An ionic covalent organic framework showing super-performance for recovery of gold from e-waste

Preparation of ionic covalent organic frameworks and its efficient recovery of gold from e-waste

Efficient gold recovery from electronic waste by thioether functionalized thiacalix[4]arene

Self-floating COF/chitosan aerogel for light-induced enhanced gold recovery

Efficient and selective gold recovery using a quaternary phosphonium functionalized chitosan based self-standing electrode

Refractory gold and silver ores present significant challenges because precious metals are encapsulated within sulfide matrices, severely limiting extraction by conventional cyanidation. In this study, a pyritic concentrate from the Bacis Mine (Durango, Mexico) was characterized and subjected to two oxidative pretreatments—roasting and alkaline pressure oxidation—before cyanidation. X-ray diffraction confirmed pyrite to be the dominant phase, with quartz and minor carbonates contributing to the material’s refractory character. Roasting at 550 °C achieved gold and silver extraction of 80% and 70%, respectively, which improved to 89% Au and 74% Ag with the addition of hydrogen peroxide. In contrast, alkaline pressure oxidation at 150 °C and 1 MPa O2 yielded the highest extraction of 92% for Au and 76% for Ag at 1 h. Thermodynamic analysis using the Fe–S Pourbaix diagram at 80 °C supported these experimental results, showing the destabilization of FeS2 under oxidizing and moderately alkaline conditions. Overall, this study demonstrates that alkaline pressure oxidation is a technically efficient and environmentally favorable pretreatment for refractory gold ores.

Electronic waste contains gold at concentrations far exceeding natural ores, yet efficient and selective recovery remains challenging. Here, we present a covalent organic framework (COF), tetra-(4-aminophenyl)-porphyrin–4,4′-(thiazolo[5,4-d]thiazol-2,5-diyl)bis(2,5-dimethoxybenzaldehyde)–COF (TAPP-TZ-OMe-COF), in which thiazole and methoxy groups create abundant AuCl4− binding sites and modulate the electronic structure via donor–acceptor interactions and p–π conjugation. These features narrow the band gap, enhance charge separation, and accelerate photogenerated electron transfer, enabling synergistic adsorption and visible-light reduction of Au(III) to Au(0). TAPP-TZ-OMe-COF delivers a gold recovery capacity of 4,109 mg g−1 and achieves 99.9% recovery from computer processing unit-board leachate with >105-fold selectivity and excellent cycling stability. This molecular-engineering approach offers a generalizable blueprint for integrating adsorption and photocatalysis in COFs, advancing the recovery of gold from complex waste streams for sustainable resource reclamation.

Precious metal recovery has become increasingly critical due to resource scarcity, while conventional extraction methods often suffer from low efficiency and pollution problem. Here, this work proposes an efficient and environmentally friendly catalytic strategy based on the integration of contact-electro-catalysis (CEC) and photocatalysis. The composite microsphere catalyst is fabricated by using low temperature co-firing TiO2/PTFE particles, which have an average diameter of ≈10 µm and expose both TiO2 and PTFE active sites on its surface, enabling dual CEC-photocatalytic synergy reactions. Compared to pristine TiO2 catalyst with similar weight, this composite microsphere catalyst exhibits a tenfold enhancement in gold extraction efficiency from electronic waste. This high-performance leaching system operates under mild conditions, alleviating the need for traditional strong oxidants and offering potential for industrial application. Density functional theory (DFT) calculations further reveal that charge transfer from H2O to PTFE and subsequently into TiO2, with favorable energy band alignment between PTFE and TiO2 ensuring efficient carrier hopping and enhanced photocatalytic activity. This composite catalytic strategy based on organic-inorganic microsphere catalysts may be extended to areas like wastewater treatment, organic synthesis, and industrial waste valorization.

This study investigated the flotation performance of W8, a blended xanthate collector containing ethyl, butyl, propyl, and amyl xanthates, combined with ammonium dibutyl dithiophosphate (ADD) for treating low-grade arsenopyrite-type gold ore from Golmud, Qinghai. Real ore flotation tests demonstrated the superior efficacy of the W8 + ADD system, achieving 84.06% gold recovery with 0.34 g/t tailings, outperforming conventional sodium amyl xanthate (SAX) + ADD and sodium propyl xanthate (SPX) + ADD systems. Systematic studies on pure arsenopyrite revealed a significant synergistic effect in the mixed SPX-SAX system (1:4 ratio), representative of W8 composition. At pH 9, the mixed collector achieved 73.5% recovery, substantially higher than individual SPX (37.5%) or SAX (45.8%). This enhanced performance was attributed to improved surface hydrophobicity (contact angle 47.68° vs. 36.92° for SAX), greater adsorption density (4.97 × 10−7 mol/g under depressant conditions), and extensive formation of molecular aggregates observed via AFM, which increased surface roughness to 28.95 nm. Flotation kinetics further confirmed the advantage of W8 + ADD, which reached 72.1% cumulative recovery in 420 s, exceeding both mixed SPX/SAX (69.5%) and single SAX (65.5%) systems. The synergistic interaction among different xanthate components in W8 enables efficient recovery of gold from this refractory ore.

