Recovery Of Precious Metals Research Articles

Light‐Promoted Extraction of Precious Metals Using a Porphyrin‐Integrated One‐Dimensional Covalent Organic Framework

AbstractPrecious metals are valuable materials for the chemical industry, but they are scarce and pose a risk of supply disruption. Recycling precious metals from waste is a promising strategy, here we tactfully utilize light irradiation as an environmental‐friendly and energy‐saving adjunctive strategy to promote the reduction of precious metal ions, thereby improving the adsorption capacity and kinetics. A newly light‐sensitive covalent organic framework (PP‐COF) was synthesized to illustrate the effectiveness and feasibility of this light auxiliary strategy. The equilibrium adsorption capacities of PP‐COF with light irradiation towards gold, platinum, and silver ions are 4729, 573, and 519 mg g−1, which are 3.3, 1.9, and 1.2 times the adsorption capacities under dark condition. Significantly, a filtration column with PP‐COF can recover more than 99.8 % of the gold ions in the simulated e‐waste leachates with light irradiation, and 1 gram of PP‐COF can recover gold from up to 0.15 tonne of e‐waste leachates. Interestingly, the captured precious metals by PP‐COF with light irradiation mainly exist in the micron‐sized particles, which can be easily separated by extraction. We believe this work can contribute to precious metal recovery and circular economy for recycling resources.

Light-Promoted Extraction of Precious Metals Using a Porphyrin-Integrated One-Dimensional Covalent Organic Framework.

Precious metals are valuable materials for the chemical industry, but they are scarce and pose a risk of supply disruption. Recycling precious metals from waste is a promising strategy, here we tactfully utilize light irradiation as an environmental-friendly and energy-saving adjunctive strategy to promote the reduction of precious metal ions, thereby improving the adsorption capacity and kinetics. A newly light-sensitive covalent organic framework (PP-COF) was synthesized to illustrate the effectiveness and feasibility of this light auxiliary strategy. The equilibrium adsorption capacities of PP-COF with light irradiation towards gold, platinum, and silver ions are 4729, 573, and 519 mg g-1, which are 3.3, 1.9, and 1.2 times the adsorption capacities under dark condition. Significantly, a filtration column with PP-COF can recover more than 99.8 % of the gold ions in the simulated e-waste leachates with light irradiation, and 1 gram of PP-COF can recover gold from up to 0.15 tonne of e-waste leachates. Interestingly, the captured precious metals by PP-COF with light irradiation mainly exist in the micron-sized particles, which can be easily separated by extraction. We believe this work can contribute to precious metal recovery and circular economy for recycling resources.

A new strategy toward synthesis of novel bifunctional N- and S-bearing sorbent for platinum(IV) removal from aqueous solutions and acidic leaching residue of Pt/Al2O3 catalyst

