A comprehensive review on the ultrasound-enhanced leaching recovery of valuable metals: Applications, mechanisms and prospects

Advancing total management of oily spent hydroprocessing catalyst: From hazardous waste to circular and eco-sustainable utilization

Hydroprocessing technology is essential for refining crude oil, playing a critical role in improving oil quality. This process consumes large quantities of catalysts, which become spent hydroprocessing catalysts because of deactivation. These spent catalysts, containing substantial amounts of residual oil, coke, and heavy metals, are recognized as challenging hazardous solid waste. However, they also contain critical rare metals and crude oil, making them an important and valuable secondary resource. Managing these ever-growing volumes of spent catalysts to ensure safe disposal of hazardous waste while maximizing circular and eco-sustainable utilization has become a pressing global challenge and key research focus. Therefore, this paper provides a comprehensive review of popular technologies and recent advancements in managing oily spent hydroprocessing catalysts, aiming to achieve the dual goals of environmental protection and maximizing resource utilization. This review first introduces the types and functions of hydroprocessing technology and catalysts and explores the causes and hazards associated with deactivating hydroprocessing catalysts. It thoroughly discusses popular and innovative emerging technologies in deoiling, regeneration, high-value reuse, and recovery metals from spent catalysts, highlighting the strengths and challenges of each method. The review concludes with outlook on future directions, proposing directions and considerations for advancing total management of oily spent hydroprocessing catalyst.

Efficient Ultrasound-Assisted Synthesis of Chemically Supported Anionic Functional Group Ionic Liquids and Its Enhanced Adsorption Performance Towards Vanadium (V)

In this study, the chemically supported ionic liquids (CSILs) were synthesized by ultrasound irradiation (UI) to improve the preparation process and further strengthen the adsorption performance of CSILs towards vanadium (V). The impacts of UI and conventional mechanic stirring (CMS) on the synthesis and adsorption characteristics of polystyrene [1-butyl-3-methylimidazolium][nitrate] (PS[C4mim][NO3]) were comparatively investigated. The experimental results demonstrate that ultrasound can dramatically shorten the preparation time from 1920 min to 15 min, and HNO3 dosage is reduced by 15.79%. Under the same adsorption conditions, the CSILs synthesized by UI achieve the maximal adsorption capacity towards vanadium (V) as 248.95 mg/g at 150 min, while the CSILs processed by CMS reach 223.90 mg/g at 105 min. Particularly, the adsorption capacity of CSILs synthesized by UI can be maintained as 96.42% of the initial value after 10 cycles of adsorption-desorption, while that of CSILs processed by CMS maintain as 94.87%. The adsorption isotherm and kinetics fitting demonstrate that vanadium (V) adsorption by two CSILs is dominated by chemisorption as a single molecular layer. Additionally, the adsorption reaction of vanadium (V) by these two CSILs are both endothermic, and entropy increases. Fourier transform infrared, scanning electron microscopy, and energy spectrometry analyses prove that PS[C4mim][NO3] is successfully prepared by UI and CMS methods, and ultrasound waves will not destroy the intact spherical structure of the support resins. The current work provides a novel insight for the efficient synthesis of CSILs, which is also a potential technique for improving the adsorption performance of the adsorbents towards valuable metals.

Ultrafast recovery of Zn from waste galvanized iron sheet by ultrasound-assisted acid pickling and ion flotation techniques

High-efficiency dezincification from waste galvanized iron sheets is crucial for resource recovery and environmental protection. In this work, ultrasound-assisted acid pickling and ion flotation techniques were combined to intensify the Zn extraction and separation from the waste galvanized iron sheets. The effects of leaching parameters on the leaching rate of Zn and Fe, Zn leaching kinetics and leaching electrochemistry were compared between conventional leaching and ultrasonic-assisted leaching. It's demonstrated that ultrafast dezincification is realized as the acid pickling time can be reduced from 10 min to 60 s with ultrasound assistance, and the Zn and Fe leaching rates are 99.9 % and 0.02 %, respectively. Ion flotation was adopted to recover the Zn ion from the circulated leaching solution using sodium dodecyl benzene sulfonate (SDBS) as the collector. After the Zn ion flotation, powdery ZnO with size distribution of 1-3 μm is prepared from the froth product after calcining at 600 ℃ for 2 h. In addition, various characterizations involving thermodynamics, XRD, XPS, SEM-EDS, TG-DSC, and FTIR analyses were employed to elucidate the mechanisms underlying the enhancement of Zn dissolution through ultrasound assistance and the Zn capture mechanism via ion flotation. Eventually, the combination of ultrasonic-assisted acid pickling and ion flotation techniques can achieve the rapid selective Zn extraction from waste galvanized iron sheet and fast separation of Zn ion from leachate, which can provide technical reference for the resource utilization of other waste metal coating plates.

