Recovery Of Precious Metals Research Articles

Simultaneous Removal of Soluble Metal Species and Nitrate from Acidic and Saline Industrial Wastewater in a Pilot-Scale Biofilm Reactor

The hydrometallurgical treatment of waste printed circuit boards for the recovery of precious metals generates acidic wastewater containing nitrate, chloride and residual base metals. The scope of this work is the study of a biological treatment process for the concurrent metal sequestering, nitrate reduction and wastewater neutralization. A pilot-scale packed-bed biofilm reactor was set up, inoculated with the strain H. denitrificans and experimentally monitored. The range of operating parameters examined included: (a) nitrate concentration 750–5750 mg/L NO3−; (b) pH 3–8; (c) Cu, Ni, Zn and Fe at 50 mg/L and 100 mg/L; and (d) chloride concentration 5%–10% as NaCl. The presence of metals did not affect denitrification at the concentrations examined. H. denitrificans completely reduced nitrate and the intermediately produced nitrite at elevated chloride levels. Denitrification shifted pH towards circumneutral to alkaline values, where iron, zinc, copper and nickel were sequestered quantitatively from solution via bioprecipitation. The proposed simple, robust and low-cost biological treatment unit is advantageous compared to the conventional wastewater treatment, where metal precipitation is based on chemical neutralization and the problem of nitrate removal remains unresolved.

From Waste to Green Applications: The Use of Recovered Gold and Palladium in Catalysis.

The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.

Effective separation and recovery of valuable metals from high value-added lead anode slime by sustainable vacuum distillation

High value-added lead anode slime (LAS) contains valuable Ag and Au, as well as high levels of harmful elements, mainly As, Sb and Te. Traditional LAS pyrometallurgical treatment, which is a complex Pb and Sb extraction flow used for precious metal recovery, has exhausted energy sources and discharged hazardous wastes that have an increasingly harmful impact on the environment. Therefore, vacuum distillation for recovering Ag and Au from LAS has been investigated. Theoretical analysis shows that the rapid and effective recovery of valuable metals from LAS can be realized. At a temperature of 1173 K and a holding time of 2.5 h in a kilogram-scale experiment, Ag and Au were effectively enriched, and the recovery efficiencies were 92.10% and 96.85%, respectively; moreover, removal rates of 90.22% for As, 65.83% for Sb, and 98.48% for Te were achieved. The phase transformation of LAS before and after the vacuum distillation process was analyzed. The volatiles can serve as a raw material to produce Sb white, while the residue can be returned to the smelting-vacuum process for Au and Ag purification. In this vacuum distillation process, no gas or wastewater is discharged, thereby recycling valuable metals in a sustainable and clean manner.

Non-cyanide reagents for gold extraction from the products of pressure oxidation of sulphide concentrates

The standard pressure oxidation (POX) technology for sulfide gold-bearing concentrates processing has many problems associated with the use of cyanide as a gold lixiviant. Therefore, works to find of alternative gold recovery methods are currently now. This paper describes some technological solutions, which can become a real alternative to cyanide technology in the future. Five different refractory gold-bearing concentrates from Russian gold deposits were investigated. Concentrate 1 was gold-copper concentrate. Concentrate 2 was gold-pyrite concentrate. Concentrates 3–5 were pyrite-arsenopyrite double refractory concentrates. The POX tests at the temperature of 110, 200 and 220 oC and the oxygen pressure of 1.5, 2.4 and 3.0 MPa were carried out. Chloride, thiosulfate, sulfite and thiocyanate were tested as gold lixiviants. The gold recovery by non-cyanide methods was 97–99%, and from double refractory concentrates was 86–92%. The tested reagents are less toxic than cyanide and makes possible to recover gold in acidic POX slurry. As well, “POX-pyrometallurgical” technology for precious metals recovery from POX cakes to lead collector was tested in pilot scale. It was shown that “POX-pyrometallurgical” technology for preg-robbing concentrates could be used. The recoveries of gold and silver are 97 and 96%, respec tively.

