Microstructural and Corrosion Properties of PEO Coated Zinc-Aluminized (ZA) Steel

Plasma Electrolytic Oxidation (PEO) is a surface treatment, similar to anodizing, that produces thick oxide films on the surface of metals. In the present work, PEO coatings were obtained on zinc-aluminized (ZA) carbon steel using a solution containing sodium silicate and potassium hydroxide as electrolyte, and working with high current densities and short treatment times in Direct Current (DC) mode. The thickness of the coating, as well as the surface morphology, were strongly influenced by the process parameters, with different dissolution grades of the ZA layer depending on the current density and treatment time. A compromise between thickness and porosity of the coating was found with low current density/long treatment time or high current density/short treatment time. The PEO layer was mainly composed of aluminum oxides and silicon compounds. The corrosion resistance increased remarkably in the samples with the PEO coating. These PEO coated samples are suitable for sealing treatments that further increase their corrosion properties or will be also an ideal substrate for commercial painting, assuring improved mechanical adhesion and protection even in the presence of damages

Strategic metals recovery from wastes

The recovery of different types of metals from wastes has had a spreading interest in the last years. One reason is that wastes, and in particular e-waste, contain metals which are considered strategic. In fact, the availability of these metals is limited and decreases, as natural resources are limited, and their prices fluctuate according to the markets and the management policy of the resource country. Actually, strategic metals are generally defined as those metals that are required for the national defense of a country, but are threatened by supply disruptions due to limited domestic production. However, the definition of strategic metals can be also including those metals that are important not only for national defense, but also for industries that play an important role in the economic development of a country such as energy, aerospace, telecommunication, computer or mobile technology. Thus, it has become quite interesting and urgent to find a strategic way to recover these metals from the wastes. In this work, the recovery of resources from different wastes was studied. In particular, after the introduction and the description of the experimental systems used in this research, the recovery of gold, together with other metals (silver, copper and tin), from the printed circuit boards (PCBs) of end of life (EOL) mobile phones is discussed in Chapter 3. Actually, both the most dangerous and the most precious metals could be founded in PCBs. In particular, it was studied a process which consists in an acid leaching process followed by the gold complexation with thiourea or thiosulphate, two substances that represent an alternative to the more toxic cyanides typically used for the selective gold dissolution. Furthermore, the effect of the ultrasound during the leaching was examined, in order to improve the recovery yield. In fact, in the latest years, ultrasound has been investigated to assist hydrometallurgical metals extraction from ores and minerals but their industrial application is until now limited, although the advantages derived from their application are: a greater metal release in shorter time, lower consumption of reagents and lower process temperature. Therefore, the use of ultrasound could represent an advantage because it increases the recovery of precious metals from the waste. Subsequently, a study was conducted to evaluate a method to recovery silver from the end-of-life solar cells and, more generally, to design a simple and cheap process for the full recovery of the materials constituent the photovoltaic panels. In fact, different methods both hydrometallurgical and pyrometallurgical were tested and the best results were obtained using a combination of a heating treatment and three hydrometallurgical ones. The process parameters were optimized, both for heating and chemical treatments. The results of this study are presented in Chapter 4. Moreover, because the idea seems economically valuable, the process in lab scale was also improve at TRL 