Mechanical pre-treatment of mobile phones and its effect on the Printed Circuit Assemblies (PCAs)

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.

Analysis of the influence of mobile phones' material composition on the economic profitability of their manual dismantling

This work presents a systematic characterisation of 100 waste mobile phones (73 feature phones and 23 smartphones) produced between 1989 and 2016. All items were inventoried and the evolvement of the relative abundances of their macro-components (mechanic and electro-mechanic parts, electronics and others) and materials was investigated. The average lifetime was 15.1 years for feature phones and 6.4 years for smartphones. The main component was plastic, on average 46%-wt. in feature phones and 37%-wt. in smartphones; over the years electronics' and plastic's amounts decreased (respectively 80% and 70%), while metal components' amount increased (12%). A cost-benefit analysis explored the profitability of the management of waste mobile phones through manual dismantling followed by the sale of the separated components and materials. The average cost of manual dismantling was estimated as 6.93 € per item according to EU average labour costs and 1.50 € per item based on minimum EU labour costs. According to the performed economic analysis, the actual market prices for the potentially recoverable materials and components of waste mobile phones were not able (particularly mixed plastics) to counterbalance the costs of manual dismantling according to the European standard labour costs.

Waste electrical and electronic equipments as urban mines in Burkina Faso: Characterization and release of metal particles

Like other developing countries, Burkina Faso is one of the preferential destinations for second-hand electrical and electronic equipments (EEE). At the end of their life, these EEEs are classified as waste electrical and electronic equipment (WEEE) including Printed Circuit Boards (PCB). A particle size reduction is realized for the release of metals by shredding and grinding to obtain particles smaller 1.5 mm. A granulometric sorting was realized and nine granulometric portions were obtained. Particles were characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS). The experiments confirmed that the fractions contained polymers, glass fibers and metals under the form of single metals or alloys. The release of metal was efficient for particles with a size smaller than 0.71 mm. Three digestion procedures were experimented on four components to assess the impact on metals leaching. Microwave-assisted digestion method was the best procedure, compared to the analysis methods ISO 11466: 1995, and method 3050B, adapted. The characterization by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) of these PCBs exhibited important amounts of precious metals (Ag, Au, Pd) and other metals in greater quantities (Cu, Pb, Ni, Co, etc.), leading to their qualification as "Urban Mines" calling for their recovery. The characterization of metals in each granulometric portion is realized. Precious and others metals were distributed in all granulometric size portions. So granulometric size reduction was not efficient for metal separation and recovery from PCBs and alternative methods should be investigated for selective precious metal recovery.

Value Retention Options in Circular Economy: Issues and Challenges of LED Lamp Preprocessing

The Circular Economy is gaining recognition for its attention to increasing material circularity by proposing a set of value retention options, and organizing business, institutions, and policies for their implementation. Light emitting diode (LED) lamp recycling is becoming increasingly important due to their growing market share and precious metal content. Instead of the current shredding approach, this study applied higher value retention options, such as testing for the functionality of the bulb at the product level, manual disassembly to reuse parts at the component level, and automatic disassembly for industrial scale reuse. This study finds that the effort that is needed to implement higher value retention options (such as reuse) requires a new form of secondary business, wider networks of recycling chains, and favorable policies. It also shows that about 50% of the lamp waste stream is still functioning and economically attractive if they are remarketed. However, the demand-pull market conditions seem to be missing. For manual disassembly, the output fractions are cleaner, but it is not economically feasible due to high labor cost. On the other hand, automatic disassembly does not produce cleaner fractions due to wide design variability. Thus, this study suggests that shifting from shredding-focused-resource recovery to reuse-based-resource circularity requires a comprehensive framework that simultaneously encourages secondary market formation, collaboration between manufacturers, recyclers and companies, and the formulation of favorable reuse policies. This study applies insights from circular economy principles to LED lamp recycling, and it also contributes to the latter by identifying challenges and possible solutions.

Environmental performance of collection boxes for end of life mobile phones

Managing waste electrical and electronic equipment is currently one of the top priority challenges of waste management in the European Union. The collection and subsequent processing of waste electrical and electronic equipment are realized by means of the so-called collective systems that employ collection boxes varying in size and materials used for their production. This study focuses on quantifying and comparing environmental impacts of often-used collection boxes on the example of mobile phone collection. The comparison was based on volume (20 l, 60 l, and 70 l) and on the material used for the construction of the box (polypropylene, corrugated cardboard, and stainless steel). Other parameters, such as lifetime, material and energy performance for production, end of life stage, and waste generation were taken in account. The evaluation was carried out using the method of life cycle assessment with the characterization model CML 2001 created in GaBi 8. The goal of the study was to identify the box with the smallest environmental impact and to identify the hotspots in the life cycles of the individual collection boxes. The results of the study show that polypropylene boxes are the most environmentally suitable for collecting small waste electrical and electronic equipment as they produce the lowest environmental impacts in all of the impact categories evaluated, while boxes made of stainless steel have been found to represent the least environmentally friendly option. The results of the study provide and suggest to the collective system basic data for choosing the type of collection box.

