End-of-Life Heavy Metal Releases from Photovoltaic Panels and Quantum Dot Films: Hazardous Waste Concerns or Not?

Abstract

To determine if there are potential concerns related to the environmental end-of-life impacts of photovoltaic (PV) or quantum-dot display (QD) technologies, the goal of this study was to assess the magnitude of heavy metal leaching using simulated landfill methodologies from devices in an attempt to forecast the lifecycle environmental impacts of subsequent generations QD-enabled PV technologies. The underlying hypotheses are (H1) existing PV and QD thin-film technologies do not release heavy metals at concentrations exceeding RCRA or State of California regulatory limits, and (H2) the disposal of PV and QD thin-film technologies does not exceed Land Disposal Restrictions (LDR). Three task-oriented objectives were completed: (O1) Five representative PV panels and two representative thin-film displays with QD technology were obtained from commercial sources. (O2) RCRA Toxicity Characteristics Leaching Procedure (TCLP) tests and California Waste Extraction Tests (WET) were conducted in addition to microwave-assisted nitric acid digestion. (O3) Results were compared to the existing regulatory limits to examine the potential environmental end-of-life concerns. The heavy metal concentrations obtained from PV panels and QD thin-film displays when exposed to simulated landfill environments and extreme case leaching scenarios were generally several orders of magnitude lower than the promulgated standards and probably not of major concerns related to end-of-life safe disposal of these commercially available products. With exception to the findings for lead under the RCRA rules, the results confirmed that PV and QD thin-film technologies do not release heavy metals at concentrations exceeding RCRA or State of California characteristic hazardous waste regulatory limits. However, lead, mercury, and potentially other heavy metal releases have to be monitored to ensure that the disposal of this type of waste is in compliance with RCRA's LDR requirements and universal treatment standards because the second underlying hypothesis could not be completely supported for the leaching of these heavy metals. It could be anticipated that newer and more sophisticated soldering materials and approaches in the next generation of PV panels would significantly reduce the use of RCRA heavy metals or nanomaterials. However, although the generated data is limited to these representative PV and QD technologies and as such should not be considered applicable to the entire gamete of present-day technologies, these findings suggest that their release from future PV QD technologies would likely be greater from non-end-of-life processes than from traditional land disposal routes.

Cadmium-Containing Quantum Dots Used in Electronic Displays: Implications for Toxicity and Environmental Transformations

“…S1). 23 While the patent was not explicit on the QD core/shell synthesis, it did mention that CdSe was an exemplary material for QDs, preferably with the presence of both CdS and ZnS shells. 9 We hypothesize that these QDs possess a cadmium selenide (CdSe) core for narrow emission, an alloyed cadmium sulfide zinc sulfide (CdS/ZnS) shell for enhancement of quantum yield and stability.…”

Dynamic material flow analysis of silicon photovoltaic modules to support a circular economy transition

“…13 Spent PV modules, particularly those of older generations, could potentially be classified as borderline hazardous waste under the Resource Conservation and Recovery Act (RCRA) 14 due to the presence of toxic heavy metals (i.e., Pb in the solder of c-Si). 13,15 However, a detailed screening-level risk assessment study by the International Energy Agency (IEA) revealed that exposure point concentrations of Pb for c-Si PV are at least one order of magnitude below U.S. EPA health screening values in soil, air, and water if modules are placed in non-sanitary landfills under worst-case leaching scenarios. 16 Recently, PV module waste was reclassified under the less restrictive Universal Waste program in California to promote module recycling and reuse at the end of life.…”

“…"Optimistic" scenarios represent an ambitious outlook for improving PV process related parameters (i.e., lifetime and efficiency). Additional details on parameters are in Table2optimistic 10% reuse of retired modules in a second life of15 years to reflect growth in module spares and progress in reuse/repair knowledge. In the absence of any recycling infrastructure, about 38.4 million MT of solar glass waste and 5.3 million MT of aluminum waste could be eliminated through 2100 compared with the baseline scenario.…”

Cadmium-Containing Quantum Dots Used in Electronic Displays: Implications for Toxicity and Environmental Transformations

“…22 A QD-containing Kindle (Amazon) film leached only 10% of its Cd after the waste extraction test (WET) using citric acid at pH 5. 23 However, these studies provide limited information on how QDs are transformed because they assess an entire product in which QDs cannot be separated from the encapsulating solid matrix and do not allow for extraction of QD materials necessary for in-depth characterization and fate analysis. Additionally, limited effort was devoted to low pH exposures, despite their environmental and biological relevance.…”

“…For example, a study on a QD-containing polymer prototype for light-emitting diodes (QD Vision) indicated that after 30 days, 7% Cd leaching under near-neutral conditions (pH 5 or 1 mM H 2 O 2 ) occurred . A QD-containing Kindle (Amazon) film leached only 10% of its Cd after the waste extraction test (WET) using citric acid at pH 5 . However, these studies provide limited information on how QDs are transformed because they assess an entire product in which QDs cannot be separated from the encapsulating solid matrix and do not allow for extraction of QD materials necessary for in-depth characterization and fate analysis.…”