The effect of organic acids as leaching agents for hydrometallurgical recovery of metals from PCBs

The hydrometallurgical treatment, compared to other recycling processes, is of great interest due to its higher efficiency and better economy. In hydrometallurgy, popular agents used in the leaching processes of e-waste include inorganic acids, ammonia, chlorides, thiourea, thiosulphates. Organic acids are also becoming more and more popular. The article presents an overview of possible paths of the metal recovery from e-waste with the use of various organic acids. The results of own research on the leaching of printed circuit boards with the use of organic acids including citric acid, oxalic acid, acetic acid, formic acid, malic acid, lactic acid are also presented

The effect of organic acids as leaching agents for hydrometallurgical recovery of metals from PCBs

The hydrometallurgical treatment, compared to other recycling processes, is of great interest due to its higher efficiency and better economy. In hydrometallurgy, popular agents used in the leaching processes of e-waste include inorganic acids, ammonia, chlorides, thiourea, thiosulphates. Organic acids are also becoming more and more popular. The article presents an overview of possible paths of the metal recovery from e-waste with the use of various organic acids. The results of own research on the leaching of printed circuit boards with the use of organic acids including citric acid, oxalic acid, acetic acid, formic acid, malic acid, lactic acid are also presented

Copper recovery from unground printed circuit board by biogenic ferric at high solid/liquid ratio

In this work, the recovery of Cu from large waste printed circuit board (PCB) pieces by biogenic ferric sulphate at high solid to liquid ratio was studied. PCB parts were packed in a column and biogenic ferric was constantly recirculated. A high oxidation reduction potential (ORP) decrease was observed in ferric leaching due to ferric ion consumption; this drop caused a slower copper dissolution kinetics. After 25 days, 62.2% of copper was leached from PCBs column. PCBs column was connected to a flooded packed-bed (FPB) bioreactor to study the biological regeneration of ferric ion consumed in chemical reaction. The bioreactor connection enabled working at a constant ORP (700 mV vs. Ag/AgCl) during the whole test time. The improvement of oxidising conditions hugely increased copper dissolution rate, reaching 90% of copper recovery after 25 days. The FPB bioreactor operated continuously without showing inhibition problems and generating a leaching liquor with a high and constant ORP. The novel proposed configuration consists of a chemical reactor, where large PCBs pieces are piled at a high solid load, connected to a FPB bioreactor that regenerates the spent ferric ion enabling the leaching without reagents consumption, is a simple, inexpensive, low energy consumption, eco-friendly and effective system to recover copper from PCBs

Microbial Processing of Waste Shredded PCBs for Copper Extraction Cum Separation—Comparing the Efficacy of Bacterial and Fungal Leaching Kinetics and Yields

The recycling of electronic scrap is an important subject not only from an environmental aspect but also for recovering metal resources such as copper. In this work, the microbial extraction of copper and other metals (Cu, Ni, Co, Fe and Al) present in the depopulated and shredded printed circuit board (PCB) is elaborated. Bacterial strains of A. ferrooxidans, A. thiooxidans and a fungal strain, A. niger are used for copper extraction along with other metals from shredded PCBs. An optimum metal recovery of 93% Cu was obtained at 308 K, pH 2 using 8% pulp density in 10 days by a mixed culture of A. ferrooxidans and A. thiooxidans. Whereas using A. niger, a metal recovery of 66% Cu was reported using similar experimental conditions. The results show the higher potential ability of bacteria as compared to fungus to bioleach copper. Additionally, the kinetics and mechanism of copper bioleaching from this e-waste by the chemolithotrophs and heterotrophs were evaluated. The leach liquor obtained from the optimized leaching process was subjected to separation and purification of copper as >99% pure copper sulfate using Acorga M5640 by solvent extraction

Copper recovery from PCBs by Acidithiobacillus ferrooxidans: toxicity of bioleached metals on biological activity