5 and the obtained results were used to apply successfully for European funding. In fact, “ReSiELP” project was approved, with the aim to improve the TRL of the technology from 5 to 7. Successively, in Chapter 5 is described the study of recovering Tantalum from EOL capacitors and Neodymium from permanent magnets. In order to separate tantalum from silica, a new treatment with hydrofluoric acid was investigated and tested, whereas the process known in literature for neodymium recovery, was modified introducing a treatment with ammonia which increase the purity of recovered neodymium and sodium double salt. After these studies about metals extraction from e-wastes, a method to increase the added value of recovered material was investigated. In fact, besides the intrinsic value of these metals, a further value could be achieved by recovering these metals in form of nanoparticles, which exhibit very interesting and promising properties in comparison with the corresponding bulk materials. Size-dependent properties include, but are not limited to, the following: optical, magnetic, catalytic, thermodynamic, electrochemical properties and electrical transport. Moreover, nanomaterials may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water treatment. Different nanoparticles were produced using as raw material the solutions in which electronic scraps were previously leached. In particular, nanoparticles of tin dioxide, silver, copper, cuprous oxide, gold and iron were synthetized and characterized and the results of the study are presented in Chapter 6. All the nanoparticles were synthesized using hydrometallurgical processes and the reagents used were environmentally friendly (like ascorbic acid or glucose syrup) as well as the technologies (ultrasound) used to produce them and to improve the yields in metals extraction from the e-waste. The use of ultrasound in nanoparticles production allows to reduce the sizes of the products thanks to the cavitation effect which produces locally extreme conditions during the nanoparticles nucleation and growth processes. Different processes were developed to produce the six different type of nanoparticles. The materials obtained were analysed by inductive coupled plasma, scanning and transmission electron microscopy, x-ray diffraction, laser diffraction particle size analyser and UV-spectroscopy. The results showed that the developed methods allow to recover the metals with high yield and to produce high purity nanoparticles of tin dioxide, silver, copper, cuprous oxide, gold and iron with sizes between 2 and 200 nm. Finally, some interesting and innovative application for the recovered metals, in particular silver and copper, were also studied and the results are presented in Chapter 7 of this thesis work. The silver and copper powder were introduced into Plasma Electrolytic Oxidation coating. Plasma electrolytic oxidation (PEO), also called ‘Microarc Oxidation’ (MAO) is relatively new surface modification technique that shows an increasing interest in the production of oxide ceramic coatings on light alloys such as aluminium, titanium or magnesium. PEO coatings can enhance the corrosion and wear resistance properties of these metals, or can confers to the light alloys various other functional properties including anti-friction, thermal protection, optical and dielectric features. Furthermore, PEO can be used as a pre-treatment to provide load support for top layers. PEO is a process derived from conventional anodizing which shows many advantages such as higher corrosion and wear resistance performances of the coatings, more environmental friendly electrolytes and the possibility to include into the coatings particles coming from the electrolyte. PEO of metals is a complex process that combines oxide film formation, dissolution and dielectric breakdown: the sample, as anode, is immersed in an electrolyte and it works with high voltages and current densities inside a tank which constitute the cathode of the electrolytic cell. Due to the high voltage that needs to overcome the dielectric breakdown potential of the oxide layer, the formation of a persistent anodic micro-discharges on the surface during the PEO treatment is observed. These short-lived micro-discharges are the key of the process; they move randomly over the