Formation of brominated and chlorinated dioxins and its prevention during a pilot test of mechanochemical treatment of PCB and PBDE contaminated soil

Abstract

The destruction of persistent organic pollutants (POPs) is a large challenge in particular in developing and emerging economies. To date, a detailed assessment of non-combustion technologies with respect to formation of dioxins is lacking. In this study, an assessment of mechanochemical (MC) destruction technology for polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in contaminated soil remediation was conducted. Actual applied conditions of pilot-scale MC POPs destruction process indicates that the temperature increase inside the ball mills has the potential to form high levels of toxic polybrominated and polychlorinated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs) when dioxin precursors are present. Therefore, the MC technology was modified for treatment of the PCB and PBDE containing soil including an efficient cooling system which could prevent the formation of PXDD/F during the destruction of PCBs and PBDEs. This is likely relevant for all contaminated soils containing relevant dioxin precursor and need to be considered for treatment of soils with MC and probably other non-combustion technologies. Graphical abstract ᅟ.

Mechanochemical mineralization of “very persistent” fluorocarbon surfactants ‒ 6:2 fluorotelomer sulfonate (6:2FTS) as an example

“…Mineralization is a key requirement for halogenated organic pollutant destruction technologies, in order to prevent release of unintentionally generated POPs, like dioxins. Newly published works demonstrates that dioxins can be formed during MC treatment of halogenated organics due to mechanothermal effect, but they are eventually destroyed after sufficiently long milling time 31 – 33 .…”

Nonthermal Mechanochemical Destruction of POPs

“…This might be caused by hits of the milling tools, which induce high local temperature increase, although for short time, on surfaces of the particle that are trapped between the hitting tools [45]. Despite such issue, it was proved that sufficiently long time milling, as well as temperature control, assures definitive dioxin removal and prevents their reformation [48]. This is owed to extensive amorphization of the fly ash components, especially carbonaceous matter, which averts de novo formation [45,47].…”

“…Hence, in case of any non-mechanical accident (e.g., unintentional emission of toxic chemicals), the process can be interrupted immediately [37]. In addition, when treating hazardous waste with high potential of dioxin de novo formation, milling chamber temperature can be kept very close to environmental temperature to avert unintentional dioxin generation [48]. In sum, MCD is a safe and green technology.…”

Methods of Responsibly Managing End-of-Life Foams and Plastics Containing Flame Retardants: Part II

“…BFRs in chemical recycling of WEEE. MC ball milling can destroy BFRs successfully, but may create byproducts or degradation products containing FRs or brominated dioxins if not operated under appropriate conditions (Cagnetta et al, 2016;Lu et al, 2017). For highly brominated species, such as decaBDE, the ball mill will dehalogenate BFRs successively and may lead to the production of more toxic lower brominated PBDE such as tetra-to heptaBDE.…”