Efficient Recovery Of Gold Research Articles

Photo-enhanced precious metal recovery enabled by trithiocyanuric-linked covalent triazine frameworks

Precious metals recovery from secondary resources is crucial for ensuring the sustainable supply of resources and development of circular economy. Herein, the trithiocyanuric-linked covalent triazine frameworks (denoted as TTC-CTFs) are proposed and constructed for efficient recovery of precious metals. As expected, the proposed TTC-CTFs afford ultrahigh uptake capacities of 3365 mg g−1 for Au(III) and 1125 mg g−1 for Pt(IV) under light irradiation, achieving the respective 2.3-fold and 1.5-fold enhancement relative to those in the dark and outperforming the previously reported materials. Meanwhile, fast kinetics and superior recyclability are achieved, as reflecting by 15 min of the equilibrium time and neglect decline in recovery efficiency during ten cycles. Post-recovery characterizations and theoretical calculations reveal the combination of adsorption, photoreduction/chemical reduction, and crystallization is responsible for the photo-enhanced Au recovery. Significantly, TTC-CTFs are also competent for selective and efficient gold recovery from the computer processing unit (CPU) leachate, as companied by 99% of recovery efficiency and considerable profit, highlighting the feasibility of the proposed TTC-CTFs for the precious metal recovery from the actual e-waste.

Efficient gold recovery from low concentrated Au(S2O3)23− solution through enhanced photocatalysis via photothermal and surface plasmon resonance assistance on MoS2/MXene/Ag

Thiosulfate technique is the most promising method to recover gold from electronic waste (e-waste) and natural ores due to its non-toxicity and high leaching efficiency. However, the bad affinity between Au(S2O3)23− and traditional adsorbents leads to unsatisfied gold recovery performance from leaching solution. In this work, highly efficient recovery of gold from low concentrated Au(S2O3)23− solution was achieved through enhanced photocatalysis process on a novel MoS2/MXene/Ag adsorbent. During recovery procedure, Au(S2O3)23− was in-situ reduced to Au0 by photogenerated electrons and then anchored on MoS2/MXene/Ag. Under Au(S2O3)23− concentration <10 ppm, over 99 % gold recovery performance could achieve within 2 h. Experimental tests have proved that MXene made fully use of near infrared (NIR) light energy to exhibit better photothermal effect, and surface plasmon resonance (SPR) effect of Ag can simultaneously facilitate the separation of electron-hole pairs on MoS2. By means of external temperature input and rapid charge carrier transmission, plenty of electrons were excited from MoS2/MXene/Ag for Au(S2O3)23− recovery. This work paved a pathway for efficient Au(S2O3)23− recovery, which catered to the demand for green production of gold in the future.

Ti3AlC2 MAX Phase: A surprising candidate material for highly selective and efficient gold recovery from strong acid solutions

Given the scarcity of natural gold sources and associated mining challenges, the recovery of gold from secondary sources, such as electronic equipment waste (e-waste), becomes imperative. E-waste is typically treated with aqua regia to obtain highly acidic gold-containing solutions, which are subsequently processed by various methods to recover gold. Gold recovery materials offer numerous benefits but often exhibit insufficient selectivity, efficiency, and cost-effectiveness. To address this problem, we herein used a nonmodified pristine Ti-Al-C MAX phase (Ti3AlC2) to realize the one-pot room-temperature recovery of gold from highly acidic solutions (pH < 1) in the form of easily collectable bulky ball-shaped Au0 aggregates. High gold selectivity (Kd = 2.03 × 106 mL/g) and extraction efficiency (∼99 %) were observed even in the presence of interfering metal ions (Pd2+, Pt4+, Co2+, Ni2+, Cu2+, Zn2+), and the maximum gold extraction capacity (>6000 mg/g) surpassed that of previously reported gold recovery materials. The recovered gold was highly pure (>90 mass%) and contained minimal amounts of the original MAX phase, which obviated the need for intensive postpurification. The results of instrumental analyses suggested that gold recovery relied on electron transfer, similar to cementation, and primarily involved the reduction of solution-phase Au3+ to Au0via electron transfer from the Ti and Al of Ti3AlC2. Thus, our work demonstrates the significant potential of pristine Ti3AlC2 for the energy-efficient recovery of gold from highly acidic solutions and paves the way for the efficient valorization of e-waste.

