Recovery Of Precious Metals Research Articles

UiO-66-NH2/chitosan with microalgae platform for gold valorization from waste microelectronics

The combination of UiO-66-NH2/chitosan (CTS) and microalgae was effective in precious metal recovery of electronic wastes (E-wastes) from discarded microchips. Herein, zirconium-based metal–organic frameworks were introduced to bind metal ions from the E-waste. Thus, UiO-66-NH2 was linked to CTS as examined by Fourier-transform infrared spectroscopy (FT-IR). Au(III) leachate solutions were prepared via acidic treatments from the microcomputer chips that were used to test metal binding using UV–Vis absorption spectroscopy. The prepared UiO-66-NH2/CTS was tested to recover Au(III) ions from the liquid phase waste, which exhibited higher adsorption capacity than UiO-66, UiO-66-CTS, and UiO-66-NH2. The inclusion of microalgae in UiO-66-NH2/CTS system enhanced gold adsorption efficiency and binding of Au(III) ions onto UiO-66-NH2/CTS and UiO-66-NH2/CTS/microalgae attained equilibrium within a few hours. UiO-66-NH2/CTS showed an adsorption capacity of ∼ 576 mg/g, which increased to ∼ 671 mg/g after the introduction of microalgae of Spirulina maxima. The pH effect on Au(III) binding revealed that electrostatic interactions between the negatively charged UiO-66 particles and gold anions decreased the adsorption capacities at higher pH values. The findings highlighted the potential use of UiO-66-NH2/CTS and microalgae for effective gold recovery from the E-waste.

Construction of Magnetic S‐Doped CoWO4 Composite for Efficient and Selective Recovery of Gold from Wastewater via Adsorption–Reduction Pathway

The design and synthesis of efficient adsorbents for the recovery of precious metals from secondary resources are of great environmental and economic significance. Herein, a magnetic sulfur‐doped composite CoFe2O4@S–CoWO4 (CF@S–CoWO4) is developed through a hydrothermal synthesis method, which is used to selectively recover gold in aqueous media. Significantly, CF@S–CoWO4 exhibits the best overall performance with gold ions adsorption capacity (Qmax) and distribution coefficient (Kd) are 1049 mg g−1 and 4.4 × 106 mL g−1, respectively, which are much higher than those of other gold adsorption materials. The selectivity coefficients (K) toward other metal ions (Pd2+, Ca2+, Mg2+, Cd2+, Al3+, Li+, Ni+) are also higher, which suggests that CF@S–CoWO4 had a preferential selectivity for Au3+ in coexisting ion solutions. Moreover, the antianion interference of the composite follows the order: SO42− > PO43− > NO3− > CO32−, and it also shows very good reusability with adsorption efficiency at 81.78% after four repeated cycles. Based on characterizations and calculation, it is found that Au(III) mainly undergoes chelation and reduction reactions in the S sites in CF@S–CoWO4, which indicates the important role of S sites. Hence the CF@S–CoWO4 composite demonstrates a promising application for the recycling of gold ions from electronic wastewater.

Ethylenediamine tetramethylenephosphonic acid as a selective collector for the improved separation of chalcopyrite against pyrite at low alkalinity

Chalcopyrite is the main Cu-containing mineral and cannot be separated well from pyrite using traditional xanthate collectors with large amounts of lime depressant, resulting in difficulties of the tailing treatment and associated precious metals recovery. Therefore, in this study, the green and odourless ethylenediamine tetramethylenephosphonic acid (EDTMPA) was introduced as a novel chalcopyrite collector. Flotation results from the binary mineral mixture and real ore demonstrated that EDTMPA could realize the selective separation of chalcopyrite from pyrite relative to ethyl xanthate (EX) without any depressants within the wide pH range of 6.0–11.0, and might replace the traditional high-alkaline lime process. Electrochemical and Fourier transform infrared spectra measurements indicated that the difference in adsorption performance of EDTMPA on chalcopyrite and pyrite was larger than that of EX, suggesting a better selectivity for EDTMPA. Density functional theory calculations demonstrated that there were stronger chemical bonds between P—O groups of EDTMPA and the Fe/Cu atoms on chalcopyrite in the form of a stable six-membered ring. Crystal chemistry calculations further revealed that the activity of metal atoms of chalcopyrite was higher than that of pyrite. Therefore, these basic theoretical results and practical application provide a guidance for the industrial application of EDTMPA in chalcopyrite flotation.

