c-Si PV module recycling: Analysis of the use of a mechanical pre-treatment to reduce the environmental impact of thermal treatment and enhance materials recovery

The current increase in the use of photovoltaic (PV) energy demands the search for solutions to recycle end-of-life modules. This study evaluated the use of a mechanical pre-treatment in the thermal recycling of c-Si crystalline PV modules, which were submitted to recycling routes to separate and concentrate the materials of interest. The first route was constituted by only thermal treatment, and the second route was constituted by a mechanical pre-treatment to remove the polymers from the backsheet, and subsequent thermal treatment. The exclusively thermal route was performed at 500°C, varying dwell times between 30 and 120 minutes in the furnace. In this route, the best results were obtained in 90 minutes, with a maximum degradation of 68% of the polymeric mass. In route 2, a micro-grinder rotary tool was used to remove the polymers from the backsheet and, subsequently, thermal treatment performed at 500°C, with dwell times in the furnace ranging between 5 and 30 minutes. The mechanical pre-treatment removed about 10.32 ± 0.92% of the mass of the laminate PV module. By this route, only 20 minutes of thermal treatment were needed for the total decomposition of the polymers, that is, a reduction of 78% in the oven time. With route 2, it was possible to obtain a concentrate with 30 times more silver than the PV laminate and 40 times more than a high-concentration ore. Furthermore, with route 2 it was possible to reduce the environmental impact of heat treatment and energy consumption.

Carbon Trading in China Reduces the Dependence of Household Waste Electrical and Electronic Equipment Recycling on Government Subsidies

China's enterprises of waste electrical and electronic equipment (WEEE) recycling suffer from low profitability that is highly dependent on government subsidies. This low economic gain impedes the sustainable growth of China's WEEE-recycling sector and also adds to the government's financial burden. Prior life-cycle studies have approved the carbon reduction potentials or net carbon credit of recycling WEEE. However, policymakers fail to know whether the revenue from selling carbon credits can offset the government's financial subsidy. We performed life-cycle and cost-benefit analyses for a case recycling enterprise that processes six categories of household appliances. The results show that the reduction potentials of greenhouse gases range from 930-3450 kgCO2e by recycling per ton of household appliances and materials substitution. The recycling enterprise would gain extra revenue ranging from 32 to 160 RMB per ton of appliance if the carbon credits were sold at China's current carbon price, i.e., 45-60 RMB tCO2e-1. Recycling waste refrigerators exhibits the highest carbon revenue, offsetting 6-17% of the government's financial subsidy. Microcomputers, by contrast, indicate the lowest carbon revenue, equivalent to 1-3% of its highest government subsidy. For each household appliance category, when the carbon price reaches 270-600 RMB tCO2e-1, selling carbon credits can fully offset the government's financial subsidy. Constrained by the processing capacity of the case enterprise, optimizations for appliance-recycling composition contribute a 15-25% profit growth to the current economic gains. Interpreting the specific profit depends on the predefined scenarios of carbon price and the substitution rate of the regenerated materials for the virginal ones. Our findings show that raising the profitability of WEEE recycling enterprises through the carbon trading policy contributes to the sustainable growth of China's WEEE-recycling sector while alleviating the government's financial burden.

Study on complex dynamics for the waste electrical and electronic equipment recycling activities oligarchs closed-loop supply chain

Nowadays, with more and more WEEE (waste electrical and electronic equipment) being abandoned, WEEE recycling activities are increasingly popular. In this paper, we build a closed-loop supply chain model and focus on the recycling behaviors of the members in this supply chain, which contains two manufacturers, the retailer, and the consumer. In the reverse chain, we set up dual channels and design two recycling methods: sell-back method and trade-in method. We use classical backward induction to run the model. And then we analyze the stability of the system and the impacts of some essential parameters by numerical simulation. The speed of the manufacture's decision adjustment has a significant effect on the stability of the model. Manufacturers should adopt a stable rather than radical price adjustment strategy in order to achieve stable profit growth in the whole supply chain and avoid a chaotic price war. Manufacturers should increase innovation investment in recycling technology to reduce the cost of remanufacturing products and improve the initiative in market competition. In the end, we adopt the parameter control method and the decision-making method to control chaos, and they both have a good control effect.

Investigation of the heterogeneity of bromine in plastic components as an indicator for brominated flame retardants in waste electrical and electronic equipment with regard to recyclability

Waste electrical and electronic equipment (WEEE) can contain brominated flame retardants (BFRs) that pose a threat to human health and the environment. In addition, Br-containing plastics reduce the recycling potential of WEEE. In order to gain a better insight into the distribution of Br in plastics from WEEE, the total concentration of Br was measured on the level of device types and plastic components using handheld X-ray fluorescence (hXRF). In 35 % of the sample size (882 components from 369 different devices, which originate from 6 device types) Br was detected, 5 % exceeded the RoHS limit. Only few and older devices contained high Br concentrations, while the majority were below the RoHS limit and could be recycled. In addition, 18 different plastic types were identified by infrared spectroscopy, with acrylonitrile butadiene styrene being the most abundant (44 % of all samples). Manual dismantling of devices into individual plastic components enabled us to examine Br hotspots and the variety of plastic types in WEEE. Based on this analytical procedure, WEEE recyclers could exclude certain equipment or plastic components (e.g. power supplies or PC housings) directly on-site prior to WEEE recycling and shredding in order to produce high-quality recycled products and avoid cross-contamination.

Distinct recovery of copper and aluminum from waste electric wires using a roll-type electrostatic separator

Electrostatic separators are commonly employed for the sorting of insulating and conducting fractions of granular mixtures. However, separation of the various metals that compose the conductive fraction still represents a major challenge for the recycling industry. The aim of this paper is to identify the conditions in which a roll-type electrostatic separator could be used for distinctly recover the copper and aluminum from waste electric wires. A numerical model of particle trajectories was employed to predefine these conditions and guide the experimental study. The electrostatic separation experiments were carried out using a reverse-S-type-plate high-voltage electrode. The visualization of particle trajectories using a high-speed camera paved the way to an original design. Thus, a metallic trap was attached to the high-voltage electrode, to facilitate the collection of the aluminum flake-like particles from a mixture that also contains copper strands. With a plastic trap replacing the metallic one, to avoid electric field modification, 68.6% of the copper was recovered with a purity attaining 99%.

Characterization of Fine Metal Particles Derived from Shredded WEEE Using a Hyperspectral Image System: Preliminary Results

Waste of electric and electronic equipment (WEEE) is the fastest-growing waste stream in Europe. The large amount of electric and electronic products introduced every year in the market makes WEEE disposal a relevant problem. On the other hand, the high abundance of key metals included in WEEE has increased the industrial interest in WEEE recycling. However, the high variability of materials used to produce electric and electronic equipment makes key metals' recovery a complex task: the separation process requires flexible systems, which are not currently implemented in recycling plants. In this context, hyperspectral sensors and imaging systems represent a suitable technology to improve WEEE recycling rates and the quality of the output products. This work introduces the preliminary tests using a hyperspectral system, integrated in an automatic WEEE recycling pilot plant, for the characterization of mixtures of fine particles derived from WEEE shredding. Several combinations of classification algorithms and techniques for signal enhancement of reflectance spectra were implemented and compared. The methodology introduced in this study has shown characterization accuracies greater than 95%.