Strong incentive politics have been elaborated for promoting the recovery of precious metals from secondary resources. Solid leaching generates acidic effluents that can be pre-treated using precipitation steps for partial separation before applying sorption for metal recovery from mild acidic solutions. For this purpose, a new sorbent was designed bearing numerous N- and S-bearing reactive groups with good affinity for platinum (as chloroanionic species). Thiazole precursors were first reacted before being grafted (by free radical reaction) with triallyl cyanurate (to form CTTR sorbent). The material was characterized by a series of analytical tools (SEM, BET, FTIR, XPS, TGA, elemental analysis, and titration). The effect of pH combined with FTIR and XPS spectroscopy analyses allowed identifying the mechanisms involved in metal binding: (a) electrostatic attraction of chloroplatinate anions with protonated amine groups (especially in acidic conditions), (b) while at moderate acidic pH metal sorption proceeds through ligand exchange and chelation onto N-based and S-based groups. Optimum sorption was found at pH close to 4 (near pHpzc value). Under selected experimental conditions, the equilibrium was reached in 25–35 min. The pseudo-first order rate equation fitted well experimental profile (though the resistance to intraparticle diffusion contributes to the kinetic control). The maximum sorption capacity at room temperature reached up to 1.58 mmol Pt g−1 (at pH 4). The sorption isotherm was successfully fitted by the Temkin equation. The sorption is spontaneous and exothermic (with reduction in maximum sorption capacity reaching up to 25 %, when temperature increases to 50 °C). Optimum platinum desorption was obtained with 0.3 M HCl solution (with solid/liquid ratio 1.67 g L−1) for complete desorption and enrichment factor close to 4.6. Complete desorption was maintained over 5 cycles, while the sorption efficiency decreased by less than 3.5 % at the fifth cycle. The sorbent showed remarkable stability for PGMs (Pd(II) in addition to Pt(IV)) against alkali-earth elements or base metals (from equimolar synthetic solutions); the selectivity is driven by the preference of the reactive groups (soft base and intermediary base) for soft PGM metals against hard and borderline metal ions; this selectivity is also affected by metal speciation (formation of chloro-anionic species). The valorization of platinum from non-compliant Pt/Al2O3 catalyst was investigated after leaching with aqua regia. Platinum was precipitated from the leachate with ammonium chloride. In a second step, aluminum was removed by precipitation at pH 5. The residual solution was then treated by adsorption on CTTR: optimum separation between Pt and Al was achieved at pH ≈ 3.

Unveiling the depression role of quercetin in selective flotation separation of chalcopyrite from pyrite at low alkalinity

In flotation, the separation and concentration of copper-iron sulfide ores are usually carried out at high alkalinity to depress pyrite, and plenty of lime could block the flotation pipeline and affect the recovery of precious metals during practical operation. Herein, the current research hotspot to achieve the separation of copper-iron sulfide ores under low alkalinity. This paper presented an eco-friendly reagent, quercetin, for the flotation separation of chalcopyrite and pyrite, and investigated the effect on the flotation performance of the two minerals. The interaction mechanism of quercetin with mineral was demonstrated using zeta potential measurements, atomic force microscopy (AFM), surface adsorption measurements, Fourier-transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). The flotation results showed that the depressive effect of quercetin on pyrite was more pronounced in comparison to its impact on chalcopyrite at pH 8.0, and the chalcopyrite recovery reached 90 %, whereas that of pyrite was under 10 %. The surface analysis revealed quercetin chemisorption on the mineral surface through interaction with metal sites. In the presence of quercetin, the quercetin significantly diminished the ability of pyrite to adsorb xanthan but had minor effects on the adsorption of chalcopyrite.

Recovery of precious metals from aqua regia leachate of e-wastes using dithiocarbamate-modified cellulose and development of a novel kinetic model

The escalating demand and dwindling natural supplies of precious metals (PMs) necessitate innovative hydrometallurgical recovery approaches with rapid kinetics and reduced environmental impact. The current study investigated the sorption and recovery of PMs from electronic waste (e-waste) utilizing dithiocarbamate-modified cellulose (DMC) and its proline derivative with epoxy cross-linkage (DMC-Pro-Epo-6) in aqua regia (AR). The effects of various sorption parameters, such as sorbent dose in feed, HCl:HNO3 ratio, AR dilution times, etc., on PM recovery were explored. Equilibrium for AuIII and PtIV sorption by DMC and DMC-Pro-Epo6 was reached in less than an hour, which is significantly faster than most reported sorbents. The maximum sorption capacities in AR settings, calculated using the Langmuir equation, were 348.0 mg g−1 for AuIII and 34.7 mg g−1 for PtIV for DMC, while DMC-Pro-Epo6 achieved 350.3 mg g−1 for AuIII and 31.1 mg g−1 for PtIV. These capacities, particularly for the higher sorption capacity of AuIII by DMCs, are attributed to the relativistic effects of gold, soft–soft interactions, and strong sulfur binding. FT-IR, FE-SEM, and EDX analyses elucidated the chelation bonding and mechanisms involved in PM sorption onto DMCs. By utilizing AR-DMC integrated techniques, step-by-step protocols were established for Au recovery from diverse e-waste sources, such as smartphones and smart chip cards. The study also highlighted the importance of chemical pre-concentration of e-waste to remove base metals, facilitating efficient PM recovery. Finally, a key innovation of this work is introducing a new pseudo-mix order fractional model, based on the preference of active sites with fractional assumptions, which more accurately correlates the sorption kinetics observed in complex systems.