Efficient and selective removal of Ag+ as nano silver particles by the composite of SiO2 supported nano ferrous oxalate

Developing novel environmentally materials with high capacity and selectivity for Ag+ adsorption by transforming Ag+ to nano silver is important for the recovery of precious metals from Ag-containing solution. The present study systematically studied the Ag + adsorption process from solution by the composite of SiO2 supported nano ferrous oxalate (SNFO) synthesized from biotite-containing minerals. Batch experiments, dynamics and isothermal adsorption fitting results showed that Ag+ removal behaviours were in accordance with the pseudo-first-order kinetic model and Langmuir model, and the maximal Ag+ removal capacity was 223.68 mg/g. Thermodynamic fitting results suggested that Ag + removal by the composite was a spontaneous and endothermic reaction process. XRD and TEM revealed that the reaction products were consisted of SiO2 and nano silver particles, and FTIR and XPS results indicated that the Ag+ removal mechanisms were attributed to the synergistic reduction interaction between ferrous and the anions of oxalate. Meanwhile, the composite possesses high selectivity for Ag+ removal even at low Ag+ concentration. Moreover, the size of nano silver particles could be adjusted by different pH values. All above results demonstrated that the composite was an ideal material for selective recovery of Ag+ from Ag+ containing effluents in the form of nano silver.

Fast and efficient adsorption of palladium from aqueous solution by magnetic metal–organic framework nanocomposite modified with poly(propylene imine) dendrimer

In this study, a magnetic metal-organic framework (MMOF) was synthesized and post-modified with poly(propyleneimine) dendrimer to fabricate a novel functional porous nanocomposite for adsorption and recovery of palladium (Pd(II)) from aqueous solution. The morphological and structural characteristics of the prepared material were identified by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmet-Teller (BET) isotherm, and vibrating sample magnetometer (VSM). The results confirmed the successful synthesis and post-modification of MMOF. Semispherical shape particles (20-50 nm) with appropriate magnetic properties and a high specific surface area of 120 m2/g were obtained. An experimental design approach was performed to show the effect of adsorption conditions on Pd(II) uptake efficiency of the dendrimer-modified magnetic adsorbent. The study showed that the Pd(II) uptake on dendrimer-modified MMOF was well described by the Langmuir isotherm model with the highest uptake capacity of 291 mg/g under optimal condition (adsorbent content of 12.5 mg, Pd ion concentration of 80 ppm, pH = 4, and contact time of 40 min). The adsorption kinetics of Pd(II) ions was suggested to be a pseudo-first-order model. The results revealed a faster adsorption rate and higher adsorption capacity (about 43%) for dendrimer-modified MMOF. Finally, the reusability of the provided adsorbent was evaluated. This work provides a valuable strategy for designing and developing efficient magnetic adsorbents based on MOFs for the adsorption and recovery of precious metals.

Trusted and Transparent Blockchain-enabled E-waste Optimization to Recover Precious Metals with Microwave Heating

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

On the Kinetic Behavior of Recycling Precious Metals (Au, Ag, Pt, and Pd) Through Copper Smelting Process

The recycling and recovery of precious metals from secondary materials, such as waste-printed circuit boards, are an important area of circular economy research due to the limited existing resources and increasing amount of e-waste produced by the rapid development of technology. In this study, the kinetic behavior of precious metals Au, Ag, Pt, and Pd between copper matte and iron-silicate slag was investigated at a typical flash smelting temperature of 1300 °C in both air and argon atmospheres. SEM–EDS, EPMA, and LA-ICP-MS-advanced analysis methods were used for sample characterization. The results indicate that precious metals favor the matte phase over slag, and the deportment to matte occurred swiftly within a short time after the system had reached the experimental temperature. With increasing contact times, the precious metals were distributed increasingly into the sulfide matte. The distribution coefficients, based on experimentally measured element concentrations, followed the order of palladium > platinum > gold > silver in both air and argon, and the matte acted as an efficient collector of these precious metals. The obtained results can be applied to industrial copper matte smelting processes, and they also help in upgrading CFD models to simulate the flash smelting process more precisely.Graphical

Comparative evaluation of dithiocarbamate-modified cellulose and commercial resins for recovery of precious metals from aqueous matrices

