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

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.

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 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.