A long-term static immersion experiment on the leaching behavior of heavy metals from waste printed circuit boards

Characteristics and factors that influence heavy metal leaching from spent catalysts

With the extensive use of nonferrous metals and metal catalysts, solid wastes containing heavy metals release metal ions into soil and surface water through erosion and leaching. This is one of the major threats to the global environment and human health. Studying the characteristics and impact factors of heavy metal leaching from solid waste is a critical part of managing spent catalysts and environmental risk. In this work, the characteristics of and factors that influence leaching and seepage release from typical spent catalysts and lead-zinc smelting slag were studied. The results indicated that metal ions leached more easily in an acidic environment (pH 4.5) and an environment with DOM than in a neutral environment (pH 7.0). Metal ion leaching was favored by a liquid-to-solid ratio of 20:1. The concentrations of metal ions released from the spent catalysts in sequential leaching experiments were higher than those in column leaching experiments. Leaching of metal ions in the presence of different leaching agents and from different spent catalysts can be described by different controlling models of the shrinking core model, but changes in the liquid-to-solid ratio showed no obvious correlation with changes in the metal release mechanism. These results provide important information for spent catalyst management and risk prevention and control.

Efficient Film Fabrication and Characterization of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS)-Metalloporphine Nanocomposite and Its Application as Semiconductor Material

The use of composite films with semiconductor behavior is an alternative to enhance the efficiency of optoelectronic devices. Composite films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and metalloporphines (MPs; M = Co, Cu, Pd) have been prepared by spin-coating. The PEDOT:PSS-MP films were treated with isopropanol (IPA) vapor to modify the polymer structure from benzoid to quinoid. The quinoid structure promotes improvements in the optical and electrical behavior of films. The composite films’ morphology and structure were characterized using infrared and Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Composite films were analyzed for their optical behavior by ultraviolet-visible spectroscopy: at λ < 450 nm, the films become transparent, indicating the capacity to be used as transparent electrodes in optoelectronic devices. At λ ≥ 450 nm, the absorbance in the films increased significantly. The CoP showed an 8 times larger current density compared to the CuP. A light induced change in the J-V curves was observed, and it is larger for the CoP. The conductivity values yielded between 1.23 × 10² and 1.92 × 10³ Scm⁻¹ and were higher in forward bias.

Gallium arsenide (GaAs) leaching behavior and surface chemistry changes in response to pH and O2

Gallium arsenide (GaAs) is a material widely used in electronic devices. Disposal of electronic waste containing GaAs in municipal solid waste landfills raises concerns about the public health and ecological risks associated with the potential release of toxic arsenic (As) species. In this study, different tests were performed to investigate the leaching behavior of particulate GaAs in aqueous solutions. In the U.S. Toxicity Characteristic Leaching Procedure (TCLP) and California Waste Extraction Test (WET), the concentrations of As released from the GaAs particles were about 2.6-2.8-fold higher than the regulatory limit (5 mg/L). A much higher As concentration (72 mg/L), accounting for as much as 15.4% of the initial As in GaAs, was solubilized in a pH-7.6 synthetic landfill leachate under ambient atmosphere after 120 days. Additional tests performed to evaluate the dissolution of GaAs under a range of redox conditions, pH levels, ionic strength, and presence of organic constituents commonly found in landfills revealed that oxic environments and mildly alkaline conditions (pH 8.1-8.5) promote release of As (chiefly arsenite) and gallium species to the surrounding aqueous environment. The rate of As release in long-term exposure experiments was initially constant but later progressively diminished, likely due to the formation of a passivating layer on the surface of GaAs consisting of corrosion products rich in poorly soluble gallium oxides (Ga₂O₃ and Ga(OH)₃). This hypothesis was confirmed by surface analysis of GaAs particles subjected to leaching using X-ray photoelectron spectroscopy (XPS). These findings suggest that further research is needed to assess the potential release of toxic As from electronic waste in municipal landfills.