• Energy Research

Abstract Recycling of polycrystalline silicon, amorphous silicon and CdTe photovoltaic panels was investigated by studying two alternative routes made up of physical operations: two blade rotors crushing followed by thermal treatment and two blade rotors crushing followed by hammer crushing. Size distribution, X-ray diffraction and X-ray fluorescence analysis of obtained products were carried out in order to evaluate their properties as valuable products. Results showed that for all kinds of investigated photovoltaic modules the two blade rotors crushing followed by hammer crushing and eventually by a thermal treatment of d >1 mm fractions, was the best option aiming to a direct recovery of glass.

Different kinds of panels (Si-based panels and CdTe panels) were treated according to a common process route made up of two main steps: a physical treatment (triple crushing and thermal treatment) and a chemical treatment. After triple crushing three fractions were obtained: an intermediate fraction (0.4-1mm) of directly recoverable glass (17%w/w); a coarse fraction (>1mm) requiring further thermal treatment in order to separate EVA-glued layers in glass fragments; a fine fraction (<0.4mm) requiring chemical treatment to dissolve metals and obtain another recoverable glass fraction. Coarse fractions (62%w/w) were treated thermally giving another recoverable glass fraction (52%w/w). Fine fractions can be further sieved into two sub-fractions: <0.08mm (3%w/w) and 0.08-0.4mm (22%w/w). Chemical characterization showed that 0.08-0.4mm fractions mainly contained Fe, Al and Zn, while precious and dangerous metals (Ag, Ti, Te, Cu and Cd) are mainly present in fractions <0.08mm. Acid leaching of 0.08-0.4mm fractions allowed to obtain a third recoverable glass fraction (22%w/w). The process route allowed to treat by the same scheme of operation both Si based panels and Cd-Te panels with an overall recycling rate of 91%.

This work assessed the economic sustainability of photovoltaic panels (PV) recycling. The PV throughout and silver (Ag) concentration in PVs are the main factor affecting recycling. For high Ag concentrations (0.2%), the recycling is sustainable without PV recycling fee if the PV throughput is higher than 18,000 t/yr. Lower processing volumes enable sustainability only with recycling fees from 0% up to 46% of the total annualized costs in the throughput range 18,000–9000 t/yr. For low Ag concentrations (0.05%) recycling fees are instead always needed to achieve profitability, unless the throughput is higher than 43,000 t/yr. Given the high Ag revenues, efforts should be done towards its recovery. If however a mixed silver-silicon fraction was sold for more than 50–70% of its actual value depending on the Ag concentration, a simplified process without hydrometallurgical separation could generate higher profitability on the short and long term. Given the decreasing Ag content in PVs, the profitability in recycling also depends on when the investments are realized. In the medium Ag concentration scenario and for Ag prices of 600 $/kg, PV fees are always required for the net present value (NPV) to be higher than CAPEX. The later the investment, the higher the PV throughputs and PV fees required to generate the same NPV. Investing in 2025 under the hypothesis of a regular loss scenario and an Ag price of 750 $/kg is the only condition that produces NPVs higher than CAPEX without PV fees if the throughput is at least 30,000 t/yr.

Disposing waste from the steel-making industry and the ongoing rise in global carbon dioxide emissions represent significant challenges to overcome. Carbonation of steel slags, the main waste material formed in steelmaking processes, is one of the possible solutions. In this research, three different kinds of mills are compared in order to most effectively approach the carbonation of argon oxygen decarburization (AOD) steel slag while simultaneously milled. Using breakage potential as a parameter for quantitative comparison, it is shown that the planetary ball mill is noticeably performing better than the vibratory mill and the McCrone mill – up to 39 % in terms of breakage of particles. The breakage potential correlates well with the carbonation rate at all three examined speeds (200 rpm, 500 rpm and 800 rpm) in the planetary ball mill. However, it is estimated that energy up to 120 kJ/g is used for the breakage of particles. Energy applied above this threshold contributes mainly to the agglomeration, but at different rates depending on the implemented speed. This difference is due to the varying contribution of two influencing parameters during simultaneous carbonation and milling - the presence of water and the number of collisions of the grinding balls with the AOD steel slag. The present work gives insights into the breakage of steel slag particles, their carbonation potential and limitations for achieving higher carbonation rates as well as predicted energy usage to obtain these processes.

Waste-to-energy processes remain essential to ensure the safe and irreversible removal of materials and substances that are (or have become) unsuitable for reuse or recycling, and hence, to keep intended cycles of materials in the circular economy clean. In this paper, the behavior of inorganic compounds in waste-to-energy combustion processes are discussed from a multi-disciplinary perspective, against a background of ever tightening emission limits and targets of increasing energy efficiency and materials recovery. This leads to the observation that, due to the typical complexity of thermally treated waste, the intelligence of combustion control systems used in state-of-the-art waste-to-energy plants needs to be expanded to better control the behavior of inorganic compounds that typically end up in waste furnaces. This paper further explains how this goal can be achieved by developing (experimentally validated) predictive numerical models that are engineering-based and/or data-driven. Additionally, the significant economic potential of advanced thermochemical intelligence towards inorganic compounds in waste-to-energy combustion control systems is estimated on the basis of typical operational figures.

Photovoltaic panels were included in EU Directive as WEEE (Wastes of Electric and Electronic Equipment) requiring the implementation of dedicated collection schemes and end-of-life treatment ensuring targets in terms of recycling rate (80%) and recovery rate (85%). Photovoltaic panels are mainly made up of high-quality solar glass (70–90%), but also metals are present in the frames (Al), the cell (Si), and metallic contacts (Cu and Ag). According to the panel composition, about $72 per 100 kg of panels can be recovered by entirely recycling the panel metal content. The PhotoLife process for the treatment of end-of-life photovoltaic panels was demonstrated at pilot scale to recycle high value glass, Al and Cu scraps. A process upgrade is here reported allowing for polymer separation and Ag and Si recycling. By this advanced PhotoLife process, 82% recycling rate, 94% recovery rate, and 75% recoverable value were attained. Simulations demonstrated the economic feasibility of the process at processing capacity of 30,000 metric ton/y of end-of-life photovoltaic panels.