This is a post-peer-review, pre-copyedit version of an article published in Waste and Biomass Valorization. The final authenticated version is available online at: http://dx.doi.org/10.1007/s12649-020-01036-y.The suitability and limits of bioleaching for copper recovery from printed circuits boards has been stated with new strategies and methodologies. The process has been tested using a continuous column reactor simulating those conditions found at industrial scale. The new strategy developed improved the kinetic reaction rate and overcomes transport limitations for the leaching solution, thus improving copper recoveries from 50 to 80% in only 6 h. This drastically reduced the time required by previous studies to achieve the same copper recovery. Inhibition effects of the biological process due to the release of metals from e-waste has been identified by means of microrespirometric monitoring tests. This systematic study allowed identifying that nickel, copper and aluminum impact the microorganisms’ activity, inactivating them in specific scenarios (depending on the concentration and the time exposed). Including the time exposure as variable, this work demonstrated that metal concentrations that have been reported as non-toxic to microorganisms, resulted toxic when the required leaching contact time was considered. Besides high iron concentrations also produce inhibitory effect on the microorganisms’ growth, despite being the energy source for their metabolism.This work has been founded by the Project 2016LLAV00034 and 2018PROD00097 founded by AGAUR and FEDER funds. Eva Benzal gratefully acknowledges a FPU-2014 predoctoral scholarship from Ministerio de Educación, Cultura y Deporte (Spain) and co-financed by FEDER funds.Peer ReviewedPostprint (author's final draft

The effect of organic acids as leaching agents for hydrometallurgical recovery of metals from PCBs

The hydrometallurgical treatment, compared to other recycling processes, is of great interest due to its higher efficiency and better economy. In hydrometallurgy, popular agents used in the leaching processes of e-waste include inorganic acids, ammonia, chlorides, thiourea, thiosulphates. Organic acids are also becoming more and more popular. The article presents an overview of possible paths of the metal recovery from e-waste with the use of various organic acids. The results of own research on the leaching of printed circuit boards with the use of organic acids including citric acid, oxalic acid, acetic acid, formic acid, malic acid, lactic acid are also presented.Web of Science613-461260

Recent chemical methods for metals recovery from printed circuit boards: a review

As the volume of e-waste continues to rise, it is crucial to sustainably manage printed circuit boards (PCBs) and their valuable metal components. PCBs are ubiquitous in modern society, powering a variety of electronic devices. The metal resource crisis and the imperative for a low-carbon circular economy have accelerated the development of e-waste recycling technology. High-value discarded PCBs represent a vital component of e-waste. However, discarded PCBs are deemed hazardous to the ecosystem due to the presence of heavy metals and brominated organic polymers. Thus, recycling metals from discarded PCBs is not only a strategic necessity for fostering a green ecological civilisation but also a crucial guarantee for ensuring a safe supply of mineral resources. This comprehensive review gives the profound details of PCBs, and the performance of and advances in the latest chemical metal recovery methods. Reviewing the latest metal recovery processes, we explored the application of diverse leaching agents, including ionic liquids (ILs), deep eutectic solvents (DESs), organic acids and amino acids. These solvents were assessed in terms of their recovery efficiencies, and most of them demonstrated excellent leaching performance. The role of optimising leaching parameters such as concentration, oxidants, pH, particle size, solid-to-liquid ratios (S/L), temperature, and contact time is underscored, offering insights into achieving sustainable PCB recycling practices. Most of these recent leaching methods successfully extracted base metals (Cu, Fe, Zn, Sn, etc.), as well as precious metals (Au and Ag), achieving leaching efficiencies exceeding 90.0%. Interestingly, their effectiveness can compete with that of traditional hydrometallurgical methods

Investigation of a hydrometallurgical process route to recover metals from waste printed circuit boards

The loss of valuable materials such as base and precious metals is increasing due to the increase in waste electronic and electric waste (WEEE). Most of these metals in WEEE are on the printed circuit boards (PCBs). This study aims to compare different pre-treatment methods to recycle copper from PCBs using a hydrometallurgical process. In order to obtain a uniform/consistent sample across all the tests done, similar custom-made PCBs with 55.45% wt copper were used to compare different parameters. Pre-treating the PCBs is the first stage of the process and it is done to liberate metals which are then dissolved in subsequent leaching stages. Eight different pre-treatment methods were explored. The pre-treated PCBs were then leached under similar conditions in a diagnostic leach test in order to get an indication of the effectiveness of the pre-treatment. Copper recoveries corresponding to each of the pretreatment methods were compared. In addition to recovery, other factors such as time taken for copper recovery, material losses incurred, practicability, environmental impact, health and safety were used to compare the pre-treatment methods. A score was given for each factor and the average was used to choose the optimal pre-treatment method. A method where the PCBs were cut into 1.5 cm x 2 cm pieces and then soaked in 2 M NaOH at 40 °C for 24 hours had the highest average score. This pre-treatment method was then used to prepare PCBs that were used for test work done with the aim to optimise copper leaching. The influence of total ammonia concentration, liquid to solid ratio and choice of ammonium salt used in the buffer system, were investigated in the copper leaching optimisation stage of this thesis. Using ammonium carbonate resulted in lower recoveries compared to ammonium sulphate in the diagnostic leach test. Increasing the ammonia concentration to 7M did not have a significant effect on the copper recovery. Decreasing the liquid to solid ratio from 20ml/g to 10ml/g resulted in a slower rate of recovery. The optimal leaching conditions were found to be; 750 ml mixture of 4 M NH3, 2 M (NH4)2SO4, 100ppm CuSO4 at 25 °C and 500 rpm using the optimal pre-treatment method for the PCBs