Recovery opportunities of valuable and critical elements from WEEE treatment residues by hydrometallurgical processes

Due to the increasing demand of metals by industry and the limited availability of natural resources, the secondary supply of these elements from discarded products, such as waste electrical and electronic equipment (WEEE), is an important strategy for pursuing a sustainable development. Nevertheless, the complex and heterogeneous composition of this waste stream stands as one of the main drawbacks in the definition of innovative recovery processes. This study investigated the recovery potential of a multi-step leaching process to extract the strategic metals, namely precious metals and rare earth elements (REEs), from the dust produced during the industrial shredding treatment of WEEE. Using a first double-oxidative step with sulfuric acid, most rare earth elements contained in the dust were dissolved at high percentages. Moreover, around 50% of gold was extracted in a second leaching step using 0.25 M thiourea, in a solid to liquid ratio of 0.2 g/70 mL, at 600 rpm. In this regard, the optimum operating conditions were studied by a 2³ full factorial design. Experimental results address the definition of a novel approach, pursuing the recovery of resources of great industrial interest from the residues originating from WEEE mechanical treatments typically performed at large scale. As this dust fraction is not sent for recovery but currently disposed, the proposed recycling strategy promotes the diversion of waste from landfill while reducing the need for virgin materials via lower-impact metallurgical processes.

High voltage fragmentation of composites from secondary raw materials - Potential and limitations

The comminution of composites for liberation of valuable components is a costly and energy-intensive process within the recycling of spent products. It therefore is continuously studied and optimized. In addition to conventional mechanical comminution innovative new principles for size reduction have been developed. One is the use of high voltage (HV) pulses, which is known to be a technology selectively liberating along phase boundaries. This technology offers the advantage of targeted liberation, preventing overgrinding of the material and thus improving the overall processing as well as product quality. In this study, the high voltage fragmentation of three different non-brittle composites (galvanized plastics, carbon fibre composites, electrode foils from Li-ion batteries) was investigated. The influence of pulse rate, number of pulses and filling level on the liberation and efficiency of comminution is discussed. Using the guideline VDI 2225 HV, fragmentation is compared to conventional mechanical comminution with respect to numerous criteria such as cost, throughput, energy consumption, availability and scalability. It was found that at current state of development, HV fragmentation cannot compete with mechanical comminution beyond laboratory scale.

Liberation of Printed Circuit Assembly (PCA) and dust generation in relation to mobile phone design in a size reduction process

Complex electronic devices entering our recycling systems often generate losses in the whole treatment chain. For better liberation, crucial for the mechanical separation process, the devices are crushed which also generates dusts that are not recovered. This study investigated the relation between the liberation of Printed Circuit Assembly (PCA) and dust generation in the crushing process of two different types of mobile phone samples. The results revealed that the overall PCA grade in both samples was approximately 70% with around 3.4% dust generation. However, the liberation distribution of PCAs differed between mobile phones resulting in better distribution for sophisticated mobile phones due among other things to the initial size of the phones. Further, the dust fractions comprised both noble and valuable metals but also contaminants that need to be taken into account when further processing is planned. A higher gold concentrate was detected in dusts from regular phones since the protective plastic casing crushed more easily thus exposing the PCA surface for grinding.

Integrated bioleaching of copper metal from waste printed circuit board-a comprehensive review of approaches and challenges

Waste electrical and electronic equipment (e-waste) is the most rapidly growing waste stream in the world, and the majority of the residues are openly disposed of in developing countries. Waste printed circuit boards (WPCBs) make up the major portion of e-waste, and their informal recycling can cause environmental pollution and health risks. Furthermore, the conventional disposal and recycling techniques-mechanical treatments used to recover valuable metals, including copper-are not sustainable in the long term. Chemical leaching is rapid and efficient but causes secondary pollution. Bioleaching is a promising approach, eco-friendly and economically feasible, but it is slower process. This review considers the recycling potential of microbes and suggests an integrated bioleaching approach for Cu extraction and recovery from WPCBs. The proposed recycling system should be more effective, efficient and both technically and economically feasible.

Copper leaching from electronic waste for the improvement of gold recycling

Gold recovery from electronic waste material with high copper content was investigated at ambient conditions. A chemical preliminary treatment was found necessary to remove the large quantities of copper before the precious metal can be extracted. For this purpose inorganic acids (HCl, HNO₃ and H₂SO₄) and two organic substances EDTA and citrate, were tested. The effect of auxiliary oxidants such as air, ozone and peroxide hydroxide was studied. In pretreatments with peroxide and HCl or citrate, copper extractions greater than 90% were achieved. In the second leaching stage for gold recovery, the solid residue of the copper extraction was contacted with thiourea solutions, resulting in greater than 90% gold removal after only one hour of reaction.