surface and produce the growth of an oxide ceramic coating and they also allow to incorporate compounds from the electrolyte into the coating. In the studies presented in this thesis silver and copper powder were introduced into PEO coating by direct addition into the electrolyte to improve respectively the antimicrobial/antifungal and the antifouling properties of the sample surfaces.Negli ultimi tempi il recupero di diversi tipi di metalli dai rifiuti ha acquistato notevole interesse. Una delle ragioni è che i rifiuti, e in particolare i rifiuti elettronici, contengono metalli considerati strategici. Infatti, la disponibilità di questi metalli è limitata e diminuisce, poiché le risorse naturali sono limitate, e i loro prezzi variano in base ai mercati e alla politica di gestione dei paesi produttori. In realtà, i metalli strategici sono generalmente definiti come metalli che sono necessari per la difesa nazionale di un paese, ma sono minacciati da interruzioni di approvvigionamento a causa della modesta produzione nazionale. Tuttavia, la definizione di metalli strategici può includere anche i metalli che sono importanti non solo per la difesa nazionale, ma anche per le industrie che svolgono un ruolo importante nello sviluppo economico di un paese, ad esempio quelle legate all’energia, all’ambito aerospaziale, a quello delle telecomunicazioni, computer e tecnologia mobile. Per queste ragioni è diventato molto interessante ed urgente trovare un modo strategico per recuperare questi metalli dai rifiuti. In questo lavoro, è stato studiato il recupero di risorse da diversi rifiuti. In particolare, dopo l'introduzione e la descrizione dei sistemi sperimentali, nel Capitolo 3 viene discusso il recupero dell'oro, unitamente ad altri metalli (argento, rame e stagno) dalle schede di circuiti stampati (PCB) a fine vita. Si consideri che i metalli più pericolosi e preziosi sono contenuti proprio nei circuiti stampati. In particolare, è stato studiato un processo che comprende un attacco acido seguito dalla complessazione oro con tiourea o tiosolfato, due sostanze che potrebbero sostituire i ben più tossici cianuri, tipicamente utilizzati per la dissoluzione dell'oro. Inoltre, è stato esaminato l'effetto degli ultrasuoni durante la lisciviazione, al fine di verificare se il loro effetto consentisse di aumentare la resa d’estrazione. Infatti, negli ultimi anni, gli ultrasuoni sono stati studiati per assistere l'estrazione idrometallurgica dei metalli da minerale ma la loro applicazione industriale è ancora limitata, nonostante diversi vantaggi siano stati riconosciuti dalla loro applicazione: una maggiore liberazione dei metalli in tempi più brevi, minore concentrazione di reagenti necessaria e basse temperature di lavoro. Pertanto, l'uso di ultrasuoni potrebbe rappresentare un vantaggio per aumentare anche il recupero dei metalli preziosi dai rifiuti. Successivamente, è stato condotto uno studio per valutare il recupero dell'argento da pannelli fotovoltaici a fine vita e, più in generale, il processo più semplice e più economico per il completo recupero di risorse dai pannelli fotovoltaici. Sono stati quindi testati diversi metodi sia idrometallurgici che pirometallurgici e i risultati migliori si sono ottenuti combinando un trattamento pirometallurgico e tre idrometallurgici. I parametri di processo, come temperatura e durata del trattamento sono stati studiati e ottimizzati, sia per il riscaldamento che per i trattamenti chimici e i risultati di questo studio sono presentati nel Capitolo 4. Inoltre, visto che l'idea sembra economicamente valida, è stata anche testata a TRL 5 e i risultati emersi sono stati utilizzati per richiedere un finanziamento europeo. Infatti, è stato approvato il progetto "ReSiELP", che in tre anni dovrebbe costruire un impianto per esportare questa tecnologia a TRL 7. Successivamente, nel Capitolo 5, è stato studiato un modo per recuperare il tantalio dai condensatori a fine vita e neodimio da magneti permanenti. Per separare il tantalio dalla silice, è stato studiato e testato un trattamento con acido fluoridrico, mentre nel recupero del neodimio il processo noto in letteratura è stato modificato introducendo un trattamento con ammoniaca che aumenta la purezza del sale doppio di neodimio e sodio che viene recuperato. Dopo questi studi