Urban Mining and Electrochemistry: Cyclic Voltammetry Study of Acidic Solutions from Electronic Wastes (Printed Circuit Boards) for Recovery of Cu, Zn, and Ni

Physical, Static, and Kinetic Analysis of the Electrochemical Deposition Process for the Recovery of Heavy Metal from Industrial Wastewater

Through the electrodeposition technique, toxic metals in wastewater can be removed and deposited on a chosen substrate with excellent selectivity. In this work, we use this technique to extract lead cations from simulated wastewater by using fluorine-doped tin oxide (FTO) substrate at various temperatures. In situ tracking of lead nucleation at advanced stages has been achieved by chronoamperometry. According to the experimental results, the theoretical models developed to study the kinetic growth of lead deposits in 2D and 3D are in good agreement. Nucleation rate and growth rate constants, for example, were found to be strongly influenced by temperature. Cottrell's equation is used to calculate the diffusion coefficient. X-ray diffraction, scanning electron microscopy, and energy-dispersiveX-ray techniques were used to investigate and characterize the lead deposits. The reported results could provide insight into the optimization of electrodeposition processes for heavy metal recovery from wastewater and electronic wastes.

Use of the O2-Thiosemicarbazide System, for the Leaching of: Gold and Copper from WEEE & Silver Contained in Mining Wastes

Environmental pollution today is a latent risk for humanity, here the need to recycle waste of all kinds. This work is related to the kinetic study of the leaching of gold and copper contained in waste electrical and electronic equipment (WEEE) and silver contained in mining wastes (MW), using the O2-thiosemicarbazide system. The results obtained show that this non-toxic leaching system is adequate for the leaching of said metals. Reaction orders were found ranging from 0 (Cu), 0.93 (Ag), and 2.01 (Au) for the effect of the reagent concentration and maximum recoveries of 77.7% (Cu), 95.8% (Au), and 60% (Ag) were obtained. Likewise, the activation energies found show that the leaching of WEEE is controlled by diffusion (Cu Ea = 9.06 and Au Ea = 18.25 kJ/Kmol), while the leaching of MW (Ea = 45.55 kJ/Kmol) is controlled by the chemical reaction. For the case of stirring rate, it was found a low effect and only particles from WEEE and MW must be suspended in solution to proceed with the leaching. The pH has effect only at values above 8, and finally, for the case of MW, the O2 partial pressure has a market effect, going the Ag leaching from 33% at 0.2 atm up to 60% at a 1 atm.

Domestic flow of e-waste in São Paulo, Brazil: Characterization to support public policies

Understanding the domestic flow of e-waste is essential for efficient waste management in urban contexts. However, diagnosis of domestic e-waste flow is complex due to its diffuse generation and dependence on consumer behavior. Here, we characterized domestic e-waste flow in São Paulo, Brazil (a megacity with roughly 11 million inhabitants in 3.5 million households), describing the stages of product acquisition, out-of-use storage, and end-of-life destination, via a population-based cross-sectional study using a statistically representative sample. We conducted household interviews using a structured questionnaire, with questions on characteristics, quantities, and behaviors of acquisition, replacement, storage, repair, and destination for 26 electric and electronic equipment (EEE) categories. Each household had on average 21 EEE (95% confidence interval [CI]: 19.7-21.7), of which 18 were in use and 3 were out-of-use. Out-of-use storage was common, occurring in 72.6% of households. Discarded EEE (i.e., e-waste) was destined for intended reuse (59.5%; 95% CI: 57.4-61.5%), recycling (20.4%; 95% CI: 18.8-22.1%), and, particularly for small EEE, municipal waste (16.0%; 95% CI: 14.5-17.6%). Other aspects of domestic e-waste flow (e.g., place and time of acquisition, second-hand acquisition, donation, intention to repair damaged EEE, and storage) were quantified and related to actions for public policies. This research shows that household surveys are useful for obtaining primary data to verify consumer behavior toward EEE. We expect the findings of this study to support decision-making for public policies related to e-waste management, particularly in countries where reverse logistics systems are in the initial phase of implementation.

Behavior of Waste Printed Circuit Board (WPCB) Materials in the Copper Matte Smelting Process

The amount of waste electrical and electronic equipment (WEEE) in the world has grown rapidly during recent decades, and with the depletion of primary ores, there is urgent need for industries to study new sources for metals. Waste printed circuit boards (WPCB) are a part of WEEE, which have a higher concentration of copper and precious metals when compared to primary ore sources. PCB materials can be processed using pyrometallurgical routes, and some industrial processes, such as copper flash smelting, have utilized this type of waste in limited amounts for years. For the purpose of recycling these materials through smelting processes, this work studied the behavior of WPCB scrap when dropped on top of molten slag. A series of experiments was carried out during this research at a temperature of 1350 °C, in an inert atmosphere with different melting times. The time required for complete melting of the PCB pieces was 2–5 min, after which molten alloy droplets containing Cu, Pb, Sn, Ni, Au, and Ag formed and started descending toward the bottom of the crucible. The ceramic fraction of the PCB material mixed with slag and the polymer fraction was pyrolyzed during the high-temperature experiments. The results give an understanding of PCB melting behavior and their use as a part of the smelting furnace feed mixture. However, more research is needed to fully understand how the different elements affect the process as the amount of PCB in the feed increases. The physical behavior and distribution of PCB materials in fayalite slag during the smelting process are outlined, and the results of this work form a basis for future studies about the chemical reaction behavior and kinetics when PCB materials are introduced into the copper smelting process.