Constructing a cationic pyridine for the highly selective and efficient recovery of gold from waste printed circuit boards

Recovering gold from rich waste printed circuit boards (WPCBs) resource are of great significance to gold development and utilization. In this paper, cationic pyridine polymers with different configurations were designed and synthesised for highly selective and efficient recovery of gold from a WPCB leaching solution. The structures and performances of the cationic pyridine polymers were analysed using a 4–aminopyridine polychloromethylstyrene (4–AP/PCMS). The results indicate that the 4–AP/PCMS performed well in an acidic environment, including in the 5 % aqua regia solution. Gold adsorption on the 4–AP/PCMS followed pseudo–second–order kinetics and Langmuir isotherm models, suggesting that chemisorption occurred via a single–layer mechanism with a maximum loading capacity of 437.68 mg/g. Further, Au(III) adsorption on the 4–AP/PCMS involved electrostatic interactions and reduction between pyridine and AuCl4−. After five adsorption–desorption cycles, the adsorption rate remained above 99 %, whereas in actual leaching solutions it reached 92.24 %. All five pyridine polymers demonstrated outstanding Au(III) selectivity over binary and multicomponent solutions containing Cu(II), Ni(II), Co(II), Zn(II), Fe(III), Cd(II), and Mg(II), benefitting from the cationic pyridine skeleton. Contact patterns between the cationic pyridine polymers and AuCl4− considerably affected the gold loading capacity, and a single–point contact was found to be favourable for gold adsorption. These results indicated that cationic pyridine polymers are promising for recovering gold from WPCB leaching solutions.

Efficient recovery of gold from solution with a thiocyanate-modified Zr-MOF: adsorption properties and DFT calculations.

The design and development of new large-capacity and selective materials for extracting rare precious metals via electronic waste is practically essential. In this paper, a new efficient UiO-66-NCS has been obtained as a consequence of the modification of the classical Zr-MOF (UiO-66-NH2), and its ability to recover gold has been investigated. These batch results adequately illustrated that UiO-66-NCS exhibited good adsorption capacity (675.5 mg g-1) and exceptional selectivity. In addition, UiO-66-NCS achieved faster adsorption equilibrium times of about 120 min. Adsorption kinetics and isotherms demonstrated that the pseudo-second-order adsorption scheme and a Langmuir-type procedure were shown by the adsorption of Au(III) on UiO-66-NCS. Characterized by pH effect experiments, TEM, XRD, and XPS, the adsorption of UiO-66-NCS with Au(III) relies on coordination, which further results in reduction, and the generated Au(0) is uniformly dispersed in the MOF. The adsorbent has considerable advantages for cyclic regeneration. Finally, DFT fitting results showed that the adsorption binding energy of UiO-66-NCS with [AuCl4]- was -8.63 kcal mol-1 for the adsorption process. UiO-66-NCS is likely to be an ideal substance for gold recovery.

Efficient gold recovery by a thiazolyl covalent organic framework.

Here, we report a thiazoyl covalent organic framework, namely ECUT-COF-29, for gold recovery. Under visible light irradiation, this material can reduce Au3+ to Au0 in a short time, and the adsorption capacity is as high as 3714 mg g-1, showing great potential in gold recovery.