sull'estrazione dei metalli da rifiuti elettronici, è stato testato un metodo per aumentare il valore del materiale recuperato. Infatti, oltre al valore intrinseco di questi metalli, un ulteriore vantaggio potrebbe essere ottenuto recuperando questi metalli sotto forma di nanoparticelle, le quali presentano proprietà molto interessanti e promettenti in confronto ai corrispondenti materiali massivi. Le proprietà di quest’ultime sono ottiche, magnetiche, catalitiche, termodinamiche ed elettrochimiche. Inoltre, i nanomateriali possono fornire soluzioni alle sfide tecnologiche e ambientali nei settori della conversione energetica, della catalisi, della medicina e del trattamento dell'acqua. In quest’ottica, sono state prodotte nanoparticelle diverse utilizzando come materie prime le soluzioni in cui erano stati precedentemente ntrattati i rifiuti elettronici. In particolare sono state sintetizzate e caratterizzate nanoparticelle di ossido di stagno, argento, rame, ossido di rame, oro e ferro, ed i risultati dello studio sono presentati nel Capitolo 6. Tutte le nanoparticelle sono state sintetizzate utilizzando processi idrometallurgici e l'utilizzo di reagenti il più possibile ecocompatibili (quali l'acido ascorbico o lo sciroppo di glucosio) nonché la sperimentazione di una tecnologia, quali gli ultrasuoni, considerata ecologica e già testata durante la lisciviazione dei rifiuti elettronici. In questo caso, l'applicazione degli ultrasuoni ha consentito di ridurre le dimensioni delle particelle sintetizzate grazie all’effetto di cavitazione che generano nel liquido. Sono stati sviluppati diversi processi per produrre i sei tipi di nanoparticelle. I materiali ottenuti sono stati analizzati con plasma ad accoppiamento induttivo (ICP), microscopia a scansione e trasmissione elettronica (SEM e TEM), diffrazione a raggi X, diffrazione laser e spettroscopia UV. I risultati hanno dimostrato che i metodi sviluppati consentono di recuperare i metalli con elevata resa e di produrre nanoparticelle di ossido di stagno, argento, rame, ossido di rame, oro e ferro ad alta purezza e di dimensioni comprese tra 2 e 200 nm. Infine, è stata studiata anche un'applicazione interessante e innovativa per i metalli recuperati, in particolare argento e rame, ed i risultati riportati nel Capitolo 7 di questa tesi. In particolare, l'argento e la polvere di rame sono stati introdotti nel rivestimento di ossidazione elettrolitica al plasma. L'ossidazione al plasma elettrolitico (PEO), chiamata anche "Microarc Oxidation" (MAO), è una tecnica di rivestimento superficiale relativamente nuova ma che inizia ad essere impiegata nella produzione di rivestimenti ceramici d’ossido su leghe leggere quali l'alluminio, il titanio o il magnesio. Il trattamento PEO può migliorare le proprietà di resistenza alla corrosione e all'usura di questi metalli o conferisce diverse altre proprietà funzionali, tra cui diminuzione dell’attrito e protezione termica. Inoltre, il PEO può essere utilizzato come pretrattamento per fornire un substrato per altri rivestimenti. Il PEO deriva dall'anodizzazione convenzionale, ma presenta molti vantaggi, come ad esempio elevate proprietà dei rivestimenti di resistenza a usura e corrosione, l’impiego di elettroliti più rispettosi dell'ambiente e la possibilità di inserire nel rivestimento particelle provenienti dall'elettrolita. Il PEO dei metalli è un processo complesso che combina la formazione di film di ossido, la dissoluzione e la rottura del dielettrico: il campione, come anodo, è immerso in un elettrolita ed il processo impiega elevate tensioni e densità di corrente all'interno di un serbatoio che funge da catodo. A causa dell'elevata tensione che deve essere al di sopra del potenziale di rottura del dielettrico, durante il trattamento PEO vi sono micro-scariche anodiche persistenti sulla superficie. Queste micro-scariche di breve durata sono la chiave del processo; si muovono casualmente sulla superficie trattata provocando la crescita di un rivestimento ceramico d’ossido e permettendo di incorporare composti nel rivestimento. Negli studi presentati in questa tesi, le polveri di argento e rame sono state introdotte nel rivestimento PEO mediante aggiunta diretta nell'elettrolita per conferire rispettivamente l'effetto antimicrobico / antimicotico e antivegetativo ai campioni