Recovery of base and precious metals from scrap TV boards using zig-zag air separator

Waste of Electrical and Electronic Equipments (WEEE) is one of the fastest growing waste streams in the world. The treatment of WEEE with high content of precious metals (Au in particular) has received the most attention due to their high economic potential. The development of simple, environmentally friendly and cost-effective methods for the recovery of metals from “low-value” WEEE (e.g., <100 g/t Au) is important from the circular economy perspective. In this study, the separation of base (Cu) and precious (Ag) metals from scrap TV boards (STVBs) by using a zig-zag air separator was investigated. Size-reduced scrap STVBs (-1 mm) were subjected to separation tests after the removal of the fine fraction (-0.1 mm). The sized scrap material (-1 +0.1 mm) was determined to have a metal content of 15.4% Cu, 47 g/t Ag and 0.05% Fe, with no gold. In the air separation tests, the effect of air flow rate (4-16 m/s) on the recovery of metals was studied. Increasing the air flow rate resulted in low metal recoveries with concurrent high metal grades in the concentrate. Separation efficiency (%) calculations showed that the most efficient separation is obtained at the highest air flow rate of 16 m/s. At this flow rate, 15.4% of the material was recovered in the concentrate which contains 62.3% Cu and 198 g/t Ag with recoveries of 63.3% Cu and 73.9% Ag. The findings indicated that zig-zag air separators can be used to obtain a metal-rich fraction under suitable conditions of the flow regime.

Turning precious metal-loaded e-waste to useful catalysts: Investigation into supercilious recovery and catalyst viability for peroxymonosulfate activation

Here, the key tasks to be accomplished are selective precious metal recovery from e-wastewater and their conversion into valuable catalysts for peroxymonosulfate (PMS) activation. In this regard, we developed a hybrid material using 3D functional graphene foam and copper para-phenylenedithol (Cu-pPDT) MOF. The prepared hybrid showed a supercilious recovery of 92–95% even up to five cycles for Au(III) and Pd(II), which can be viewed as a reference for both the 2D graphene and the MOFs family. The outstanding performance has been attributed principally to the impact of diverse functionality as well as the unique morphology of 3D graphene foam, which provided a wide range of surface area and additional active sites in the hybrid frameworks. To prepare the surface-loaded metal nanoparticle catalysts, the sorbed samples recovered after precious metal extraction were calcined at 800 °C. The viability of the developed catalysts for the breakdown of 4-nitrophenol (4-NP) via PMS activation was investigated. Electron paramagnetic resonance spectroscopy (EPR) and experiments with radical scavengers suggest that sulfate and hydroxyl radicals are the main reactive species involved in the breakdown of 4-NP. This is because the active graphitic carbon matrix and the exposed precious metal and copper active sites work together in a way that is more effective.

Recovery of precious metals from e-wastes through conventional and phytoremediation treatment methods: a review and prediction

Recovery of precious metals from e-wastes through conventional and phytoremediation treatment methods: a review and prediction

An Overview of Precious Metal Recovery from Steel Industry Slag: Recovery Strategy and Utilization

Steel slag is a solid waste of the steel industry, produced during steel production. Three types of slag, namely electric arc furnace (EAF), basic oxygen furnace (BOF), and Linz-Donawitz processed slag (LD-slag) are the steel industry byproducts. That slag comprises precious elements including zinc (Zn), chromium (Cr), iron (Fe), nickel (Ni), silicon (Si) , aluminum (Al), and vanadium (V) and is considered a secondary source of many metals. These metal constituents can be recovered from slags by employing mineral processing techniques like crushing, grinding, magnetic separation, eddy current separation, flotation, leaching, and/or roasting. Metal extraction from steelmaking slag and slag utilization is essential not only for conserving metal supplies but also for environmental protection. This review article evaluated and summarized various extraction methods including magnetic separation, roasting, pyrometallurgical method, hydrometallurgical and bio hydrometallurgical technique to recover precious metal constituents from obtained slag. The state-of-the-art of metal recovery from slag using the aforementioned methodologies and the merits, and demerits of each procedure have been illustrated comprehensively. Suggestions have been made to overcome the shortfall and or lacuna of the technology for better performance and efficiency. The opportunities and difficulties portion of this article paints a vivid picture of turning such a beneficial technology into a more adaptable procedure with some additions that may motivate and lead future research in new directions. The essence of this survey indicates that extracted metal and treated slag might be reutilized in various fields ranging from biomedical to fertilizer applications.

