Application of the surface response methodology (RSM) to optimise alkaline leaching of vanadium and molybdenum from man-made raw materials

The 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.

The rapid growth of electronic waste can be viewed as both an environmental threat and an attractive source of minerals that can reduce the mining of natural resources. In this work, response surface methodology was used to optimize an electrochemical process for the extraction and recovery of base metals from electronic waste using a mild oxidant (Fe3+). Through this process, the effective extraction of base metals can be achieved, enriching the concentration of precious metals and significantly reducing environmental impacts and operating costs associated with waste generation and chemical consumption. The optimization was performed using a bench-scale system specifically designed for this process. Operating parameters such as flow rate, applied current density, and iron concentration were optimized to reduce the specific energy consumption of the electrochemical recovery process to 1.94 kWh per kilogram of metal recovered.

There is urgent need for more effective recycling of Earth's technology metal supply. Precious and specialty metals that constitute this supply are essential components of clean tech applications, high-tech electronic devices, and other products that are vital to the global economy. These metals form integral parts of a wide variety of products making recycling a complex process. Collection of end-of-life (EoL) products and pre-conditioning them for recovery of target metals are important first steps in the recycling process, followed by metallurgical and chemical processes indispensable for generating pure metals fit for reuse in another product cycle. Successful achievements have been made in precious metal recovery using integrated smelter and advanced refining technologies. Recycling of metals is very efficient for industrial applications in closed cycles, such as recovery of platinum group metals from process catalysts used in the chemical industry. Recovery of precious metals in open cycles typical in most consumer applications is more challenging. Although at the metallurgical refining stage very efficient recovery processes with high metal yields are well established, the complex structures and procedures used to collect and precondition EoL consumer products currently lead to significant losses. Recycling works relatively well for autocatalytic converters, while recovery of precious and specialty metals from electronic waste, such as computers, cell phones, or TVs still offers a huge improvement potential. Collection rates are low, and a significant share of EoL electronics from North America and other industrialized countries finally ends up, often illegally, in inefficient and environmentally harmful informal recycling operations in non-Organization for Economic Cooperation and Development (OECD) nations. The amount of e-waste generated globally is estimated to be 30-50 million tons annually, but it needs to be understood that only a fraction of this is relevant for the recycling of precious and specialty metals, namely electronics such as information and communication technology (ICT)-equipment and audio and video devices. White goods as well as electric household products, such as vacuum cleaners, toasters or electric tools are of importance for the recycling of steel, base metals (e.g., Cu) and plastics but contain very small amounts of precious and specialty metals. Only a fraction of the total e-waste is currently properly recycled. Globally, most e-waste is discarded into landfill or open dumps, incinerated, or stored. Even formal recycling in industrialized countries often bears large improvement potential, especially in the sorting and preconditioning steps. Recycling of technology metals holds many benefits for society including conservation of a valuable resource; reduction of the environmental burden of mining that, otherwise, would be required to replace the lost metal; and metal supply security. E-waste products, when collected, contain appreciable amounts of technology metals. Recovery of these metals from such an urban mine is appealing because some metals occur usually in much higher concentrations than in virgin ore bodies. However, the elemental composition of electronic devices can be very complex, comprising over 40 chemical elements in combinations not existing in geological deposits, and also including many organic substances (plastics, halogenated flame retardants, resins). It is impossible to recover all metals from such complex mixes, and hence choices need to be made and the rules of thermodynamics determine the limits of even the most advanced processes. The principal challenge is to recover as much of the valuable substances as is technically and economically feasible while ensuring that toxic elements are well controlled and no harmful emissions into air, effluents, or soil result from the recycling process itself. It is essential that various stakeholders become aware of the importance of technology metals to global society and of the challenges linked to their proper recycling. These stakeholders need to become partners in preserving these metals, which are essential to the continuation of domestic, commercial, industrial, and military activities world-wide.

The fundamental investigation on extraction of Pd(II), Pt(IV), Cr(VI), Cu(II), Ni(II) and Zn(II) from an aqueous solution by using microcapsules containing a metal extractant was investigated. As extractants, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and tri-n-octylamine loaded with hydrochloric acid (TOA-HCl) were used. The extractants were successfully encapsulated in the microcapsules during the in situ microencapsulation process. The extractability of the metals into the microcapsules was estimated from the extraction isotherm of the metals. According to the Langmuir model, the saturation amount of metal extracted and the extraction equilibrium constant were determined. The microcapsules containing EHPNA and TOA-HCl were suitable for the extraction of base metals and precious metals, respectively. It is anticipated that a reactor in which two columns packed with each microcapsule containing EHPNA and TOA-HCl are connected in series would be useful for separation and recovery of precious metals from base metals.