Green preparation of magnetic porous carbon by high value utilization of metallurgical waste liquid for efficient extraction of pesticide residues in the environment

Metal-organic frameworks were prepared from Fe-containing waste liquid generated during the refining process of nickel metallurgical slag as a metal source, providing a green treatment method for industrial waste liquid. The Fe-containing waste liquid was used as a raw material for the coordination synthesis of MIL-100(Fe) with 1,3,5-benzenetricarboxylic acid, whereas the ionic liquid-modified magnetic porous carbon material (Fe3O4@C/[BMIM]PF6) was prepared by loading [BMIM]PF6 into the pore size of Fe3O4@C obtained by carbonization derivatization. Since Fe3O4@C/[BMIM]PF6 exhibits strong hydrophobicity and contains unsaturated functional groups as well as hydrogen bond acceptors in structure, and a large pore size, it was used as a highly efficient adsorbent for the extraction of trace pyrethroid insecticides in the environment. Fe3O4@C/[BMIM]PF6 demonstrated excellent extraction ability, and the recoveries of the four pyrethroid insecticides in the actual samples analyzed ranged from 85.75 to 112.13%. Fe3O4@C/[BMIM]PF6 has excellent reusability and batch-to-batch reproducibility, and the relative standard deviations for the extraction recoveries of pyrethroids insecticides from the five batches were 2.14%-3.65%. The MIL-100(Fe) synthesized from high-volume preparation experiments exhibited excellent physical/chemical properties. Therefore, the green prepared Fe3O4@C/[BMIM]PF6 based on waste liquid has excellent extraction properties, and the study provides a green and low-energy treatment method for waste liquids generated by metallurgy.

Selective leaching mechanisms of zinc from industrial waste using hybrid acids: Sustainable synthesis of Nano-ZnO

Zinc-containing dust (ZCD) has received extensive attention because it is a hazardous waste rich in various metals. This study innovatively proposed a hybrid acid leaching agent based on malic acid (MA) and sulfuric acid to selectively extract Zn from ZCD and successfully prepare nano-ZnO materials. The leaching experiments show that among the combinations of various organic acids and sulfuric acid, MA and sulfuric acid are superior in the selective leaching of Zn. Under optimal conditions, the leaching ratios of Zn, Pb, and Fe are 97.70%, 0.88%, and 2.95%, respectively. In addition, the use of hybrid acids can reduce sulfuric acid consumption by more than 46%. The Molecular dynamics simulation indicate that the interaction between the hybrid acid with ZnO and PbO was stronger (PbO > ZnO > Fe2O3). The radial distribution function (RDF) reveals that Zn and Pb ions form strong coordination structures with some oxygen atoms in MA, thereby confirming that MA plays a crucial role in preventing the dissolution of Fe. Finally, spherical nano-ZnO with a purity of 98.14% and an average particle size of 68.60 nm is obtained from the leaching solutions by precipitation method. This study provides a green and sustainable alternative for the selective recovery of Zn from ZCD.

Ultrasonic-assisted membrane processes for the systematic purification of glycyrrhiza wastewater