Efficient recovery of gold using Macroporous Metal-Organic framework prepared by the 'MOF in MOF' method

The design of an efficient adsorbent for Au(III) has remained a challenging research focus, as the adsorbent needs to overcome competition from other ions while simultaneously addressing pore blockage caused by the reduction of Au(III) to elemental gold. In this study, we report the synthesis of a hierarchically porous metal–organic frameworks (MOFs) with ultra-large pores (300 nm) using the “MOF in MOF” method. This material facilitates enhanced adsorption kinetics by increasing the rate of gold ion adsorption and effectively prevents pore blockage resulting from Au(III) reduction, enabling access to the majority of adsorption sites. Batch experiments were conducted, and various complex water mixtures, including freshwater, simulated electronic waste solution, and gold ore leachate, were tested to demonstrate the rapid extraction of trace amounts of gold by the developed adsorbent. Remarkably, without additional functionalization, the adsorbent solely based on its pore advantage achieved a gold adsorption capacity of 1184 mg/g and reached 80 % adsorption within just 5 min (C0 = 100 mg/L, V/m = 2 L/g). Furthermore, the gold recovered from the leachate of gold ore exhibited a purity of 23.8 K (99.2 % purity).

Sustainable and effective gold(I) separation from aurocyanides wastewater and its mechanism using guanidinium ionic liquids

Efficient recovery of gold(I) from aurocyanide wastewater offers a dual opportunity for secondary resource utilization and environmental harm reduction. Herein, four environmentally friendly hexaalkylguanidium ionic liquids (HGILs) were synthesized and for the first time used to extract gold(I) from aurocyanide wastewater. Critical parameters, including HGILs and modifier species, dosage, pH, initial gold(I) concentration, and temperature, were optimized. The HGIL systems exhibited excellent gold(I) extraction performance with over 99.0% of gold(I) being extracted under optimal conditions. The composition ratio of the extracted complex was determined by Job's method and slope analysis. Spectral characterization included X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy and density functional theory calculations confirmed that gold(I) extraction followed an anion exchange mechanism. A dicyanoaurate Au(CN)2− anion and two n-octanol molecules produced the supermolecule anion [Au(CN)2−·2 n-octanol] via hydrogen bonding, which combined with a guanidium cation to generate the stable extraction complex [HGIL+·Au(CN)2−·2 n-octanol] through electrostatic attraction. The gold(I) loaded in the ionic liquid phase was effectively stripped with potassium thiocyanate solution. The regenerated HGIL system maintained a high gold(I) extraction efficiency of over 90.0% after five extraction–stripping cycles. In addition, a two-step stripping strategy was developed for the selective separation of gold(I) and other impurity metal ions from real aurocyanide wastewater. This study proposes an efficient green process for recovering gold(I) from mine wastewater, which has potential practical application prospects.

Polythioamide-g-C3N4 for highly efficient and selective gold recovery

Gold recovery from secondary sources is essential for sustainable supply. To develop a gold recovery approach with high efficiency and selectivity, polythioamide-functionalized carbon nitride (PTA-g-C3N4) was synthesized and applied to photo-induced gold extraction. PTA-g-C3N4 was synthesized by multicomponent polymerization of elemental sulfur, organic amines, acids and carbon nitrides. The maximum adsorption capacity of PTA-g-C3N4 reached 3668 mg·g−1, far exceeding other reported materials. Moreover, PTA-g-C3N4 enabled rapid (<3 min) and efficient gold recovery (>99%) from dilute solutions, and more importantly, the extraction for gold is highly selective in complicated wastewater and authentic e-waste leachates. High purity metallic gold with >95% content was obtained by incineration of the used material. Regeneration scheme and economic analysis further support the applicability. Mechanism studies revealed the formation of an efficient two-phase interface capable of selective adsorption and reduction of gold ions, where bifunctional PTA exhibited high affinity for AuCl4− and sacrificial behavior to accelerate photo-reduction.