&lt;p&gt;Biomining is the common term used to define processes that utilize biological systems to facilitate the extraction of metals from ores. Nowadays, a biomining concept can be defined as a two stage combined biological systems (1st stage bioleaching and 2nd stage biosorption) in order to perform the extraction and recovery of the metals from secondary sources such as industrial and mining waste, waste electrical and electronic equipment (WEEE), bottom ash and end of life vehicles. Overwhelming demand and limited sources of metals have resulted in searching new sources so that attentions have been shifted from mining process towards recycling of secondary resources for the recovery of metals. There are several metallurgical processes for metal recovery from the secondary sources such as pyrometallurgical processing, hydrometallurgical and bio/hydrometal-lurgical processing. Biomining processes are estimated to be relatively low-cost, environmentally friendly and suitable for both large scale as well as small scale applications under the bio/hydrometallurgical processing. Thus, the process involves physical separation (pre-treatment) and biomining (bioleaching and biosorption) and hydrometallurgical processes for recovery of base metals, rare earth elements (REEs) and precious metals from e-waste was evaluated.&lt;/p&gt;

Critical metals, identified from supply, demand, imports, and market factors, include rare earth elements (REE), platinum group metals, precious metals, and other valuable metals such as lithium, cobalt, nickel, and uranium. Extraction of metals from U.S. saline aqueous, emphasizing saline, sources is explored as an alternative to hardrock ore mining. Potential aqueous sources include seawater, desalination brines, oil-and-gas produced waters, geothermal aquifers, and acid mine drainage, among others. A feasibility assessment reveals opportunities for recovery of lithium, strontium, magnesium, and several REE from select sources, in quantities significant for U.S. manufacturing and for reduction of U.S. reliance on international supply chains. This is a conservative assessment given that water quality data are lacking for a significant number of critical metals in certain sources. The technology landscape for extraction and recovery of critical metals from aqueous sources is explored, identifying relevant processes along with knowledge gaps. Our analysis indicates that aqueous mining would result in much lower environmental impacts on water, air, and land than ore mining. Preliminary assessments of the economics and energy consumption of recovery show potential for recovery of critical metals.

Electronic waste (E-waste) is accumulating rapidly globally and pose a significant environmental challenge. One of the ways to cover the cost of waste processing (in addition to reducing the costs associated with landfill) is through recovery of metals. In addition, toxic and dangerous metals can and must be removed prior to repurposing, incineration or pyrolysis of the plastic substrates. E-waste is usually either transported to landfills or processed by pyrometallurgical and hydrometallurgical processes. Recently, a number of hydrometallurgical approaches have been considered in metals recovery from different electronic components. In this study, glycine (amino acetic acid) or its salts is considered as a lixiviant in an alkaline environment for base and precious metals recovery from shredded and ground printed circuit boards (PCBs). It was found that alkaline glycine solutions selectively dissolve copper, zinc, and lead over precious metals. Gold and silver were then recovered in a subsequent leaching step using glycine and small amounts of cyanide (at starvation levels, implying no free cyanide is present). The leach system remains alkaline throughout both stages of processing. In the two-stage glycine leaching system, gold, silver, zinc, lead and copper recoveries were 92.1%, 85.3%, 98.5%, 89.8%, and 99.1% respectively. The recoveries of precious and base metals by direct cyanidation, single stage glycine–cyanide leaching, and ammonia leaching were lower than the recoveries of these metals using the two-stage glycine and glycine–cyanide systems.

Selective recovery of silver and palladium from acidic waste solutions using dithiocarbamate-functionalized cellulose

Industrial wastewater sludge is one of the vital sources of metals, including heavy metals, valuable metals, and precise metals. Apart from metals' necessity and economic value, some are toxic and harmful to the environment. This review explores the technologies currently applied for extracting and recovering heavy metals from industrial wastewater sludge. The technologies have been explained, and the merits and demerits of methods, as reported in past investigations, have been highlighted. The salient findings of this review are that the hydrometallurgical processes using acid leaching (H 2 SO 4 , HNO 3 , HCl, etc.) have been considered for the metal extraction process. Metal dissolution, concentration/purification, and recovery are the main stages of hydrometallurgical processes. The selection of successive metal recovery methods depends on the concentration of metals and chemical characteristics of industrial wastewater sludge. Different metal purification and concentrations were reported, including adsorption, ion exchange solvent extraction, and so forth, while precipitation and electrodeposition were mainly applied for metal recovery from industrial wastewater sludge. In this review, the cost and economic viability of the metal recovery process are also evaluated by previous reported studies. This review may be considered a valuable source of information for environmentally friendly and cost‐effective methods for metal recovery from industrial wastewater sludge.