Influence of Static Sorption Parameters on the Recovery of Precious Metals from Wastes of the Refining Processes

Influence of Static Sorption Parameters on the Recovery of Precious Metals from Wastes of the Refining Processes

Aqueous Pretreatment Effect to Improve Au, Ag, and Pt Recovery from Spent Automotive Catalysts

Automotive catalysts represent a secondary source for precious metals recovery. These elements are usually obtained from minerals. Recently, methods have been sought to recover them from waste materials. The main route consists of pyrometallurgical treatments at high temperatures with the generation of other pollutants and very high energy consumption. With hydrometallurgy, routes can be developed which favor the aqueous extraction of said elements at room temperature. In an automotive catalyst, there are different metals which can interfere in the recovery process. In this study, sodium citrate (Na3C6H5O7•H2O), nitric acid (HNO3), and hydrochloric acid (HCl) were evaluated as a hydrometallurgical pretreatment to dissolve Fe, Zn, and Pb contained in a spent automotive catalyst and to improve the subsequent extraction of the precious metals contained therein (Au, Ag, and Pt). Afterwards, the aqueous extraction of precious elements with thiourea (SC(NH2)2) was carried out, comparing the effect of the pretreatment reagents. Finally, the feasibility and effect of each pretreatment as a route for precious metals recovery were analyzed with the aim to avoid processes at high temperatures.

Highly selective separation of palladium from spent catalysts by ozonation with ultrasonic enhancement in a low-acid medium

It is of great significance to consider the recovery of palladium from spent catalyst in terms of resource reserve and environmental protection. However, the leaching percentage of palladium is limited by high oxidation potential and cladding layer. In order to solve this process problem, externalfield enhancementmethod with ultrasonic-assisted ozone is proposed for the recycling of palladium in this study. Mechanical and cavitation effects of ultrasonic can destroy cladding layer and promote solid–liquid interface reaction. The highly oxidizing free radicals generated by ultrasonic excitation of ozone can improve the oxidation of the reaction system and accelerate the oxidation rate of palladium. The leaching percentage of palladium is 93.7% under ultrasonic/ozone condition, which is 23.7% higher than that under conventional conditions. The leaching reaction kinetics shows that the reaction barrier is reduced and the apparent activation energy is reduced by 35.25 kJ/mol after introducing ultrasound and ozone. Additionally, mineralogical analysis is carried out to analyze the enhanced leaching mechanism of palladium. This work demonstrates the value of advanced oxidation process with ultrasonic-assisted ozone in efficient and green recovery of precious metals from secondary resources.

Non-toxic, high selectivity process for the extraction of precious metals from waste printed circuit boards

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.

Mineralogical study of electrum grain size, shape and mineral chemistry in process streams from the Krumovgrad mine, Bulgaria

The gold ore mined at the Krumovgrad mine, Bulgaria is processed by flotation following grinding and regrinding stages securing the targeted liberation size of the electrum which is the principal precious metal-bearing mineral. The findings from a SEM-based automated mineralogy study aiming to quantify electrum occurrences in the processing scheme are presented and the implications of these characteristics on precious metals recovery are discussed. It has been found that Au/Ag grade ratios in the electrum tend to increase in the concentrate streams and decrease in the tailings. The mineralogical analysis indicated that in comparison to the precious metals grains met in the reground rougher concentrate, those detected in the cleaner concentrate are characterized by about 10 % higher gold content. Moreover, particles possessing zones largely enriched in gold (zones where electrum is detected as having at least 90 % gold grade) are more frequently observed in the cleaner concentrate. Grains morphology suggests that the stirred media detritor (SMD) used in the regrinding circuit does not significantly modify particle shape. Likewise, opting for a staged flotation reactors (SFRs) as the main flotation units seem to be a judicious choice by maintaining conditions favouring the recovery of the ultrafine gold.

Silver(I) Recovery by Ion Flotation Process from Aqueous Solutions in Cells with Spargers

Extractive metallurgy has recently turned its attention to waste treatment for the recovery of precious metals through innovative metallurgical processes, such as ion flotation. This work studied the influence of several chemical and physical factors, such as the concentration of xanthate [x], frother agent [e], dithiophosphate [xl], pH, superficial gas velocity Jg, percentage of gas holdup Eg, bubble diameter (Db) calculated with the drift flux model, and the type of sparger, in the efficiency of silver(I) recovery by the ion flotation technique in sub-aerated cells. The results obtained indicate a 90.7% v/v recovery of silver(I) under conditions of 3.77 × 10−4 M [x], 1.25 × 10−4 M [e], Jg 0.5 cm/s, Jl 0.19 cm/s, Eg of 4.1% v/v, and Optimal Db of 0.11 cm, with a rigid bubble generator, achieving an apparent flotation kinetics of 4.16 1/min. The use of combinations [x]–[xl] achieve a silver(I) recovery of 86.9% with a Jg of 1.0 cm/s. The best recovery efficiencies achieved 93% w/w silver(I) are with pH 8.0, [e] of 1.25 × 10−4, Jl of 0.19 (cm/s) and a rigid sparger compared to a flexible one.

