Experimental Research On Thermal Decomposition Kinetics And Synergistic Smelting Of Waste Printed Circuit Boards

There are many valuable metals in waste of printed circuit board,which have high economic value,and organic matter and heavy metals in them are easily harmful to the environment.The waste of printed circuit board(WPCB)have have caused great trouble to the environment.Disposing of waste of printed circuit board through collaborative smelting can not only efficiently recover valuable metals in them,but also effectively use industrial waste slag,realize the recycling of industrial solid waste,and reduce the generation of industrial waste slag.It is a relatively promising recycling technology.In this paper,the thermal decomposition kinetics of waste of printed circuit board under different atmospheres are studied by thermogravimetric analysis,and the thermal decomposition mechanism of waste of printed circuit board is explored.Taking FeO-SiO₂-CaO-Al₂O₃-1.5%MgO slag system as the research object,Fact Sage thermodynamics software is used to carry out slag type theoretical research,and the reason slag type range is determined,which can guide the subsequent process test.The main findings are as following:(1)In an Ar atmosphere,the temperature range of pyrolysis of waste of printed circuit board is 260°C⁵00°C,and the mass loss is 30%.The pyrolysis process of waste of printed circuit board in an argon atmosphere is formed by the superposition of the preliminary pyrolysis of epoxy resin,the pyrolysis of organic small molecules,and the pyrolysis of bromine flame retardants.The initial pyrolysis of epoxy resin mainly occurs in the temperature range of 230°C⁴30°C,the reaction mechanism function is a chemical reaction,E=136.86 k J/mol;the pyrolysis reaction of bromine flame retardant organic matter mainly occurs at 280°C.In the temperature range of350°C,the mechanism function of bromine is a chemical reaction,E=152.59 k J/mol;the pyrolysis reaction of small molecular polymers occurs in the temperature range of232°C⁶80°C,and the mechanism function is random nucleation and subsequent growth,the reaction order is 4,E=142.94 k J/mol.(2)In an O₂ atmosphere,the temperature range of thermal decomposition of waste of printed circuit board is mainly 200°C⁶00°C,and the mass loss is approximately 40%.The thermal decomposition process of waste of printed circuit board in an oxygen atmosphere is formed by the superposition of the thermal decomposition of epoxy resin and the thermal decomposition of bromine flame retardants.The thermal decomposition reaction of epoxy resin mainly occurs in the temperature range of 280°C³50°C,and the reaction mechanism is a chemical reaction,E=134.65 k J/mol.The thermal decomposition reaction of bromine flame retardant occurs in the temperature range of 250°C³60°C,and the reaction mechanism function is a chemical reaction,E=357.78 k J/mol.(3)The FeO-SiO₂-CaO-Al₂O₃-1.5%MgO slag system phase diagram was drawn using Fact Sage software,and the influencing factors of slag melting temperature and viscosity were investigated,and a reasonable range of slag type was determined.Increasing the Fe/SiO₂(mass ratio)in the slag can reduce the viscosity of the slag,but it will increase the melting temperature of the slag and increase the cost and difficulty of smelting.Increase CaO/SiO₂(mass ratio)of slag,the melting temperature of the slag decreases first and then gradually increases,and the viscosity of the slag gradually decreases.The presence of Al₂O₃ in the slag will cause the melting temperature and viscosity to increase.The results show that the Fe/SiO₂ in the slag is between 0.75¹.15,the CaO/SiO₂ is between 0.35⁰.6,and the Al₂O₃ content is less than 9.5%,the melting temperature of the slag is less than 1200°C,and the viscosity is less than 0.5 Pa·s.At this time,it is beneficial to the progress of the smelting process.(4)Based on the theoretical study of FeO-SiO₂-CaO-Al₂O₃-1.5%MgO slag system,the smelting test was conducted under the experimental conditions of Fe/SiO₂=1.05,CaO/SiO₂=0.55,and oxygen enrichment concentration of 30%.The feasibility of synergistic smelting of waste of printed circuit board to prepare alloys is confirmed.Using ICP to quantitatively analyze the content of the components in the alloy and slag,the results show that the direct yield of metal copper in waste of printed circuit board can reach 82.42%,the direct yield of metallic tin can reach98.76%,and the direct yield of metallic nickel can reach 78.09%.The phase morphology and element distribution in the alloy and slag were characterised by XRD and SEM-EDS.The results showed that most of the valuable metal elements such as Cu,Sn and Ni in the waste print circuit board entered the metal phase during the smelting process to form a copper-tin-nickel alloy.Elements such as Ca,Si,Al in the circuit board to enter the slag phase to form various silicates and aluminates..