Biolixiviación de cobre a partir de placas de circuito impreso (PCBS) mediante hongos filamentosos aislados de efluentes Industriales del parque industrial de Rio Seco (PIRS), en condiciones de biorreactor

Los Residuos de Aparatos Eléctricos y Electrónicos (RAEE) son una fuente muy rica en diversos metales de importancia económica, presentando aproximadamente hasta un 30% de su contenido, actualmente el consumo de RAEE ha aumentado significativamente en todo el mundo, generando a su vez grandes cantidades de residuos los cuales no son reciclados adecuadamente por falta de tecnologías que presenten desventajas energéticas y ambientales. En tal sentido, la presente investigación estudió el potencial de hongos filamentosos aislados de efluentes industriales del Parque Industrial de Río Seco (PIRS) para biolixiviar el Cu presente en los PCBs de residuos de aparatos eléctricos. Para ello, primero se preparó y cuantificó el Cu presente en los PCBs mediante ICP, luego se determinó la tolerancia de los hongos aislados frente a concentraciones de Cu medio de cultivo sólido (50 – 4000 mgL^(-1)) y líquido (50 – 300 mgL^(-1)), densidades de PCBs (2.5 – 20 gL^(-1)), como también se determinó el método de biolixiviación fúngica (un paso, dos pasos y medio agotado) más eficiente para posterior ser realizado a escala de biorreactor. Los resultados muestran que los PCBs presentan una concentración de 1063 mgL^(-1) de Cu. Por otra parte se aislaron e identificaron morfológicamente 8 especies de hongos de las cuales A. níger presentó mayor tolerancia, presentando crecimiento hasta 2000 y 150 mgL^(-1) de Cu en medio de cultivo sólido y líquido respectivamente. Así mismo A. níger presentó un mayor desarrollo de biomasa fúngica a una densidad de 10 gL^(-1) de PCBs en medio líquido. Además el método de biolixiviación fúngica donde cuales A. niger que disolvió la mayor cantidad de Cu en solución, correspondió al método de one step (un tiempo) con 316.39 mgL^(-1), seguido por el método de two step (2 tiempos) con 192.39 mgL^(-1) y método de spent medium (medio agotado) con 122.19 mgL^(-1). La biolixiviación de los PCBs en biorreactores muestran que A. níger después de 15 días de evaluación, presenta una eficiencia de biolixiviación de Cu igual a 26.08% y una bioacumulacion del 20.54%, obteniendo una biorecuperación total de hasta el 46.62 %. Por lo anterior se sugiere que A. niger es una cepa candidata para biolixiviar el Cu presente en los PCB

Study and optimisation of copper bioleaching process for electronic waste valorisation