Biotechnological Approaches for Metal Recovery from Electronic Wastes.

The disposal of electronic waste (EW) in open landfills has caused several toxic environmental effects. The harmful metallic components released in the environment due to deposition of EW act as hazards for living systems. EW management has been widely studied in recent days across the world. Though, several processes are implemented in extraction, recycling and recovery of heavy metals from the EW, most of them are not effective in recovering the precious metals. Various chemical processes are executed for efficient extraction of precious metals from e-wastes. Though the techniques are easy to process and rapid, however, the chemical leaching also has detrimental environmental consequences. Biological approaches, on the other hand, solves the purpose for efficient and environmentally friendly recovery of precious metals. Thus, both resource recovery as well as remediation can be targeted simultaneously. Biotechnological methods offer sustainable and efficient solutions for metal recovery from electronic wastes, presenting a viable alternative to traditional methods. Continued advancements in this field hold significant promise for addressing the growing e-waste challenge.

Boosting Reactive Oxygen Species Generation via Contact‐Electro‐Catalysis with FeIII‐Initiated Self‐cycled Fenton System

AbstractContact Electro‐Catalysis (CEC) using commercial dielectric materials in contact‐separation cycles with water can trigger interfacial electron transfer and induce the generation of reactive oxygen species (ROS). However, the inherent hydrophobicity of commercial dielectric materials limits the effective reaction sites, and the generated ROS inevitably undergo self‐combination to form hydrogen peroxide (H2O2). In typical CEC systems, H2O2 does not further decompose into ROS, leading to suboptimal reaction rates. Addressing the generation and activation of H2O2 is therefore crucial for advancing CEC. Here, we synthesized a catalyst by loading the dielectric material polytetrafluoroethylene (PTFE) onto ZSM‐5 (PTFE/ZSM‐5, PZ for short), achieving uniform dispersion of the catalyst in water for the first time. The introduction of an FeIII‐initiated self‐cycling Fenton system (SF‐CEC), with the synergistic effects of O2 activation and FeIII‐activated H2O2, further enhanced ROS generation. In the FeIII‐initiated SF‐CEC system, the synergistic effects of ROS and protonated azo dyes enabled nearly 99 % degradation of azo dyes within 10 minutes, a sixfold improvement compared to the CEC system. This represents the fastest degradation rate of methyl orange dye induced by ultrasound to date. Without extra oxidants, this system enabled stable dissolution of precious metals in weakly acidic solutions at room temperature, achieving 80 % gold dissolution within 2 hours, 2.5 times faster than similar CEC systems. This study also corrects the unfavorable perception of CEC applications under acidic conditions, providing new insights for the fields of dye degradation and precious metal recovery.

Anion Selectivities in Zwitterion Grafted Nanopores: Effect of Zwitterion Architecture.

