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Biotechnologies for metal recovery from wastes
Full text linkLa crescita dei rifiuti da apparecchiature elettriche ed elettroniche ha spinto la ricerca verso lo sviluppo di processi sostenibili per la loro valorizzazione. I circuiti stampati (CS) a fine vita rappresentano uno dei principali rifiuti di questa categoria. L’interesse per questi scarti è dovuto alla concentrazione di Cu e Zn, corrispondente a circa il 25% e 2% rispettivamente. L’interesse per le biotecnologie continua a crescere come possibile strategia per la loro valorizzazione. Tuttavia, il limite principale di questi approcci è la bassa concentrazione dei CS trattati, il che li rende poco applicabili a livello industriale. Per superare tale criticità, questa ricerca introduce un approccio biotecnologico innovativo condotto con At. ferrooxidans. Il processo sviluppato permette di aumentarne la concentrazione grazie ad un approccio in più fasi, in grado di ridurre la tossicità dei metalli sul metabolismo dei batteri. Il processo usa il Fe3+ prodotto dall’ossidazione batterica per lisciviare il Cu e lo Zn dai CS. Le condizioni migliori individuate sono: 30°C, concentrazione dei CS del 5% (m/v), 10 g/L di Fe2+, tempo di trattamento di 11 giorni.
La cinetica della reazione chimica tra il Cu e il Fe3+ è stata studiata tramite un modello matematico ed è stata stimata un’energia di attivazione pari a 18-25 kJ/mol. Il meccanismo del processo biologico è stato studiato nel dettaglio integrando i risultati del precedente modello con due equazioni differenziali per descrivere il tasso di crescita e il metabolismo del batterio. Il modello sviluppato è consistente con un R2 superiore a 0.97. Inoltre, questo modello potrebbe essere utile per lo sviluppo di tale tecnologia a livello industriale.
Nella fase successiva, la ricerca si è focalizzata sul recupero selettivo dei metalli dalla soluzione di lisciviazione. Le migliori condizioni operative individuate sono: precipitazione del Fe con NaOH, seguita dal processo di cementazione del Cu con lo Zn e il recupero finale dello Zn con acido ossalico. Le efficienze e purezze dei metalli recuperati sono superiori al 95%.
I risultati sperimentali sono ulteriormente valorizzati dallo studio della carbon footprint, che ha dimostrato il vantaggio ambientale del nuovo approccio, confrontandolo con il trattamento chimico con Fe3+ e con processi riportati in letteratura (idrometallurgici e biotrattamenti). La valutazione dell’impatto ambientale ha guidato l’ottimizzazione del processo sviluppato in scala laboratorio. Grazie a questo metodo, sono state identificate le condizioni migliori affinché il processo biotecnologico sia realmente l’approccio più sostenibile. In generale, la valutazione ambientale ha individuato come principali problemi: la richiesta di energia nel processo di biolisciviazione e la quantità di materie prime nel recupero selettivo dei metalli. Questi risultati preliminari hanno determinato la scelta degli esperimenti successivi. Nel dettaglio, il processo biotecnologico è stato migliorato aumentando la concentrazione dei CS da 5% al 10% (m/v) mantenendo efficienze superiori al 95% per entrambi i metalli. Questo miglioramento ha permesso di dimezzare la richiesta di energia. Inoltre, il carico ambientale del processo di recupero può essere ridotto o escludendo il recupero dello Zn o sostituendo le tecniche idrometallurgiche con approcci elettrochimici.
Nell’ultimo capitolo, si è preso in considerazione un processo biotecnologico alternativo, utilizzando il fungo A. niger per estrarre i metalli dai CS. Le condizioni migliori identificate includono l’aggiunta dei CS dopo 14 giorni, l’uso del Fe3+ e una concentrazione del substrato pari a 2.5% (m/v). Efficienze d’estrazione pari al 60% per il Cu e al 40% per lo Zn sono state ottenute dopo 21 giorni di fermentazione. Il design del processo è stato ulteriormente migliorato utilizzando il siero del latte come substrato per la crescita fungina e la produzione di acido citrico.The increase of waste from electric and electronic equipment has pushed the research towards the development of high sustainability treatments for their exploitation. The end-of-life printed circuit boards (PCBs) represent one of the most significant waste in this class. The interest for these scraps is due to the high Cu and Zn concentrations, around 25% and 2% respectively. Biohydrometallurgical strategies are gaining increasing prominence, for the possibility to decrease the environmental costs. Nevertheless, these techniques show the main limit due to the low treated PCB amount, which makes unsustainable the further scale-up. To overcome this criticality, the present research introduces an innovative bioleaching process carried out by At. ferrooxidans. The developed technology allows to reach high PCB concentration thanks to a high efficiency two-step design, able to reduce the metal toxicity on the bacteria metabolism. The treatment uses the Fe3+ generated by bacterial oxidation, as oxidant, to leach Cu and Zn from PCBs. The possibility to overcome the solid concentration criticality is combined with high yield of 95% for Cu and Zn. The best selected conditions are: 30°C, pulp density of 5% (w/v), 10 g/L of Fe2+, time of treatment 11 days.