In the current economical context, the use of waste material with economic potential should be a priority. In this sense, the increasing production of electrical and electronic equipment waste (WEEE) makes these materials a potential source for valuable and scarce metals. For this reason, it is important to develop new metal recovery methodologies economically that are more profitable, sustainable and environmental friendly. A possible solution to this problem is to take advantage of the metabolic activity of certain microorganisms, mainly bacteria, to regenerate the responsible agents for the extraction of metals from the matrix in which they are contained once the useful life of them has ended. This process is known as bioleaching or biological leaching. In this thesis, a study of this biotechnological process for metal recovery from WEEE has been carried out. Firstly, bioleaching to recover copper from low-grade chalcopyrite was studied to establish the bases of the methodology, already applied in the biomining field, as well as to check the feasibility of the technique in this field. Subsequently, bioleaching was extended to be applied in the field of the electronic waste, thus recovering metals from printed circuit boards (PCB) based on their high metal content and their limited availability in the nature. Given the interest of this process, not very studied in the field of the electronic waste, an adjustment of those parameters that allow optimizing the operation is necessary. For this reason, the effect of several parameters has been studied such as pH effect, PCB concentration or particle size, as well as the most appropriate system to perform the process (flasks, bioreactor or column). After bioleaching, the extracted metals remain in the leaching solution, so a last step to obtain the metals in their metallic state again and separated from the initial matrix should be perform which closes the recovery cycle. The study to recover the bioleached copper has been carried out more superficially in this thesis, focusing on cementation as a simple and cheaper alternative to other more complex processes such as electrolysis. In addition to the metals extraction through bioleaching, this thesis has been also focused on studying the limits of the technology due to the complex and varied composition of the waste, such as the toxic effect that bioleached metals could cause to the microorganisms involved in the process or the evaluation of possible substrate inhibition. The measurement of the biological activity may be the solution when there are limitations of quantifying biomass in systems where the formation of precipitates can be habitual, as in bioleaching occurred. For this reason, a microrespirometry-based procedure has been developed that allows to directly measure the oxygen consumption and, thus, the microbial activity at real time. In microrespirometry, the formation of precipitates does not interfere with the measurement which allows obtaining a reliable result of the microbial concentration. Thus, after affirming the feasibility of bioleaching as a simpler, cheaper and environmental friendly alternative to traditional physical-chemical processes, this thesis establishes the most favourable conditions to obtain the greatest possible copper recovery through bioleaching. These bases are the previous phase to scale-up the technology to be implemented in an industrial environment.En el actual contexto económico, el provecho de materiales residuales con potencial económico debería ser prioritario. En este sentido, la creciente producción de residuos eléctricos y electrónicos (REES) convierte estos materiales en una potencial fuente de metales muy valiosos y escasos. Por este motivo, es importante desarrollar nuevas tecnologías de valorización de metales que sean económicamente más rentables, sostenibles y respetuosas con el medio ambiente. Una posible solución para este problema consiste en aprovechar la actividad metabólica de determinados microrganismos, principalmente bacterias, para regenerar los agentes responsables de la extracción de metales de la matriz donde se encuentran inmovilizados una vez finalizada la vida útil del aparato eléctrico que los contiene. Este proceso es conocido como biolixiviación o lixiviación biológica. En esta tesis se ha llevado a cabo el estudio de este proceso biotecnológico para la recuperación de metales procedentes de REES. En primer lugar, se estudió la biolixiviación para recuperar cobre a partir de calcopirita de baja ley para establecer el procedimiento de la metodología, ya aplicada en el campo de la biominería, y comprobar la viabilidad de la técnica en este campo. Posteriormente, la biolixiviación fue aplicada al campo de los residuos electrónicos, realizando así la extracción de metales de placas de circuito impreso (PCB, del inglés, printed circuit boards), basándose en la gran cantidad de metales que éstos contienen y su limitada disponibilidad en la naturaleza. Ante el interés de este proceso, no muy estudiado en el campo de los residuos electrónicos, es necesario ajustar aquellos parámetros que permitan optimizar la operación. Por este motivo, se ha estudiado el efecto de varios parámetros que afectan al proceso como el pH, la concentración de residuo o el tamaño de partícula, así como también el sistema más adecuado para llevar a cabo el proceso (matraz, biorreactor o columna). Tras la biolixiviación, los metales extraídos permanecen en solución por lo que es necesario realizar una última etapa para llegar a obtener los metales en su estado metálico nuevamente, aunque separado de la matriz inicial en este caso, y cerrar así el ciclo de la recuperación. En esta tesis el estudio para recuperar el cobre lixiviado se ha realizado de forma más superficial, centrándose en la cementación como alternativa simple y económica a otros procesos más complejos como la electrólisis. Además de la extracción de metales mediante biolixiviación, esta tesis también se ha centrado en estudiar factores que limitan la tecnología debido a la compleja y variada composición de los residuos, como es el efecto tóxico que pueden provocar los metales biolixiviados sobre los microorganismos involucrados en el proceso, así como la evaluación de la inhibición por sustrato. La medición de la actividad biológica puede ser la solución cuando haya limitaciones de cuantificar la biomasa en sistemas donde la formación de precipitados suele ser habitual, como es el caso de la biolixiviación. Por este motivo se ha desarrollado un procedimiento basado en la microrespirometría que permite obtener de forma directa el consumo de oxígeno y, por tanto, la actividad a tiempo real de una muestra biológica. En las microrespirometrías la formación de precipitados no interfiere en la medición por lo que permite obtener un resultado fiable de la concentración microbiana. Así pues, tras afirmarse la viabilidad de la biolixiviación como alternativa más simple, económica y medioambientalmente sostenible a los procesos físico-químicos tradicionales, esta tesis establece las condiciones más favorables para obtener la mayor recuperación de cobre posible mediante biolixiviación. Estas bases son la fase previa para escalar la tecnología a implementar en un entorno industrial.Recursos naturals i medi ambien