High alkalinity facilitates copper–sulfur flotation separation but also leads to issues such as high reagent consumption, pipeline scaling, and gold loss in tailings. The ore from a copper mine in Serbia contains 2.86% copper, 1.64 g/t gold, and 20.39% sulfur, with copper occurring mainly in covellite and enargite. To achieve efficient separation and recovery of copper–sulfur, a systematic study was conducted using micro-flotation, Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle analysis to investigate the inhibition and activation patterns of pyrite under low and high alkalinity conditions. The results indicate that the combined use of hydrogen peroxide and lime as inhibitor enables efficient separation of pyrite and covellite under low-alkalinity conditions. This effect is attributed to its ability to enhance oxidation of the pyrite surface, which generates more hydrophilic substances. Under low-alkalinity conditions (slurry pH = 10) regulated with hydrogen peroxide and lime in a covellite flotation cycle, and under acidic conditions (slurry pH = 6) in the pyrite flotation cycle, satisfactory results are obtained in both flotation cycles in comparison with industrial data. The copper flotation index was similar, but pyrite and gold recovery increased by 2.3% and ~4%, respectively, over those using lime alone. This process reduced the activator dosage required for pyrite activation substantially, while improving gold recovery. Results demonstrate an efficient method for copper–sulfur separation and recovery, providing theoretical guidance or industrial production processes.

Precious metal processing includes both mechanical and hydrometallurgical enrichment methods. The risk of environmental contamination is high in hydrometallurgical processing, as it mainly uses toxic chemicals. The environmentally friendly gravi ty concentration method is mainly used in the initial stage of combined technology. For example, the com bined enrichment technology scheme can be visualized as follows: gravity -flotation -metallurgy, gravity -flotation -magnetic separation, gravity -flotation. In preciou s metals processing, flotation enrichment is often used , where traditional approaches (use of a single reagent as a collector, sample grinding without classification) do not always ensure the maximum recovery of gold and silver in the concentrate, whic h is replaced in production by the environmentally harmful h ydrometallurgical method. The paper presents the results of obtaining high quality concentrate from poor ores of precious metals by flotation enrichment method. In order to obtain a high -quality flota tion concentrate (to avoid sample crushing), the initial sample was crushed into separate size classes , as it is well known that the correct calculation of crushing and grinding has a double effect in the mineral enrichment process : 1. m ore than 50% of the economic costs in the enrichment process are crushing/grinding costs; 2. w hen crushing the sample, silt is formed, which complicates the enrichment process. A large amount of silt enters the concentrate, which adversely affects the performance of the enrichment process. Close sizing grinding has reduced the number of multiple operations for concentrate clearing. The effect of simultaneous use of two collector reagents (reagents with short and long hydrocarbon numbers) in the flotation pr ocess to obtain high -quality concentrate was evaluated. The attachment of the collector mineral to the surface is determined by its hydrocarbon number. The longer the hydrocarbon ra dical in the reagent, the greater the stability of attachment to the mineral. The disadvantage of such reagents is that it takes a relatively longer time to make the mineral hydrophobic than reagents with a weaker effect. The effectiveness of using two collectors simultaneously is explained as follows: the reagent w ith a short hy drocarbon number instantly imparted hydrophobicity to the target minerals, while the reagent with a long hydrocarbon number prolonged this ability. As a result, the target minerals were inco rporated into the concentrate and the loss of useful components in the tailings was reduced. A single clearing of the concentrate resulted in a high -quality concentrate of precious metals with a yield of 1.7%, a gold content of 39.33 g/t, and a silver content of 52.88 g/t.

A tailored nitrogen-rich polymer for highly efficient and selective capture of gold from waste printed circuit boards.

Enzymatic bio-oxidation technology as novel approach for pretreatment of refractory sulfide ores.

Review of gold-ligand interactions: Implications for metallurgical processes and nanoparticle synthesis.

Utilization of industrial by-products as nutrients for gold bioleaching from waste random access memory.