Strategic metals recovery from wastes

The recovery of different types of metals from wastes has had a spreading interest in the last years. One reason is that wastes, and in particular e-waste, contain metals which are considered strategic. In fact, the availability of these metals is limited and decreases, as natural resources are limited, and their prices fluctuate according to the markets and the management policy of the resource country. Actually, strategic metals are generally defined as those metals that are required for the national defense of a country, but are threatened by supply disruptions due to limited domestic production. However, the definition of strategic metals can be also including those metals that are important not only for national defense, but also for industries that play an important role in the economic development of a country such as energy, aerospace, telecommunication, computer or mobile technology. Thus, it has become quite interesting and urgent to find a strategic way to recover these metals from the wastes. In this work, the recovery of resources from different wastes was studied. In particular, after the introduction and the description of the experimental systems used in this research, the recovery of gold, together with other metals (silver, copper and tin), from the printed circuit boards (PCBs) of end of life (EOL) mobile phones is discussed in Chapter 3. Actually, both the most dangerous and the most precious metals could be founded in PCBs. In particular, it was studied a process which consists in an acid leaching process followed by the gold complexation with thiourea or thiosulphate, two substances that represent an alternative to the more toxic cyanides typically used for the selective gold dissolution. Furthermore, the effect of the ultrasound during the leaching was examined, in order to improve the recovery yield. In fact, in the latest years, ultrasound has been investigated to assist hydrometallurgical metals extraction from ores and minerals but their industrial application is until now limited, although the advantages derived from their application are: a greater metal release in shorter time, lower consumption of reagents and lower process temperature. Therefore, the use of ultrasound could represent an advantage because it increases the recovery of precious metals from the waste. Subsequently, a study was conducted to evaluate a method to recovery silver from the end-of-life solar cells and, more generally, to design a simple and cheap process for the full recovery of the materials constituent the photovoltaic panels. In fact, different methods both hydrometallurgical and pyrometallurgical were tested and the best results were obtained using a combination of a heating treatment and three hydrometallurgical ones. The process parameters were optimized, both for heating and chemical treatments. The results of this study are presented in Chapter 4. Moreover, because the idea seems economically valuable, the process in lab scale was also improve at TRL 5 and the obtained results were used to apply successfully for European funding. In fact, “ReSiELP” project was approved, with the aim to improve the TRL of the technology from 5 to 7. Successively, in Chapter 5 is described the study of recovering Tantalum from EOL capacitors and Neodymium from permanent magnets. In order to separate tantalum from silica, a new treatment with hydrofluoric acid was investigated and tested, whereas the process known in literature for neodymium recovery, was modified introducing a treatment with ammonia which increase the purity of recovered neodymium and sodium double salt. After these studies about metals extraction from e-wastes, a method to increase the added value of recovered material was investigated. In fact, besides the intrinsic value of these metals, a further value could be achieved by recovering these metals in form of nanoparticles, which exhibit very interesting and promising properties in comparison with the corresponding bulk materials. Size-dependent properties include, but are not limited to, the following: optical, magnetic, catalytic, thermodynamic, electrochemical properties and electrical transport. Moreover, nanomaterials may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water treatment. Different nanoparticles were produced using as raw material the solutions in which electronic scraps were previously leached. In particular, nanoparticles of tin dioxide, silver, copper, cuprous oxide, gold and iron were synthetized and characterized and the results of the study are presented in Chapter 6. All the nanoparticles were synthesized using hydrometallurgical processes and the reagents used were environmentally friendly (like ascorbic acid or glucose syrup) as well as the technologies (ultrasound) used to produce them and to improve the yields in metals extraction from the e-waste. The use of ultrasound in nanoparticles production allows to reduce the sizes of the products thanks to the cavitation effect which produces locally extreme conditions during the nanoparticles nucleation and growth processes. Different processes were developed to produce the six different type of nanoparticles. The materials obtained were analysed by inductive coupled plasma, scanning and transmission electron microscopy, x-ray diffraction, laser diffraction particle size analyser and UV-spectroscopy. The results showed that the developed methods allow to recover the metals with high yield and to produce high purity nanoparticles of tin dioxide, silver, copper, cuprous oxide, gold and iron with sizes between 2 and 200 nm. Finally, some interesting and innovative application for the recovered metals, in particular silver and copper, were also studied and the results are presented in Chapter 7 of this thesis work. The silver and copper powder were introduced into Plasma Electrolytic Oxidation coating. Plasma electrolytic oxidation (PEO), also called ‘Microarc Oxidation’ (MAO) is relatively new surface modification technique that shows an increasing interest in the production of oxide ceramic coatings on light alloys such as aluminium, titanium or magnesium. PEO coatings can enhance the corrosion and wear resistance properties of these metals, or can confers to the light alloys various other functional properties including anti-friction, thermal protection, optical and dielectric features. Furthermore, PEO can be used as a pre-treatment to provide load support for top layers. PEO is a process derived from conventional anodizing which shows many advantages such as higher corrosion and wear resistance performances of the coatings, more environmental friendly electrolytes and the possibility to include into the coatings particles coming from the electrolyte. PEO of metals is a complex process that combines oxide film formation, dissolution and dielectric breakdown: the sample, as anode, is immersed in an electrolyte and it works with high voltages and current densities inside a tank which constitute the cathode of the electrolytic cell. Due to the high voltage that needs to overcome the dielectric breakdown potential of the oxide layer, the formation of a persistent anodic micro-discharges on the surface during the PEO treatment is observed. These short-lived micro-discharges are the key of the process; they move randomly over the surface and produce the growth of an oxide ceramic coating and they also allow to incorporate compounds from the electrolyte into the coating. In the studies presented in this thesis silver and copper powder were introduced into PEO coating by direct addition into the electrolyte to improve respectively the antimicrobial/antifungal and the antifouling properties of the sample surfaces