A mathematical model to study the kinetic of the chemical reaction for the Cu leaching from PCBs, by Fe3+, is reported and an activation energy of 18-25 kJ/mol is estimated. The mechanism of the bioleaching process is studied in detail, integrating the previous model results with two differential equation to describe the bacteria growth and metabolism rate. The developed model is consistent with a R2 higher than 0.97. The results confirm the positive effect of the new innovative process. The determined mathematical model, suitable for the implementation at industrial scale, could be an important tool to predict the bioleaching mechanism.
In the next step, the research is focused on the selective metal recovery from the leaching solution. The best identified conditions include: the Fe precipitation with NaOH, followed by the Cu cementation with Zn and a final Zn precipitation with oxalic acid. The metals show recovery efficiencies and purities higher than 95%.
The experimental results are further enhanced by the carbon footprint assessment which proved the environmental advantage, compared to both the reference chemical treatment through Fe3+ and literature processes (hydrometallurgical and bioleaching approaches). The environmental impact assessment drives the optimization and improvement of the developed process in laboratory scale. It is used to identify the best conditions for the bioleaching process able to make the treatment actually sustainable. Overall, the environmental assessment identifies, as main criticalities to solve: the high energy demand of bioleaching process and the raw materials demand of the following recovery steps. These preliminary results have determined the choices in the further experiments. More in detail, the bioleaching process is improved by the increase of treated PCB concentration from 5% to 10% (w/v) maintaining a leaching efficiency higher than 95% for Cu and Zn. This technical improvement is translated into the halved of energy demand. Furthermore, the environmental load of recovery can be reduced by a double strategy: avoiding Zn recovery or substituting the hydrometallurgical techniques by electrochemical approaches.
In the last chapter, a sustainable process, which uses the fungal strain Aspergillus niger for metal extraction from PCBs, is described. The best identified conditions are PCB addition after 14 days, Fe3+ as oxidant agent, and a pulp density of 2.5% (w/v). Extraction efficiencies of 60% and 40% for Cu and Zn, respectively, are achieved after 21 days of fermentation. The ecodesign of the process is further enhanced by using milk whey as substrate for the fungal growth and the consequent citric acid production
Marine materials as innovative metal sorbents suitable for applications in wastewater treatments
Full text linkThe growing interest for urban mining strategies has pushed the research towards innovative strategies for metal recovery from electronic waste. Nevertheless, the treatment of the resulting metal-rich wastewater is still an issue. In this context, the present paper shows a method to use the capacity of Ulva algae to adsorb metals for the treatment of a synthetic solutions which simulates that resulting from a printed circuit board recycling process. The experiments considered a copper-zinc-iron system, showing a copper adsorption capacity of biomaterial up to 65 mg/g, at pH 5, favoured by iron presence. The process needs a short time (around 15 min) and it is suitable to be performed in a fixed-bed column able to treat more than 30 L of copper-contaminated wastewater, decreasing the energetic costs for mixing (compared to the typical slurry-reactor configuration) with an almost completed metal removal. The sustainability of the process is further improved by the selection of a macroalga which often accumulates on beaches (becoming a waste to remove) complying with the circular economy pillars
Non-toxic, high selectivity process for the extraction of precious metals from waste printed circuit boards
Full text linkThe work presented here focused on the extraction of gold (Au), silver (Ag) and palladium (Pd) from electronic waste using a solution of ammonium thiosulfate. Thiosulfate was used as a valid alternative to cyanide for precious metal extractions, due to its non-toxicity and high selectivity. The interactions between sodium thiosulfate, total ammonia/ammonium, precious metal concentrations and the particle size of the waste printed circuit boards (WPCBs) were studied by the response surface methodology (RSM) and the principal component analysis (PCA) to maximize precious metal mobilization. Au extraction reached a high efficiency with a granulometry of less than 0.25 mm, but the consumption of reagents was high. On the other hand, Ag extraction depended neither on thiosulfate/ammonia concentration nor granulometry of WPCBs and it showed efficiency of 90% also with the biggest particle size (0.50 < Ø < 1.00 mm). Pd extraction, similarly to Au, showed the best efficiency with the smallest and the medium WPCB sizes, but required less reagents compared to Au. The results showed that precious metal leaching is a complex process (mainly for Au, which requires more severe conditions in order to achieve high extraction efficiencies) correlated with reagent concentrations, precious metal concentrations and WPCB particle sizes. These results have great potentiality, suggesting the possibility of a more selective recovery of precious metals based on the different granulometry of the WPCBs. Furthermore, the high extraction efficiencies obtained for all the metals bode well in the perspective of large-scale applications. [Figure not available: see fulltext.
