Release Kinetics Of Brominated Flame Retardants(BFRs) From Plastic Granules Of E-waste And The Microwave-induced Degradation Of BFRs

With the rapaid development of science and technology,the replacement of electronic products is speeding up and the increasing electronic waste has become increasingly prominent factor that affects global environment and human health.Not only the number of electronic waste is huge,but also many poisonous and harmful persistent organic pollutants?POPs?are contained in the e-waste,including the bromine flame retardants?BFRs?.In the recycling process of e-waste,bromine flame retardants would continually be released into the environment matrix,the prediction of release kinetics of the bromine flame retardants contained in electronic waste is a major event in the field of environmental science.Moreover the extensive ways of recycling,such as the heat treatment of electronic waste and open burnig,also accelerate the release of bromine generation of flame retardants,such as BDE-209.So it is urgent to develop an effective method to eliminate the bromine flame retardants in the burnt gas of e-waste.This study takes the electronic waste plastic gransules as the subject,and BFRs,including polybrominated diphenyl ether?PBDEs?and 2-bis?2,4,6-tribromophenoxy?ethane?BTBPE?contained in the e-waste granules as the target compounds,to investigate the release kinetics of the bromine generation from electronic waste plastic gransules.And taking BDE-209 as the target pollutant and adopting porous zeolite minerals as the adsorption carrier of BDE-209 combined with microwave induced degradation firstly,we established a new method of removing the BDE-209 contained in the exhaust gas during the heat treatment of electronic waste plastic.The main results of this study are as follows:First of all,combing air passive sampling with the soxhlet extraction,we studied the release kinetics of nine PBDEs and BTBPE from millimeter-sized granules of two scrap computer displays at environmentally relevant temperature?10,30,50 oC?.The release rates of PBDEs and BTBPE contained in the e-waste plastic granules in the air were first reported,and we also estimated the diffusion coefficients of nine PBDEs and BTBPE contained in the electronic waste plastic gransules,the activation energy,as well as the release of the half-life.The release kinetics of bromine flame retardants in the electronic waste plastic can be modeled as one-dimensional diffusion model and the temperature dependence of diffusion coefficients can be described with Arrhenius equation.The estimated diffusion coefficients of BFRs in natural environment?at 30 °C?from the e-waste plastic matrics were in the range of 10-27.16-10-27.16 m2 ·s-1,and the eatimated diffusion activation energies were between 88.4 and 154.2 kJ·mol-1.The release half-life of bromine flame retardants from the plastic granules in natural environment can reach several thousands to billions of years.According to the diffusion coefficients of BDE-209 in the CRT(2.28 × 10-27 m²·s^-1)and LCD?1.89 × 10-24 m2 ·s-1?,the estimated emission flux of BDE-209 in the pearl river delta region of Guangdong Province of China,was 63 and 1818 kg/yr,respectively.Secondly,combing water passive sampling with the liquid-liquid extraction,we studied the release kinetics of nine PBDEs and BTBPE from millimeter-sized granules?< 1.7 mm?processed from the plastic exteriors of two scrap computer displays at environmentally relevant temperature?10,30 oC?.The release rates of PBDEs and BTBPE contained in the e-waste plastic granules in the water were first reported,and we also estimated the diffusion coefficients of nine PBDEs and BTBPE contained in the electronic waste plastic granules,the activation energy,as well as the release of the half-life.Results show that the release flux of BFRs from the plastic granules placed in the water were comparable to that in the air and the inpute flux to the environment medium in the natural tempreture?17.4 oC?is also very low.Using the onedimensional diffusion model describes the release kinetics of bromine flame retardants in the electronic waste plastic.The diffusion coefficients of BFRs in the microplastics?17.4 oC?were estimated to be in the range of 10-26.46-10-19.26 m²·s^-1,and the natural logarithms of diffusion coefficients of bromine flame retardants released from electronic waste plastic particles decrease linearly with the increase of the diameter of molecules.The eatimated apparent activation energies were in the range of 64.13-131.83 kJ·mol-1,and increase linearly with the increase of the diameter of molecules.The half-lives of BFR releases?i.e.,50% depletion?from the microplastics ranged from hundreds to tens of billions of years.Regardless of bromine flame retardant diffusing from the e-waste plastic granules into the water or air,the results confirmed the diffusion process in the plastic matrics is the rate-determining step again.Although the release rate of bromine flame retardants in plastics matrics depolyed in water and air is detected,the release rate to other types of environmental media?sediment and soil?should be also very similar.The experiment results in this study can help predict the pollution of bromide flame retardant contained in the marine microplastic?< 5 mm?.Finally,we take the porous mineral materials as adsorption carrier of BDE-209 dissolved in the organic solvents to simulate the adsoption of BDE-209 in the burnt gas of electronic plastic in the process of heat treatment process,and then realize the removal of BDE-209 combining with the microwave induced degradation technology.When studying the different mineral materials for adsorption and microwave induced degradation,we select a series of porous zeolite minerals,including CBV-100,300,400,720,760,780,diatomite,4A and MCM-41,to examine porous the effect of zeolite pore size,the surface cation,Si/Al on the adsorption and degradation of BDE-209.Results show that the effect of the pore diameter of porous zeolite on the adsorption is mostly obvious,and the Si/Al is next,the type of cationic surface almost had no effect.Microwave degradation of BDE-209 adsorpted by porous zeolite is effected from three respects.Y type zeolite CBV-100 with the proper pore size,surface cationic type and density,showed the good adsorption and biodegradation of BDE-209.Because the surface cationic type of CBV-100 is Na+,which has a higher dielectric constant to absorb more microwave energy contributing to the formation of "hot spots",thereby promoting the microwave degradation of BDE-209.After conducting the microwave extraction of the zeolite CBV-100 loaded by BDE-209 after microwave induced degradation,no other low bromine biphenyl ethers were detected.With the method of ultrasonic extraction from the zeolite after microwave induced degradation using 20% hydrochloric acid solution,a large number of bromine ion was detected.It can be speculated the microwave degradation mechanism of BDE-209 is through the rupture of C-Br bond.Through the amount of Br-and the degradation molar mass of BDE-209,we can draw a conclusion that ten C-Br of BDE-209 can be completely broken at the same time,or lower bromine biphenyl ether can be produced by the microwave degradation of BDE-209 but they can be cracked into samll molecules so that can not be detected.