A significant amount of glycyrrhiza wastewater is generated in the cleaning process of glycyrrhiza. The wastewater contains polysaccharide, glycyrrhizic acid, liquiritin, and other polyphenols, which is expensive for cleanup and wastes medical resources. To reduce environmental pollution from glycyrrhiza wastewater and increase the resource usage efficiency of glycyrrhiza components. According to the physicochemical properties of the component in glycyrrhiza wastewater, the ultrasonic assisted membrane separation mode was adopted to regulate the micellar state of glycyrrhizic acid and enhance the differences in membrane separation of polysaccharides, saponins, and flavones, in order to achieve the classification and separation of polysaccharides, saponins, and flavones while removing organic matter in glycyrrhiza wastewater. However, the efficiency, application, and mechanism of ultrasonic-assisted membrane technology for the separation of polysaccharides, saponins, and flavonoids from glycyrrhiza wastewater remain unclear. This study presents a green and feasible technical strategy for glycyrrhiza wastewater treatment that was developed by adjusting the parameters of ultrasonic assisted membrane separation. In this study, the systematic separation mode of ultrasonic enhanced ultrafiltration combined with nanofiltration is provided. The SCQ-9200E ultrasonic system was provided for the study with adjustable ultrasonic power, and the ultrasonic frequency was 40 kHz. The glycyrrhizic acid micelle was changed using ultrasonic power, pH, and molecular weight cut off (MWCO), and the separation differences among polysaccharide, glycyrrhizic acid, and liquiritin were enhanced. The optimal polysaccharide separation parameters used in the first step: MWCO 30 kDa, ultrasonic power 500 W and pH 5.00, and the rejections of polysaccharide, glycyrrhizic acid, and liquiritin were 87.72 %, 8.01 %, and 6.57 %, respectively. The second step included the following parameters for the separation of liquiritin and glycyrrhizic acid: MWCO 10 kDa, ultrasonic power 100 W and pH 8.00, the rejections of liquiritin and glycyrrhizic acid were 9.22 % and 40.65 %, respectively. The third step is to remove the low molecular sugar in liquiritin by nanofiltration: MWCO 800 Da, pH 8.00, retention solution diluted and separated twice, the rejection of liquiritin and total sugar were 95.72 % and 3.70 %, respectively. Ultrasonic may regulate the microtopography of glycyrrhiza wastewater with the power intensity of 50 W/L, improving the mass transfer efficiency of glycyrrhizic acid and liquiritin in the ultrafiltration separation process. As the separation volume of wastewater increased from 2.00 L to 20.00 L, the concentrations of polysaccharide, glycyrrhizic acid, and liquiritin increased by 2.5-35.4 times, 0.6-15.2 times, and 2.4-32.8 times, respectively, significantly increasing the content of index components in wastewater and solving the problem of recycling and resource utilization in glycyrrhiza wastewater.

Mechanism and kinetics of ultrasound-enhanced CaCO3 precipitation for indium enrichment in zinc oxide dust leaching solution

In this study, ultrasound-enhanced calcium carbonate precipitation was used to enrich indium in zinc oxide dust leachate, and the effects of precipitation endpoint pH and ultrasound power on the indium precipitation behaviour were investigated, and the optimal conditions of ultrasound-enhanced precipitation were obtained to be the precipitation endpoint pH of 4.0 and the ultrasound power of 200 W. The precipitation rate of indium under these conditions was 99.79 %. At the same time, the effects of ultrasonication and conventional stirring on the indium precipitation kinetics were compared, which proved that ultrasound can shorten the time for precipitation to reach equilibrium and reduce the amount of calcium carbonate used, and the theory of ultrasonication activation energy was put forward. The activation energy of ultrasonication was Eu-a = 2.63 KJ/mol, and that of conventional precipitation was 9.78KJ/mol, which proved that ultrasonication could reduce the activation energy of the precipitation reaction, and promote the rapid precipitation reaction. The kinetic model of ultrasound-enhanced indium precipitation is lnC0-lnCt = exp(0.11339-318.54/W).t + A. In addition, the mechanism of ultrasound-enhanced calcium carbonate precipitation of indium was revealed by XRD, SEM-EDS, XPS and TEM analyses of the precipitated residue, it was demonstrated that ultrasound can inhibit the precipitation of zinc, and the ZnCO3 phase was found in the ultrasonically precipitated residue. This study provides a new idea for indium enrichment, and the future focus will be on the scale-up of the ultrasound-enhanced precipitation device.

