coke to generate reducing gas CO.During the entire reduction process,the reaction cycle is realized.The main reaction in the process of microwave carbothermal reduction of copper slag during the indirect reduction of CO.