The separation of ions of similar charge is a crucial challenge in many applications, from water treatment to precious metal recovery. Membranes with cross-linked zwitterionic amphiphilic copolymer (ZAC-X) selective layers, which feature self-assembled, zwitterion-lined nanodomains for permeation, offer unique permselectivity between monovalent anions (e.g., Cl-/F-). This has motivated studies on the mechanisms of transport and selectivity in this family of materials. In this study, we conducted molecular dynamics simulations of aqueous salt solutions within zwitterion-functionalized nanopores to elucidate the influence of dipole orientation of the ZI ligands on anion diffusivities, partitioning, and permeabilities. Our model compares systems with contrasting ZI organization: surface-cation-anion (S-ZI+-ZI-, Motif A) and surface-anion-cation (S-ZI--ZI+, Motif B). Our results reveal that Motif A exhibits less pronounced ion pairing due to a spatial separation in the radial profiles of cations and anions. Motif B demonstrates prominent ion pairing for smaller anions owing to their overlap with cation distributions. Further, our potential of mean force profiles reveals that anion partitioning increases with anion size in both ligand motifs, whereas Motif B exhibits significantly higher partitioning selectivity toward larger anions compared to Motif A. Our results for ion diffusivities show that the self-diffusivities of both anions and cations are lower for Motif B compared to Motif A. Such trends in anion partitioning and diffusivities can be explained by differences in the interactions and steric hindrance experienced by the anionic species in Motifs A and B. Finally, our results for anion permselectivity, obtained by combining partitioning and diffusivity, indicate that partitioning trends dominate over diffusivity trends. Consequently, anion permeability increases with anion size, and ligand Motif B yields much higher permselectivity toward larger anions compared to ligand Motif A.

Flash Joule heating technology in two-dimensional materials and beyond

In recent decades, ongoing exploration on material synthesis, coupled with advancements in science and technology, has led to the invention and application of numerous specialized devices. To fulfill the demand for high-performance materials in modern society, flash Joule heating (FJH) has been invented and applied in this context to achieve high efficiency, low cost, and environmental sustainability in material synthesis. This technology offers fast heating and cooling rates, high energy utilization, and promising results in material synthesis. FJH finds its applications in synthesizing two-dimensional materials, recycling battery metals, graphite, cathode, and recovery of precious metals from mines. This review presents an overview of FJH technology and its applications and prospects.

Highly Selective Recovery of Gold by In Situ Magnetic Field-Assisted Fe/Co-MOF@PDA/NdFeB Double Network Gel.

There are enormous economic benefits to conveniently increasing the selective recovery capacity of gold. Fe/Co-MOF@PDA/NdFeB double-network organogel (Fe/Co-MOF@PDA NH) is synthesized by aggregation assembly strategy. The package of PDA provides a large number of nitrogen-containing functional groups that can serve as adsorption sites for gold ions, resulting in a 21.8% increase in the ability of the material to recover gold. Fe/Co-MOF@PDA NH possesses high gold recovery capacity (1478.87mg g-1) and excellent gold selectivity (Kd = 5.71mL g-1). With the assistance of an in situ magnetic field, the gold recovery capacity of Fe/Co-MOF@PDA NH is increased from 1217.93 to 1478.87mg g-1, and the recovery rate increased by 24.7%. The above excellent performance is attributed to the efficient reduction of gold by FDC/FC+, Co2+/Co3+ double reducing couple, and the optimization of the reduction reaction by the magnetic field. After the samples are calcined, high-purity gold (95.6%, 22K gold) is recovered by magnetic separation. This study proposes a forward-looking in situ energy field-assisted strategy to enhance precious metal recovery, which has a guiding role in the development of low-carbon industries.

Leaching of Neodymium From Hard Disk Drive Magnet Waste Using Citric Acid‐ Design of Experiments and Optimization

AbstractNeodymium magnet waste recycling and precious metal recovery have drawn a lot of researchers’ attention because of their vital role in contemporary technology. In this work, the potential of citric acid for the leaching of neodymium from hard disk drive waste magnets has been examined using statistical approaches like full factorial design(FFD) and central composite design (CCD).The variables have been screened and conditions are optimized to obtain higher leaching. The polynomial quadratic Model proves effective to predict optimized conditions for neodymium leaching. Leachant concentration and temperature were screened as the most effective factors. Optimization conditions for the leaching process were achieved through central composite design, revealing that 2 mol/L citric acid and a temperature of 333 K provide the ideal conditions for the complete dissolution of neodymium. This extensive study contributes to sustainable materials management and resource conservation by illuminating the effective recovery of important metals from neodymium magnets.