Overcoming passivation through improved mass transport in dense ionic fluids

Deep Eutectic Solvents (DESs) have recently been shown to be part of a dense ionic fluid continuum between ionic liquids and concentrated aqueous brines. Charge transport was shown to be governed by fluidity, with no discontinuity between molar conductivity and fluidity irrespective of cation, charge density or ionic radius. By adjusting the activity of water and chloride ions, mass transport, speciation and reactivity can be altered. It has been shown that while brines provide a high chloride content at a lower viscosity than DESs, unlike DESs, brines are unable to prevent metal passivation due to their high water content. This results in the possibility to impart a level of selectivity towards metal dissolution (or passivation) when processing mixed metal materials. Forced convection can be used to avoid the issue of slow mass transport in viscous media, and the use of jets or targeted ultrasound are effective methods for overcoming this issue. High-powered ultrasound was applied to copper, cobalt, and aluminium electrodes undergoing anodic dissolution, and linear sweep voltammetry showed a linear current-voltage response at potentials anodic of the oxidation potential under sonication, with total charge passed being 5 to 134 times greater than under silent conditions. Application of ultrasound to silver and nickel electrodes displayed an initial linear current-voltage response, but the increased water content of the brines resulted in passivation. Mass transport throughout the bulk solution is governed by the forced convection imparted by the ultrasound and ionic species must only migrate across the electrical double layer. It is shown that the anodic dissolution of a range of metals classically expected to passivate, e.g. aluminium, can be significantly accelerated under insonation conditions.

Mechanism and kinetics study of vanadium leaching from landfilled metallurgical residues by ultrasonic with ozonation enhancement in a low-acid medium

Landfilled metallurgical residues are valuable raw materials for the recovery of strategic vanadium resources. However, efficient separation of vanadium from these residues is challenging due to its strong oxidation resistance and coating within silicate inclusions. To address this issue, this study proposes an enhanced leaching process utilizing the synergistic effect of O3-catalyzed ultrasonic field in a low concentration sulfuric acid system. Results show that following a 10-minute O3 and ultrasonic treatment, the direct leaching rate of vanadium experienced a remarkable 46.7 % increase. Quenching experiments revealed a hierarchical order of active species within the reaction process:⋅OH >⋅O2-> H+, with⋅OH oxidation exhibiting the most pronounced capacity for disrupting the inclusion structure. Electron Paramagnetic Resonance analysis indicated that the highest⋅OH yield arose from the combined application of ultrasound and ozone. Kinetic investigations demonstrated that the vanadium leaching process is governed by interfacial chemical reactions. The activation energy of vanadium oxidation leaching under ultrasonic-O3 conditions was determined to be 40.41 kJ/mol, representing a 20.19 % reduction compared to ultrasonic conditions alone. Through the integration of analysis, characterization, and comparative evaluations, it was discerned that the synergistic impact of ultrasonic and ozone treatments significantly enhances the breakdown of silicate inclusions by low-concentration HF, particularly in the conversion of SiOSi bonds into SiOH bonds and SiF bonds. In summary, the refined leaching methodology incorporating ozone catalysis in conjunction with ultrasonic treatment provides a new idea for the separation and extraction of refractory residual vanadium.

Antimony(V) Adsorption and Partitioning by Humic Acid-Modified Ferrihydrite: Insights into Environmental Remediation and Transformation Processes

Antimony (Sb) migration in soil and water systems is predominantly governed by its adsorption onto ferrihydrite (FH), a process strongly influenced by natural organic matter. This study investigates the adsorption behavior, stability, and mechanism of FH and FH-humic acid (FH-HA) complexes on Sb(V), along with the fate of adsorbed Sb(V) during FH aging. Batch adsorption experiments reveal that initial pH and concentration significantly influence Sb(V) sorption. Lower pH levels decrease adsorption, while higher concentrations enhance it. Sb(V) adsorption increases with prolonged contact time, with FH exhibiting a higher adsorption capacity than FH-HA complexes. Incorporating HA onto FH surfaces reduces reactive adsorption sites, decreasing Sb(V) adsorption. Adsorbed FH-HA complexes exhibit a higher specific surface area than co-precipitated FH-HA, demonstrating stronger Sb(V) adsorption capacity under various conditions. X-ray photoelectron spectroscopy (XPS) confirms that Sb(V) adsorption primarily occurs through ligand exchange, forming Fe-O-Sb complexes. HA inhibits the migration of Sb(V), thereby enhancing its retention within the FH and FH-HA complexes. During FH transformation, a portion of Sb(V) may replace Fe(III) within converted iron minerals. However, the combination of relatively high adsorption capacity and significantly lower desorption rates makes adsorbed FH-HA complexes promising candidates for sustained Sb adsorption over extended periods. These findings enhance our understanding of Sb(V) behavior and offer insights for effective remediation strategies in complex environmental systems.