Economic and ecological issues motivate the recovery of precious metals (PMs: Ag, Au, Pd, and Pt) from secondary sources. From the viewpoint of eco-friendliness and cost-effectiveness, biomass-based resins are superior to synthetic polymer-based resins for PM recovery. Herein, a detailed comparative study of bio-sorbent dithiocarbamate-modified cellulose (DMC) and synthetic polymer-based commercial resins (Q–10R, Lewatit MonoPlus TP 214, Diaion WA30, and Dowex 1X8) for PM recovery from waste resources was conducted. The performances and applicability of the selected resins were investigated in terms of sorption selectivity, effect of competing anions, sorption isotherms, impact of temperature, and PM extractability from industrial wastes. Although the sorption selectivity toward PMs in acidic solutions by DMC and other resins was comparable, the sorption efficiency of commercial resins was adversely affected by competing anions. The sorption of PMs fitted the Langmuir model for all the studied resins, except Q–10R, which followed the Freundlich model. The maximum sorption capacity of DMC was 2.2–42 times higher than those of the resins. Furthermore, the PM extraction performance of DMC from industrial wastes exceeded that of the commercial resins, with a sorption efficiency ≥99% and a DMC dosage of 5–40 times lower.

Recovery of Biotoxic Silver Nanoparticles Using Living Electroactive Biofilm Protected by Polydopamine

The recovery of precious metals by biosynthesis of metal nanoparticles (NPs) has been a wide concern. The biotoxicity of metal ions and metal NPs is the main bottleneck restricting the bacterial activity and reduction performance. Here, bio-electrochemical systems were used to harvest electroactive biofilms (EABs), where cells were naturally protected by extracellular polymeric substances to keep the activity of the bacteria during this process. The biofilm with polydopamine (PDA) was further encapsulated as additional shield. Silver nanoparticles (AgNPs) were formed on the surface of bacterial cells, while the electroactivity of the biofilm could be fully recovered after Ag+ reduction. The PDA increased the bacterial viability by 90%–105%, confirmed as an effective protection against biotoxic Ag+ and AgNPs. The exposure to Ag+ and AgNPs changed the component and the main function of the microbial community, shifting from bacterial Fe reduction to archaeal methanogenesis. These results demonstrated that the electrochemical acclimation of EABs and encapsulation with PDA were effective in protecting bacteria from being inhibited by toxic metal ions. These approaches have a bright future in the green synthesis of nanomaterials, biotoxic wastewater treatment, and sustainable bio-catalysis.

Highly efficient and selective recovery of Au(III) from aqueous solution by bisthiourea immobilized UiO-66-NH2: Performance and mechanisms

The design and synthesis of efficient adsorbents for recovery of precious metal from secondary resources are of great environmental and economic significance. In present study, an efficient and redox-active adsorbent (UiO-66-BTU) was fabricated by modifying Zr-MOF (Zirconium-based Metal Organic Framework) with bisthiourea for gold recovery in aqueous solution. It is indicated that Au(III) adsorbing onto UiO-66-BTU is an irreversible, favorable chemisorption process conformed to D-R model and pseudo-second-order model. The UiO-66-BTU showed significant adsorption ability (680.20 mg/g at pH 2.0) and high selectivity towards Au(III) in presence of various mixed ions in actual wastewater, which were mainly attributed to the Lewis soft–soft interaction, ion-exchange/electrostatic interactions, and redox reaction between Au(III) and S-containing functional groups. Notably, we demonstrated that the reduction of Au(III) to metallic gold as a dominant recovery mechanism involving the in situ confined nucleation, fusion and growth of AuNPs to branched Au precipitation, with Au(0) accounted for approximately 80% for the recycling products. Furthermore, the UiO-66-BTU membrane achieved similar high adsorption capacity and the membrane surface remains active to efficiently recovered metallic particles with an excellent repeatability at eight cycles of adsorption. The reduced Au particles formed isolated clusters with bigger size and regular hexagonal shape. Consequently, UiO-66-BTU has great potential for gold recycling in industrial practice.

Turning waste into wealth

Turning waste into wealth

Alkyl‐Linked Porphyrin Porous Polymers for Gas Capture and Precious Metal Adsorption

Precious Metal Recovery Adsorbents for selective binding of precious metals are presented in the article number 2000078 by Cafer T. Yavuz and co-workers for a sustainable method of treating electronic waste (e-waste). The new materials are easily made in large scale and due to their low cost, they present a profitable recycling method even without reuse.