Boosting Reactive Oxygen Species Generation via Contact-Electro-Catalysis with FeIII-Initiated Self-cycled Fenton System.

Contact Electro-Catalysis (CEC) using commercial dielectric materials in contact-separation cycles with water can trigger interfacial electron transfer and induce the generation of reactive oxygen species (ROS). However, the inherent hydrophobicity of commercial dielectric materials limits the effective reaction sites, and the generated ROS inevitably undergo self-combination to form hydrogen peroxide (H2O2). In typical CEC systems, H2O2 does not further decompose into ROS, leading to suboptimal reaction rates. Addressing the generation and activation of H2O2 is therefore crucial for advancing CEC. Here, we synthesized a catalyst by loading the dielectric material polytetrafluoroethylene (PTFE) onto ZSM-5 (PTFE/ZSM-5, PZ for short), achieving uniform dispersion of the catalyst in water for the first time. The introduction of an FeIII-initiated self-cycling Fenton system (SF-CEC), with the synergistic effects of O2 activation and FeIII-activated H2O2, further enhanced ROS generation. In the FeIII-initiated SF-CEC system, the synergistic effects of ROS and protonated azo dyes enabled nearly 99 % degradation of azo dyes within 10 minutes, a sixfold improvement compared to the CEC system. This represents the fastest degradation rate of methyl orange dye induced by ultrasound to date. Without extra oxidants, this system enabled stable dissolution of precious metals in weakly acidic solutions at room temperature, achieving 80 % gold dissolution within 2 hours, 2.5 times faster than similar CEC systems. This study also corrects the unfavorable perception of CEC applications under acidic conditions, providing new insights for the fields of dye degradation and precious metal recovery.

Enhancing recovery of gold(III) from hydrochloric acid solutions using gemini surfactant microemulsions: The effect of spacer group

The recovery of precious metals from waste has garnered significant attention owing to their non-renewable nature and essential role in the burgeoning information industry. However, enhancing the extraction efficiency of microemulsions remains a significant challenge. In this study, three water-in-oil microemulsions were formulated using gemini surfactants with different spacers (14-OH-14, 14-SO4-14, and 14-3-14) as emulsifiers, supplemented with n-butanol as a cosurfactant, n-heptane as the oil phase, and NaCl aqueous solution as the internal aqueous phase. These microemulsions were employed for the extraction of gold(III) from hydrochloric acid solutions. The results illustrate that all three microemulsions effectively extracted gold(III) through a spontaneous, exothermic, enthalpy-driven anion-exchange mechanism, achieving notable extraction efficiency. In contrast to 14-3-14, incorporating –OH into the spacer significantly augments the positive electrostatic potential through the cationization of –OH in an HCl solution, resulting in a higher binding constant (2.43) and thereby improving the extraction efficiency. However, the presence of −SO4 diminishes the positive electrostatic potential through partial neutralization, resulting in a lower binding constant (1.17), which is detrimental to the extraction process. Response surface optimization revealed that concentrations of C(14-OH-14) and V(1-butanol) significantly influence extraction efficiency and exhibit pronounced interaction. At optimal conditions (C(14-OH-14) = 0.09 mol·L−1, V(1-butanol) = 47.41 %, R=20, and C(NaCl) = 1.57 mol·L−1), over 95.54 % of gold(III) can be extracted from actual e-waste solutions. This study offers an alternative approach for designing or selecting surfactants in microemulsion-based extraction of gold(III) from e-waste.