Physicochemical reactions in e-waste recycling

Electronic waste (e-waste) recycling is becoming a global concern owing to its immense quantity, hazardous character and the potential loss of valuable metals. The many processes involved in e-waste recycling stem from a mixture of physicochemical reactions, and understanding the principles of these reactions can lead to more efficient recycling methods. In this Review, we discuss the principles behind photochemistry, thermochemistry, mechanochemistry, electrochemistry and sonochemistry for metal recovery, polymer decomposition and pollutant elimination from e-waste. We also discuss how these processes induce or improve reaction rates, selectivity and controllability of e-waste recycling based on thermodynamics and kinetics, free radicals, chemical bond energy, electrical potential regulation and more. Lastly, key factors, limitations and suggestions for improvements of these physicochemical reactions for e-waste recycling are highlighted, wherein we also indicate possible research directions for the future.

An original strategy and evaluation of a reaction mechanism for recovering valuable metals from zinc oxide dust containing intractable germanide

A novel leaching-roasting-leaching strategy was used to recover valuable metals from zinc oxide dust containing intractable germanide. In the ultrasonic enhanced oxidation leaching stage, potassium permanganate and ultrasonication were introduced to strengthen the dissolution of sulphide. During the roasting stage, sodium carbonate and magnesium nitrate were added to promote the reaction between the insoluble tetrahedral germanium dioxide and complex forms of germanium-containing compounds. Simultaneously, the sulphur produced in the ultrasonic enhanced oxidation leaching stage was used to change the phases of tin dioxide and zinc ferrite, thereby releasing germanium into its lattice. Finally, the germanium in the roasting slag was recovered by conventional leaching, and the grades of lead and tin in the residue were enriched to 35.21% and 11.31%, respectively. Compared with the conventional acid leaching process of enterprise, the total reaction time of this method was shortened to 80 min, and the recovery rates of zinc and germanium increased by approximately 10% and 40%, respectively. The entire process is clean and environmentally friendly and does not cause adverse effects on the recovery of lead and tin. Overall, this study provides new insights into the design of valuable metal recovery methods for zinc oxide dust containing intractable germanide.

Intensifying separation of Pb and Sn from waste Pb-Sn alloy by ultrasound-assisted acid leaching: Selective dissolution and sonochemistry mechanism

Clean and efficient extraction and separation of precious metals from discarded Pb-Sn alloy is critical to the sustainable utilization of solid waste resources. Dense oxide layer and compact alloy texture in the waste Pb-Sn alloy pose challenges to the effective leaching process. Ultrasonic waves are demonstrated to improve separation efficiency via the favorable physical and chemical effects in solution system. In this study, ultrasound-assisted leaching technology is attempted to rapidly and selectively extract Pb from the waste Pb-Sn alloy, and gives emphasis on ultrasonic electrochemical behaviors. The Eh-pH diagrams of Sn-H2O and Pb-H2O systems were firstly analyzed to lay the selective dissolution foundation. It's indicated that oxidizing HNO3 lixiviant is suitable to realize the selective separation of Pb. Both Sn and Pb can be dissolved to ionic Sn2+ and Pb2+ in the HNO3 solution. However, Sn2+ rapidly oxidizes to Sn4+ and Sn4+ further hydrolyzes to insoluble SnO2, which will agglomerate on unreacted materials to limit internal metal leaching in conventional leaching process. Due to the vibratory stripping of oxide layer by physical effect of ultrasound, the conventional acid leaching time for Pb extraction can be halved with the ultrasound assistance. About 99.12 % Pb and only 0.1 % Sn are dissolved in ultrasound-assisted leaching under the following optimal parameters: 0.5 mol/L HNO3, leaching temperature of 80 °C, time of 30 min, liquid-to-solid ratio of 20 mL/g, and ultrasound intensity of 0.52 W/cm2. Leaching kinetics of Pb, phase transition, microstructure evolution, Pb-Sn galvanic corrosion and dissolution polarization curve were studied to determine the ultrasonic enhanced dissolution mechanism. Notably, Pb and Sn form a microcorrosion galvanic cell in which Sn acts as a cathode and is protected while the Pb undergoes intensifying corrosion as the anode giving rise to the higher Pb dissolution efficiency. Eventually, it's suggested that Pb can be rapidly extracted and separated from the waste Pb-Sn alloy during the ultrasound-assisted HNO3 leaching process via the ultrasound physical and chemical effects, especially the sonochemistry aspect of intensified spot corrosion and galvanic corrosion. The proposed ultrasonic electrochemical corrosion in this work were applicable to the extraction of valuable metals from various waste alloys through leaching method.