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.

Synthesis of novel magnetic pitch-based hypercrosslinked polymers as adsorbents for effective recovery of Ag+ with high selectivity

Silver is an important precious metal with superior ductility, electrical and thermal conductivity, photosensitivity, and antibacterial properties. However, without proper recycling and treatment, silver emissions may pose a threat to the human health and subsistence environment due to their toxicity. Therefore, it is environmentally and economically important to recover Ag from waste electronic equipment and anode slime. Herein, carboxyl functionalized modified magnetic nanoparticles (Fe3O4@3-phenylglutaricacid nanoparticles) were designed and prepared to obtain the low-cost magnetic pitch-based HCP adsorbents (MPHCP and P-MPHCP). The novelty of present work is that superior adsorption capacity and magnetic responsiveness of adsorbent can be obtained by a simple one-step Friedel-Crafts reaction with very low-cost raw material. The maximum Ag+ adsorption capacity of MPHCP and P-MPHCP were 321 and 353 mg/g, respectively. The adsorption was completed within a short duration of 15 min for MPHCP and P-MPHCP at an initial Ag+ concentration of 100 mg/L. Moreover, the most selective is P-MPHCP wherein Ag+ is α = 61 times more selective than Pb2+ at a concentration of 100 mg/L.The adsorption capacity of MPHCP and P-MPHCP towards Ag+ still maintains above 89% after ten cycles of adsorption-desorption. This study not only provides new guidance for the development of porous polymeric adsorbents but also provides technical feasibility for the field of recovery and reutilization of precious metals, which has a very extensive practical application prospect.

Adsorbent Material Based on Carbon Black and Bismuth with Tunable Properties for Gold Recovery.

Adsorption recovery of precious metals on a variety of solid substrates has steadily gained increased attention in recent years. Special attention was paid to the studies on the characterization of the adsorptive properties of materials with a high affinity for gold depending on the nature of the pendant groups present in the structure of the material. The aim of the present work was to synthesize and characterize a new material by using the sol-gel synthesis method (designated as BCb/CB). In this case, synthesis involved the following precursors: bismuth carbonate (III), carbon black, and IGEPAL surfactant (octylphenoxypolyethoxyethanol). Immobilization of the heterojunction as bismuth oxide over a flexible support such as carbon black (CB) can prevent their elution in solution and make it versatile for its use in a system. In this work, a new adsorbent material based on bismuth carbonate supported over carbon black (BCb/CB) was developed and used further for gold recovery from aqueous solutions. The required material was characterized physically/chemically by scanning electron microscopy (SEM); energy dispersive X-ray spectrometry (EDX); X-ray diffraction (XRD); thermal analysis (DTG/DTA); atomic force microscopy (AFM). The Brunauer-Emmett-Teller (BET) method was used to determine the specific surface area indicating a value of approximately 40 m2/g, higher than the surface of CB precursor (36 m2/g). The adsorptive properties and the adsorption mechanism of the materials were highlighted in order to recover Au(III). For this, static adsorption studies were carried out. The parameters that influence the adsorption process were studied, namely: the pH, the contact time, the temperature, and the initial concentration of the gold ions in the used solution. In order to establish the mechanism of the adsorption process, kinetic, thermodynamic, and equilibrium studies were carried out. Experimental data proved that the gold recovery can be conducted with maximum performance at pH 3, at room temperature. Thermodynamic studies proved that the gold adsorption on BCb/CB material is a spontaneous and endothermal process. The results indicate a total adsorption capacity of 13.1 mg Au(III)/g material. By using this material in real solutions, a recovery efficiency of 90.5% was obtained, concomitant with a higher selectivity (around 95%).

Optimization of Precious Metals Recovery from Electronic Waste by Chromobacterium violaceum Using Response Surface Methodology (RSM).