Innovative bio-acid leaching method for high recovery of critical metals from end-of-life light emitting diodes

This study delves into the application of oxidative refining for the recovery and concentration of precious metals, namely palladium (Pd) and gold (Au), from waste electrical and electronic equipment by WEEE recycling, leveraging pyrometallurgical techniques. The primary objective is to optimize refining parameters, encompassing variations in gas pressure, temperature, and gas composition, to maximize the extraction and purification of precious metals from recycled materials. Through an array of comprehensive characterization techniques, encompassing microstructural analysis, elemental composition assessment, and metal concentration measurement, this study scrutinizes the potential of oxidative refining. The conclusive findings underscore the remarkable potential of oxidative refining in augmenting the efficiency and effectiveness of metal recovery from waste printed circuit boards (PCBs), with a pronounced emphasis on the concentration of Pd and Au. This research not only highlights the promise of oxidative refining but also concludes that optimizing process parameters, such as a N2/O2 mixed gas pressure of 4 L/min, a process time of 40 min, and a temperature of 1400 °C, is imperative for achieving the highest efficiency in metal recovery from electronic waste, especially precious metals like Pd and Au. It further contributes to the sustainable management of electronic waste and the strategic extraction of valuable precious metals.

Extraction of heavy metals from MSWI fly ash using hydrochloric acid and sodium chloride solution

Optimisation of saturation magnetisation of iron nanoparticles synthesized by hydrogen reduction: Taguchi technique, response surface method, and multiple linear and quadratic regression analyses

Blockchain technology facilitates trust and transparency in the decision-making process and enables the transaction's verifiability by reading immutable distributed ledgers. It has been innovatively applied this technology in the E-waste optimization for the recovery of precious metals using microwave heat treatment. This present paper presents the maximum recovery of precious and base metals from E-waste with a numerical technique called surface response methodology, and was compared with the actual experimental results. The main goal of this paper is to recover the precious metals like copper and gold with its adjacent metals from unwanted and discarded printed circuit boards, integrated circuits, and standards connectors, with the input variables of microwave power, maximum temperature, and aqua leaching ratio. The obtained empirical information of recovered metals was recorded in immutable distributed ledgers so that every member of the blockchain network can be read and verified through the stored records. These records were also utilized to minimize the error and maximize the precious metal outcomes. The result with blockchain network also shows that identical resemblance between the experimental and statistical predicted data obtained with surface methodology. Further, Smart Contracts has been created and deployed to store and retrieve empirical records in the Hyperledger Fabric Blockchain Platform and then measured the performance using Hyperledger Caliper Benchmark

Printed circuit boards contain precious metals. They are produced in large volumes, rendering them an important component of the electronic waste. In view of the heterogeneity of the metals present, reprocessing of electronic waste is a heinous task. The present study focused on leaching of valuable metals from electronic waste printed circuit boards using Aspergillus niger DDNS1. The adaptation phases began at 0.1, 0.5 and 1.0% of fine powder of printed circuit boards with 10% inoculum and were optimized with three effective factors, viz. initial pH, particle size and pulp density, to achieve the maximum simultaneous recovery of the valuable metals. The interactions of these metals were also deciphered using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectrum and atomic absorption spectroscopy. The results indicated that extraction of the precious metals was accomplished mainly through the unique organic acids originating from A. niger DDNS1. The initial pH played an important role in the extraction of the precious metals and the metals precipitate formation. The leaching rate of the metals was generally higher at low powder dosage of printed circuit boards. The toxicity of the printed circuit boards had little effect on two-step bioleaching at the pulp density of 0.1% compared to one-step bioleaching. The two-step bioleaching process was followed under organic acid-forming conditions for the maximum mobilization of metals. Thus, the precious metals from printed circuit boards could be mobilized through fungal bioleaching which promises an important industrial application in recycling of electronic wastes.