Efficient recovery of gold from low concentration Au(S2O3)23– solution by fabricating Ag/MoS2 Ohmic contact

The surface decoration of precious metal particles is one of the most effective strategies for improving the photocatalytic activity of semiconductors. In this work, a MoS2-based Ohmic contact was fabricated by depositing Ag nanoparticles on the surface of MoS2 nanosheets (MoS2 NSs) to enhance the photoreduction of Au(Ⅰ) from a low concentration Au(S2O3)23– solution. After the fabrication of Ohmic contact, more efficient interface charge transfer can be achieved under the drive of built-in electric field. As a result, the photogenerated singlet excitons in MoS2 NSs are readily dissociated into free charges with the electrons drifting to Ag NPs, leading to a higher electron concentration on the surface of Ag/MoS2 NSs. The gold recovery of Ag/MoS2 NSs-4.15% reaches up to 96.67% for the low concentration Au(S2O3)23– solution, which is about 3.9 times higher than that of pristine MoS2 NSs (24.82%). The results of this work are encouraging for further development in the surface science of photocatalysis and demonstrate a pathway for efficient gold recovery via photoreduction.

Efficient gold recovery from waste electronic and electric equipment by amino-modified covalent triazine frameworks

Recycling gold from e-waste is not only conducive to alleviating the pressure on resources and environment, but also has high economic value. Therefore, construction of adsorbents with high capacity and selectivity and low cost is significative for gold recovery from waste electronic and electric equipment (WEEE). Herein, amino-functionalized covalent triazine frameworks (NH2-CTFs) were synthesized by ionothermal conditions. NH2-CTF-1 and NH2-CTF-2 with high porosity and good thermal stability exhibit excellent gold recovery performance. Meanwhile, gold ions can be in situ reduced into gold nanoparticles by NH2-CTFs along with the adsorption process. Furthermore, NH2-CTF-1 and NH2-CTF-2 present good gold adsorption selectivity from WEEE. Notably, NH2-CTF-1 possesses high gold adsorption capacity (909 mg g−1) and outstanding recovery profit. These excellent performances confirm the potential of NH2-CTF-1 and NH2-CTF-2 for gold recovery from WEEE.

Efficient gold recovery by microbial electrochemical technologies

The applicability of microbial electrochemical technologies for the recovery of gold was investigated. Two-chamber microbial fuel cells (MFC) with bioanodes buried in sediment were used in two operating modes. The cathodes (gold foil or graphitized paper), submerged in HAuCl4, solutions, were short-circuited with the bioanodes, and thus for the first time, the microbial electrochemical snorkel (MES) was applied for gold recovery. Operation in MFC mode, where the cathode and the anode were connected through an external resistor equal to the internal resistance of the system was also implemented. The electrochemical results along with the microscopic analyses, XPS data, and the estimated rate constants show the better performance of the MES over the MFC and predict the putative mechanism of the cathodic gold deposition. The gold removal and recovery reached ca. 95% within a day and the cathodic efficiency approached almost 100%. 7% higher gold recovery and 5% higher gold removal were achieved in the MES mode, which reveals the advantage of the operation under short-circuit conditions. The deposited on the cathode gold is in its elemental state. The similar results obtained with the two types of cathodes justify replacing the gold electrodes with much cheaper graphitized paper to reduce the cost. In addition, it has been demonstrated that gold can be also recovered by MES from the aqueous solutions of its complex Na3[Au(S2O3)2], simulating leachates from printed circuit board waste, which expands the limits of its practical application.

Manganese and oxygen dual-doping MoS2 boosts reduction and adsorption activity toward efficient recovery of gold(I) from thiosulfate solutions