The Green Indium Patented Technology SCRIPT, for Indium Recovery from Liquid Crystal Displays: Bench Scale Validation Driven by Sustainability Assessment
Full text linkIndium is considered a valuable and irreplaceable material for a variety of applications that improve the quality of human life. Due to its limited availability and the growing demand, it is mandatory to find sustainable solutions for indium recovery from end-of-life devices. The green indium patented technology SCRIPT (ITA202018000008207) focuses on recovering indium from ground LCD panels, developed through laboratory scale investigation. The process ensures high recovery efficiencies of indium (>90%), features a simple design, and fully exploits the solid residue with the production of a concrete for building applications. This manuscript presents a study focused on the validation and optimization of the patented SCRIPT technology at the bench scale, driven by sustainability assessment. Bench scale experiments successfully validated the technology, improving its technology readiness level. Furthermore, an environmental sustainability assessment highlighted the importance of treating the finest fraction, which has the highest indium concentration. Optimization tests at the bench scale demonstrated that water could be recirculated for more than five cycles. The economic sustainability tests highlighted that when the indium concentration in the material fed into the recycling plant is above 1000 mg/kg, the technology is cost effective and worth investment. Our study is fundamental for boosting indium recycling in the world. Moreover, our methodological approach represents a guideline for achieving sustainability goals within circular economy approaches for strategic metals in complex matrices
Optimization of Sustainable Processes for the Extraction of Precious Metals from End-of-life Printed Circuit Boards
No full textThe technology advancement and innovation has been very significant and fast, in the last decades. This aspect is particularly evident in the electric and electronic equipment (EEE) field, where new devices are produced every year. The manufacture development is translated in two main issues: the highest metal required and the greatest waste flows to manage. To solve this double criticality, the old linear management method, in which every product became a waste, must evolve in a circular approach based on the principle “resource-product-regenerated resource” (urban mining). The end-of-life printed circuit boards (PCB) represent one of the most significant wastes from electric and electronic equipment (WEEE). In addition to their availability, the interest for these scraps is mainly justified by the high precious metal concentration (e.g. gold, silver, and palladium), which makes them a promising secondary resource. Several approaches are developed for precious metal recoveries from PCB, mainly by pyrometallurgy or hydrometallurgy. Biohydrometallurgical and green hydrometallurgical processes, using more sustainable reagents, are gaining increasing prominence, for their possibility to decrease the environmental costs, compared to the most traditional hydrometallurgy with chemical cyanide lixiviant. The present work aims to supply two innovative solutions: biotechnology by Pseudomonas aeruginosa for the biological cyanide production, and a green-hydrometallurgical process, using the thiosulphate as lixiviant agent for precious metal (i.e. Au and Ag) recovery. The central composite design of a response surface methodology (CCD-RSM) is used to optimize the cyanide production by P. aeruginosa evaluating the influence of both initial pH and glycine concentration. The same statistical approach (CCD-RSM) is used to find the best operative conditions for the precious metal leaching from PCB by thiosulphate, assessing the interaction among sodium thiosulphate, total ammonia/ammonium, particle size and time. The experimental results are further enhanced by the carbon footprint assessment which has quantified the possible environmental advantages of the developed solutions of PCB recycling, able to integrate the circular economy principles
Vanadium, molybdenum and nickel: A sustainability analysis of the extraction from ores versus recovery from spent catalysts
Full text linkThe current increasing demand of raw materials has pushed the worldwide research towards the development of innovative processes able to recover metals from end-of-life materials. Considering their content of Mo, Ni and V combined with the availability on the market, the waste hydrodesulfurization catalysts represents an interesting secondary raw material. In the perspective of the implementation of circular economy strategies, a real effective recycling must combine a high efficiency with high environmental sustainability level. With this aim, the present paper carried out a sustainability evaluation by the life cycle assessment (LCA) tool to compare an innovative recycling of catalysts with the primary production of V, Mo, and Ni. The analysis proved that the secondary production allows a CO2-eq. emission saving higher than 40 %, corresponding to a carbon credit up to around 2,000,000 per year, strongly linked to the kind of supplied energy (country based). The analysis further proved that the waste catalysts, can be integrated with the most common steel scraps treatment with the implementation of a successful and sustainable industry of secondary V
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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