The small-scale gold mining sector (SSGM) in Zimbabwe is a significant contributor to the country’s economy, at 12% of total exports. Although official output figures are rising, the general belief is that most of the small-scale gold production is unaccounted for, as it only reports gold produced from amalgamation and carbon adsorption, which the Government monitors through Statutory Instruments. However, gold produced from unregulated methods often ends up in illicit gold trading, with Zinc cementation being one of the unregulated gold recovery methods that small-scale gold miners rampantly abuse due to its ease of filtration and low cost. Governing legislation or Statutory Instruments for control of Zinc cementation are non-existent, creating easy loopholes for abuse and strong links to illicit financial flows. This study investigates the feasibility of regularising Zinc cementation as a gold recovery method for small-scale operations in Zimbabwe, ensuring effective monitoring and surveillance. Optimum parameters for Zinc cementation were determined experimentally. The determination of optimum parameters for Zinc cementation was done using a 2<sup>3</sup> fractional factorial design and gold deportment analysis was conducted using samples from a small-scale gold mine located on the early Precambrian, Bulawayan, andesitic and dacitic meta-volcanic geological formation in Zimbabwe’s Matabeleland mining region. The influence of free cyanide concentration, dissolved oxygen concentration and pH on gold recovery was evaluated. Experimental work showed the feasibility of using Zinc Cementation as a possible recovery route for gold in SSGM with optimum parameters of: - pH value 11.5, free cyanide concentration 0.05g/L and dissolved oxygen concentration of 0.5ppm. The analysis showed that pH and Oxygen concentration increase gold recovery by a factor of 40%, with pH having the most significant effect on gold recovery. The study concludes that Zinc Cementation for small-scale hydrometallurgical gold extraction is an effective recovery method and should be regularised by the Government through a Statutory Instrument for easier monitoring and surveillance. Further studies on various ores from different provinces are recommended to incorporate diverse mineralogical differences into the design. Additionally, setting up a pilot plant to refine the metallurgical plant requirements for controlling zinc cementation is suggested.

Enzymatic Biooxidation Technology (EnBiTe): Process Optimization for Recovery of Gold from Refractory Sulfide Ores in Cold Conditions

The escalating demand for precious metals in high-tech industries and jewelry, combined with the depletion of their reserves, underscores the need for efficient methods of gold recovery from industrial effluents. An interpolymer system comprising industrial ion exchangers KU-2-8 (in H+ form) and AV-17-8 (in OH− form) demonstrated strong selective sorption capacity for Au(I) ions from a simulated Au(I)/Fe(II) mixed solution. The optimal KU-2-8:AV-17-8 (3:3) system achieved a sorption efficiency of 97.0% for Au(I) ions after 48 h with a desorption efficiency of 98.0% using a thiourea/sulfuric acid solution. The distribution coefficient (Kd) for Au(I) ions reached a maximum of 3233.3 mL/g at the 3:3 ratio, with a separation coefficient (β) of 40.62, indicating exceptional selectivity over Fe(II) ions. Fourier-transform infrared (FTIR) spectroscopy revealed structural changes post-sorption, including shifts in absorption bands (e.g., from 1273.5 cm−1 to 1292.9 cm−1) and the appearance of new bands (e.g., at 3171.1 cm−1), confirming stable ion interactions. Thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) demonstrated enhanced thermal stability post-sorption, with reduced mass loss up to 100 °C. These findings highlight the KU-2-8:AV-17-8 (3:3) interpolymer system’s high selectivity, robust sorption capacity, and efficient desorption, presenting a sustainable solution for gold recovery in hydrometallurgical applications.

Depletion of placer deposits containing gravity-concentrated gold objectively implies the need to use physical and chemical geotechnologies in their development, i.e. heap, cuvette, vat or drillhole in-situ leaching. A vat leaching circuit is proposed for fine-grained and flake gold, which is mostly lost with the tails during washing of placer sands. This circuit involves vat leaching with in-situ sorption of dissolved gold from the pulp, ensuring maximum recovery of the precious metal while minimizing environmental damage. The article discusses the technology of sorption leaching of gold from man-made placers, implemented using a device that reduces the processing cycle time and increases the operational capacity of the sorbent, thereby improving gold recovery (re-extraction). The results are presented of experiments on activation leaching of hard-to-extract gold forms, utilizing various complexing reagents, with parameters for preparing technological solutions and pulp processing systematically varied.

Gold recovery from electronic waste (e-waste) presents a significant materials challenge, as conventional systems lack structural tunability, exhibit poor metal selectivity, and fail to integrate adsorption and photoreduction functionalities effectively. Herein, we present a topology-guided strategy based on two isomeric π-conjugated covalent organic frameworks (COFs) (v-2D-COF-Dz and v-2D-COF-Pz), incorporating diazine (ortho-N) and pyrazine (para-N) units, respectively, for integrated gold adsorption and photoreduction. The nitrogen topology not only stabilizes the π-conjugated backbone but also significantly modulates the frameworks' optoelectronic and redox properties. Notably, v-2D-COF-Dz exhibits a markedly higher Au3⁺ adsorption capacity (2465versus 1854mgg-1), attributed to enhanced interfacial electron localization and directional charge transfer to Au3⁺ centers. Both frameworks achieve over 99% gold extraction from real e-waste leachates under visible-light irradiation. Spectroscopic characterization and DFT analysis reveal that nitrogen topology governs metal coordination strength and electronic coupling, enabling precise Au-Cl bond activation. This work establishes a nitrogen-topology-directed design paradigm for light-driven, COF-based precious metal recovery systems.