The necessity for application of molybdenum disulfide (MoS2) in photocatalytic reduction field required speedy improvement with high reduction and adsorption performance. Here, manganese (Mn) and oxygen (O) dual-doping strategy were taken for demonstrating that enhancing photocatalytic reduction could achieve simultaneous modulation of the reduction and adsorption parameters by optimizing the electronic configuration and hydrophilicity ability in MoS2. Benefiting from the Mn and O dual-doping collective effect, the developed Mn,O-MoS2 exhibited outstanding photocatalytic reduction and recovery performances of gold(I) from thiosulfate leaching solutions with reduction capacity of 1386.98 mg/g and the corresponding recovery of 92.50%. Besides, Mn and O atoms dual doping in MoS2 accelerated the recovery rate, which was 3 folds higher compared with that of MoS2. Experimental and first-principle approaches suggested that the reduction and adsorption ability of MoS2 were strengthened through tuning the electronic structure and surface property with Mn and O dopants: (1) Mn atoms notably enhanced the conductivity and optimized the electronic structure for facilitating the reduction performance; (2) The incorporated O atoms greatly promoted the adsorption of [Au(S2O3)2]3- by improving the affinity of water molecules and Mn,O-MoS2. The work provides a promising strategy to manipulate two-dimensional materials for various applications about catalysts and adsorbent.

Manganese and Oxygen Dual-Doping MoS &lt;sub&gt;2&lt;/sub&gt; Boosts Reduction and Adsorption Activity Toward Efficient Recovery of Gold(I) from Thiosulfate Solutions

Manganese and Oxygen Dual-Doping MoS &lt;sub&gt;2&lt;/sub&gt; Boosts Reduction and Adsorption Activity Toward Efficient Recovery of Gold(I) from Thiosulfate Solutions

Efficient Gold Recovery from Cyanide Solution Using Magnetic Activated Carbon.

Activated carbon has been used for gold recovery in the gold mining industry commercially for decades. The high specific surface area and porosity, good affinity to aurocyanide ions, and abundant resources make activated carbon an efficient and economical material for the adsorption of aurocyanide. However, the separation of activated carbon from the slurry is usually a challenge, and the adsorption rate of activated carbon is limited by the coarse particle size. Herein, a simple and sustainable way to recover gold from cyanide solution using magnetic activated carbon synthesized via a solvothermal method has been developed. The synthesized magnetic activated carbon possesses good magnetism (44.57 emu/g) and specific surface area equal to 249.7 m2/g. The magnetic activated carbon showed 99.1% recovery efficiency of gold from 10 mg/L solution within 5 h, which is much faster compared to the commercial granular activated carbon, and the magnetic activated carbon can be easily separated from the solution with an external magnet. The adsorption ability of this magnetic activated carbon has been tested under different conditions in the cyanide solution, the adsorption isotherm and kinetics are also investigated. The magnetic activated carbon was also recycled in the adsorption-desorption tests and showed good reusability.

Efficient Recovery of Gold(I) from Thiosulfate Solutions through Photocatalytic Reduction with Mn(II)-Doped MoS2

Developing efficient materials for the extraction of gold(I) was pivotal for application of ammoniacal thiosulfate leaching technology. Mn-doped molybdenum disulfide (Mn-MoS2) spheres were fabricated by a facile hydrothermal route for photocatalytic reduction of the gold(I) thiosulfate complex ([Au(S2O3)2]3–) in this work. The experimental results exhibited that [Au(S2O3)2]3– was efficiently recycled in the form of gold nanoparticles by Mn-MoS2. The reduction capacity (936.9 mg/g) and rate (2.74 mg/(g min) in 300 min) was 1.5 and 2.72 times higher than that of MoS2, respectively. The inside photocatalytic reduction mechanism was studied by combining an experimental and first-principles approach. Outstanding reduction performance of [Au(S2O3)2]3– was attributed to the enhanced transfer of photoinduced electrons after Mn doping. In addition, S atoms in the Mn-S bond could well interact with Au(I), which slightly promoted the adsorption of [Au(S2O3)2]3– on Mn-MoS2. The discovery provided a promising strategy for the efficient extraction of gold(I) from thiosulfate leaching solutions.