Analisi Metallografiche e prove di durezza su simulacri di anelli in 30CrMo4 fucinati e bonificati

Introduzione su azienda e materiale, metodo di indagine, prove di durezza e micrograie sul materiale, profilo di durezza e prova Jomin

Recupero di metalli preziosi da rifiuti tramite processi idrometallurgici

Obiettivo di questo lavoro è stato recuperare l’oro, assieme al rame ed argento, dalle schede elettroniche di telefoni cellulari mediante la tecnica idrometallurgica supportata dagli ultrasuoni, utilizzando come reagente la tiourea, in sostituzione dei cianuri.Sono stati valutati diversi parametri ed in particolare gli ultrasuoni sulla resa d'estrazione. Anche differenti metodi di recupero sono stati esaminati: cementazione con polveri metalliche ed elettrodeposizion

Method and plant for recycling photovoltaic panels

A method is described for recycling photovoltaic panels of the type comprising a glass attached to a plurality of photovoltaic cells by means of an insulating junction plate, wherein the photovoltaic cells comprise silicon elements and metallic contacts. The method comprises detaching the glass from the photovoltaic cells and subsequently separating the glass from the photovoltaic cells by means of an air flow. In detail, to separate the glass from the photovoltaic cells, the glass and the photovoltaic cells are dropped from a falling point and, during their fall, glass and photovoltaic cells are impinged with an air flow that is directed along a substantially horizontal direction and which is such to obtain a separation of the falling paths of the glass and of the silicon elements sufficient to drop them into a glass collecting element and a silicon collecting element respectively, placed below the falling point. A plant adapted to implement the method is also described

METODO ED IMPIANTO PER IL RICICLAGGIO DI PANNELLI FOTOVOLTAICI

Viene descritto un metodo per il riciclaggio di pannelli fotovoltaici del tipo comprendenti un vetro attaccato ad una pluralit\ue0 di celle fotovoltaiche mediante una lastra isolante di giunzione, in cui le celle fotovoltaiche comprendono elementi di silicio e contatti metallici. Il metodo prevede di distaccare il vetro dalle celle fotovoltaiche e successivamente separare il vetro dalle celle fotovoltaiche mediante un flusso d\u2019aria. Nel dettaglio, per separare il vetro dalle celle fotovoltaiche si fanno cadere il vetro e le celle fotovoltaiche da un punto di caduta, e durante la loro caduta si investono vetro e celle fotovoltaiche con un flusso d\u2019aria che \ue8 diretto lungo una direzione sostanzialmente orizzontale e che \ue8 tale da ottenere una separazione dei percorsi di caduta del vetro e degli elementi di silicio sufficiente a farli cadere rispettivamente in un contenitore del vetro e in un contenitore del silicio posti al di sotto del punto di caduta. Viene altres\uec descritto un impianto atto ad implementare il metodo