Turning Waste into Wealth: Remotely NIR Light-Controlled Precious Metal Recovery by Covalently Functionalized Black Phosphorus.

It is a great challenge to refine precious metals from e-wastes under mild conditions without hazardous reagents. Herein, black phosphorus (BP) was covalently functionalized with poly(N-isopropylacrylamide) (PNIPAM) to obtain thermo/near-infrared (NIR)-responsive BP-P for precious metal recovery. Precious metals (Au, Ag, and Pd) with higher redox potentials than BP-P could be efficiently recovered by reduction-driven enrichment. Taking Au as an example, the recovery process presented fast kinetics (<15 min), excellent selectivity, and high efficiency (≈98 %). Remote operation with NIR light could generate heat by BP, which induced the hydrophilic-to-hydrophobic transition of PNIPAM, allowing the spontaneous gathering, facile collection, and practical recycle of BP-P following Au extraction. Thanks to the unique features of BP-P, not only could high-quality Au nanoparticles (20-30 nm) be economically extracted (cost: $0.731-1.222 g-1 Au nanoparticles; 5-6 orders of magnitude lower than the market price), but also the formed BP-P-Au nanocomposites have potential application in hydrogen evolution reaction.

Hydrometallurgical Recycling Process for Mobile Phone Printed Circuit Boards Using Ozone

Printed circuit boards (PCBs) can be an important source of non-ferrous metals (Al, Sn, Zn, and Ni) and precious metals (Au, Ag, Cu, and Pd). With the continuous increase in demand for metals due to the depletion of ores, recycling of this waste is becoming an attractive alternative. The printed circuits also contain hazardous metals, such as Pb, Hg, As, and Cd. Due to the huge increase in the amount of e-waste, the processing of printed circuit boards for metal recovery and proper handling of hazardous substances has a positive effect on the environment. Pyrometallurgical and hydrometallurgical methods are used for the treatment of this waste. Various oxidizing agents are used in the hydrometallurgical processes, including ozone. PCBs from mobile phones were assessed for the recovery of Cu, Sn, and precious metals. The ground and sieved materials were leached in nitric acid, hydrochloric acid, and sulfuric acid at various process parameters, such as leaching time, leaching agent, and temperature. It was found that the best result was obtained using hydrochloric acid with the addition of ozone at 353 K for a period of 4 h to obtain 68.45 g/dm3 of copper. Preliminary results of electrolysis and cementation are also presented.

Alkyl‐Linked Porphyrin Porous Polymers for Gas Capture and Precious Metal Adsorption

In gas adsorption and metal recovery, inexpensive and covalently bonded porous polymers offer industrial feasibility, despite the challenge of having reactive functionalities while maintaining porosity. Herein, three highly porous covalent organic polymers (COPs), COP‐210, COP‐211, and COP‐212, with porphyrin functionalities that are readily synthesized by a Friedel–Crafts reaction using chlorinated solvents as linkers are reported. The polymers exhibit competitive adsorption capacities for CO2, H2, and CH4. Their porphyrin sites proved particularly effective in precious metal recovery, where COPs exhibit high selectivity toward gold, platinum, palladium, and silver. Analysis reveals that reductive metal capture is prevalent for gold and silver. Platinum is also captured through a combination of reduction and chelation. The gold adsorption capacities are 0.901–1.250 g g−1 with fast adsorption kinetics at low pH. COP‐212 selectively recovers 95.6% of gold from actual electronic waste (e‐waste) collected from junkyards. The results show that the inexpensive and scalable porous porphyrin polymers offer great potential in gas capture, separation, and precious metal recovery.

Simultaneous Recovery of Precious and Heavy Metal Ions from Waste Electrical and Electronic Equipment (WEEE) Using Polymer Films Containing Cyphos IL 101.