Performance-Based Selection of the Cathode Material for the Electrodeposition-Redox Replacement Process of Gold Recovery from Chloride Solutions

Recently, an emerging electrodeposition-redox replacement (EDRR) method was demonstrated to provide exceptionally efficient gold recovery from cyanide-free hydrometallurgical solutions. However, the effect of electrode material and its corrosion resistance in this process was overlooked, even though the EDRR process is carried out in extremely corrosive, acidic chloride solution that also contains significant amounts of strong oxidants, i.e., cupric ions. In the current study, nickel alloy C-2000, stainless steels 316L and 654SMO, and grade 2 titanium were for the first time critically evaluated as potential cathode materials for EDRR. The particular emphasis was placed on better understanding of the effect of cathode substrate on the overall efficiency of the gold recovery process. The use of a multiple attribute decision-making method of material selection allowed reaching of a well-founded compromise between the corrosion properties of the electrodes and process efficiency of gold extraction. The 654SMO steel demonstrated outstanding performance among the examined materials, as it enabled gold recovery of 28.1 pct after 3000 EDRR cycles, while its corrosion rate (CR) was only 0.02 mm/year.

The efficacy of a new iodination roasting technology to recover gold and silver from refractory gold tailing

Gold tailing is residue waste, but it’s also a secondary resource. Thus far, little is known about the iodination roasting and it was first used to dispose gold tailing. Here, we show that iodination roasting can efficient recovery of gold and silver from the refractory gold tailing with higher recovery efficiency than chlorination roasting. Different factors affecting the recovery effectiveness of gold and silver were investigated to obtain the maximum gold and silver recovery efficiencies. We achieved recovery efficiencies of 99.92% and 87.78% for gold and silver by the iodination roasting, and thus can be applied to treat and recover various kinds of gold and silver residues from the solid phase. We also provide roasting principles of the iodination roasting process using experimental design method by changing the contact between Iodine Donor (KI) and gold tailing, and found that Iodine Donor decomposes to iodine gas and the iodine gas reacts with the Au and Ag, which is similar to the reported mechanism of chlorination roasting. Moreover, the behavior results of other elements during iodination roasting confirm that it could selective enrichment of gold and silver from gold tailing.

Recovery of gold through adsorption onto sericin and alginate particles chemically crosslinked by proanthocyanidins

The recovery of gold from wastewater has been encouraged in the last years due to this metal high cost, elevated demand, and low availability. Sericin and alginate particles chemically crosslinked by proanthocyanidins (SAPAS) were successfully used in this study for this purpose. The maximum adsorption capacity predicted by the Dubinin-Radushkevich model was 237.60 mg/g at 303 K. The thermodynamic parameters revealed that the process is spontaneous, endothermic and also governed by entropic changes. The characterization of SAPAS before and after gold adsorption (SAPAS-Gold) suggested that the uptake of this metal involves ion exchange and subsequent reduction. The thermogravimetric analysis showed that elemental gold may be recovered from SAPAS surface by the incineration process. Alternatively, both the reuse of SAPAS and the efficient recovery of gold (84.389 ± 2.103%) is possible by employing the desorption process with thiourea (0.5M)/hydrochloric acid (2M) solution.

Microbial recovery of gold from neutral and acidic solutions by the baker's yeast Saccharomyces cerevisiae

An environmentally friendly method using the baker's yeast Saccharomyces cerevisiae was developed to recover soluble Au(III) from neutral and acidic solutions at room temperature. Resting cells of S. cerevisiae were able to reduce aqueous Au(III) ions in HAuCl4 solution to metallic Au(0) at pH 7.0 within 120 min when formate was provided as the electron donor under anaerobic conditions. Gold nanoparticles were deposited on the cell surface of S. cerevisiae. The S. cerevisiae cells were also applicable to a bio-material for adsorbing aqueous Au(III) ions from HAuCl4 solution at pH 1.0 under air atmosphere. When processing the aqua regia leachate of electronic waste (Central Processing Units, CPU), the S. cerevisiae cells were able to rapidly and selectively collect aqueous Au(III) ions from the aqua regia leachate at pH 1.2 within 10 min. Our proposed microbial methods enable the rapid and efficient recovery of gold over the pH range 1.0 to 7.0.