A Two-Step Leaching Process Using Thiourea for the Recovery of Precious Metals from Waste Printed Circuit Boards

The development of efficient recovery methods for waste printed circuit boards (WPCBs) not only tackles the environmental risks of disposal but also promotes the conservation of resources within the electronics industry. This study proposes a two-step leaching approach for recovering metals from WPCBs. Initially, transition metals are leached using nitric acid, followed by the recovery of precious metals with thiourea in the second stage. In the first stage, dissolution rates exceeding 90 wt% were achieved for transition metals, including Cu, Fe, Ni, Pb, and Sn. In this stage, the dissolution of precious metals (i.e., Au and Pd) was insignificant. In the second stage, the effect of four parameters was investigated, including the impact of temperature, concentrations of ferric ions, sulfuric media, and thiourea on the recovery of Au and Pd. Precise control over sulfate concentration played a vital role in achieving maximum Au recovery. The optimal acid concentration was 0.2 M, resulting in a recovery rate of ~50 wt%. Ferric ion concentration positively affects Au recovery, whereas, in extracting Pd, optimal conditions imposed the absence of ferric ions. Thiourea concentration positively impacted Au and Pd recovery rates, peaking at 49 wt% for Au at 1 M and 44 wt% for Pd at 1.5 M. Prolonged leaching resulted in declining Au recovery rates, indicating a decrease in reagent concentration. Temperature variation yielded similar outcomes, with 50 °C resulting in peak recovery rates of 53 wt% for Au and 54 wt% for Pd. Metal dissolution kinetics during leaching were analyzed using pseudo-first-order and pseudo-second-order models. The second-order model proved suitable for transition metals in the first stage, while only for Au and Pd in the second stage (with R2 = 0.99).

Elemental Analysis of Discarded Printed Circuit Boards using Different Analytical Techniques and Recovery of Silver

The rapid advancement of technology and the demands of our consumer-driven society significantly contribute to the growing volume of e-waste generated annually. This category includes all discarded components and products from electronic and electrical equipment that are not intended for reuse. Among these, Printed Circuit Boards (PCBs) are essential elements in all electrical and electronic devices and are difficult to reuse or recycle considering the complex structure of PCB. This study focuses on analyzing PCBs for their elemental content and the recovery of precious metal, silver. Elemental concentration was analysed using Neutron Activation Analysis (NAA), nano-colorimetry, potentiometry and Atomic Absorption Spectrometry(AAS) techniques .The findings reveal that Non -metallic part in analysed PCBs is about 80-84 % while among metallic concentrations, copper concentration was found to be highest (42.88-90.80 mg/g) and that of lead lowest (0.26-0.75mg/g).The total amount of silver in three PCB samples is approximately 2 mg/g, with a recovery rate was about 66%. However, the fourth sample contains a lower total amount of silver, with a recovery rate of 52.79%

Hydrogen bonding-based deep eutectic solvents for choline chloride/sulfamide and its application in the recycling of precious metals

The depletion of natural resources for precious metals is occurring as the economy expands, and conventional recovery techniques often involve the use of hazardous reagents. We have successfully developed a novel deep eutectic solvent, choline chloride/sulfamide, which exhibits exceptional efficiency in forming a highly effective deep eutectic dissolution reagent with dibromohydantoin for the efficient recovery of precious metals. The acidity provided by sulfamide and the oxygen negative ions generated by choline chloride jointly initiate an attack on the N-Br bond in dibromohydantoin. Bromine radicals and Br2 together promote the oxidation of precious metals. The Cl- and Br- ions form complexes to generate AuCl2Br2-, which effectively stabilizes the Au3+ species in solution. Under optimal reaction conditions, Au0 can be completely dissolved within 25 minutes. The average rate of gold dissolution in this DES dissolution reagent was 10,235.9 mg Au/(h·mol DBD), which is more than 200 times the average rate of gold dissolution in conventional cyanide. Moreover, DES dissolution reagent allows for recycling of the precious metal up to 6 times with dissolution rates consistently above 95 %. By adding it into an oxalic acid solution, the gold complex can be reduced to Au0 to achieve recycling of precious metals.