In this article, the application of a polymer film containing the ionic liquid Cyphos IL 101 for the simultaneous recovery of precious and heavy metal ions ((Ni(II), Zn(II), Co(II), Cu(II), Sn(II), Pb(II), Ag(I), Pd(II), and Au(III)) from waste electrical and electronic equipment (WEEE) is described. The experiments were performed for solutions containing metal ions released from computer e-waste due to leaching carried out with concentrated nitric(V) acid and aqua regia. It was found that the applied polymer film allows for the efficient recovery of precious metals (98.9% of gold, 79.3% of silver, and 63.6% of palladium). The recovery of non-ferrous metals (Co, Ni, Cu, Zn, Sn, and Pb) was less efficient (25–40%). Moreover, the results of the performed sorption/desorption processes show that the polymer film with Cyphos IL 101 can be successfully used after regeneration to recover metals ions several times.

A method for extracting valuable metals from low nickel matte by non-oxidative leaching with H2SO4

The Rapid development of new energy vehicle industry leads to the sharp demand for nickel, cobalt and precious metals in recent years. Because of the similar chemical properties, these metals often exist in Ni-Cu sulfide ores. Traditional treatment of Ni-Cu sulfide ores includes smelting and converting operation. In the smelting process, nickel, copper, cobalt and precious metals are enriched. And then, the low nickel matte obtained by smelting operation was treated by converting process. However, nearly half of cobalt is transferred into slag phase in converting process, leading to a large loss of cobalt. Aiming to increase the recovery of cobalt and precious metals from Ni-Cu sulfide ores, the low nickel matte is treated directly by hydrometallurgical process instead of converting. Because of the weaker affinity of Fe, Co and Ni for sulfur than Cu, the sulfides of Fe, Co and Ni may be decomposed in sulfuric acid solution, while Cu2S and inert precious metals cannot be leached and still remained in the residue. The hydrogen sulfide emitted in the leaching process of low nickel matte can be used to prepare sulfur by Claus method, which has been widely applied in chemical industry. Based on the above considerations, this work developed a promising method for treating low nickel matte. Atmospheric H2SO4 leaching, oversaturated sulfate solutions leaching and iron removal process were carried out, respectively. The leaching efficiencies of more than 99% of nickel, cobalt and iron were obtained, while copper ion cannot be detected in the solution. This process provides a new pathway for the comprehensive utilization of copper-nickel sulfide ore.

Adsorption of Ag+ ions using hydroxyapatite powder and recovery silver by electrodeposition

AbstractNowadays, waste of electrical and electronic apparatuses generated in huge amount surround the earth and has become a global environmental issue. Electronic waste contains large amounts of metal ions, such as Au, Ag, Cu, Pd, Pb and Cd etc., resulting in a threat to the environment, ecosystems and human health. Therefore, removal of metal ions and recovery of precious metals are extremely necessary. Hydroxyapatite material was reported that they can remove heavy metal ions in water with high efficiency. In this work, Ag+ ions in water were adsorbed using hydroxyapatite (HAp) powder and recovery silver by electrodeposition. The adsorption efficiency of silver was about 61 % at 50 oC after 60 minutes of contact time. The Ag+ adsorption process using HAp powder followed Langmuir adsorption isotherms with the maximum monolayer adsorption capacity of 18.7 mg/g. 60 % of silver can recovery by electrodeposition after 4 hours at the apply current of 10 mA at 50 °C.

EVALUATION OF ELEMENTS DISTRIBUTION IN PRINTED CIRCUIT BOARDS FROM MOBILE PHONES BY MICRO X-RAY FLUORESCENCE

A micro X-ray fluorescence-based approach for the chemical characterization of spent printed circuit boards (SPCB) from mobile phones was applied. More in detail, twelve spent mobile phones were grouped in three clusters depending on brands, models and release year and a study to evaluate the technological evolution of SPCBs over time was carried out. Precious and dangerous elements were investigated and some differences between samples belonging to the different groups were detected. For instance, the distribution of gold on the SPCB layers was more widespread for the older analyzed samples, and a smaller and smaller quantities of bromine and lead were detected in the more recent models in accordance with the Restriction of Hazardous Substances Directive 2002/95/EC. The analysis of SPCB composition can help to correctly manage such a complex waste, maximizing the recovery of base, critical and precious metals and considering the possible presence of harmful elements to be carefully managed. The experimental results showed as, through the proposed approach, it is possible to obtain chemical elements distribution maps of SPCBs surface, thus allowing to define optimal strategies for their further handling (i.e. classification) and processing (i.e. critical/precious metals recovery).