An energy-saving and environment-friendly technology for debromination of plastic waste: Novel models of heat transfer and movement behavior of bromine

Enhancing Debromination Efficiency through Introducing Water Vapor Atmosphere to Overcome Limitations of Conventional Pyrolysis

Bromine removal is significant in the recycling of waste printed circuit boards (WPCBs). This study found that the critical factors limiting the debromination efficiency of conventional pyrolysis are the formation of coke impeding mass transfer and conversion of bromine into less volatile species, such as coking-Br and copper bromide. According to frontier molecular orbital analysis and thermodynamic equilibrium analysis, C-O bonds of resin are sites prone to electrophilic reactions and copper bromide in residue may undergo hydrolysis; therefore, introducing H2O during pyrolysis was a feasible method for thorough debromination. Through pyrolysis in a water vapor atmosphere, the diffusion limitation of debromination was overcome, and resin was converted into light components; thereby, rapid and deep removal of bromine was achieved. The result indicated that 99.7% of bromine was removed, and the residue could be used as a clean secondary resource. According to life-cycle assessment, pyrolysis of WPCBs in water vapor could be expected to reduce 77 Kt of CO2 emission and increase financial benefits by 60 million dollars, annually.

Mechanochemical destruction and mineralization of solid-phase hexabromocyclododecane assisted by microscale zero-valent aluminum

Hexabromocyclododecane (HBCD) has been listed in Annex A of the Stockholm Convention as a persistent and bio-accumulative chemical. While HBCD is often present in the solid form for its low solubility, cost-effective technologies have been lacking for the degradation of solid-phase HBCD. In this work, mechanochemical (MC) destruction of high-energy ball milling was employed for direct destruction of solid-phase HBCD, where a strong reducer, microscale zero-valent aluminum (mZVAl), was used as the co-milling agent. The new mZVAl-assisted MC process achieved complete debromination and mineralization of HBCD within 3 h milling. The optimal operating parameters were determined, including the milling atmosphere, the milling speed, the mZVAl-to-HBCD molar ratio, and the ball-to-mZVAl mass ratio. Fourier transform infrared spectrometry and Raman analyses revealed that the organic structures of HBCD were destroyed and organic bromine was completely converted into inorganic bromide, accompanied by the generation of amorphous and graphite carbon. Analysis of the milled samples by GC-MS demonstrated the absence of obvious organic matter after MC treatment, also indicating the complete degradation and conversion of HBCD to inorganic compounds. Further X-ray photoelectron spectroscopic analysis indicates that the fresh surface of mZVAl was generated upon the MC treatment, and Al(0) served as a strong reducing agent (e-donor) for reductive debromination and destruction of the carbon skeleton. The mZVAl-assisted MC milling appears promising as a non-combustion approach for effective destruction and carbonization/mineralization of solid-phase HBCD or potentially other persistent organic pollutants.

New Models to Reduce the Health Risks of Informal WEEE Recyclers in MTN Phone Village, Rumukurushi, Port Harcourt, Nigeria

Waste electrical and electronic equipment (WEEE) management in Port Harcourt, an oil-producing city in Nigeria, has become an environmental challenge for the location. WEEE recycling is predominantly managed by informal recyclers, who lack the skills to perform risk-free recycling, hence raising health risks to individuals in associated communities and degrading the environment. Formal recycling, which embraces the best practices for effective WEEE management, is faced with several limitations, such as a lack of detailed guidelines on waste recycling, reuse, and final disposal techniques, with no opportunities for landfilling. A qualitative approach was adopted for this study. Data were gathered via questionnaires and analysed graphically. A background literature review of the assessment of informal recycling methods and associated challenges was performed. Hence, a new concept for the local management of WEEE processing was introduced. This concept limits the role of informal recyclers to WEEE collection. In this case, informal recyclers are paid for WEEE collection; they no longer engage in further WEEE processing. The results show that 48% and 40% agree to partner and collaborate with government agencies, respectively. Conversely, 52% and 40% agree and strongly agree, respectively, to limit their activities to WEEE collection only if the government is willing to pay for the services.

Optimizing the Leaching Parameters and Studying the Kinetics of Copper Recovery from Waste Printed Circuit Boards

The study of copper (Cu) recovery is crucial for the entire recovery process of waste printed circuit boards (WPCBs), and Cu can be leached efficiently via a sulfuric acid-hydrogen peroxide (H₂SO₄-H₂O₂) system. To achieve high Cu recovery, it is important to evaluate the parameters of the leaching process and understand the Cu leaching kinetics. Applying statistical and mathematical techniques to the leaching process will further benefit the optimization of the Cu leaching parameters. Moreover, the leaching kinetics of Cu in the H₂SO₄-H₂O₂ solution is yet to be fully understood. Hence, in the present work, process parameters, such as temperature, H₂SO₄ and H₂O₂ concentrations, solid-liquid ratio, particle size, and stirring speed, were optimized statistically by the response surface methodology (RSM). The results showed that the leaching kinetics conformed to the Avrami model. The maximum Cu leaching efficiency was 99.47%, and it was obtained based on the following optimal conditions: 30.98 °C, 2.6 mol/L H₂SO₄, 1.87 mol/L H₂O₂, a solid-liquid ratio of 0.05 g/mL, 135 mesh, and 378 rpm. RSM was used for the optimization of the process parameters, and the leaching kinetics in this system was clarified. This study provides an important pathway for the investigation of other metal recoveries from WPCBs.