Mass balance and economic study of a treatment chain for rare earths, base metals and precious metals recovery from used smartphones

In the present study, a comprehensive hydrometallurgical process was developed for the recovery of several types of metals from used cell phone printed circuit board assemblies. The overall process is divided into four stages of selective leaching of rare earth elements (REE), copper, nickel, silver and finally gold. After solubilization, the metals were purified using precipitation, solvent extraction, electrodeposition, and cementation techniques. Laboratory pilot-scale tests of the complete smart phone printed circuit board processing line showed REE, copper, nickel, silver, and gold recovery efficiencies of 78.0 %, 98.8 %, 81.8 %, 100 % and 96.1 %, respectively. The purity of the products obtained is evaluated at 94.8 % for rare earth oxides (70.0 % Nd2O3, 18.5 % Pr2O3, 2.8 % Dy2O3 and 2.4 % Sm2O3), 99.8 % for elemental copper, 94.3 % for nickel oxide, 93.8 % for silver and 89.3 % for gold. A scenario involving the installation of a plant processing 1 t/h of waste was evaluated using SuperPro Designer software. For a total investment of $53.22 million and an operating cost of $18.23 million per year, the main revenue is $65.77 million per year, with a return on investment of 91.6 % and a payback period of 1.1 years.

Application of ion-exchange dynamic conditions in the recovery of precious metals from refining waste

The objective of this study was to assess the potential for recovering precious metals from technological solutions using an ion-exchange dynamic method. Precious metals like platinum, palladium, rhodium, and gold are essential materials in various industries such as: automotive, electronics, pharmaceuticals, and jewellery. Due to their limited occurrence in primary sources, there is a growing trend in the market to extract these metals from secondary sources. The research involved conducting sorption and elution tests under different parameters to investigate their impact on the process in dynamic conditions. Additionally, an attempt was made to calculate the operational and total capacity of the resins, which has not been done previously for industrial solutions. The results showed that using Puromet MTS9200, Puromet MTS9850, and Lewatit MonoPlus MP600 resins, the sorption process could be effectively carried out in dynamic conditions with a contact time of 5 min between the technological solution and the resin bed. For optimal elution, the contact time between the eluent solution and the bed should range between 10 and 30 min. To improve rhodium sorption efficiency, it was found that neutralizing the technological solution to a pH of approximately 7 and using Lewatit MonoPlus MP600 resin could be beneficial.

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery.

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Enhanced recovery of low-grade copper ore and associated precious metals from iron tailings: A case study in China

In the processing of copper and precious metal recovery in a mine in Chengde, Hebei Province, the decrease in copper mineral content and finer grain size distribution of the selected ores have caused challenges in the existing milling process. This has led to difficulties in achieving significant dissociation of chalcopyrite, resulting in decreased separation efficiency of copper and associated precious metals. Particularly, there is a notable loss of precious metals in the flotation tailings. Using BPMA and other detection equipment, the occurrence state, distribution patterns, and liberation degree of copper and associated precious metals in iron tailings were investigated. Subsequent flotation experiments examined the impact of grinding regimes on mineral liberation and reagent regimes on mineral enrichment. Subsequently, flotation experiments were conducted to examine the influence of grinding regimes on mineral liberation and reagent regimes on mineral enrichment. The research findings revealed that copper and precious metal contents in iron tailings are extremely low and finely disseminated within gangue minerals, posing challenges for liberation. Under the optimal conditions determined from flotation experiments, a laboratory closed-circuit process consisting of one rougher, one scavenger, and two cleaner stages yielded a copper concentrate with a grade of 11.33 %, a recovery efficiency of 66.95 %, and containing 9.42 g/t gold, 52.72 g/t silver, 2.78 g/t platinum, and 8.46 g/t palladium. The SEM-EDS analysis further emphasizes the necessity to tailor grinding and flotation processes to optimize the liberation and subsequent recovery of these valuable minerals, avoiding excessive grinding of gangue minerals which could negatively impact flotation performance.