Qualitative and quantitative metals liberation assessment for characterization of various waste printed circuit boards for recycling

Composition and recycling of smartphones: A mini-review on gaps and opportunities

After more than a decade since smartphones became consolidated in the market, many recycling solutions have been proposed to deal with them. To continue developing useful solutions and enable adjustment of routes, this mini-review aims to analyse the current research scenario, presenting relevant gaps, trends and opportunities. From a structured searching and screening procedure, a vast source of data was arranged and is available to extract useful information (43 studies on composition and 93 studies on recycling). The study provides discussions about the history of smartphone development, constituent materials and recycling methods for different components, comparisons between feature phones and smartphones and others. Among some conclusions, the authors highlight the lack of studies on pre-extractive methods, green chemistry, recovery of critical and precious metals, determination of priority materials for recovery and solutions for entire devices. In the end, a list containing six research gaps for composition studies and seven research gaps for recycling studies is provided and may be seen as opportunities for future research.

Copper recovery through biohydrometallurgy route: chemical and physical characterization of magnetic (m), non-magnetic (nm) and mix samples from obsolete smartphones

The more modern electronics are, the smaller and complex printed circuit boards are. Thus, these materials are continually changed (physicochemically), increasing the copper concentrations in smartphones. In this sense, it is challenging to set standardized recycling processes to improve metal recovery. In addition, biohydrometallurgy is a clean and cheap process to obtain critical metals from low-grade sources and waste electronic equipment. Therefore, the aim of this work was to characterize, physicochemically, 21 PCBs from smartphones manufactured from 2010 to 2015, and then to recover the copper by Acidithiobacillus ferrooxidans (biohydrometallurgy). The PCBs were comminuted and separated into Magnetic (M), Nonmagnetic (NM) and without magnetic separation (MIX) samples. It was identified 217.8; 560.3 and 401.3 mg Cu/g of PCBs for M, NM and MIX samples, respectively. Regarding biohydrometallurgy, the culture media iron-supplemented (NM + Fe and MIX + Fe) increased the copper content by 2.6 and 7.2%, respectively, and the magnetic separation step was insignificant.

Characterization and genomic analysis of two novel psychrotolerant Acidithiobacillus ferrooxidans strains from polar and subpolar environments

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20°C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry.

Evaluation of US EPA Method 3052 Microwave Acid Digestion for Quantification of Majority Metals in Waste Printed Circuit Boards

Metal content determination is one of the critical aspects of preparing electronic waste for metal recycling. In spite of the fact that end-of-life printed circuit boards are considered to be a secondary resource reservoir, no standard procedure exists for determining the total metal content in this heterogeneous multicomponent material containing plastics, metals, alloys and ceramics. We investigated the utilization of United States Environmental Protection Agency (US EPA) microwave acid digestion (Method 3052) and various modifications of this procedure for effective releasing of Cu, Fe, Ni, Pb and Zn from waste printed circuit boards (WPCBs) from mobile phones. The maximum contents of Cu (22.6 wt.%), Fe (5.0 wt.%), Ni (2.0 wt.%) and Zn (2.6 wt.%) were obtained using the standard (unmodified) US EPA 3052 digestion procedure, but the total digestion of PCB material was not achieved. The solid residue material after digestion by means of the US EPA 3052 method consisted predominantly of oxides (Ca, Mg and Al) and fluorides (Ca and Mg), and some particles contained minor amounts of Fe and Cu.

Assessing enablers of e-waste management in circular economy using DEMATEL method: An Indian perspective

With increasing population, excessive use of electrical and electronic products and extreme demand of resources have compelled the linear economy to transform into Circular Economy (CE). In the current scenario, e-waste management has become the top priority of all the developed and developing nations especially those in the transition phase. The generation of e-waste has increased proportionally across the world and created an intense pressure on the firms to implement sustainable practices to redesign and recycle the products. The current status of the developing countries like India confronts number of challenges to manage e-waste produced, and the only possible solution is to minimize the waste generation and practicing recycling processes. For transforming into CEs, there is a need to identify the most influencing key enablers through which an effective and robust e-waste management (e-WM) system can be developed. An extensive literature review and expert judgments are expended to identify the most influencing key enablers of e-WM in circular economies, and, being the highest producer of e-waste, Mumbai (Maharashtra) has been chosen as the case location. To explore the strength of causal and effect enablers, the DEMATEL method is applied. This study has shown that 'Environmental management system' (EMS) is the most significant and important driving enabler to influence all the other existing enablers. This study has also highlighted that e-WM can be efficient if it focuses on producing eco-friendly products, developing strict legislations, building green image and supporting the producers to implement CE practices. This study helps stakeholders and policy makers to reduce the burden from the environment and focus on developing an efficient e-WM system on the basis of identified key enablers like EMS and collaboration with environmental partners to contribute towards CE transition.

Comprehensive elemental analysis of consumer electronic devices: Rare earth, precious, and critical elements

Over the past few decades, electronic devices of all kinds, and especially consumer electronics, have evolved in function and composition, in parallel to increasing manufacture and use. There is great potential for recovering economic value and reducing environmental impact by recycling devices and extracting various elements. However, there are few studies that comprehensively identify the elemental content of electronic devices or electronic waste. In the present study, consumer electronics and components (hard drives, ethernet hubs, portable media players, printers, answering machines, mobile phones, Digital Versatile Disc (DVD) players, computer wiring, and printed circuit boards) and electronic waste (low-grade scrap from one commercial recycling facility) were analyzed for rare earth, precious and critical metals. The overall procedure included size reduction, microwave assisted digestion, and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) analysis. Fifty-six elements were quantified or detected in these devices: 14 rare earth elements, six platinum group metals, 20 critical metals, and 16 other elements, including some precious metals. A single device could include a wide range of elements: 48 metals were quantified in the computer hard drives. The estimated economic value of the metals in each device ranged from $12.94 USD (computer wiring) to $454 USD (hard drives). The variety of metals in electronic devices suggests that end-of-life management strategies should focus on recycling and recovery, which also decreases the overall environmental impacts of the devices, especially associated with mining and refining metals.