Synthesis of SnO2 and Ag Nanoparticles from Electronic Wastes with the Assistance of Ultrasound and Microwaves

In this work, SnO2 and Ag nanoparticles were produced with a raw material nitric acid solution, which came from the leaching of printed circuit boards. First, a precursor of tin oxide was precipitated from the nitric acid solution by three different techniques: (I) conventional heating, (II) microwave irradiation, and (III) ultrasound treatment. Second, this precursor was transformed into tin oxide nanoparticles by heat treatment in a furnace. Third, hydrochloric acid was added to the nitric acid solution to induce the precipitation of silver chloride. Fourth, silver chloride was reduced to metallic silver nanoparticles in an ammonia solution using glucose syrup as both the reducing agent and the capping agent. The reduction reaction was carried out through (I) conventional heating, (II) microwave irradiation, and (III) ultrasound treatment. The nanoparticles were characterized by scanning electron microscope (SEM), x-ray diffractometer (XRD), infrared (IR)-spectroscopy, transmission electron microscope (TEM), ultraviolet (UV)-spectroscopy, and laser diffraction particle size analyzer

Gold recovery from PCBs with thiosulfate as complexing agent

Waste of electrical and electronic equipment (WEEE) is the fastest growing advanced type of solid waste streams in the urban environment worldwide and contains interesting amounts of precious metals. Hydrometallurgical technique is fast emerging as preferred process for the recovery of a variety of metals due to its lower energy consume and lower smelter emissions than conventional pyrometallurgical processes. In this work, a hydrometallurgical process for the recovery of gold and silver from electronic scraps was studied. In place of cyanide, thiosulfate was chosen as complexing agent for gold. Thiosulfate leaching can be considered a non-toxic process and the gold dissolution rates can be faster than conventional cyanidation. The electronic scraps, obtained from \u201cend of life\u201d mobile phones, were crushed and pre-treated with nitric acid before the leaching. Different parameters were studied: concentration of thiosulfate, temperature and reaction time. Moreover, the use of ultrasound to assist the hydrometallurgical gold extraction was investigated, as its application in ores leaching shows a greater metals release in shorter time and the advantage of working at lower concentration of reagents and at lower temperature. In this work, the use of ultrasound allowed a higher recovery of the precious metals than conventional leaching in all the conditions studied (different concentrations of reagents, temperature and reaction time). Moreover, the studied process allowed also the recovery of the other metals present in the waste (Cu, Sn and Ag)

Green synthesis of copper nanoparticles with ultrasound assistance

study of the synthesis of metallic copper (Cu) nanoparticles using ultrasound assistance and green reagents is presented. Copper recovered from the pretreatment of electronic circuit boards was used as the raw material in this study. Different process parameters, namely, the effect of ultrasound, reducing agents and capping agents, were investigated, where L-ascorbic acid and sodium borohydride were used as reducing agents. In order to make the process environmentally friendly, the synthesis was performed in aqueous solutions, in ambient conditions, and exposed to air. The nanoparticles were characterized with SEM, TEM, XRD, UV-spectroscopy, and by using laser diffraction particle size analyzer. Results show that, using L-ascorbic acid as reducing agents, the use of ultrasound leads to the production of Cu nanoparticles, with a reaction time of 10 min, compared with a time of several hours when performing the synthesis without ultrasound. The nanoparticles produced by this method have dimensions of approximately 5 nm and remain stable in the solutions for days. Moreover, by using Cu nitrate from the leaching solution of electronic scraps, obtaining nanoparticles with high purity has been made possible