An effective recovery technology will be valuable in the future because the concentration of the precious metal contained in the source can be a key driver in recycling technology. This study aims to use response surface methodology (RSM) through Minitab software to discover the optimum oxygen level (mgL-1), e-waste pulp density (% w/v), and glycine concentration (mgL-1) for the maximum recovery of gold (Au) and silver (Ag). The method of precious metals recovery used for this study was taken from the bioleaching using 2 L of batch stirred tank reactor (BSTR). A Box-Behnken of RSM experimental statistical designs was used to optimize the experimental procedure. The result of the RSM optimization showed that the highest recovery was achieved at an oxygen concentration of 0.56 mgL-1, a pulp density of 1.95%, and a glycine concentration of 2.49 mgL-1, which resulted in the recovery of 62.40% of Au. The pulp density and glycine concentration greatly impact how much Au is bioleached by C. violaceum. As a result, not all of the variables analyzed seem crucial for getting the best precious metals recovery, and some adjustments may be useful in the future.

Polyelectrolyte complex-derived adsorbent capsules capable of selective recovery of precious metal from multiple mixtures

Polyelectrolyte complexes (PECs) are valuable functional materials for many industrial applications, yet it is difficult to augment their morphologies for desired applications. Herewith, PEC capsules were strategically fabricated via salt-induced coacervation of poly(diallyldimethylammonium chloride) and poly(styrenesulfonate). The adsorbents showed Au(III) selectivity in multimetal mixtures of Au-Pt-Pd and Au-Cu-Co-Zn. The binding sites were offered by R4N+ through electrostatic attraction, as elucidated with XPS. Selectivity was influenced by concentration, contact time and stirring speed. A new phenomenon of competing ion rejection was established to be caused by combined Au(III)/water penetration into the capsules, leading to decrease in bulk solution volume at equilibrium. The maximum Au(III) uptake was 176.63 ± 15.57 and 110.84 ± 2.32 mg/g for the Au-Pt-Pd and Au-Cu-Co-Zn systems, achievable within ∼ 1 and > 6 h, respectively. The loaded Au(III) was eluted with 0.1 M thiourea and regenerated for at least five cycles, making it practically feasible for resource recovery through urban mining.

A novel phosphonic acid functionalized poly(vinyl chloride) electrospun nanofiber for efficient adsorption of gold from aqueous solution

Separation of gold from wastewater is an efficient approach to recycle the noble metal resources. Polymer-based adsorbents are widely used in separation because they are inexpensive and modifiable. Herein, a novel phosphonic acid functionalized poly(vinyl chloride) (PVC-APA) nanofiber was fabricated by the functionalization and electrospinning of PVC. PVC-APA exhibited superior adsorption performance for Au with a maximum adsorption capacity of 336.36 mg/g. The adsorption behavior conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm, which was a spontaneous and endothermic process. The adsorption affinity between PVC-APA and Au was very strong even under the interference of multiple ions. Moreover, the reusability of PVC-APA was also satisfying. Comprehensive characterizations and comparative experiments revealed that two hydroxyl oxygen atoms in the phosphonic acid group and one nitrogen atom in the amine group can act as a tridentate ligand to chelate with Au. The adsorbed Au(III) ions can be partially reduced to Au0 by amino groups through a redox reaction. This work broadens the application of PVC in the field of precious metal recovery.

Recovery of precious metals from processed wastewater: conventional techniques nexus advanced and pragmatic alternatives

Abstract The loss of highly sought-after metals such as gold, silver, and platinum during extraction processes not only constitutes a significant waste of valuable resources but also contributes to alarming environmental pollution. The ever-growing adverse impacts of these highly valued metals significantly increase the contamination of water bodies on discharge, while reducing the reusability potential of their corresponding processed wastewater. It is, therefore, of great interest to identify pragmatic solutions for the recovery of precious materials from processed water. In this review, pollution from targeted precious metals such as gold, silver, platinum, palladium, iridium, ruthenium, and rhodium was reviewed and analyzed. Also, the hazardous effects are elicited, and detection techniques are enumerated. An insightful approach to more recent treatment techniques was also discussed. The study reveals nano- and bio-sorption techniques as adoptable pragmatic alternatives, among other techniques, especially for industrial applications with merits of cost, time, waste management, and eco-friendliness. The results indicate that gold (46.2%), palladium (23.1%), platinum (19.2%), and silver (11.5%) are of utmost interest when considering recent recovery techniques. High yield and cost analysis reduction are reasons for the observed preference of this recovery process when considering groups of precious metals. The challenges and prospects of nanomaterials are highlighted.